diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
index f5a08e2d7..f2d8007df 100644
--- a/.github/CONTRIBUTING.md
+++ b/.github/CONTRIBUTING.md
@@ -81,7 +81,7 @@ nox -s build
 ### Full setup
 
 To setup an ideal development environment, run the following commands on a
-system with CMake 3.14+:
+system with CMake 3.15+:
 
 ```bash
 python3 -m venv venv
@@ -96,8 +96,8 @@ Tips:
 * You can use `virtualenv` (faster, from PyPI) instead of `venv`.
 * You can select any name for your environment folder; if it contains "env" it
   will be ignored by git.
-* If you don't have CMake 3.14+, just add "cmake" to the pip install command.
-* You can use `-DPYBIND11_FINDPYTHON=ON` to use FindPython on CMake 3.12+
+* If you don't have CMake 3.15+, just add "cmake" to the pip install command.
+* You can use `-DPYBIND11_FINDPYTHON=ON` to use FindPython.
 * In classic mode, you may need to set `-DPYTHON_EXECUTABLE=/path/to/python`.
   FindPython uses `-DPython_ROOT_DIR=/path/to` or
   `-DPython_EXECUTABLE=/path/to/python`.
@@ -149,8 +149,8 @@ To run the tests, you can "build" the check target:
 cmake --build build --target check
 ```
 
-`--target` can be spelled `-t` in CMake 3.15+. You can also run individual
-tests with these targets:
+`--target` can be spelled `-t`. You can also run individual tests with these
+targets:
 
 * `pytest`: Python tests only, using the
 [pytest](https://docs.pytest.org/en/stable/) framework
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9b4851951..d77071aba 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -68,7 +68,18 @@ jobs:
           # Extra ubuntu latest job
           - runs-on: ubuntu-latest
             python: '3.11'
-
+          - runs-on: ubuntu-latest
+            python: '3.12'
+            args: >
+              -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
+          - runs-on: macos-13
+            python: '3.12'
+            args: >
+              -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
+          - runs-on: windows-2022
+            python: '3.12'
+            args: >
+              -DCMAKE_CXX_FLAGS="/DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT /GR /EHsc"
 
     name: "🐍 ${{ matrix.python }} • ${{ matrix.runs-on }} • x64 ${{ matrix.args }}"
     runs-on: ${{ matrix.runs-on }}
diff --git a/.github/workflows/ci_sh_def.yml b/.github/workflows/ci_sh_def.yml
deleted file mode 100644
index 68a739850..000000000
--- a/.github/workflows/ci_sh_def.yml
+++ /dev/null
@@ -1,1262 +0,0 @@
-# PLEASE KEEP THIS GROUP OF FILES IN SYNC AT ALL TIMES:
-#     ci.yml
-#     ci_sh_def.yml
-#     ci_sh_def.yml.patch
-# To import changes made to ci.yml *** ESPECIALLY AFTER `git merge master` ***:
-#     patch -i ci_sh_def.yml.patch -o ci_sh_def.yml
-# To update the patch file after making changes to ci_sh.yml:
-#     diff -u ci.yml ci_sh_def.yml > ci_sh_def.yml.patch
-#     git commit -a -m 'Tracking ci.yml changes from master.'
-#
-# Thanks a lot to @rhaschke for PR #2930!
-
-name: "CI-SH-DEF"
-
-on:
-  workflow_dispatch:
-  pull_request:
-  push:
-    branches:
-      - master
-      - stable
-      - smart_holder
-      - v*
-
-permissions: read-all
-
-concurrency:
-  group: test-sh-def-${{ github.ref }}
-  cancel-in-progress: true
-
-env:
-  PIP_BREAK_SYSTEM_PACKAGES: 1
-  PIP_ONLY_BINARY: numpy
-  FORCE_COLOR: 3
-  PYTEST_TIMEOUT: 300
-  # For cmake:
-  VERBOSE: 1
-
-jobs:
-  # This is the "main" test suite, which tests a large number of different
-  # versions of default compilers and Python versions in GitHub Actions.
-  standard:
-    strategy:
-      fail-fast: false
-      matrix:
-        runs-on: [ubuntu-20.04, windows-2022, macos-13]
-        python:
-        - '3.8'
-        - '3.9'
-        - '3.12'
-        - '3.13'
-        - 'pypy-3.8'
-        - 'pypy-3.9'
-        - 'pypy-3.10'
-
-        # Items in here will either be added to the build matrix (if not
-        # present), or add new keys to an existing matrix element if all the
-        # existing keys match.
-        #
-        # We support an optional key: args, for cmake args
-        include:
-          # Just add a key
-          - runs-on: ubuntu-20.04
-            python: '3.8'
-            args: >
-              -DPYBIND11_FINDPYTHON=ON
-              -DCMAKE_CXX_FLAGS="-D_=1"
-            exercise_D_: 1
-          - runs-on: ubuntu-20.04
-            python: 'pypy-3.8'
-            args: >
-              -DPYBIND11_FINDPYTHON=ON
-          - runs-on: windows-2019
-            python: '3.8'
-            args: >
-              -DPYBIND11_FINDPYTHON=ON
-          # Inject a couple Windows 2019 runs
-          - runs-on: windows-2019
-            python: '3.9'
-          # Extra ubuntu latest job
-          - runs-on: ubuntu-latest
-            python: '3.11'
-
-
-    name: "🐍 ${{ matrix.python }} • ${{ matrix.runs-on }} • x64 ${{ matrix.args }}"
-    runs-on: ${{ matrix.runs-on }}
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Setup Python ${{ matrix.python }}
-      uses: actions/setup-python@v5
-      with:
-        python-version: ${{ matrix.python }}
-        allow-prereleases: true
-
-    - name: Setup Boost (Linux)
-      # Can't use boost + define _
-      if: runner.os == 'Linux' && matrix.exercise_D_ != 1
-      run: sudo apt-get install libboost-dev
-
-    - name: Setup Boost (macOS)
-      if: runner.os == 'macOS'
-      run: brew install boost
-
-    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v2.0
-
-    - name: Cache wheels
-      if: runner.os == 'macOS'
-      uses: actions/cache@v4
-      with:
-        # This path is specific to macOS - we really only need it for PyPy NumPy wheels
-        # See https://github.com/actions/cache/blob/master/examples.md#python---pip
-        # for ways to do this more generally
-        path: ~/Library/Caches/pip
-        # Look to see if there is a cache hit for the corresponding requirements file
-        key: ${{ runner.os }}-pip-${{ matrix.python }}-x64-${{ hashFiles('tests/requirements.txt') }}
-
-    - name: Prepare env
-      run: |
-        python -m pip install -r tests/requirements.txt
-
-    - name: Setup annotations on Linux
-      if: runner.os == 'Linux'
-      run: python -m pip install pytest-github-actions-annotate-failures
-
-    # First build - C++11 mode and inplace
-    # More-or-less randomly adding -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON here
-    # (same for PYBIND11_NUMPY_1_ONLY, but requires a NumPy 1.x at runtime).
-    - name: Configure C++11 ${{ matrix.args }}
-      run: >
-        cmake -S . -B .
-        -DPYBIND11_WERROR=ON
-        -DPYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION=ON
-        -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON
-        -DPYBIND11_NUMPY_1_ONLY=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_STANDARD=11
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT ${{runner.os == 'Windows' && '/GR /EHsc' || ''}}"
-        ${{ matrix.args }}
-
-    - name: Build C++11
-      run: cmake --build . -j 2
-
-    - name: Python tests C++11
-      run: cmake --build . --target pytest -j 2
-
-    - name: C++11 tests
-      run: cmake --build . --target cpptest -j 2
-
-    - name: Interface test C++11
-      run: cmake --build . --target test_cmake_build
-
-    - name: Clean directory
-      run: git clean -fdx
-
-    # Second build - C++17 mode and in a build directory
-    # More-or-less randomly adding -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF here.
-    # (same for PYBIND11_NUMPY_1_ONLY, but requires a NumPy 1.x at runtime).
-    - name: Configure C++17
-      run: >
-        cmake -S . -B build2
-        -DPYBIND11_WERROR=ON
-        -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
-        -DPYBIND11_NUMPY_1_ONLY=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_STANDARD=17
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT ${{runner.os == 'Windows' && '/GR /EHsc' || ''}}"
-        ${{ matrix.args }}
-
-    - name: Build
-      run: cmake --build build2 -j 2
-
-    - name: Python tests
-      run: cmake --build build2 --target pytest
-
-    - name: C++ tests
-      run: cmake --build build2 --target cpptest
-
-    # Third build - C++17 mode with unstable ABI
-    - name: Configure (unstable ABI)
-      run: >
-        cmake -S . -B build3
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_STANDARD=17
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT ${{runner.os == 'Windows' && '/GR /EHsc' || ''}}"
-        -DPYBIND11_INTERNALS_VERSION=10000000
-        ${{ matrix.args }}
-
-    - name: Build (unstable ABI)
-      run: cmake --build build3 -j 2
-
-    - name: Python tests (unstable ABI)
-      run: cmake --build build3 --target pytest
-
-    - name: Interface test
-      run: cmake --build build2 --target test_cmake_build
-
-    # This makes sure the setup_helpers module can build packages using
-    # setuptools
-    - name: Setuptools helpers test
-      run: |
-        pip install setuptools
-        pytest tests/extra_setuptools
-      if: "!(matrix.runs-on == 'windows-2022')"
-
-  manylinux:
-    name: Manylinux on 🐍 3.13t • GIL
-    runs-on: ubuntu-latest
-    timeout-minutes: 40
-    container: quay.io/pypa/musllinux_1_2_x86_64:latest
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
-
-      - name: Prepare venv
-        run: python3.13t -m venv .venv
-
-      - name: Install Python deps
-        run: .venv/bin/pip install -r tests/requirements.txt
-
-      - name: Configure C++11
-        run: >
-          cmake -S. -Bbuild
-          -DPYBIND11_WERROR=ON
-          -DDOWNLOAD_CATCH=ON
-          -DDOWNLOAD_EIGEN=ON
-          -DPython_ROOT_DIR=.venv
-          -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-
-      - name: Build C++11
-        run: cmake --build build -j2
-
-      - name: Python tests C++11
-        run: cmake --build build --target pytest -j2
-
-  deadsnakes:
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-        # TODO: Fails on 3.10, investigate
-        # JOB DISABLED (NEEDS WORK): https://github.com/pybind/pybind11/issues/4889
-        # - python-version: "3.9"
-        #   python-debug: true
-        #   valgrind: true
-        - python-version: "3.11"
-          python-debug: false
-
-    name: "🐍 ${{ matrix.python-version }}${{ matrix.python-debug && '-dbg' || '' }} (deadsnakes)${{ matrix.valgrind && ' • Valgrind' || '' }} • x64"
-    runs-on: ubuntu-20.04
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Setup Python ${{ matrix.python-version }} (deadsnakes)
-      uses: deadsnakes/action@v3.1.0
-      with:
-        python-version: ${{ matrix.python-version }}
-        debug: ${{ matrix.python-debug }}
-
-    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v2.0
-
-    - name: Valgrind cache
-      if: matrix.valgrind
-      uses: actions/cache@v4
-      id: cache-valgrind
-      with:
-        path: valgrind
-        key: 3.16.1 # Valgrind version
-
-    - name: Compile Valgrind
-      if: matrix.valgrind && steps.cache-valgrind.outputs.cache-hit != 'true'
-      run: |
-        VALGRIND_VERSION=3.16.1
-        curl https://sourceware.org/pub/valgrind/valgrind-$VALGRIND_VERSION.tar.bz2 -o - | tar xj
-        mv valgrind-$VALGRIND_VERSION valgrind
-        cd valgrind
-        ./configure
-        make -j 2 > /dev/null
-
-    - name: Install Valgrind
-      if: matrix.valgrind
-      working-directory: valgrind
-      run: |
-        sudo make install
-        sudo apt-get update
-        sudo apt-get install libc6-dbg  # Needed by Valgrind
-
-    - name: Prepare env
-      run: |
-        python -m pip install -r tests/requirements.txt
-
-    - name: Configure
-      run: >
-        cmake -S . -B build
-        -DCMAKE_BUILD_TYPE=Debug
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_STANDARD=17
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-
-    - name: Build
-      run: cmake --build build -j 2
-
-    - name: Python tests
-      run: cmake --build build --target pytest
-
-    - name: C++ tests
-      run: cmake --build build --target cpptest
-
-    - name: Run Valgrind on Python tests
-      if: matrix.valgrind
-      run: cmake --build build --target memcheck
-
-
-  # Testing on clang using the excellent silkeh clang docker images
-  clang:
-    runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        clang:
-          - dev
-        std:
-          - 11
-        container_suffix:
-          - ""
-        include:
-          - clang: 5
-            std: 14
-          - clang: 11
-            std: 20
-          - clang: 12
-            std: 20
-          - clang: 13
-            std: 20
-          - clang: 14
-            std: 20
-          - clang: 15
-            std: 20
-            container_suffix: "-bullseye"
-          - clang: 16
-            std: 20
-            container_suffix: "-bullseye"
-          - clang: 17
-            std: 20
-            container_suffix: "-bookworm"
-          - clang: 18
-            std: 20
-            container_suffix: "-bookworm"
-
-    name: "🐍 3 • Clang ${{ matrix.clang }} • C++${{ matrix.std }} • x64"
-    container: "silkeh/clang:${{ matrix.clang }}${{ matrix.container_suffix }}"
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Add wget and python3
-      run: apt-get update && apt-get install -y python3-dev python3-numpy python3-pytest libeigen3-dev
-
-    - name: Configure
-      shell: bash
-      run: >
-        cmake -S . -B build
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DCMAKE_CXX_STANDARD=${{ matrix.std }}
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-
-    - name: Build
-      run: cmake --build build -j 2
-
-    - name: Python tests
-      run: cmake --build build --target pytest
-
-    - name: C++ tests
-      run: cmake --build build --target cpptest
-
-    - name: Interface test
-      run: cmake --build build --target test_cmake_build
-
-
-  # Testing NVCC; forces sources to behave like .cu files
-  cuda:
-    runs-on: ubuntu-latest
-    name: "🐍 3.10 • CUDA 12.2 • Ubuntu 22.04"
-    container: nvidia/cuda:12.2.0-devel-ubuntu22.04
-
-    steps:
-    - uses: actions/checkout@v4
-
-    # tzdata will try to ask for the timezone, so set the DEBIAN_FRONTEND
-    - name: Install 🐍 3
-      run: apt-get update && DEBIAN_FRONTEND="noninteractive" apt-get install -y cmake git python3-dev python3-pytest python3-numpy
-
-    - name: Configure
-      run: cmake -S . -B build -DPYBIND11_CUDA_TESTS=ON -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-
-    - name: Build
-      run: cmake --build build -j2 --verbose
-
-    - name: Python tests
-      run: cmake --build build --target pytest
-
-
-# TODO: Internal compiler error - report to NVidia
-#  # Testing CentOS 8 + PGI compilers
-#  centos-nvhpc8:
-#    runs-on: ubuntu-latest
-#    name: "🐍 3 • CentOS8 / PGI 20.11 • x64"
-#    container: centos:8
-#
-#    steps:
-#    - uses: actions/checkout@v4
-#
-#    - name: Add Python 3 and a few requirements
-#      run: yum update -y && yum install -y git python3-devel python3-numpy python3-pytest make environment-modules
-#
-#    - name: Install CMake with pip
-#      run: |
-#        python3 -m pip install --upgrade pip
-#        python3 -m pip install cmake --prefer-binary
-#
-#    - name: Install NVidia HPC SDK
-#      run: >
-#        yum -y install
-#        https://developer.download.nvidia.com/hpc-sdk/20.11/nvhpc-20-11-20.11-1.x86_64.rpm
-#        https://developer.download.nvidia.com/hpc-sdk/20.11/nvhpc-2020-20.11-1.x86_64.rpm
-#
-#    - name: Configure
-#      shell: bash
-#      run: |
-#        source /etc/profile.d/modules.sh
-#        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/20.11
-#        cmake -S . -B build -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_STANDARD=14 -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-#
-#    - name: Build
-#      run: cmake --build build -j 2 --verbose
-#
-#    - name: Python tests
-#      run: cmake --build build --target pytest
-#
-#    - name: C++ tests
-#      run: cmake --build build --target cpptest
-#
-#    - name: Interface test
-#      run: cmake --build build --target test_cmake_build
-
-
-  # Testing on Ubuntu + NVHPC (previous PGI) compilers, which seems to require more workarounds
-  ubuntu-nvhpc7:
-    runs-on: ubuntu-20.04
-    name: "🐍 3 • NVHPC 23.5 • C++17 • x64"
-
-    env:
-      # tzdata will try to ask for the timezone, so set the DEBIAN_FRONTEND
-      DEBIAN_FRONTEND: 'noninteractive'
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Add NVHPC Repo
-      run: |
-        echo 'deb [trusted=yes] https://developer.download.nvidia.com/hpc-sdk/ubuntu/amd64 /' | \
-          sudo tee /etc/apt/sources.list.d/nvhpc.list
-
-    - name: Install 🐍 3 & NVHPC
-      run: |
-        sudo apt-get update -y && \
-        sudo apt-get install -y cmake environment-modules git python3-dev python3-pip python3-numpy && \
-        sudo apt-get install -y --no-install-recommends nvhpc-23-5 && \
-        sudo rm -rf /var/lib/apt/lists/*
-        python3 -m pip install --upgrade pip
-        python3 -m pip install --upgrade pytest
-
-    # On some systems, you many need further workarounds:
-    # https://github.com/pybind/pybind11/pull/2475
-    - name: Configure
-      shell: bash
-      run: |
-        source /etc/profile.d/modules.sh
-        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/23.5
-        cmake -S . -B build -DDOWNLOAD_CATCH=ON \
-                            -DCMAKE_CXX_STANDARD=17 \
-                            -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") \
-                            -DCMAKE_CXX_FLAGS="-Wc,--pending_instantiations=0 -DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT" \
-                            -DPYBIND11_TEST_FILTER="test_smart_ptr.cpp"
-
-    - name: Build
-      run: cmake --build build -j 2 --verbose
-
-    - name: Python tests
-      run: cmake --build build --target pytest
-
-    - name: C++ tests
-      run: cmake --build build --target cpptest
-
-    - name: Interface test
-      run: cmake --build build --target test_cmake_build
-
-
-  # Testing on GCC using the GCC docker images (only recent images supported)
-  gcc:
-    runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - { gcc: 9, std: 20 }
-          - { gcc: 10, std: 17 }
-          - { gcc: 10, std: 20 }
-          - { gcc: 11, std: 20 }
-          - { gcc: 12, std: 20 }
-          - { gcc: 13, std: 20 }
-
-    name: "🐍 3 • GCC ${{ matrix.gcc }} • C++${{ matrix.std }}• x64"
-    container: "gcc:${{ matrix.gcc }}"
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Add Python 3
-      run: apt-get update; apt-get install -y python3-dev python3-numpy python3-pytest python3-pip libeigen3-dev
-
-    - name: Update pip
-      run: python3 -m pip install --upgrade pip
-
-    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v2.0
-
-    - name: Configure
-      shell: bash
-      run: >
-        cmake -S . -B build
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DCMAKE_CXX_STANDARD=${{ matrix.std }}
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-
-    - name: Build
-      run: cmake --build build -j 2
-
-    - name: Python tests
-      run: cmake --build build --target pytest
-
-    - name: C++ tests
-      run: cmake --build build --target cpptest
-
-    - name: Interface test
-      run: cmake --build build --target test_cmake_build
-
-    - name: Configure - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-      if: matrix.gcc == '12'
-      shell: bash
-      run: >
-        cmake -S . -B build_partial
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DCMAKE_CXX_STANDARD=${{ matrix.std }}
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
-
-    - name: Build - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-      if: matrix.gcc == '12'
-      run: cmake --build build_partial -j 2
-
-    - name: Python tests - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-      if: matrix.gcc == '12'
-      run: cmake --build build_partial --target pytest
-
-  # Testing on ICC using the oneAPI apt repo
-  icc:
-    runs-on: ubuntu-20.04
-
-    name: "🐍 3 • ICC latest • x64"
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Add apt repo
-      run: |
-        sudo apt-get update
-        sudo apt-get install -y wget build-essential pkg-config cmake ca-certificates gnupg
-        wget https://apt.repos.intel.com/intel-gpg-keys/GPG-PUB-KEY-INTEL-SW-PRODUCTS-2023.PUB
-        sudo apt-key add GPG-PUB-KEY-INTEL-SW-PRODUCTS-2023.PUB
-        echo "deb https://apt.repos.intel.com/oneapi all main" | sudo tee /etc/apt/sources.list.d/oneAPI.list
-
-    - name: Add ICC & Python 3
-      run: sudo apt-get update; sudo apt-get install -y intel-oneapi-compiler-dpcpp-cpp-and-cpp-classic cmake python3-dev python3-numpy python3-pytest python3-pip
-
-    - name: Update pip
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        python3 -m pip install --upgrade pip
-
-    - name: Install dependencies
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        python3 -m pip install -r tests/requirements.txt
-
-    - name: Configure C++11
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake -S . -B build-11     \
-        -DPYBIND11_WERROR=ON    \
-        -DDOWNLOAD_CATCH=ON     \
-        -DDOWNLOAD_EIGEN=OFF    \
-        -DCMAKE_CXX_STANDARD=11             \
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"  \
-        -DCMAKE_CXX_COMPILER=$(which icpc)  \
-        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-
-    - name: Build C++11
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-11 -j 2 -v
-
-    - name: Python tests C++11
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        sudo service apport stop
-        cmake --build build-11 --target check
-
-    - name: C++ tests C++11
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-11 --target cpptest
-
-    - name: Interface test C++11
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-11 --target test_cmake_build
-
-    - name: Configure C++17
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake -S . -B build-17     \
-        -DPYBIND11_WERROR=ON    \
-        -DDOWNLOAD_CATCH=ON     \
-        -DDOWNLOAD_EIGEN=OFF    \
-        -DCMAKE_CXX_STANDARD=17             \
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"  \
-        -DCMAKE_CXX_COMPILER=$(which icpc)  \
-        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-
-    - name: Build C++17
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-17 -j 2 -v
-
-    - name: Python tests C++17
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        sudo service apport stop
-        cmake --build build-17 --target check
-
-    - name: C++ tests C++17
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-17 --target cpptest
-
-    - name: Interface test C++17
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-17 --target test_cmake_build
-
-
-  # Testing on CentOS (manylinux uses a centos base).
-  centos:
-    runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        container:
-          - "almalinux:8"
-          - "almalinux:9"
-
-    name: "🐍 3 • ${{ matrix.container }} • x64"
-    container: "${{ matrix.container }}"
-
-    steps:
-    - name: Latest actions/checkout
-      uses: actions/checkout@v4
-
-    - name: Add Python 3.8
-      if: matrix.container == 'almalinux:8'
-      run: dnf update -y && dnf install -y python38-devel gcc-c++ make git
-
-    - name: Add Python 3 (default)
-      if: matrix.container != 'almalinux:8'
-      run: dnf update -y && dnf install -y python3-devel gcc-c++ make git
-
-    - name: Update pip
-      run: python3 -m pip install --upgrade pip
-
-    - name: Install dependencies
-      run: |
-        python3 -m pip install cmake -r tests/requirements.txt
-
-    - name: Ensure NumPy 2 is used (required Python >= 3.9)
-      if: matrix.container == 'almalinux:9'
-      run: |
-        python3 -m pip install 'numpy>=2.0.0b1' 'scipy>=1.13.0rc1'
-
-    - name: Configure
-      shell: bash
-      run: >
-        cmake -S . -B build
-        -DCMAKE_BUILD_TYPE=MinSizeRel
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_STANDARD=11
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-
-    - name: Build
-      run: cmake --build build -j 2
-
-    - name: Python tests
-      run: cmake --build build --target pytest
-
-    - name: C++ tests
-      run: cmake --build build --target cpptest
-
-    - name: Interface test
-      run: cmake --build build --target test_cmake_build
-
-
-  # This tests an "install" with the CMake tools
-  install-classic:
-    name: "🐍 3.9 • Debian • x86 •  Install"
-    runs-on: ubuntu-latest
-    container: i386/debian:bullseye
-
-    steps:
-    - uses: actions/checkout@v1  # v1 is required to run inside docker
-
-    - name: Install requirements
-      run: |
-        apt-get update
-        apt-get install -y git make cmake g++ libeigen3-dev python3-dev python3-pip
-        pip3 install "pytest==6.*"
-
-    - name: Configure for install
-      run: >
-        cmake .
-        -DPYBIND11_INSTALL=1 -DPYBIND11_TEST=0
-        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-
-    - name: Make and install
-      run: make install
-
-    - name: Copy tests to new directory
-      run: cp -a tests /pybind11-tests
-
-    - name: Make a new test directory
-      run: mkdir /build-tests
-
-    - name: Configure tests
-      run: >
-        cmake ../pybind11-tests
-        -DDOWNLOAD_CATCH=ON
-        -DPYBIND11_WERROR=ON
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-      working-directory: /build-tests
-
-    - name: Python tests
-      run: make pytest -j 2
-      working-directory: /build-tests
-
-
-  # This verifies that the documentation is not horribly broken, and does a
-  # basic validation check on the SDist.
-  doxygen:
-    name: "Documentation build test"
-    runs-on: ubuntu-latest
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - uses: actions/setup-python@v5
-      with:
-        python-version: "3.x"
-
-    - name: Install Doxygen
-      run: sudo apt-get install -y doxygen librsvg2-bin # Changed to rsvg-convert in 20.04
-
-    - name: Build docs
-      run: pipx run nox -s docs
-
-    - name: Make SDist
-      run: pipx run nox -s build -- --sdist
-
-    - run: git status --ignored
-
-    - name: Check local include dir
-      run: >
-        ls pybind11;
-        python3 -c "import pybind11, pathlib; assert (a := pybind11.get_include()) == (b := str(pathlib.Path('include').resolve())), f'{a} != {b}'"
-
-    - name: Compare Dists (headers only)
-      working-directory: include
-      run: |
-        python3 -m pip install --user -U ../dist/*.tar.gz
-        installed=$(python3 -c "import pybind11; print(pybind11.get_include() + '/pybind11')")
-        diff -rq $installed ./pybind11
-
-  win32:
-    strategy:
-      fail-fast: false
-      matrix:
-        python:
-        - '3.8'
-        - '3.9'
-        - '3.10'
-        - '3.11'
-        - '3.12'
-
-        include:
-          - python: '3.12'
-            args: -DCMAKE_CXX_STANDARD=20
-          - python: '3.11'
-            args: -DCMAKE_CXX_STANDARD=20
-          - python: '3.10'
-            args: -DCMAKE_CXX_STANDARD=20
-          - python: '3.9'
-            args: -DCMAKE_CXX_STANDARD=20
-          - python: '3.8'
-            args: -DCMAKE_CXX_STANDARD=17
-
-
-    name: "🐍 ${{ matrix.python }} • MSVC 2019 • x86 ${{ matrix.args }}"
-    runs-on: windows-2019
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Setup Python ${{ matrix.python }}
-      uses: actions/setup-python@v5
-      with:
-        python-version: ${{ matrix.python }}
-        architecture: x86
-
-    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v2.0
-
-    - name: Prepare MSVC
-      uses: ilammy/msvc-dev-cmd@v1.13.0
-      with:
-        arch: x86
-
-    - name: Prepare env
-      run: |
-        python -m pip install -r tests/requirements.txt
-
-    # First build - C++11 mode and inplace
-    - name: Configure ${{ matrix.args }}
-      run: >
-        cmake -S . -B build
-        -G "Visual Studio 16 2019" -A Win32
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_FLAGS="/GR /EHsc /DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        ${{ matrix.args }}
-    - name: Build C++11
-      run: cmake --build build -j 2
-
-    - name: Python tests
-      run: cmake --build build -t pytest
-
-  win32-debug:
-    strategy:
-      fail-fast: false
-      matrix:
-        python:
-        - 3.8
-        - 3.9
-
-        include:
-          - python: 3.9
-            args: -DCMAKE_CXX_STANDARD=20
-          - python: 3.8
-            args: -DCMAKE_CXX_STANDARD=17
-
-    name: "🐍 ${{ matrix.python }} • MSVC 2019 (Debug) • x86 ${{ matrix.args }}"
-    runs-on: windows-2019
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Setup Python ${{ matrix.python }}
-      uses: actions/setup-python@v5
-      with:
-        python-version: ${{ matrix.python }}
-        architecture: x86
-
-    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v2.0
-
-    - name: Prepare MSVC
-      uses: ilammy/msvc-dev-cmd@v1.13.0
-      with:
-        arch: x86
-
-    - name: Prepare env
-      run: |
-        python -m pip install -r tests/requirements.txt
-
-    # First build - C++11 mode and inplace
-    - name: Configure ${{ matrix.args }}
-      run: >
-        cmake -S . -B build
-        -G "Visual Studio 16 2019" -A Win32
-        -DCMAKE_BUILD_TYPE=Debug
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_FLAGS="/GR /EHsc /DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        ${{ matrix.args }}
-    - name: Build C++11
-      run: cmake --build build --config Debug -j 2
-
-    - name: Python tests
-      run: cmake --build build --config Debug -t pytest
-
-
-  windows-2022:
-    strategy:
-      fail-fast: false
-      matrix:
-        python:
-        - 3.9
-
-    name: "🐍 ${{ matrix.python }} • MSVC 2022 C++20 • x64"
-    runs-on: windows-2022
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Setup Python ${{ matrix.python }}
-      uses: actions/setup-python@v5
-      with:
-        python-version: ${{ matrix.python }}
-
-    - name: Prepare env
-      # Ensure use of NumPy 2 (via NumPy nightlies but can be changed soon)
-      run: |
-        python3 -m pip install -r tests/requirements.txt
-        python3 -m pip install 'numpy>=2.0.0b1' 'scipy>=1.13.0rc1'
-
-    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v2.0
-
-    - name: Configure C++20
-      run: >
-        cmake -S . -B build
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_STANDARD=20
-        -DCMAKE_CXX_FLAGS="/GR /EHsc /DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-
-    - name: Build C++20
-      run: cmake --build build -j 2
-
-    - name: Python tests
-      run: cmake --build build --target pytest
-
-    - name: C++20 tests
-      run: cmake --build build --target cpptest -j 2
-
-    - name: Interface test C++20
-      run: cmake --build build --target test_cmake_build
-
-    - name: Configure C++20 - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-      run: >
-        cmake -S . -B build_partial
-        -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_STANDARD=20
-        -DCMAKE_CXX_FLAGS="/GR /EHsc /DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
-
-    - name: Build C++20 - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-      run: cmake --build build_partial -j 2
-
-    - name: Python tests - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-      run: cmake --build build_partial --target pytest
-
-  mingw:
-    name: "🐍 3 • windows-latest • ${{ matrix.sys }}"
-    runs-on: windows-latest
-    defaults:
-      run:
-        shell: msys2 {0}
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - { sys: mingw64, env: x86_64 }
-          - { sys: mingw32, env: i686 }
-    steps:
-    - uses: msys2/setup-msys2@v2
-      with:
-        msystem: ${{matrix.sys}}
-        install: >-
-          git
-          mingw-w64-${{matrix.env}}-gcc
-          mingw-w64-${{matrix.env}}-python-pip
-          mingw-w64-${{matrix.env}}-python-numpy
-          mingw-w64-${{matrix.env}}-cmake
-          mingw-w64-${{matrix.env}}-make
-          mingw-w64-${{matrix.env}}-python-pytest
-          mingw-w64-${{matrix.env}}-boost
-          mingw-w64-${{matrix.env}}-catch
-
-    - uses: msys2/setup-msys2@v2
-      if: matrix.sys == 'mingw64'
-      with:
-        msystem: ${{matrix.sys}}
-        install: >-
-          git
-          mingw-w64-${{matrix.env}}-python-scipy
-          mingw-w64-${{matrix.env}}-eigen3
-
-    - uses: actions/checkout@v4
-
-    - name: Configure C++11
-      # LTO leads to many undefined reference like
-      # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
-      run: >-
-        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
-        -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        -S . -B build
-
-    - name: Build C++11
-      run: cmake --build build -j 2
-
-    - name: Python tests C++11
-      run: cmake --build build --target pytest -j 2
-
-    - name: C++11 tests
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build --target cpptest -j 2
-
-    - name: Interface test C++11
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build --target test_cmake_build
-
-    - name: Clean directory
-      run: git clean -fdx
-
-    - name: Configure C++14
-      run: >-
-        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
-        -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        -S . -B build2
-
-    - name: Build C++14
-      run: cmake --build build2 -j 2
-
-    - name: Python tests C++14
-      run: cmake --build build2 --target pytest -j 2
-
-    - name: C++14 tests
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build2 --target cpptest -j 2
-
-    - name: Interface test C++14
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build2 --target test_cmake_build
-
-    - name: Clean directory
-      run: git clean -fdx
-
-    - name: Configure C++17
-      run: >-
-        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
-        -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
-        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-        -S . -B build3
-
-    - name: Build C++17
-      run: cmake --build build3 -j 2
-
-    - name: Python tests C++17
-      run: cmake --build build3 --target pytest -j 2
-
-    - name: C++17 tests
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build3 --target cpptest -j 2
-
-    - name: Interface test C++17
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build3 --target test_cmake_build
-
-  windows_clang:
-
-    strategy:
-      matrix:
-        os: [windows-latest]
-        python: ['3.10']
-
-    runs-on: "${{ matrix.os }}"
-
-    name: "🐍 ${{ matrix.python }} • ${{ matrix.os }} • clang-latest"
-
-    steps:
-      - name: Show env
-        run: env
-
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Set up Clang
-        uses: egor-tensin/setup-clang@v1
-
-      - name: Setup Python ${{ matrix.python }}
-        uses: actions/setup-python@v5
-        with:
-          python-version: ${{ matrix.python }}
-
-      - name: Update CMake
-        uses: jwlawson/actions-setup-cmake@v2.0
-
-      - name: Install ninja-build tool
-        uses: seanmiddleditch/gha-setup-ninja@v5
-
-      - name: Run pip installs
-        run: |
-          python -m pip install --upgrade pip
-          python -m pip install -r tests/requirements.txt
-
-      - name: Show Clang++ version
-        run: clang++ --version
-
-      - name: Show CMake version
-        run: cmake --version
-
-      # TODO: WERROR=ON
-      - name: Configure Clang
-        run: >
-          cmake -G Ninja -S . -B .
-          -DPYBIND11_WERROR=OFF
-          -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
-          -DDOWNLOAD_CATCH=ON
-          -DDOWNLOAD_EIGEN=ON
-          -DCMAKE_CXX_COMPILER=clang++
-          -DCMAKE_CXX_STANDARD=17
-          -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-
-      - name: Build
-        run: cmake --build . -j 2
-
-      - name: Python tests
-        run: cmake --build . --target pytest -j 2
-
-      - name: C++ tests
-        run: cmake --build . --target cpptest -j 2
-
-      - name: Interface test
-        run: cmake --build . --target test_cmake_build -j 2
-
-      - name: Clean directory
-        run: git clean -fdx
-
-  macos_brew_install_llvm:
-    name: "macos-13 • brew install llvm"
-    runs-on: macos-13
-
-    env:
-      # https://apple.stackexchange.com/questions/227026/how-to-install-recent-clang-with-homebrew
-      LDFLAGS: '-L/usr/local/opt/llvm/lib -Wl,-rpath,/usr/local/opt/llvm/lib'
-
-    steps:
-      - name: Update PATH
-        run: echo "/usr/local/opt/llvm/bin" >> $GITHUB_PATH
-
-      - name: Show env
-        run: env
-
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Show Clang++ version before brew install llvm
-        run: clang++ --version
-
-      - name: brew install llvm
-        run: brew install llvm
-
-      - name: Show Clang++ version after brew install llvm
-        run: clang++ --version
-
-      - name: Update CMake
-        uses: jwlawson/actions-setup-cmake@v2.0
-
-      - name: Run pip installs
-        run: |
-          python3 -m pip install --upgrade pip
-          python3 -m pip install -r tests/requirements.txt
-          python3 -m pip install numpy
-          python3 -m pip install scipy
-
-      - name: Show CMake version
-        run: cmake --version
-
-      - name: CMake Configure
-        run: >
-          cmake -S . -B .
-          -DPYBIND11_WERROR=ON
-          -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
-          -DDOWNLOAD_CATCH=ON
-          -DDOWNLOAD_EIGEN=ON
-          -DCMAKE_CXX_COMPILER=clang++
-          -DCMAKE_CXX_STANDARD=17
-          -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-
-      - name: Build
-        run: cmake --build . -j 2
-
-      - name: Python tests
-        run: cmake --build . --target pytest -j 2
-
-      - name: C++ tests
-        run: cmake --build . --target cpptest -j 2
-
-      - name: Interface test
-        run: cmake --build . --target test_cmake_build -j 2
-
-      - name: CMake Configure - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-        run: >
-          cmake -S . -B build_partial
-          -DPYBIND11_WERROR=ON
-          -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
-          -DDOWNLOAD_CATCH=ON
-          -DDOWNLOAD_EIGEN=ON
-          -DCMAKE_CXX_COMPILER=clang++
-          -DCMAKE_CXX_STANDARD=17
-          -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-          "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
-
-      - name: Build - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-        run: cmake --build build_partial -j 2
-
-      - name: Python tests - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-        run: cmake --build build_partial --target pytest -j 2
-
-      - name: Clean directory
-        run: git clean -fdx
diff --git a/.github/workflows/ci_sh_def.yml.patch b/.github/workflows/ci_sh_def.yml.patch
deleted file mode 100644
index ecfd7639c..000000000
--- a/.github/workflows/ci_sh_def.yml.patch
+++ /dev/null
@@ -1,223 +0,0 @@
---- ci.yml	2024-07-30 11:20:28.997003056 -0700
-+++ ci_sh_def.yml	2024-07-30 11:21:39.724969167 -0700
-@@ -1,4 +1,16 @@
--name: CI
-+# PLEASE KEEP THIS GROUP OF FILES IN SYNC AT ALL TIMES:
-+#     ci.yml
-+#     ci_sh_def.yml
-+#     ci_sh_def.yml.patch
-+# To import changes made to ci.yml *** ESPECIALLY AFTER `git merge master` ***:
-+#     patch -i ci_sh_def.yml.patch -o ci_sh_def.yml
-+# To update the patch file after making changes to ci_sh.yml:
-+#     diff -u ci.yml ci_sh_def.yml > ci_sh_def.yml.patch
-+#     git commit -a -m 'Tracking ci.yml changes from master.'
-+#
-+# Thanks a lot to @rhaschke for PR #2930!
-+
-+name: "CI-SH-DEF"
- 
- on:
-   workflow_dispatch:
-@@ -13,7 +25,7 @@
- permissions: read-all
- 
- concurrency:
--  group: test-sh-avl${{ github.ref }}
-+  group: test-sh-def-${{ github.ref }}
-   cancel-in-progress: true
- 
- env:
-@@ -126,6 +138,7 @@
-         -DDOWNLOAD_CATCH=ON
-         -DDOWNLOAD_EIGEN=ON
-         -DCMAKE_CXX_STANDARD=11
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT ${{runner.os == 'Windows' && '/GR /EHsc' || ''}}"
-         ${{ matrix.args }}
- 
-     - name: Build C++11
-@@ -155,6 +168,7 @@
-         -DDOWNLOAD_CATCH=ON
-         -DDOWNLOAD_EIGEN=ON
-         -DCMAKE_CXX_STANDARD=17
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT ${{runner.os == 'Windows' && '/GR /EHsc' || ''}}"
-         ${{ matrix.args }}
- 
-     - name: Build
-@@ -174,6 +188,7 @@
-         -DDOWNLOAD_CATCH=ON
-         -DDOWNLOAD_EIGEN=ON
-         -DCMAKE_CXX_STANDARD=17
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT ${{runner.os == 'Windows' && '/GR /EHsc' || ''}}"
-         -DPYBIND11_INTERNALS_VERSION=10000000
-         ${{ matrix.args }}
- 
-@@ -217,6 +232,7 @@
-           -DDOWNLOAD_CATCH=ON
-           -DDOWNLOAD_EIGEN=ON
-           -DPython_ROOT_DIR=.venv
-+          -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
- 
-       - name: Build C++11
-         run: cmake --build build -j2
-@@ -290,6 +306,7 @@
-         -DDOWNLOAD_CATCH=ON
-         -DDOWNLOAD_EIGEN=ON
-         -DCMAKE_CXX_STANDARD=17
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
- 
-     - name: Build
-       run: cmake --build build -j 2
-@@ -357,6 +374,7 @@
-         -DPYBIND11_WERROR=ON
-         -DDOWNLOAD_CATCH=ON
-         -DCMAKE_CXX_STANDARD=${{ matrix.std }}
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
- 
-     - name: Build
-@@ -386,7 +404,7 @@
-       run: apt-get update && DEBIAN_FRONTEND="noninteractive" apt-get install -y cmake git python3-dev python3-pytest python3-numpy
- 
-     - name: Configure
--      run: cmake -S . -B build -DPYBIND11_CUDA_TESTS=ON -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
-+      run: cmake -S . -B build -DPYBIND11_CUDA_TESTS=ON -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
- 
-     - name: Build
-       run: cmake --build build -j2 --verbose
-@@ -474,7 +492,7 @@
-         cmake -S . -B build -DDOWNLOAD_CATCH=ON \
-                             -DCMAKE_CXX_STANDARD=17 \
-                             -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") \
--                            -DCMAKE_CXX_FLAGS="-Wc,--pending_instantiations=0" \
-+                            -DCMAKE_CXX_FLAGS="-Wc,--pending_instantiations=0 -DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT" \
-                             -DPYBIND11_TEST_FILTER="test_smart_ptr.cpp"
- 
-     - name: Build
-@@ -526,6 +544,7 @@
-         -DPYBIND11_WERROR=ON
-         -DDOWNLOAD_CATCH=ON
-         -DCMAKE_CXX_STANDARD=${{ matrix.std }}
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
- 
-     - name: Build
-@@ -548,6 +567,7 @@
-         -DPYBIND11_WERROR=ON
-         -DDOWNLOAD_CATCH=ON
-         -DCMAKE_CXX_STANDARD=${{ matrix.std }}
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-         "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
- 
-@@ -597,6 +617,7 @@
-         -DDOWNLOAD_CATCH=ON     \
-         -DDOWNLOAD_EIGEN=OFF    \
-         -DCMAKE_CXX_STANDARD=11             \
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"  \
-         -DCMAKE_CXX_COMPILER=$(which icpc)  \
-         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
- 
-@@ -629,6 +650,7 @@
-         -DDOWNLOAD_CATCH=ON     \
-         -DDOWNLOAD_EIGEN=OFF    \
-         -DCMAKE_CXX_STANDARD=17             \
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"  \
-         -DCMAKE_CXX_COMPILER=$(which icpc)  \
-         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
- 
-@@ -700,6 +722,7 @@
-         -DDOWNLOAD_CATCH=ON
-         -DDOWNLOAD_EIGEN=ON
-         -DCMAKE_CXX_STANDARD=11
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
- 
-     - name: Build
-@@ -750,6 +773,7 @@
-         cmake ../pybind11-tests
-         -DDOWNLOAD_CATCH=ON
-         -DPYBIND11_WERROR=ON
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-       working-directory: /build-tests
- 
-@@ -850,6 +874,7 @@
-         -DPYBIND11_WERROR=ON
-         -DDOWNLOAD_CATCH=ON
-         -DDOWNLOAD_EIGEN=ON
-+        -DCMAKE_CXX_FLAGS="/GR /EHsc /DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         ${{ matrix.args }}
-     - name: Build C++11
-       run: cmake --build build -j 2
-@@ -904,6 +929,7 @@
-         -DPYBIND11_WERROR=ON
-         -DDOWNLOAD_CATCH=ON
-         -DDOWNLOAD_EIGEN=ON
-+        -DCMAKE_CXX_FLAGS="/GR /EHsc /DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         ${{ matrix.args }}
-     - name: Build C++11
-       run: cmake --build build --config Debug -j 2
-@@ -946,6 +972,7 @@
-         -DDOWNLOAD_CATCH=ON
-         -DDOWNLOAD_EIGEN=ON
-         -DCMAKE_CXX_STANDARD=20
-+        -DCMAKE_CXX_FLAGS="/GR /EHsc /DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
- 
-     - name: Build C++20
-       run: cmake --build build -j 2
-@@ -966,6 +993,7 @@
-         -DDOWNLOAD_CATCH=ON
-         -DDOWNLOAD_EIGEN=ON
-         -DCMAKE_CXX_STANDARD=20
-+        -DCMAKE_CXX_FLAGS="/GR /EHsc /DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
- 
-     - name: Build C++20 - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-@@ -1018,6 +1046,7 @@
-       run: >-
-         cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
-         -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         -S . -B build
- 
-     - name: Build C++11
-@@ -1039,6 +1068,7 @@
-       run: >-
-         cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
-         -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         -S . -B build2
- 
-     - name: Build C++14
-@@ -1060,6 +1090,7 @@
-       run: >-
-         cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
-         -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
-+        -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-         -S . -B build3
- 
-     - name: Build C++17
-@@ -1127,6 +1158,7 @@
-           -DDOWNLOAD_EIGEN=ON
-           -DCMAKE_CXX_COMPILER=clang++
-           -DCMAKE_CXX_STANDARD=17
-+          -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
- 
-       - name: Build
-         run: cmake --build . -j 2
-@@ -1192,6 +1224,7 @@
-           -DDOWNLOAD_EIGEN=ON
-           -DCMAKE_CXX_COMPILER=clang++
-           -DCMAKE_CXX_STANDARD=17
-+          -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-           -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
- 
-       - name: Build
-@@ -1215,6 +1248,7 @@
-           -DDOWNLOAD_EIGEN=ON
-           -DCMAKE_CXX_COMPILER=clang++
-           -DCMAKE_CXX_STANDARD=17
-+          -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
-           -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-           "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
- 
diff --git a/.github/workflows/configure.yml b/.github/workflows/configure.yml
index 8242db7b1..8e89e6f39 100644
--- a/.github/workflows/configure.yml
+++ b/.github/workflows/configure.yml
@@ -32,7 +32,7 @@ jobs:
         include:
         - runs-on: ubuntu-20.04
           arch: x64
-          cmake: "3.5"
+          cmake: "3.15"
 
         - runs-on: ubuntu-20.04
           arch: x64
@@ -40,7 +40,7 @@ jobs:
 
         - runs-on: macos-13
           arch: x64
-          cmake: "3.8"
+          cmake: "3.15"
 
         - runs-on: windows-2019
           arch: x64 # x86 compilers seem to be missing on 2019 image
diff --git a/.github/workflows/emscripten.yaml b/.github/workflows/emscripten.yaml
index cbd7f5d54..fe4cd821c 100644
--- a/.github/workflows/emscripten.yaml
+++ b/.github/workflows/emscripten.yaml
@@ -5,6 +5,9 @@ on:
   pull_request:
     branches:
     - master
+    - stable
+    - smart_holder
+    - v*
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
@@ -23,8 +26,6 @@ jobs:
     - uses: pypa/cibuildwheel@v2.20
       env:
         PYODIDE_BUILD_EXPORTS: whole_archive
-        CFLAGS: -fexceptions
-        LDFLAGS: -fexceptions
       with:
         package-dir: tests
         only: cp312-pyodide_wasm32
diff --git a/.github/workflows/pip.yml b/.github/workflows/pip.yml
index e98bea3aa..f45adf4ca 100644
--- a/.github/workflows/pip.yml
+++ b/.github/workflows/pip.yml
@@ -103,7 +103,7 @@ jobs:
     - uses: actions/download-artifact@v4
 
     - name: Generate artifact attestation for sdist and wheel
-      uses: actions/attest-build-provenance@210c1913531870065f03ce1f9440dd87bc0938cd # v1.4.0
+      uses: actions/attest-build-provenance@310b0a4a3b0b78ef57ecda988ee04b132db73ef8 # v1.4.1
       with:
         subject-path: "*/pybind11*"
 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 82eca8923..681953900 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -10,16 +10,7 @@ if(NOT CMAKE_VERSION VERSION_LESS "3.27")
   cmake_policy(GET CMP0148 _pybind11_cmp0148)
 endif()
 
-cmake_minimum_required(VERSION 3.5)
-
-# The `cmake_minimum_required(VERSION 3.5...3.29)` syntax does not work with
-# some versions of VS that have a patched CMake 3.11. This forces us to emulate
-# the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.29)
-  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-  cmake_policy(VERSION 3.29)
-endif()
+cmake_minimum_required(VERSION 3.15...3.30)
 
 if(_pybind11_cmp0148)
   cmake_policy(SET CMP0148 ${_pybind11_cmp0148})
@@ -27,9 +18,7 @@ if(_pybind11_cmp0148)
 endif()
 
 # Avoid infinite recursion if tests include this as a subdirectory
-if(DEFINED PYBIND11_MASTER_PROJECT)
-  return()
-endif()
+include_guard(GLOBAL)
 
 # Extract project version from source
 file(STRINGS "${CMAKE_CURRENT_SOURCE_DIR}/include/pybind11/detail/common.h"
@@ -74,14 +63,6 @@ if(CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR)
 
   set(PYBIND11_MASTER_PROJECT ON)
 
-  if(OSX AND CMAKE_VERSION VERSION_LESS 3.7)
-    # Bug in macOS CMake < 3.7 is unable to download catch
-    message(WARNING "CMAKE 3.7+ needed on macOS to download catch, and newer HIGHLY recommended")
-  elseif(WINDOWS AND CMAKE_VERSION VERSION_LESS 3.8)
-    # Only tested with 3.8+ in CI.
-    message(WARNING "CMAKE 3.8+ tested on Windows, previous versions untested")
-  endif()
-
   message(STATUS "CMake ${CMAKE_VERSION}")
 
   if(CMAKE_CXX_STANDARD)
@@ -133,8 +114,7 @@ cmake_dependent_option(
   "Install pybind11 headers in Python include directory instead of default installation prefix"
   OFF "PYBIND11_INSTALL" OFF)
 
-cmake_dependent_option(PYBIND11_FINDPYTHON "Force new FindPython" ${_pybind11_findpython_default}
-                       "NOT CMAKE_VERSION VERSION_LESS 3.12" OFF)
+option(PYBIND11_FINDPYTHON "Force new FindPython" ${_pybind11_findpython_default})
 
 # Allow PYTHON_EXECUTABLE if in FINDPYTHON mode and building pybind11's tests
 # (makes transition easier while we support both modes).
@@ -154,7 +134,7 @@ set(PYBIND11_HEADERS
     include/pybind11/detail/init.h
     include/pybind11/detail/internals.h
     include/pybind11/detail/native_enum_data.h
-    include/pybind11/detail/smart_holder_poc.h
+    include/pybind11/detail/struct_smart_holder.h
     include/pybind11/detail/type_caster_base.h
     include/pybind11/detail/typeid.h
     include/pybind11/detail/using_smart_holder.h
@@ -190,7 +170,7 @@ set(PYBIND11_HEADERS
     include/pybind11/typing.h)
 
 # Compare with grep and warn if mismatched
-if(PYBIND11_MASTER_PROJECT AND NOT CMAKE_VERSION VERSION_LESS 3.12)
+if(PYBIND11_MASTER_PROJECT)
   file(
     GLOB_RECURSE _pybind11_header_check
     LIST_DIRECTORIES false
@@ -208,10 +188,7 @@ if(PYBIND11_MASTER_PROJECT AND NOT CMAKE_VERSION VERSION_LESS 3.12)
   endif()
 endif()
 
-# CMake 3.12 added list(TRANSFORM <list> PREPEND
-# But we can't use it yet
-string(REPLACE "include/" "${CMAKE_CURRENT_SOURCE_DIR}/include/" PYBIND11_HEADERS
-               "${PYBIND11_HEADERS}")
+list(TRANSFORM PYBIND11_HEADERS PREPEND "${CMAKE_CURRENT_SOURCE_DIR}/")
 
 # Cache variable so this can be used in parent projects
 set(pybind11_INCLUDE_DIR
@@ -281,25 +258,11 @@ if(PYBIND11_INSTALL)
     tools/${PROJECT_NAME}Config.cmake.in "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
     INSTALL_DESTINATION ${PYBIND11_CMAKECONFIG_INSTALL_DIR})
 
-  if(CMAKE_VERSION VERSION_LESS 3.14)
-    # Remove CMAKE_SIZEOF_VOID_P from ConfigVersion.cmake since the library does
-    # not depend on architecture specific settings or libraries.
-    set(_PYBIND11_CMAKE_SIZEOF_VOID_P ${CMAKE_SIZEOF_VOID_P})
-    unset(CMAKE_SIZEOF_VOID_P)
-
-    write_basic_package_version_file(
-      ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake
-      VERSION ${PROJECT_VERSION}
-      COMPATIBILITY AnyNewerVersion)
-
-    set(CMAKE_SIZEOF_VOID_P ${_PYBIND11_CMAKE_SIZEOF_VOID_P})
-  else()
-    # CMake 3.14+ natively supports header-only libraries
-    write_basic_package_version_file(
-      ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake
-      VERSION ${PROJECT_VERSION}
-      COMPATIBILITY AnyNewerVersion ARCH_INDEPENDENT)
-  endif()
+  # CMake natively supports header-only libraries
+  write_basic_package_version_file(
+    ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake
+    VERSION ${PROJECT_VERSION}
+    COMPATIBILITY AnyNewerVersion ARCH_INDEPENDENT)
 
   install(
     FILES ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Config.cmake
diff --git a/docs/advanced/cast/eigen.rst b/docs/advanced/cast/eigen.rst
index a5c11a3f1..894ce97f3 100644
--- a/docs/advanced/cast/eigen.rst
+++ b/docs/advanced/cast/eigen.rst
@@ -259,7 +259,7 @@ copying to take place:
         "small"_a            // <- This one can be copied if needed
     );
 
-With the above binding code, attempting to call the the ``some_method(m)``
+With the above binding code, attempting to call the ``some_method(m)``
 method on a ``MyClass`` object, or attempting to call ``some_function(m, m2)``
 will raise a ``RuntimeError`` rather than making a temporary copy of the array.
 It will, however, allow the ``m2`` argument to be copied into a temporary if
diff --git a/docs/advanced/cast/stl.rst b/docs/advanced/cast/stl.rst
index 03d49b295..42b85532d 100644
--- a/docs/advanced/cast/stl.rst
+++ b/docs/advanced/cast/stl.rst
@@ -162,7 +162,7 @@ the declaration
 
 .. code-block:: cpp
 
-    PYBIND11_MAKE_OPAQUE(std::vector<int>);
+    PYBIND11_MAKE_OPAQUE(std::vector<int>)
 
 before any binding code (e.g. invocations to ``class_::def()``, etc.). This
 macro must be specified at the top level (and outside of any namespaces), since
@@ -207,8 +207,8 @@ The following example showcases usage of :file:`pybind11/stl_bind.h`:
     // Don't forget this
     #include <pybind11/stl_bind.h>
 
-    PYBIND11_MAKE_OPAQUE(std::vector<int>);
-    PYBIND11_MAKE_OPAQUE(std::map<std::string, double>);
+    PYBIND11_MAKE_OPAQUE(std::vector<int>)
+    PYBIND11_MAKE_OPAQUE(std::map<std::string, double>)
 
     // ...
 
diff --git a/docs/advanced/embedding.rst b/docs/advanced/embedding.rst
index cbed82158..e78a8f4ce 100644
--- a/docs/advanced/embedding.rst
+++ b/docs/advanced/embedding.rst
@@ -18,7 +18,7 @@ information, see :doc:`/compiling`.
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.5...3.29)
+    cmake_minimum_required(VERSION 3.15...3.30)
     project(example)
 
     find_package(pybind11 REQUIRED)  # or `add_subdirectory(pybind11)`
diff --git a/docs/advanced/smart_ptrs.rst b/docs/advanced/smart_ptrs.rst
index 6f004a597..e2e9f3f37 100644
--- a/docs/advanced/smart_ptrs.rst
+++ b/docs/advanced/smart_ptrs.rst
@@ -131,7 +131,7 @@ top namespace level before any binding code:
 
 .. code-block:: cpp
 
-    PYBIND11_DECLARE_HOLDER_TYPE(T, SmartPtr<T>);
+    PYBIND11_DECLARE_HOLDER_TYPE(T, SmartPtr<T>)
 
 The first argument of :func:`PYBIND11_DECLARE_HOLDER_TYPE` should be a
 placeholder name that is used as a template parameter of the second argument.
@@ -143,7 +143,7 @@ by default. Specify
 
 .. code-block:: cpp
 
-    PYBIND11_DECLARE_HOLDER_TYPE(T, SmartPtr<T>, true);
+    PYBIND11_DECLARE_HOLDER_TYPE(T, SmartPtr<T>, true)
 
 if ``SmartPtr<T>`` can always be initialized from a ``T*`` pointer without the
 risk of inconsistencies (such as multiple independent ``SmartPtr`` instances
@@ -161,7 +161,7 @@ specialized:
 .. code-block:: cpp
 
     // Always needed for custom holder types
-    PYBIND11_DECLARE_HOLDER_TYPE(T, SmartPtr<T>);
+    PYBIND11_DECLARE_HOLDER_TYPE(T, SmartPtr<T>)
 
     // Only needed if the type's `.get()` goes by another name
     namespace PYBIND11_NAMESPACE { namespace detail {
diff --git a/docs/basics.rst b/docs/basics.rst
index e9b24c7fa..cd97c100e 100644
--- a/docs/basics.rst
+++ b/docs/basics.rst
@@ -78,6 +78,13 @@ For brevity, all code examples assume that the following two lines are present:
 
     namespace py = pybind11;
 
+.. note::
+
+    ``pybind11/pybind11.h`` includes ``Python.h``, as such it must be the first file
+    included in any source file or header for `the same reasons as Python.h`_.
+
+.. _`the same reasons as Python.h`: https://docs.python.org/3/extending/extending.html#a-simple-example
+
 Some features may require additional headers, but those will be specified as needed.
 
 .. _simple_example:
diff --git a/docs/changelog.rst b/docs/changelog.rst
index ab6c713c1..014531774 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -15,6 +15,115 @@ IN DEVELOPMENT
 
 Changes will be summarized here periodically.
 
+New Features:
+
+* Support for Python 3.7 was removed. (Official end-of-life: 2023-06-27).
+  `#5191 <https://github.com/pybind/pybind11/pull/5191>`_
+
+* stl.h ``list|set|map_caster`` were made more user friendly: it is no longer
+  necessary to explicitly convert Python iterables to ``tuple()``, ``set()``,
+  or ``map()`` in many common situations.
+  `#4686 <https://github.com/pybind/pybind11/pull/4686>`_
+
+* Support for CMake older than 3.15 removed. CMake 3.15-3.30 supported.
+  `#5304 <https://github.com/pybind/pybind11/pull/5304>`_
+
+* The ``array_caster`` in pybind11/stl.h was enhanced to support value types that are not default-constructible.
+  `#5305 <https://github.com/pybind/pybind11/pull/5305>`_
+
+Version 2.13.5 (August 22, 2024)
+--------------------------------
+
+Bug fixes:
+
+* Fix includes when using Windows long paths (``\\?\`` prefix).
+  `#5321 <https://github.com/pybind/pybind11/pull/5321>`_
+
+* Support ``-Wpedantic`` in C++20 mode.
+  `#5322 <https://github.com/pybind/pybind11/pull/5322>`_
+
+* Fix and test ``<ranges>`` support for ``py::tuple`` and ``py::list``.
+  `#5314 <https://github.com/pybind/pybind11/pull/5314>`_
+
+Version 2.13.4 (August 14, 2024)
+--------------------------------
+
+Bug fixes:
+
+* Fix paths with spaces, including on Windows.
+  (Replaces regression from `#5302 <https://github.com/pybind/pybind11/pull/5302>`_)
+  `#4874 <https://github.com/pybind/pybind11/pull/4874>`_
+
+Documentation:
+
+* Remove repetitive words.
+  `#5308 <https://github.com/pybind/pybind11/pull/5308>`_
+
+
+Version 2.13.3 (August 13, 2024)
+--------------------------------
+
+Bug fixes:
+
+* Quote paths from pybind11-config
+  `#5302 <https://github.com/pybind/pybind11/pull/5302>`_
+
+
+* Fix typo in Emscripten support when in config mode (CMake)
+  `#5301 <https://github.com/pybind/pybind11/pull/5301>`_
+
+
+Version 2.13.2 (August 13, 2024)
+--------------------------------
+
+New Features:
+
+* A ``pybind11::detail::type_caster_std_function_specializations`` feature was added, to support specializations for
+  ``std::function``'s with return types that require custom to-Python conversion behavior (to primary use case is to catch and
+  convert exceptions).
+  `#4597 <https://github.com/pybind/pybind11/pull/4597>`_
+
+
+Changes:
+
+
+* Use ``PyMutex`` instead of ``std::mutex`` for internal locking in the free-threaded build.
+  `#5219 <https://github.com/pybind/pybind11/pull/5219>`_
+
+* Add a special type annotation for C++ empty tuple.
+  `#5214 <https://github.com/pybind/pybind11/pull/5214>`_
+
+* When compiling for WebAssembly, add the required exception flags (CMake 3.13+).
+  `#5298 <https://github.com/pybind/pybind11/pull/5298>`_
+
+Bug fixes:
+
+* Make ``gil_safe_call_once_and_store`` thread-safe in free-threaded CPython.
+  `#5246 <https://github.com/pybind/pybind11/pull/5246>`_
+
+* A missing ``#include <algorithm>`` in pybind11/typing.h was added to fix build errors (in case user code does not already depend
+  on that include).
+  `#5208 <https://github.com/pybind/pybind11/pull/5208>`_
+
+* Fix regression introduced in #5201 for GCC<10.3 in C++20 mode.
+  `#5205 <https://github.com/pybind/pybind11/pull/5205>`_
+
+
+.. fix(cmake)
+
+* Remove extra = when assigning flto value in the case for Clang in CMake.
+  `#5207 <https://github.com/pybind/pybind11/pull/5207>`_
+
+
+Tests:
+
+* Adding WASM testing to our CI (Pyodide / Emscripten via scikit-build-core).
+  `#4745 <https://github.com/pybind/pybind11/pull/4745>`_
+
+* clang-tidy (in GitHub Actions) was updated from clang 15 to clang 18.
+  `#5272 <https://github.com/pybind/pybind11/pull/5272>`_
+
+
 Version 2.13.1 (June 26, 2024)
 ------------------------------
 
diff --git a/docs/compiling.rst b/docs/compiling.rst
index 0c788335d..94042c3e5 100644
--- a/docs/compiling.rst
+++ b/docs/compiling.rst
@@ -18,7 +18,7 @@ A Python extension module can be created with just a few lines of code:
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.15...3.29)
+    cmake_minimum_required(VERSION 3.15...3.30)
     project(example LANGUAGES CXX)
 
     set(PYBIND11_FINDPYTHON ON)
@@ -319,11 +319,11 @@ Building with CMake
 
 For C++ codebases that have an existing CMake-based build system, a Python
 extension module can be created with just a few lines of code, as seen above in
-the module section. Pybind11 currently supports a lower minimum if you don't
-use the modern FindPython, though be aware that CMake 3.27 removed the old
-mechanism, so pybind11 will automatically switch if the old mechanism is not
-available. Please opt into the new mechanism if at all possible. Our default
-may change in future versions. This is the minimum required:
+the module section. Pybind11 currently defaults to the old mechanism, though be
+aware that CMake 3.27 removed the old mechanism, so pybind11 will automatically
+switch if the old mechanism is not available. Please opt into the new mechanism
+if at all possible. Our default may change in future versions. This is the
+minimum required:
 
 
 
@@ -333,6 +333,9 @@ may change in future versions. This is the minimum required:
 .. versionchanged:: 2.11
    CMake 3.5+ is required.
 
+.. versionchanged:: 2.14
+   CMake 3.15+ is required.
+
 
 Further information can be found at :doc:`cmake/index`.
 
@@ -388,7 +391,7 @@ that will be respected instead of the built-in flag search.
 
 The ``OPT_SIZE`` flag enables size-based optimization equivalent to the
 standard ``/Os`` or ``-Os`` compiler flags and the ``MinSizeRel`` build type,
-which avoid optimizations that that can substantially increase the size of the
+which avoid optimizations that can substantially increase the size of the
 resulting binary. This flag is particularly useful in projects that are split
 into performance-critical parts and associated bindings. In this case, we can
 compile the project in release mode (and hence, optimize performance globally),
@@ -444,7 +447,7 @@ See the `Config file`_ docstring for details of relevant CMake variables.
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.4...3.18)
+    cmake_minimum_required(VERSION 3.15...3.30)
     project(example LANGUAGES CXX)
 
     find_package(pybind11 REQUIRED)
@@ -483,14 +486,13 @@ can refer to the same [cmake_example]_ repository for a full sample project
 FindPython mode
 ---------------
 
-CMake 3.12+ (3.15+ recommended, 3.18.2+ ideal) added a new module called
-FindPython that had a highly improved search algorithm and modern targets
-and tools. If you use FindPython, pybind11 will detect this and use the
-existing targets instead:
+Modern CMake (3.18.2+ ideal) added a new module called FindPython that had a
+highly improved search algorithm and modern targets and tools. If you use
+FindPython, pybind11 will detect this and use the existing targets instead:
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.15...3.22)
+    cmake_minimum_required(VERSION 3.15...3.30)
     project(example LANGUAGES CXX)
 
     find_package(Python 3.8 COMPONENTS Interpreter Development REQUIRED)
@@ -541,7 +543,7 @@ available in all modes. The targets provided are:
      Just the "linking" part of pybind11:module
 
    ``pybind11::module``
-     Everything for extension modules - ``pybind11::pybind11`` + ``Python::Module`` (FindPython CMake 3.15+) or ``pybind11::python_link_helper``
+     Everything for extension modules - ``pybind11::pybind11`` + ``Python::Module`` (FindPython) or ``pybind11::python_link_helper``
 
    ``pybind11::embed``
      Everything for embedding the Python interpreter - ``pybind11::pybind11`` + ``Python::Python`` (FindPython) or Python libs
@@ -568,7 +570,7 @@ You can use these targets to build complex applications. For example, the
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.5...3.29)
+    cmake_minimum_required(VERSION 3.15...3.30)
     project(example LANGUAGES CXX)
 
     find_package(pybind11 REQUIRED)  # or add_subdirectory(pybind11)
@@ -626,7 +628,7 @@ information about usage in C++, see :doc:`/advanced/embedding`.
 
 .. code-block:: cmake
 
-    cmake_minimum_required(VERSION 3.5...3.29)
+    cmake_minimum_required(VERSION 3.15...3.30)
     project(example LANGUAGES CXX)
 
     find_package(pybind11 REQUIRED)  # or add_subdirectory(pybind11)
@@ -719,7 +721,7 @@ customizable pybind11-based wrappers by parsing C++ header files.
 
 [litgen]_ is an automatic python bindings generator with a focus on generating
 documented and discoverable bindings: bindings will nicely reproduce the documentation
-found in headers. It is is based on srcML (srcml.org), a highly scalable, multi-language
+found in headers. It is based on srcML (srcml.org), a highly scalable, multi-language
 parsing tool with a developer centric approach. The API that you want to expose to python
 must be C++14 compatible (but your implementation can use more modern constructs).
 
diff --git a/docs/faq.rst b/docs/faq.rst
index 1eb00efad..92777b5b3 100644
--- a/docs/faq.rst
+++ b/docs/faq.rst
@@ -258,9 +258,9 @@ CMake configure line. (Replace ``$(which python)`` with a path to python if
 your prefer.)
 
 You can alternatively try ``-DPYBIND11_FINDPYTHON=ON``, which will activate the
-new CMake FindPython support instead of pybind11's custom search. Requires
-CMake 3.12+, and 3.15+ or 3.18.2+ are even better. You can set this in your
-``CMakeLists.txt`` before adding or finding pybind11, as well.
+new CMake FindPython support instead of pybind11's custom search. Newer CMake,
+like, 3.18.2+, is recommended. You can set this in your ``CMakeLists.txt``
+before adding or finding pybind11, as well.
 
 Inconsistent detection of Python version in CMake and pybind11
 ==============================================================
@@ -281,11 +281,11 @@ There are three possible solutions:
    from CMake and rely on pybind11 in detecting Python version. If this is not
    possible, the CMake machinery should be called *before* including pybind11.
 2. Set ``PYBIND11_FINDPYTHON`` to ``True`` or use ``find_package(Python
-   COMPONENTS Interpreter Development)`` on modern CMake (3.12+, 3.15+ better,
-   3.18.2+ best). Pybind11 in these cases uses the new CMake FindPython instead
-   of the old, deprecated search tools, and these modules are much better at
-   finding the correct Python. If FindPythonLibs/Interp are not available
-   (CMake 3.27+), then this will be ignored and FindPython will be used.
+   COMPONENTS Interpreter Development)`` on modern CMake ( 3.18.2+ best).
+   Pybind11 in these cases uses the new CMake FindPython instead of the old,
+   deprecated search tools, and these modules are much better at finding the
+   correct Python. If FindPythonLibs/Interp are not available (CMake 3.27+),
+   then this will be ignored and FindPython will be used.
 3. Set ``PYBIND11_NOPYTHON`` to ``TRUE``. Pybind11 will not search for Python.
    However, you will have to use the target-based system, and do more setup
    yourself, because it does not know about or include things that depend on
diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index 4c397c7d1..049d995d0 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -957,8 +957,12 @@ public:
     using base::value;
 
     bool load(handle src, bool convert) {
-        return base::template load_impl<copyable_holder_caster<type, std::shared_ptr<type>>>(
-            src, convert);
+        if (base::template load_impl<copyable_holder_caster<type, std::shared_ptr<type>>>(
+                src, convert)) {
+            sh_load_helper.maybe_set_python_instance_is_alias(src);
+            return true;
+        }
+        return false;
     }
 
     explicit operator std::shared_ptr<type> *() {
@@ -966,14 +970,14 @@ public:
             pybind11_fail("Passing `std::shared_ptr<T> *` from Python to C++ is not supported "
                           "(inherently unsafe).");
         }
-        return std::addressof(shared_ptr_holder);
+        return std::addressof(shared_ptr_storage);
     }
 
     explicit operator std::shared_ptr<type> &() {
         if (typeinfo->holder_enum_v == detail::holder_enum_t::smart_holder) {
-            shared_ptr_holder = sh_load_helper.load_as_shared_ptr(value);
+            shared_ptr_storage = sh_load_helper.load_as_shared_ptr(value);
         }
-        return shared_ptr_holder;
+        return shared_ptr_storage;
     }
 
     static handle
@@ -1013,12 +1017,13 @@ protected:
     void load_value(value_and_holder &&v_h) {
         if (typeinfo->holder_enum_v == detail::holder_enum_t::smart_holder) {
             sh_load_helper.loaded_v_h = v_h;
+            sh_load_helper.was_populated = true;
             value = sh_load_helper.get_void_ptr_or_nullptr();
             return;
         }
         if (v_h.holder_constructed()) {
             value = v_h.value_ptr();
-            shared_ptr_holder = v_h.template holder<std::shared_ptr<type>>();
+            shared_ptr_storage = v_h.template holder<std::shared_ptr<type>>();
             return;
         }
         throw cast_error("Unable to cast from non-held to held instance (T& to Holder<T>) "
@@ -1047,8 +1052,8 @@ protected:
                 if (typeinfo->holder_enum_v == detail::holder_enum_t::smart_holder) {
                     sh_load_helper.loaded_v_h = sub_caster.sh_load_helper.loaded_v_h;
                 } else {
-                    shared_ptr_holder
-                        = std::shared_ptr<type>(sub_caster.shared_ptr_holder, (type *) value);
+                    shared_ptr_storage
+                        = std::shared_ptr<type>(sub_caster.shared_ptr_storage, (type *) value);
                 }
                 return true;
             }
@@ -1058,8 +1063,8 @@ protected:
 
     static bool try_direct_conversions(handle) { return false; }
 
-    std::shared_ptr<type> shared_ptr_holder;
     smart_holder_type_caster_support::load_helper<remove_cv_t<type>> sh_load_helper; // Const2Mutbl
+    std::shared_ptr<type> shared_ptr_storage;
 };
 
 #endif // PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
@@ -1134,20 +1139,25 @@ public:
             policy = return_value_policy::reference_internal;
         }
         if (policy != return_value_policy::reference_internal) {
-            throw cast_error("Invalid return_value_policy for unique_ptr&");
+            throw cast_error("Invalid return_value_policy for const unique_ptr&");
         }
         return type_caster_base<type>::cast(src.get(), policy, parent);
     }
 
     bool load(handle src, bool convert) {
-        return base::template load_impl<
-            move_only_holder_caster<type, std::unique_ptr<type, deleter>>>(src, convert);
+        if (base::template load_impl<
+                move_only_holder_caster<type, std::unique_ptr<type, deleter>>>(src, convert)) {
+            sh_load_helper.maybe_set_python_instance_is_alias(src);
+            return true;
+        }
+        return false;
     }
 
     void load_value(value_and_holder &&v_h) {
         if (typeinfo->holder_enum_v == detail::holder_enum_t::smart_holder) {
             sh_load_helper.loaded_v_h = v_h;
             sh_load_helper.loaded_v_h.type = typeinfo;
+            sh_load_helper.was_populated = true;
             value = sh_load_helper.get_void_ptr_or_nullptr();
             return;
         }
@@ -1156,8 +1166,14 @@ public:
             + clean_type_id(typeinfo->cpptype->name()) + ")");
     }
 
-    template <typename>
-    using cast_op_type = std::unique_ptr<type, deleter>;
+    template <typename T_>
+    using cast_op_type
+        = conditional_t<std::is_same<typename std::remove_volatile<T_>::type,
+                                     const std::unique_ptr<type, deleter> &>::value
+                            || std::is_same<typename std::remove_volatile<T_>::type,
+                                            const std::unique_ptr<const type, deleter> &>::value,
+                        const std::unique_ptr<type, deleter> &,
+                        std::unique_ptr<type, deleter>>;
 
     explicit operator std::unique_ptr<type, deleter>() {
         if (typeinfo->holder_enum_v == detail::holder_enum_t::smart_holder) {
@@ -1166,6 +1182,28 @@ public:
         pybind11_fail("Expected to be UNREACHABLE: " __FILE__ ":" PYBIND11_TOSTRING(__LINE__));
     }
 
+    explicit operator const std::unique_ptr<type, deleter> &() {
+        if (typeinfo->holder_enum_v == detail::holder_enum_t::smart_holder) {
+            // Get shared_ptr to ensure that the Python object is not disowned elsewhere.
+            shared_ptr_storage = sh_load_helper.load_as_shared_ptr(value);
+            // Build a temporary unique_ptr that is meant to never expire.
+            unique_ptr_storage = std::shared_ptr<std::unique_ptr<type, deleter>>(
+                new std::unique_ptr<type, deleter>{
+                    sh_load_helper.template load_as_const_unique_ptr<deleter>(
+                        shared_ptr_storage.get())},
+                [](std::unique_ptr<type, deleter> *ptr) {
+                    if (!ptr) {
+                        pybind11_fail("FATAL: `const std::unique_ptr<T, D> &` was disowned "
+                                      "(EXPECT UNDEFINED BEHAVIOR).");
+                    }
+                    (void) ptr->release();
+                    delete ptr;
+                });
+            return *unique_ptr_storage;
+        }
+        pybind11_fail("Expected to be UNREACHABLE: " __FILE__ ":" PYBIND11_TOSTRING(__LINE__));
+    }
+
     bool try_implicit_casts(handle src, bool convert) {
         for (auto &cast : typeinfo->implicit_casts) {
             move_only_holder_caster sub_caster(*cast.first);
@@ -1186,6 +1224,8 @@ public:
     static bool try_direct_conversions(handle) { return false; }
 
     smart_holder_type_caster_support::load_helper<remove_cv_t<type>> sh_load_helper; // Const2Mutbl
+    std::shared_ptr<type> shared_ptr_storage; // Serves as a pseudo lock.
+    std::shared_ptr<std::unique_ptr<type, deleter>> unique_ptr_storage;
 };
 
 #endif // PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
diff --git a/include/pybind11/detail/class.h b/include/pybind11/detail/class.h
index b79c701c0..191315c0e 100644
--- a/include/pybind11/detail/class.h
+++ b/include/pybind11/detail/class.h
@@ -9,8 +9,8 @@
 
 #pragma once
 
-#include "../attr.h"
-#include "../options.h"
+#include <pybind11/attr.h>
+#include <pybind11/options.h>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
diff --git a/include/pybind11/detail/common.h b/include/pybind11/detail/common.h
index b18dc8501..c75e8ab21 100644
--- a/include/pybind11/detail/common.h
+++ b/include/pybind11/detail/common.h
@@ -479,6 +479,8 @@ PYBIND11_WARNING_POP
         }
 
 \endrst */
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_CLANG("-Wgnu-zero-variadic-macro-arguments")
 #define PYBIND11_MODULE(name, variable, ...)                                                      \
     static ::pybind11::module_::module_def PYBIND11_CONCAT(pybind11_module_def_, name)            \
         PYBIND11_MAYBE_UNUSED;                                                                    \
@@ -499,6 +501,7 @@ PYBIND11_WARNING_POP
         PYBIND11_CATCH_INIT_EXCEPTIONS                                                            \
     }                                                                                             \
     void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_ & (variable))
+PYBIND11_WARNING_POP
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
@@ -554,7 +557,7 @@ enum class return_value_policy : uint8_t {
         object without taking ownership similar to the above
         return_value_policy::reference policy. In contrast to that policy, the
         function or property's implicit this argument (called the parent) is
-        considered to be the the owner of the return value (the child).
+        considered to be the owner of the return value (the child).
         pybind11 then couples the lifetime of the parent to the child via a
         reference relationship that ensures that the parent cannot be garbage
         collected while Python is still using the child. More advanced
@@ -637,6 +640,11 @@ struct instance {
     bool simple_instance_registered : 1;
     /// If true, get_internals().patients has an entry for this object
     bool has_patients : 1;
+// Cannot use PYBIND11_INTERNALS_VERSION >= 6 here without refactoring.
+#if PYBIND11_VERSION_MAJOR >= 3
+    /// If true, this Python object needs to be kept alive for the lifetime of the C++ value.
+    bool is_alias : 1;
+#endif
 
     /// Initializes all of the above type/values/holders data (but not the instance values
     /// themselves)
diff --git a/include/pybind11/detail/internals.h b/include/pybind11/detail/internals.h
index cf36bf498..a41c9a97b 100644
--- a/include/pybind11/detail/internals.h
+++ b/include/pybind11/detail/internals.h
@@ -12,10 +12,10 @@
 #include "common.h"
 
 #if defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
-#    include "../gil.h"
+#    include <pybind11/gil.h>
 #endif
 
-#include "../pytypes.h"
+#include <pybind11/pytypes.h>
 
 #include <exception>
 #include <mutex>
diff --git a/include/pybind11/detail/smart_holder_poc.h b/include/pybind11/detail/struct_smart_holder.h
similarity index 84%
rename from include/pybind11/detail/smart_holder_poc.h
rename to include/pybind11/detail/struct_smart_holder.h
index 89742ab27..b1e24d7bb 100644
--- a/include/pybind11/detail/smart_holder_poc.h
+++ b/include/pybind11/detail/struct_smart_holder.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2020-2021 The Pybind Development Team.
+// Copyright (c) 2020-2024 The Pybind Development Team.
 // All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
@@ -44,16 +44,6 @@ Details:
 * The `void_cast_raw_ptr` option is needed to make the `smart_holder` `vptr`
   member invisible to the `shared_from_this` mechanism, in case the lifetime
   of a `PyObject` is tied to the pointee.
-
-* Regarding `PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP` below:
-  This define serves as a marker for code that is NOT used
-  from smart_holder_type_casters.h, but is exercised only from
-  tests/pure_cpp/smart_holder_poc_test.cpp. The marked code was useful
-  mainly for bootstrapping the smart_holder work. At this stage, with
-  smart_holder_type_casters.h in production use (at Google) since around
-  February 2021, it could be moved from here to tests/pure_cpp/ (help welcome).
-  It will probably be best in most cases to add tests for new functionality
-  under test/test_class_sh_*.
 */
 
 #pragma once
@@ -146,7 +136,6 @@ struct smart_holder {
     bool vptr_is_external_shared_ptr : 1;
     bool is_populated : 1;
     bool is_disowned : 1;
-    bool pointee_depends_on_holder_owner : 1; // SMART_HOLDER_WIP: See PR #2839.
 
     // Design choice: smart_holder is movable but not copyable.
     smart_holder(smart_holder &&) = default;
@@ -156,8 +145,7 @@ struct smart_holder {
 
     smart_holder()
         : vptr_is_using_noop_deleter{false}, vptr_is_using_builtin_delete{false},
-          vptr_is_external_shared_ptr{false}, is_populated{false}, is_disowned{false},
-          pointee_depends_on_holder_owner{false} {}
+          vptr_is_external_shared_ptr{false}, is_populated{false}, is_disowned{false} {}
 
     bool has_pointee() const { return vptr != nullptr; }
 
@@ -243,6 +231,24 @@ struct smart_holder {
         vptr_del_ptr->armed_flag = armed_flag;
     }
 
+    // Caller is responsible for precondition: ensure_compatible_rtti_uqp_del<T, D>() must succeed.
+    template <typename T, typename D>
+    std::unique_ptr<D> extract_deleter(const char *context) const {
+        const auto *gd = std::get_deleter<guarded_delete>(vptr);
+        if (gd && gd->use_del_fun) {
+            const auto &custom_deleter_ptr = gd->del_fun.template target<custom_deleter<T, D>>();
+            if (custom_deleter_ptr == nullptr) {
+                throw std::runtime_error(
+                    std::string("smart_holder::extract_deleter() precondition failure (") + context
+                    + ").");
+            }
+            static_assert(std::is_copy_constructible<D>::value,
+                          "Required for compatibility with smart_holder functionality.");
+            return std::unique_ptr<D>(new D(custom_deleter_ptr->deleter));
+        }
+        return nullptr;
+    }
+
     static smart_holder from_raw_ptr_unowned(void *raw_ptr) {
         smart_holder hld;
         hld.vptr.reset(raw_ptr, [](void *) {});
@@ -256,26 +262,6 @@ struct smart_holder {
         return static_cast<T *>(vptr.get());
     }
 
-#ifdef PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP // See comment near top.
-    template <typename T>
-    T &as_lvalue_ref() const {
-        static const char *context = "as_lvalue_ref";
-        ensure_is_populated(context);
-        ensure_has_pointee(context);
-        return *as_raw_ptr_unowned<T>();
-    }
-#endif
-
-#ifdef PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP // See comment near top.
-    template <typename T>
-    T &&as_rvalue_ref() const {
-        static const char *context = "as_rvalue_ref";
-        ensure_is_populated(context);
-        ensure_has_pointee(context);
-        return std::move(*as_raw_ptr_unowned<T>());
-    }
-#endif
-
     template <typename T>
     static smart_holder from_raw_ptr_take_ownership(T *raw_ptr, bool void_cast_raw_ptr = false) {
         ensure_pointee_is_destructible<T>("from_raw_ptr_take_ownership");
@@ -319,16 +305,6 @@ struct smart_holder {
         release_disowned();
     }
 
-#ifdef PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP // See comment near top.
-    template <typename T>
-    T *as_raw_ptr_release_ownership(const char *context = "as_raw_ptr_release_ownership") {
-        ensure_can_release_ownership(context);
-        T *raw_ptr = as_raw_ptr_unowned<T>();
-        release_ownership();
-        return raw_ptr;
-    }
-#endif
-
     template <typename T, typename D>
     static smart_holder from_unique_ptr(std::unique_ptr<T, D> &&unq_ptr,
                                         void *void_ptr = nullptr) {
@@ -351,19 +327,6 @@ struct smart_holder {
         return hld;
     }
 
-#ifdef PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP // See comment near top.
-    template <typename T, typename D = std::default_delete<T>>
-    std::unique_ptr<T, D> as_unique_ptr() {
-        static const char *context = "as_unique_ptr";
-        ensure_compatible_rtti_uqp_del<T, D>(context);
-        ensure_use_count_1(context);
-        T *raw_ptr = as_raw_ptr_unowned<T>();
-        release_ownership();
-        // KNOWN DEFECT (see PR #4850): Does not copy the deleter.
-        return std::unique_ptr<T, D>(raw_ptr);
-    }
-#endif
-
     template <typename T>
     static smart_holder from_shared_ptr(std::shared_ptr<T> shd_ptr) {
         smart_holder hld;
diff --git a/include/pybind11/detail/type_caster_base.h b/include/pybind11/detail/type_caster_base.h
index 92415718f..f1a5d0d8d 100644
--- a/include/pybind11/detail/type_caster_base.h
+++ b/include/pybind11/detail/type_caster_base.h
@@ -9,9 +9,10 @@
 
 #pragma once
 
-#include "../gil.h"
-#include "../pytypes.h"
-#include "../trampoline_self_life_support.h"
+#include <pybind11/gil.h>
+#include <pybind11/pytypes.h>
+#include <pybind11/trampoline_self_life_support.h>
+
 #include "common.h"
 #include "descr.h"
 #include "dynamic_raw_ptr_cast_if_possible.h"
@@ -704,6 +705,15 @@ inline std::unique_ptr<T, D> unique_with_deleter(T *raw_ptr, std::unique_ptr<D>
 
 template <typename T>
 struct load_helper : value_and_holder_helper {
+    bool was_populated = false;
+    bool python_instance_is_alias = false;
+
+    void maybe_set_python_instance_is_alias(handle src) {
+        if (was_populated) {
+            python_instance_is_alias = reinterpret_cast<instance *>(src.ptr())->is_alias;
+        }
+    }
+
     static std::shared_ptr<T> make_shared_ptr_with_responsible_parent(T *raw_ptr, handle parent) {
         return std::shared_ptr<T>(raw_ptr, shared_ptr_parent_life_support(parent.ptr()));
     }
@@ -724,7 +734,7 @@ struct load_helper : value_and_holder_helper {
             throw std::runtime_error("Non-owning holder (load_as_shared_ptr).");
         }
         auto *type_raw_ptr = static_cast<T *>(void_raw_ptr);
-        if (hld.pointee_depends_on_holder_owner) {
+        if (python_instance_is_alias) {
             auto *vptr_gd_ptr = std::get_deleter<pybindit::memory::guarded_delete>(hld.vptr);
             if (vptr_gd_ptr != nullptr) {
                 std::shared_ptr<void> released_ptr = vptr_gd_ptr->released_ptr.lock();
@@ -778,28 +788,13 @@ struct load_helper : value_and_holder_helper {
 
         auto *self_life_support
             = dynamic_raw_ptr_cast_if_possible<trampoline_self_life_support>(raw_type_ptr);
-        if (self_life_support == nullptr && holder().pointee_depends_on_holder_owner) {
+        if (self_life_support == nullptr && python_instance_is_alias) {
             throw value_error("Alias class (also known as trampoline) does not inherit from "
                               "py::trampoline_self_life_support, therefore the ownership of this "
                               "instance cannot safely be transferred to C++.");
         }
 
-        // Temporary variable to store the extracted deleter in.
-        std::unique_ptr<D> extracted_deleter;
-
-        auto *gd = std::get_deleter<pybindit::memory::guarded_delete>(holder().vptr);
-        if (gd && gd->use_del_fun) { // Note the ensure_compatible_rtti_uqp_del<T, D>() call above.
-            // In smart_holder_poc, a custom  deleter is always stored in a guarded delete.
-            // The guarded delete's std::function<void(void*)> actually points at the
-            // custom_deleter type, so we can verify it is of the custom deleter type and
-            // finally extract its deleter.
-            using custom_deleter_D = pybindit::memory::custom_deleter<T, D>;
-            const auto &custom_deleter_ptr = gd->del_fun.template target<custom_deleter_D>();
-            assert(custom_deleter_ptr != nullptr);
-            // Now that we have confirmed the type of the deleter matches the desired return
-            // value we can extract the function.
-            extracted_deleter = std::unique_ptr<D>(new D(std::move(custom_deleter_ptr->deleter)));
-        }
+        std::unique_ptr<D> extracted_deleter = holder().template extract_deleter<T, D>(context);
 
         // Critical transfer-of-ownership section. This must stay together.
         if (self_life_support != nullptr) {
@@ -819,6 +814,19 @@ struct load_helper : value_and_holder_helper {
 
         return result;
     }
+
+    // This assumes load_as_shared_ptr succeeded(), and the returned shared_ptr is still alive.
+    // The returned unique_ptr is meant to never expire (the behavior is undefined otherwise).
+    template <typename D>
+    std::unique_ptr<T, D>
+    load_as_const_unique_ptr(T *raw_type_ptr, const char *context = "load_as_const_unique_ptr") {
+        if (!have_holder()) {
+            return unique_with_deleter<T, D>(nullptr, std::unique_ptr<D>());
+        }
+        holder().template ensure_compatible_rtti_uqp_del<T, D>(context);
+        return unique_with_deleter<T, D>(
+            raw_type_ptr, std::move(holder().template extract_deleter<T, D>(context)));
+    }
 };
 
 PYBIND11_NAMESPACE_END(smart_holder_type_caster_support)
diff --git a/include/pybind11/detail/using_smart_holder.h b/include/pybind11/detail/using_smart_holder.h
index 3d0463209..826e6b2c6 100644
--- a/include/pybind11/detail/using_smart_holder.h
+++ b/include/pybind11/detail/using_smart_holder.h
@@ -10,7 +10,7 @@
 #include <type_traits>
 
 #ifdef PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-#    include "smart_holder_poc.h"
+#    include "struct_smart_holder.h"
 #endif
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
diff --git a/include/pybind11/eigen/matrix.h b/include/pybind11/eigen/matrix.h
index 8d4342f81..5cf1f0a2a 100644
--- a/include/pybind11/eigen/matrix.h
+++ b/include/pybind11/eigen/matrix.h
@@ -9,7 +9,8 @@
 
 #pragma once
 
-#include "../numpy.h"
+#include <pybind11/numpy.h>
+
 #include "common.h"
 
 /* HINT: To suppress warnings originating from the Eigen headers, use -isystem.
diff --git a/include/pybind11/eigen/tensor.h b/include/pybind11/eigen/tensor.h
index 14bb91c40..0a9d7c252 100644
--- a/include/pybind11/eigen/tensor.h
+++ b/include/pybind11/eigen/tensor.h
@@ -7,7 +7,8 @@
 
 #pragma once
 
-#include "../numpy.h"
+#include <pybind11/numpy.h>
+
 #include "common.h"
 
 #if defined(__GNUC__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
diff --git a/include/pybind11/functional.h b/include/pybind11/functional.h
index 6856119cd..4b3610117 100644
--- a/include/pybind11/functional.h
+++ b/include/pybind11/functional.h
@@ -9,12 +9,55 @@
 
 #pragma once
 
+#define PYBIND11_HAS_TYPE_CASTER_STD_FUNCTION_SPECIALIZATIONS
+
 #include "pybind11.h"
 
 #include <functional>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
+PYBIND11_NAMESPACE_BEGIN(type_caster_std_function_specializations)
+
+// ensure GIL is held during functor destruction
+struct func_handle {
+    function f;
+#if !(defined(_MSC_VER) && _MSC_VER == 1916 && defined(PYBIND11_CPP17))
+    // This triggers a syntax error under very special conditions (very weird indeed).
+    explicit
+#endif
+        func_handle(function &&f_) noexcept
+        : f(std::move(f_)) {
+    }
+    func_handle(const func_handle &f_) { operator=(f_); }
+    func_handle &operator=(const func_handle &f_) {
+        gil_scoped_acquire acq;
+        f = f_.f;
+        return *this;
+    }
+    ~func_handle() {
+        gil_scoped_acquire acq;
+        function kill_f(std::move(f));
+    }
+};
+
+// to emulate 'move initialization capture' in C++11
+struct func_wrapper_base {
+    func_handle hfunc;
+    explicit func_wrapper_base(func_handle &&hf) noexcept : hfunc(hf) {}
+};
+
+template <typename Return, typename... Args>
+struct func_wrapper : func_wrapper_base {
+    using func_wrapper_base::func_wrapper_base;
+    Return operator()(Args... args) const {
+        gil_scoped_acquire acq;
+        // casts the returned object as a rvalue to the return type
+        return hfunc.f(std::forward<Args>(args)...).template cast<Return>();
+    }
+};
+
+PYBIND11_NAMESPACE_END(type_caster_std_function_specializations)
 
 template <typename Return, typename... Args>
 struct type_caster<std::function<Return(Args...)>> {
@@ -77,40 +120,8 @@ public:
             // See PR #1413 for full details
         }
 
-        // ensure GIL is held during functor destruction
-        struct func_handle {
-            function f;
-#if !(defined(_MSC_VER) && _MSC_VER == 1916 && defined(PYBIND11_CPP17))
-            // This triggers a syntax error under very special conditions (very weird indeed).
-            explicit
-#endif
-                func_handle(function &&f_) noexcept
-                : f(std::move(f_)) {
-            }
-            func_handle(const func_handle &f_) { operator=(f_); }
-            func_handle &operator=(const func_handle &f_) {
-                gil_scoped_acquire acq;
-                f = f_.f;
-                return *this;
-            }
-            ~func_handle() {
-                gil_scoped_acquire acq;
-                function kill_f(std::move(f));
-            }
-        };
-
-        // to emulate 'move initialization capture' in C++11
-        struct func_wrapper {
-            func_handle hfunc;
-            explicit func_wrapper(func_handle &&hf) noexcept : hfunc(std::move(hf)) {}
-            Return operator()(Args... args) const {
-                gil_scoped_acquire acq;
-                // casts the returned object as a rvalue to the return type
-                return hfunc.f(std::forward<Args>(args)...).template cast<Return>();
-            }
-        };
-
-        value = func_wrapper(func_handle(std::move(func)));
+        value = type_caster_std_function_specializations::func_wrapper<Return, Args...>(
+            type_caster_std_function_specializations::func_handle(std::move(func)));
         return true;
     }
 
diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index 0bdc72c21..f2534e78d 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -2278,7 +2278,8 @@ private:
         }
         auto *uninitialized_location = std::addressof(v_h.holder<holder_type>());
         auto *value_ptr_w_t = v_h.value_ptr<type>();
-        bool pointee_depends_on_holder_owner
+        // Try downcast from `type` to `type_alias`:
+        inst->is_alias
             = detail::dynamic_raw_ptr_cast_if_possible<type_alias>(value_ptr_w_t) != nullptr;
         if (holder_void_ptr) {
             // Note: inst->owned ignored.
@@ -2288,14 +2289,12 @@ private:
                        uninitialized_location, value_ptr_w_t, value_ptr_w_t)) {
             if (inst->owned) {
                 new (uninitialized_location) holder_type(holder_type::from_raw_ptr_take_ownership(
-                    value_ptr_w_t, /*void_cast_raw_ptr*/ pointee_depends_on_holder_owner));
+                    value_ptr_w_t, /*void_cast_raw_ptr*/ inst->is_alias));
             } else {
                 new (uninitialized_location)
                     holder_type(holder_type::from_raw_ptr_unowned(value_ptr_w_t));
             }
         }
-        v_h.holder<holder_type>().pointee_depends_on_holder_owner
-            = pointee_depends_on_holder_owner;
         v_h.set_holder_constructed();
     }
 
diff --git a/include/pybind11/pytypes.h b/include/pybind11/pytypes.h
index a5d9e5aa9..719bf8aa7 100644
--- a/include/pybind11/pytypes.h
+++ b/include/pybind11/pytypes.h
@@ -1263,6 +1263,7 @@ protected:
     using pointer = arrow_proxy<const handle>;
 
     sequence_fast_readonly(handle obj, ssize_t n) : ptr(PySequence_Fast_ITEMS(obj.ptr()) + n) {}
+    sequence_fast_readonly() = default;
 
     // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
     reference dereference() const { return *ptr; }
@@ -1285,6 +1286,7 @@ protected:
     using pointer = arrow_proxy<const sequence_accessor>;
 
     sequence_slow_readwrite(handle obj, ssize_t index) : obj(obj), index(index) {}
+    sequence_slow_readwrite() = default;
 
     reference dereference() const { return {obj, static_cast<size_t>(index)}; }
     void increment() { ++index; }
diff --git a/include/pybind11/stl.h b/include/pybind11/stl.h
index 71bc5902e..6a148e740 100644
--- a/include/pybind11/stl.h
+++ b/include/pybind11/stl.h
@@ -11,10 +11,14 @@
 
 #include "pybind11.h"
 #include "detail/common.h"
+#include "detail/descr.h"
+#include "detail/type_caster_base.h"
 
 #include <deque>
+#include <initializer_list>
 #include <list>
 #include <map>
+#include <memory>
 #include <ostream>
 #include <set>
 #include <unordered_map>
@@ -35,6 +39,89 @@
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
 
+//
+// Begin: Equivalent of
+//        https://github.com/google/clif/blob/ae4eee1de07cdf115c0c9bf9fec9ff28efce6f6c/clif/python/runtime.cc#L388-L438
+/*
+The three `PyObjectTypeIsConvertibleTo*()` functions below are
+the result of converging the behaviors of pybind11 and PyCLIF
+(http://github.com/google/clif).
+
+Originally PyCLIF was extremely far on the permissive side of the spectrum,
+while pybind11 was very far on the strict side. Originally PyCLIF accepted any
+Python iterable as input for a C++ `vector`/`set`/`map` argument, as long as
+the elements were convertible. The obvious (in hindsight) problem was that
+any empty Python iterable could be passed to any of these C++ types, e.g. `{}`
+was accepted for C++ `vector`/`set` arguments, or `[]` for C++ `map` arguments.
+
+The functions below strike a practical permissive-vs-strict compromise,
+informed by tens of thousands of use cases in the wild. A main objective is
+to prevent accidents and improve readability:
+
+- Python literals must match the C++ types.
+
+- For C++ `set`: The potentially reducing conversion from a Python sequence
+  (e.g. Python `list` or `tuple`) to a C++ `set` must be explicit, by going
+  through a Python `set`.
+
+- However, a Python `set` can still be passed to a C++ `vector`. The rationale
+  is that this conversion is not reducing. Implicit conversions of this kind
+  are also fairly commonly used, therefore enforcing explicit conversions
+  would have an unfavorable cost : benefit ratio; more sloppily speaking,
+  such an enforcement would be more annoying than helpful.
+*/
+
+inline bool PyObjectIsInstanceWithOneOfTpNames(PyObject *obj,
+                                               std::initializer_list<const char *> tp_names) {
+    if (PyType_Check(obj)) {
+        return false;
+    }
+    const char *obj_tp_name = Py_TYPE(obj)->tp_name;
+    for (const auto *tp_name : tp_names) {
+        if (std::strcmp(obj_tp_name, tp_name) == 0) {
+            return true;
+        }
+    }
+    return false;
+}
+
+inline bool PyObjectTypeIsConvertibleToStdVector(PyObject *obj) {
+    if (PySequence_Check(obj) != 0) {
+        return !PyUnicode_Check(obj) && !PyBytes_Check(obj);
+    }
+    return (PyGen_Check(obj) != 0) || (PyAnySet_Check(obj) != 0)
+           || PyObjectIsInstanceWithOneOfTpNames(
+               obj, {"dict_keys", "dict_values", "dict_items", "map", "zip"});
+}
+
+inline bool PyObjectTypeIsConvertibleToStdSet(PyObject *obj) {
+    return (PyAnySet_Check(obj) != 0) || PyObjectIsInstanceWithOneOfTpNames(obj, {"dict_keys"});
+}
+
+inline bool PyObjectTypeIsConvertibleToStdMap(PyObject *obj) {
+    if (PyDict_Check(obj)) {
+        return true;
+    }
+    // Implicit requirement in the conditions below:
+    // A type with `.__getitem__()` & `.items()` methods must implement these
+    // to be compatible with https://docs.python.org/3/c-api/mapping.html
+    if (PyMapping_Check(obj) == 0) {
+        return false;
+    }
+    PyObject *items = PyObject_GetAttrString(obj, "items");
+    if (items == nullptr) {
+        PyErr_Clear();
+        return false;
+    }
+    bool is_convertible = (PyCallable_Check(items) != 0);
+    Py_DECREF(items);
+    return is_convertible;
+}
+
+//
+// End: Equivalent of clif/python/runtime.cc
+//
+
 /// Extracts an const lvalue reference or rvalue reference for U based on the type of T (e.g. for
 /// forwarding a container element).  Typically used indirect via forwarded_type(), below.
 template <typename T, typename U>
@@ -66,17 +153,10 @@ private:
     }
     void reserve_maybe(const anyset &, void *) {}
 
-public:
-    bool load(handle src, bool convert) {
-        if (!isinstance<anyset>(src)) {
-            return false;
-        }
-        auto s = reinterpret_borrow<anyset>(src);
-        value.clear();
-        reserve_maybe(s, &value);
-        for (auto entry : s) {
+    bool convert_iterable(const iterable &itbl, bool convert) {
+        for (const auto &it : itbl) {
             key_conv conv;
-            if (!conv.load(entry, convert)) {
+            if (!conv.load(it, convert)) {
                 return false;
             }
             value.insert(cast_op<Key &&>(std::move(conv)));
@@ -84,6 +164,29 @@ public:
         return true;
     }
 
+    bool convert_anyset(anyset s, bool convert) {
+        value.clear();
+        reserve_maybe(s, &value);
+        return convert_iterable(s, convert);
+    }
+
+public:
+    bool load(handle src, bool convert) {
+        if (!PyObjectTypeIsConvertibleToStdSet(src.ptr())) {
+            return false;
+        }
+        if (isinstance<anyset>(src)) {
+            value.clear();
+            return convert_anyset(reinterpret_borrow<anyset>(src), convert);
+        }
+        if (!convert) {
+            return false;
+        }
+        assert(isinstance<iterable>(src));
+        value.clear();
+        return convert_iterable(reinterpret_borrow<iterable>(src), convert);
+    }
+
     template <typename T>
     static handle cast(T &&src, return_value_policy policy, handle parent) {
         if (!std::is_lvalue_reference<T>::value) {
@@ -115,15 +218,10 @@ private:
     }
     void reserve_maybe(const dict &, void *) {}
 
-public:
-    bool load(handle src, bool convert) {
-        if (!isinstance<dict>(src)) {
-            return false;
-        }
-        auto d = reinterpret_borrow<dict>(src);
+    bool convert_elements(const dict &d, bool convert) {
         value.clear();
         reserve_maybe(d, &value);
-        for (auto it : d) {
+        for (const auto &it : d) {
             key_conv kconv;
             value_conv vconv;
             if (!kconv.load(it.first.ptr(), convert) || !vconv.load(it.second.ptr(), convert)) {
@@ -134,6 +232,25 @@ public:
         return true;
     }
 
+public:
+    bool load(handle src, bool convert) {
+        if (!PyObjectTypeIsConvertibleToStdMap(src.ptr())) {
+            return false;
+        }
+        if (isinstance<dict>(src)) {
+            return convert_elements(reinterpret_borrow<dict>(src), convert);
+        }
+        if (!convert) {
+            return false;
+        }
+        auto items = reinterpret_steal<object>(PyMapping_Items(src.ptr()));
+        if (!items) {
+            throw error_already_set();
+        }
+        assert(isinstance<iterable>(items));
+        return convert_elements(dict(reinterpret_borrow<iterable>(items)), convert);
+    }
+
     template <typename T>
     static handle cast(T &&src, return_value_policy policy, handle parent) {
         dict d;
@@ -166,20 +283,21 @@ struct list_caster {
     using value_conv = make_caster<Value>;
 
     bool load(handle src, bool convert) {
-        if (!isinstance<sequence>(src) || isinstance<bytes>(src) || isinstance<str>(src)) {
+        if (!PyObjectTypeIsConvertibleToStdVector(src.ptr())) {
             return false;
         }
-        auto s = reinterpret_borrow<sequence>(src);
-        value.clear();
-        reserve_maybe(s, &value);
-        for (const auto &it : s) {
-            value_conv conv;
-            if (!conv.load(it, convert)) {
-                return false;
-            }
-            value.push_back(cast_op<Value &&>(std::move(conv)));
+        if (isinstance<sequence>(src)) {
+            return convert_elements(src, convert);
         }
-        return true;
+        if (!convert) {
+            return false;
+        }
+        // Designed to be behavior-equivalent to passing tuple(src) from Python:
+        // The conversion to a tuple will first exhaust the generator object, to ensure that
+        // the generator is not left in an unpredictable (to the caller) partially-consumed
+        // state.
+        assert(isinstance<iterable>(src));
+        return convert_elements(tuple(reinterpret_borrow<iterable>(src)), convert);
     }
 
 private:
@@ -189,6 +307,20 @@ private:
     }
     void reserve_maybe(const sequence &, void *) {}
 
+    bool convert_elements(handle seq, bool convert) {
+        auto s = reinterpret_borrow<sequence>(seq);
+        value.clear();
+        reserve_maybe(s, &value);
+        for (const auto &it : seq) {
+            value_conv conv;
+            if (!conv.load(it, convert)) {
+                return false;
+            }
+            value.push_back(cast_op<Value &&>(std::move(conv)));
+        }
+        return true;
+    }
+
 public:
     template <typename T>
     static handle cast(T &&src, return_value_policy policy, handle parent) {
@@ -220,43 +352,87 @@ struct type_caster<std::deque<Type, Alloc>> : list_caster<std::deque<Type, Alloc
 template <typename Type, typename Alloc>
 struct type_caster<std::list<Type, Alloc>> : list_caster<std::list<Type, Alloc>, Type> {};
 
+template <typename ArrayType, typename V, size_t... I>
+ArrayType vector_to_array_impl(V &&v, index_sequence<I...>) {
+    return {{std::move(v[I])...}};
+}
+
+// Based on https://en.cppreference.com/w/cpp/container/array/to_array
+template <typename ArrayType, size_t N, typename V>
+ArrayType vector_to_array(V &&v) {
+    return vector_to_array_impl<ArrayType, V>(std::forward<V>(v), make_index_sequence<N>{});
+}
+
 template <typename ArrayType, typename Value, bool Resizable, size_t Size = 0>
 struct array_caster {
     using value_conv = make_caster<Value>;
 
 private:
-    template <bool R = Resizable>
-    bool require_size(enable_if_t<R, size_t> size) {
-        if (value.size() != size) {
-            value.resize(size);
-        }
-        return true;
-    }
-    template <bool R = Resizable>
-    bool require_size(enable_if_t<!R, size_t> size) {
-        return size == Size;
-    }
+    std::unique_ptr<ArrayType> value;
 
-public:
-    bool load(handle src, bool convert) {
-        if (!isinstance<sequence>(src)) {
-            return false;
-        }
-        auto l = reinterpret_borrow<sequence>(src);
-        if (!require_size(l.size())) {
-            return false;
-        }
+    template <bool R = Resizable, enable_if_t<R, int> = 0>
+    bool convert_elements(handle seq, bool convert) {
+        auto l = reinterpret_borrow<sequence>(seq);
+        value.reset(new ArrayType{});
+        // Using `resize` to preserve the behavior exactly as it was before PR #5305
+        // For the `resize` to work, `Value` must be default constructible.
+        // For `std::valarray`, this is a requirement:
+        // https://en.cppreference.com/w/cpp/named_req/NumericType
+        value->resize(l.size());
         size_t ctr = 0;
         for (const auto &it : l) {
             value_conv conv;
             if (!conv.load(it, convert)) {
                 return false;
             }
-            value[ctr++] = cast_op<Value &&>(std::move(conv));
+            (*value)[ctr++] = cast_op<Value &&>(std::move(conv));
         }
         return true;
     }
 
+    template <bool R = Resizable, enable_if_t<!R, int> = 0>
+    bool convert_elements(handle seq, bool convert) {
+        auto l = reinterpret_borrow<sequence>(seq);
+        if (l.size() != Size) {
+            return false;
+        }
+        // The `temp` storage is needed to support `Value` types that are not
+        // default-constructible.
+        // Deliberate choice: no template specializations, for simplicity, and
+        // because the compile time overhead for the specializations is deemed
+        // more significant than the runtime overhead for the `temp` storage.
+        std::vector<Value> temp;
+        temp.reserve(l.size());
+        for (auto it : l) {
+            value_conv conv;
+            if (!conv.load(it, convert)) {
+                return false;
+            }
+            temp.emplace_back(cast_op<Value &&>(std::move(conv)));
+        }
+        value.reset(new ArrayType(vector_to_array<ArrayType, Size>(std::move(temp))));
+        return true;
+    }
+
+public:
+    bool load(handle src, bool convert) {
+        if (!PyObjectTypeIsConvertibleToStdVector(src.ptr())) {
+            return false;
+        }
+        if (isinstance<sequence>(src)) {
+            return convert_elements(src, convert);
+        }
+        if (!convert) {
+            return false;
+        }
+        // Designed to be behavior-equivalent to passing tuple(src) from Python:
+        // The conversion to a tuple will first exhaust the generator object, to ensure that
+        // the generator is not left in an unpredictable (to the caller) partially-consumed
+        // state.
+        assert(isinstance<iterable>(src));
+        return convert_elements(tuple(reinterpret_borrow<iterable>(src)), convert);
+    }
+
     template <typename T>
     static handle cast(T &&src, return_value_policy policy, handle parent) {
         list l(src.size());
@@ -272,12 +448,36 @@ public:
         return l.release();
     }
 
-    PYBIND11_TYPE_CASTER(ArrayType,
-                         const_name<Resizable>(const_name(""), const_name("Annotated["))
-                             + const_name("list[") + value_conv::name + const_name("]")
-                             + const_name<Resizable>(const_name(""),
-                                                     const_name(", FixedSize(")
-                                                         + const_name<Size>() + const_name(")]")));
+    // Code copied from PYBIND11_TYPE_CASTER macro.
+    // Intentionally preserving the behavior exactly as it was before PR #5305
+    template <typename T_, enable_if_t<std::is_same<ArrayType, remove_cv_t<T_>>::value, int> = 0>
+    static handle cast(T_ *src, return_value_policy policy, handle parent) {
+        if (!src) {
+            return none().release();
+        }
+        if (policy == return_value_policy::take_ownership) {
+            auto h = cast(std::move(*src), policy, parent);
+            delete src; // WARNING: Assumes `src` was allocated with `new`.
+            return h;
+        }
+        return cast(*src, policy, parent);
+    }
+
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator ArrayType *() { return &(*value); }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator ArrayType &() { return *value; }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator ArrayType &&() && { return std::move(*value); }
+
+    template <typename T_>
+    using cast_op_type = movable_cast_op_type<T_>;
+
+    static constexpr auto name
+        = const_name<Resizable>(const_name(""), const_name("Annotated[")) + const_name("list[")
+          + value_conv::name + const_name("]")
+          + const_name<Resizable>(
+              const_name(""), const_name(", FixedSize(") + const_name<Size>() + const_name(")]"));
 };
 
 template <typename Type, size_t Size>
diff --git a/include/pybind11/stl/filesystem.h b/include/pybind11/stl/filesystem.h
index 935d79481..c16a9ae5c 100644
--- a/include/pybind11/stl/filesystem.h
+++ b/include/pybind11/stl/filesystem.h
@@ -4,11 +4,11 @@
 
 #pragma once
 
-#include "../pybind11.h"
-#include "../detail/common.h"
-#include "../detail/descr.h"
-#include "../cast.h"
-#include "../pytypes.h"
+#include <pybind11/cast.h>
+#include <pybind11/detail/common.h>
+#include <pybind11/detail/descr.h>
+#include <pybind11/pybind11.h>
+#include <pybind11/pytypes.h>
 
 #include <string>
 
diff --git a/pybind11/__main__.py b/pybind11/__main__.py
index b656ce6fe..0abc7e211 100644
--- a/pybind11/__main__.py
+++ b/pybind11/__main__.py
@@ -2,12 +2,35 @@
 from __future__ import annotations
 
 import argparse
+import re
 import sys
 import sysconfig
 
 from ._version import __version__
 from .commands import get_cmake_dir, get_include, get_pkgconfig_dir
 
+# This is the conditional used for os.path being posixpath
+if "posix" in sys.builtin_module_names:
+    from shlex import quote
+elif "nt" in sys.builtin_module_names:
+    # See https://github.com/mesonbuild/meson/blob/db22551ed9d2dd7889abea01cc1c7bba02bf1c75/mesonbuild/utils/universal.py#L1092-L1121
+    # and the original documents:
+    # https://docs.microsoft.com/en-us/cpp/c-language/parsing-c-command-line-arguments and
+    # https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04/23/everyone-quotes-command-line-arguments-the-wrong-way/
+    UNSAFE = re.compile("[ \t\n\r]")
+
+    def quote(s: str) -> str:
+        if s and not UNSAFE.search(s):
+            return s
+
+        # Paths cannot contain a '"' on Windows, so we don't need to worry
+        # about nuanced counting here.
+        return f'"{s}\\"' if s.endswith("\\") else f'"{s}"'
+else:
+
+    def quote(s: str) -> str:
+        return s
+
 
 def print_includes() -> None:
     dirs = [
@@ -22,7 +45,7 @@ def print_includes() -> None:
         if d and d not in unique_dirs:
             unique_dirs.append(d)
 
-    print(" ".join("-I" + d for d in unique_dirs))
+    print(" ".join(quote(f"-I{d}") for d in unique_dirs))
 
 
 def main() -> None:
@@ -54,9 +77,9 @@ def main() -> None:
     if args.includes:
         print_includes()
     if args.cmakedir:
-        print(get_cmake_dir())
+        print(quote(get_cmake_dir()))
     if args.pkgconfigdir:
-        print(get_pkgconfig_dir())
+        print(quote(get_pkgconfig_dir()))
 
 
 if __name__ == "__main__":
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 1a3ef7149..ef30c95d7 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -5,16 +5,7 @@
 # All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-cmake_minimum_required(VERSION 3.5)
-
-# The `cmake_minimum_required(VERSION 3.5...3.29)` syntax does not work with
-# some versions of VS that have a patched CMake 3.11. This forces us to emulate
-# the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.29)
-  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-  cmake_policy(VERSION 3.29)
-endif()
+cmake_minimum_required(VERSION 3.15...3.30)
 
 # Filter out items; print an optional message if any items filtered. This ignores extensions.
 #
@@ -76,8 +67,8 @@ project(pybind11_tests CXX)
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/../tools")
 
 option(PYBIND11_WERROR "Report all warnings as errors" OFF)
-option(DOWNLOAD_EIGEN "Download EIGEN (requires CMake 3.11+)" OFF)
-option(PYBIND11_CUDA_TESTS "Enable building CUDA tests (requires CMake 3.12+)" OFF)
+option(DOWNLOAD_EIGEN "Download EIGEN" OFF)
+option(PYBIND11_CUDA_TESTS "Enable building CUDA tests" OFF)
 set(PYBIND11_TEST_OVERRIDE
     ""
     CACHE STRING "Tests from ;-separated list of *.cpp files will be built instead of all tests")
@@ -130,7 +121,6 @@ set(PYBIND11_TEST_FILES
     test_class_sh_factory_constructors
     test_class_sh_inheritance
     test_class_sh_mi_thunks
-    test_class_sh_module_local.py
     test_class_sh_property
     test_class_sh_property_non_owning
     test_class_sh_shared_ptr_copy_move
@@ -178,6 +168,7 @@ set(PYBIND11_TEST_FILES
     test_tagbased_polymorphic
     test_thread
     test_type_caster_pyobject_ptr
+    test_type_caster_std_function_specializations
     test_union
     test_unnamed_namespace_a
     test_unnamed_namespace_b
@@ -245,8 +236,6 @@ tests_extra_targets("test_exceptions.py;test_local_bindings.py;test_stl.py;test_
 # And add additional targets for other tests.
 tests_extra_targets("test_exceptions.py" "cross_module_interleaved_error_already_set")
 tests_extra_targets("test_gil_scoped.py" "cross_module_gil_utils")
-tests_extra_targets("test_class_sh_module_local.py"
-                    "class_sh_module_local_0;class_sh_module_local_1;class_sh_module_local_2")
 
 set(PYBIND11_EIGEN_REPO
     "https://gitlab.com/libeigen/eigen.git"
@@ -270,25 +259,21 @@ endif()
 if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
   # Try loading via newer Eigen's Eigen3Config first (bypassing tools/FindEigen3.cmake).
   # Eigen 3.3.1+ exports a cmake 3.0+ target for handling dependency requirements, but also
-  # produces a fatal error if loaded from a pre-3.0 cmake.
   if(DOWNLOAD_EIGEN)
-    if(CMAKE_VERSION VERSION_LESS 3.11)
-      message(FATAL_ERROR "CMake 3.11+ required when using DOWNLOAD_EIGEN")
+    if(CMAKE_VERSION VERSION_LESS 3.18)
+      set(_opts)
+    else()
+      set(_opts SOURCE_SUBDIR no-cmake-build)
     endif()
-
     include(FetchContent)
     FetchContent_Declare(
       eigen
       GIT_REPOSITORY "${PYBIND11_EIGEN_REPO}"
-      GIT_TAG "${PYBIND11_EIGEN_VERSION_HASH}")
-
-    FetchContent_GetProperties(eigen)
-    if(NOT eigen_POPULATED)
-      message(
-        STATUS
-          "Downloading Eigen ${PYBIND11_EIGEN_VERSION_STRING} (${PYBIND11_EIGEN_VERSION_HASH}) from ${PYBIND11_EIGEN_REPO}"
-      )
-      FetchContent_Populate(eigen)
+      GIT_TAG "${PYBIND11_EIGEN_VERSION_HASH}"
+      ${_opts})
+    FetchContent_MakeAvailable(eigen)
+    if(NOT CMAKE_VERSION VERSION_LESS 3.18)
+      set(EIGEN3_INCLUDE_DIR "${eigen_SOURCE_DIR}")
     endif()
 
     set(EIGEN3_INCLUDE_DIR ${eigen_SOURCE_DIR})
@@ -336,8 +321,7 @@ if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
     if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
       list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
     endif()
-    message(
-      STATUS "Building tests WITHOUT Eigen, use -DDOWNLOAD_EIGEN=ON on CMake 3.11+ to download")
+    message(STATUS "Building tests WITHOUT Eigen, use -DDOWNLOAD_EIGEN=ON to download")
   endif()
 endif()
 
@@ -417,6 +401,9 @@ function(pybind11_enable_warnings target_name)
               -Wdeprecated
               -Wundef
               -Wnon-virtual-dtor)
+    if(DEFINED CMAKE_CXX_STANDARD AND NOT CMAKE_CXX_STANDARD VERSION_LESS 20)
+      target_compile_options(${target_name} PRIVATE -Wpedantic)
+    endif()
   endif()
 
   if(PYBIND11_WERROR)
@@ -522,12 +509,10 @@ foreach(target ${test_targets})
 endforeach()
 
 # Provide nice organisation in IDEs
-if(NOT CMAKE_VERSION VERSION_LESS 3.8)
-  source_group(
-    TREE "${CMAKE_CURRENT_SOURCE_DIR}/../include"
-    PREFIX "Header Files"
-    FILES ${PYBIND11_HEADERS})
-endif()
+source_group(
+  TREE "${CMAKE_CURRENT_SOURCE_DIR}/../include"
+  PREFIX "Header Files"
+  FILES ${PYBIND11_HEADERS})
 
 # Make sure pytest is found or produce a warning
 pybind11_find_import(pytest VERSION 3.1)
diff --git a/tests/class_sh_module_local_0.cpp b/tests/class_sh_module_local_0.cpp
deleted file mode 100644
index 4b570624a..000000000
--- a/tests/class_sh_module_local_0.cpp
+++ /dev/null
@@ -1,34 +0,0 @@
-#include <pybind11/smart_holder.h>
-
-#include <string>
-
-namespace pybind11_tests {
-namespace class_sh_module_local {
-
-struct atyp { // Short for "any type".
-    std::string mtxt;
-};
-
-std::string get_mtxt(const atyp &obj) { return obj.mtxt; }
-
-atyp rtrn_valu_atyp() { return atyp(); }
-
-} // namespace class_sh_module_local
-} // namespace pybind11_tests
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_module_local::atyp)
-
-PYBIND11_MODULE(class_sh_module_local_0, m) {
-    m.attr("defined_PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT") =
-#ifndef PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-        false;
-#else
-        true;
-
-    using namespace pybind11_tests::class_sh_module_local;
-
-    m.def("get_mtxt", get_mtxt);
-
-    m.def("rtrn_valu_atyp", rtrn_valu_atyp);
-#endif // PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-}
diff --git a/tests/class_sh_module_local_1.cpp b/tests/class_sh_module_local_1.cpp
deleted file mode 100644
index 5197d25f9..000000000
--- a/tests/class_sh_module_local_1.cpp
+++ /dev/null
@@ -1,40 +0,0 @@
-// Identical to class_sh_module_local_2.cpp, except 2 replaced with 1.
-#include <pybind11/smart_holder.h>
-
-#include <string>
-
-namespace pybind11_tests {
-namespace class_sh_module_local {
-
-struct atyp { // Short for "any type".
-    std::string mtxt;
-};
-
-std::string get_mtxt(const atyp &obj) { return obj.mtxt; }
-
-} // namespace class_sh_module_local
-} // namespace pybind11_tests
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_module_local::atyp)
-
-PYBIND11_MODULE(class_sh_module_local_1, m) {
-    m.attr("defined_PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT") =
-#ifndef PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-        false;
-#else
-        true;
-
-    namespace py = pybind11;
-    using namespace pybind11_tests::class_sh_module_local;
-
-    py::classh<atyp>(m, "atyp", py::module_local())
-        .def(py::init([](const std::string &mtxt) {
-            atyp obj;
-            obj.mtxt = mtxt;
-            return obj;
-        }))
-        .def("tag", [](const atyp &) { return 1; });
-
-    m.def("get_mtxt", get_mtxt);
-#endif // PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-}
diff --git a/tests/class_sh_module_local_2.cpp b/tests/class_sh_module_local_2.cpp
deleted file mode 100644
index 0e3a39ba3..000000000
--- a/tests/class_sh_module_local_2.cpp
+++ /dev/null
@@ -1,40 +0,0 @@
-// Identical to class_sh_module_local_1.cpp, except 1 replaced with 2.
-#include <pybind11/smart_holder.h>
-
-#include <string>
-
-namespace pybind11_tests {
-namespace class_sh_module_local {
-
-struct atyp { // Short for "any type".
-    std::string mtxt;
-};
-
-std::string get_mtxt(const atyp &obj) { return obj.mtxt; }
-
-} // namespace class_sh_module_local
-} // namespace pybind11_tests
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_module_local::atyp)
-
-PYBIND11_MODULE(class_sh_module_local_2, m) {
-    m.attr("defined_PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT") =
-#ifndef PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-        false;
-#else
-        true;
-
-    namespace py = pybind11;
-    using namespace pybind11_tests::class_sh_module_local;
-
-    py::classh<atyp>(m, "atyp", py::module_local())
-        .def(py::init([](const std::string &mtxt) {
-            atyp obj;
-            obj.mtxt = mtxt;
-            return obj;
-        }))
-        .def("tag", [](const atyp &) { return 2; });
-
-    m.def("get_mtxt", get_mtxt);
-#endif // PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-}
diff --git a/tests/extra_python_package/test_files.py b/tests/extra_python_package/test_files.py
index e95ed4d36..ad2e7c7bd 100644
--- a/tests/extra_python_package/test_files.py
+++ b/tests/extra_python_package/test_files.py
@@ -9,7 +9,6 @@ import tarfile
 import zipfile
 
 # These tests must be run explicitly
-# They require CMake 3.15+ (--install)
 
 DIR = os.path.abspath(os.path.dirname(__file__))
 MAIN_DIR = os.path.dirname(os.path.dirname(DIR))
@@ -61,7 +60,7 @@ detail_headers = {
     "include/pybind11/detail/init.h",
     "include/pybind11/detail/internals.h",
     "include/pybind11/detail/native_enum_data.h",
-    "include/pybind11/detail/smart_holder_poc.h",
+    "include/pybind11/detail/struct_smart_holder.h",
     "include/pybind11/detail/type_caster_base.h",
     "include/pybind11/detail/typeid.h",
     "include/pybind11/detail/using_smart_holder.h",
diff --git a/tests/local_bindings.h b/tests/local_bindings.h
index 01d278535..dea181310 100644
--- a/tests/local_bindings.h
+++ b/tests/local_bindings.h
@@ -56,13 +56,13 @@ private:
     std::string message = "";
 };
 
-PYBIND11_MAKE_OPAQUE(LocalVec);
-PYBIND11_MAKE_OPAQUE(LocalVec2);
-PYBIND11_MAKE_OPAQUE(LocalMap);
-PYBIND11_MAKE_OPAQUE(NonLocalVec);
-// PYBIND11_MAKE_OPAQUE(NonLocalVec2); // same type as LocalVec2
-PYBIND11_MAKE_OPAQUE(NonLocalMap);
-PYBIND11_MAKE_OPAQUE(NonLocalMap2);
+PYBIND11_MAKE_OPAQUE(LocalVec)
+PYBIND11_MAKE_OPAQUE(LocalVec2)
+PYBIND11_MAKE_OPAQUE(LocalMap)
+PYBIND11_MAKE_OPAQUE(NonLocalVec)
+// PYBIND11_MAKE_OPAQUE(NonLocalVec2) // same type as LocalVec2
+PYBIND11_MAKE_OPAQUE(NonLocalMap)
+PYBIND11_MAKE_OPAQUE(NonLocalMap2)
 
 // Simple bindings (used with the above):
 template <typename T, int Adjust = 0, typename... Args>
@@ -70,7 +70,7 @@ py::class_<T> bind_local(Args &&...args) {
     return py::class_<T>(std::forward<Args>(args)...).def(py::init<int>()).def("get", [](T &i) {
         return i.i + Adjust;
     });
-};
+}
 
 // Simulate a foreign library base class (to match the example in the docs):
 namespace pets {
diff --git a/tests/pure_cpp/smart_holder_poc.h b/tests/pure_cpp/smart_holder_poc.h
new file mode 100644
index 000000000..320311b7d
--- /dev/null
+++ b/tests/pure_cpp/smart_holder_poc.h
@@ -0,0 +1,51 @@
+// Copyright (c) 2020-2024 The Pybind Development Team.
+// All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#pragma once
+
+#include "pybind11/detail/struct_smart_holder.h"
+
+namespace pybindit {
+namespace memory {
+namespace smart_holder_poc { // Proof-of-Concept implementations.
+
+template <typename T>
+T &as_lvalue_ref(const smart_holder &hld) {
+    static const char *context = "as_lvalue_ref";
+    hld.ensure_is_populated(context);
+    hld.ensure_has_pointee(context);
+    return *hld.as_raw_ptr_unowned<T>();
+}
+
+template <typename T>
+T &&as_rvalue_ref(const smart_holder &hld) {
+    static const char *context = "as_rvalue_ref";
+    hld.ensure_is_populated(context);
+    hld.ensure_has_pointee(context);
+    return std::move(*hld.as_raw_ptr_unowned<T>());
+}
+
+template <typename T>
+T *as_raw_ptr_release_ownership(smart_holder &hld,
+                                const char *context = "as_raw_ptr_release_ownership") {
+    hld.ensure_can_release_ownership(context);
+    T *raw_ptr = hld.as_raw_ptr_unowned<T>();
+    hld.release_ownership();
+    return raw_ptr;
+}
+
+template <typename T, typename D = std::default_delete<T>>
+std::unique_ptr<T, D> as_unique_ptr(smart_holder &hld) {
+    static const char *context = "as_unique_ptr";
+    hld.ensure_compatible_rtti_uqp_del<T, D>(context);
+    hld.ensure_use_count_1(context);
+    T *raw_ptr = hld.as_raw_ptr_unowned<T>();
+    hld.release_ownership();
+    // KNOWN DEFECT (see PR #4850): Does not copy the deleter.
+    return std::unique_ptr<T, D>(raw_ptr);
+}
+
+} // namespace smart_holder_poc
+} // namespace memory
+} // namespace pybindit
diff --git a/tests/pure_cpp/smart_holder_poc_test.cpp b/tests/pure_cpp/smart_holder_poc_test.cpp
index a9ad0364e..24ab643ee 100644
--- a/tests/pure_cpp/smart_holder_poc_test.cpp
+++ b/tests/pure_cpp/smart_holder_poc_test.cpp
@@ -1,6 +1,4 @@
-#define PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP
-
-#include "pybind11/detail/smart_holder_poc.h"
+#include "smart_holder_poc.h"
 
 #include <functional>
 #include <memory>
@@ -16,6 +14,7 @@
 #include "catch.hpp"
 
 using pybindit::memory::smart_holder;
+namespace poc = pybindit::memory::smart_holder_poc;
 
 namespace helpers {
 
@@ -70,14 +69,14 @@ TEST_CASE("from_raw_ptr_unowned+as_raw_ptr_unowned", "[S]") {
 TEST_CASE("from_raw_ptr_unowned+as_lvalue_ref", "[S]") {
     static int value = 19;
     auto hld = smart_holder::from_raw_ptr_unowned(&value);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_raw_ptr_unowned+as_rvalue_ref", "[S]") {
     helpers::movable_int orig(19);
     {
         auto hld = smart_holder::from_raw_ptr_unowned(&orig);
-        helpers::movable_int othr(hld.as_rvalue_ref<helpers::movable_int>());
+        helpers::movable_int othr(poc::as_rvalue_ref<helpers::movable_int>(hld));
         REQUIRE(othr.valu == 19);
         REQUIRE(orig.valu == 91);
     }
@@ -86,21 +85,21 @@ TEST_CASE("from_raw_ptr_unowned+as_rvalue_ref", "[S]") {
 TEST_CASE("from_raw_ptr_unowned+as_raw_ptr_release_ownership", "[E]") {
     static int value = 19;
     auto hld = smart_holder::from_raw_ptr_unowned(&value);
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown non-owning holder (as_raw_ptr_release_ownership).");
 }
 
 TEST_CASE("from_raw_ptr_unowned+as_unique_ptr", "[E]") {
     static int value = 19;
     auto hld = smart_holder::from_raw_ptr_unowned(&value);
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(),
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
                         "Cannot disown non-owning holder (as_unique_ptr).");
 }
 
 TEST_CASE("from_raw_ptr_unowned+as_unique_ptr_with_deleter", "[E]") {
     static int value = 19;
     auto hld = smart_holder::from_raw_ptr_unowned(&value);
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld)),
                         "Missing unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -113,12 +112,12 @@ TEST_CASE("from_raw_ptr_unowned+as_shared_ptr", "[S]") {
 TEST_CASE("from_raw_ptr_take_ownership+as_lvalue_ref", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     REQUIRE(hld.has_pointee());
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_raw_ptr_take_ownership+as_raw_ptr_release_ownership1", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    auto new_owner = std::unique_ptr<int>(hld.as_raw_ptr_release_ownership<int>());
+    auto new_owner = std::unique_ptr<int>(poc::as_raw_ptr_release_ownership<int>(hld));
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -126,13 +125,13 @@ TEST_CASE("from_raw_ptr_take_ownership+as_raw_ptr_release_ownership1", "[S]") {
 TEST_CASE("from_raw_ptr_take_ownership+as_raw_ptr_release_ownership2", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     auto shd_ptr = hld.as_shared_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown use_count != 1 (as_raw_ptr_release_ownership).");
 }
 
 TEST_CASE("from_raw_ptr_take_ownership+as_unique_ptr1", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    std::unique_ptr<int> new_owner = hld.as_unique_ptr<int>();
+    std::unique_ptr<int> new_owner = poc::as_unique_ptr<int>(hld);
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -140,12 +139,13 @@ TEST_CASE("from_raw_ptr_take_ownership+as_unique_ptr1", "[S]") {
 TEST_CASE("from_raw_ptr_take_ownership+as_unique_ptr2", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     auto shd_ptr = hld.as_shared_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(), "Cannot disown use_count != 1 (as_unique_ptr).");
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
+                        "Cannot disown use_count != 1 (as_unique_ptr).");
 }
 
 TEST_CASE("from_raw_ptr_take_ownership+as_unique_ptr_with_deleter", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld)),
                         "Missing unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -160,14 +160,14 @@ TEST_CASE("from_raw_ptr_take_ownership+disown+reclaim_disowned", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     std::unique_ptr<int> new_owner(hld.as_raw_ptr_unowned<int>());
     hld.disown();
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
     REQUIRE(*new_owner == 19);
     hld.reclaim_disowned(); // Manually veriified: without this, clang++ -fsanitize=address reports
                             // "detected memory leaks".
     // NOLINTNEXTLINE(bugprone-unused-return-value)
     (void) new_owner.release(); // Manually verified: without this, clang++ -fsanitize=address
                                 // reports "attempting double-free".
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
     REQUIRE(new_owner.get() == nullptr);
 }
 
@@ -175,7 +175,7 @@ TEST_CASE("from_raw_ptr_take_ownership+disown+release_disowned", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     std::unique_ptr<int> new_owner(hld.as_raw_ptr_unowned<int>());
     hld.disown();
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
     REQUIRE(*new_owner == 19);
     hld.release_disowned();
     REQUIRE(!hld.has_pointee());
@@ -195,14 +195,14 @@ TEST_CASE("from_unique_ptr+as_lvalue_ref", "[S]") {
     std::unique_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_unique_ptr+as_raw_ptr_release_ownership1", "[S]") {
     std::unique_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    auto new_owner = std::unique_ptr<int>(hld.as_raw_ptr_release_ownership<int>());
+    auto new_owner = std::unique_ptr<int>(poc::as_raw_ptr_release_ownership<int>(hld));
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -212,7 +212,7 @@ TEST_CASE("from_unique_ptr+as_raw_ptr_release_ownership2", "[E]") {
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
     auto shd_ptr = hld.as_shared_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown use_count != 1 (as_raw_ptr_release_ownership).");
 }
 
@@ -220,7 +220,7 @@ TEST_CASE("from_unique_ptr+as_unique_ptr1", "[S]") {
     std::unique_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    std::unique_ptr<int> new_owner = hld.as_unique_ptr<int>();
+    std::unique_ptr<int> new_owner = poc::as_unique_ptr<int>(hld);
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -230,14 +230,15 @@ TEST_CASE("from_unique_ptr+as_unique_ptr2", "[E]") {
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
     auto shd_ptr = hld.as_shared_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(), "Cannot disown use_count != 1 (as_unique_ptr).");
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
+                        "Cannot disown use_count != 1 (as_unique_ptr).");
 }
 
 TEST_CASE("from_unique_ptr+as_unique_ptr_with_deleter", "[E]") {
     std::unique_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld)),
                         "Incompatible unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -254,7 +255,7 @@ TEST_CASE("from_unique_ptr_derived+as_unique_ptr_base", "[S]") {
     std::unique_ptr<helpers::derived> orig_owner(new helpers::derived());
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    std::unique_ptr<helpers::base> new_owner = hld.as_unique_ptr<helpers::base>();
+    std::unique_ptr<helpers::base> new_owner = poc::as_unique_ptr<helpers::base>(hld);
     REQUIRE(!hld.has_pointee());
     REQUIRE(new_owner->get() == 100);
 }
@@ -265,7 +266,7 @@ TEST_CASE("from_unique_ptr_derived+as_unique_ptr_base2", "[E]") {
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
     REQUIRE_THROWS_WITH(
-        (hld.as_unique_ptr<helpers::base, helpers::functor_builtin_delete<helpers::base>>()),
+        (poc::as_unique_ptr<helpers::base, helpers::functor_builtin_delete<helpers::base>>(hld)),
         "Incompatible unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -273,7 +274,7 @@ TEST_CASE("from_unique_ptr_with_deleter+as_lvalue_ref", "[S]") {
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_unique_ptr_with_std_function_deleter+as_lvalue_ref", "[S]") {
@@ -281,14 +282,14 @@ TEST_CASE("from_unique_ptr_with_std_function_deleter+as_lvalue_ref", "[S]") {
         new int(19), [](const int *raw_ptr) { delete raw_ptr; });
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_unique_ptr_with_deleter+as_raw_ptr_release_ownership", "[E]") {
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown custom deleter (as_raw_ptr_release_ownership).");
 }
 
@@ -296,7 +297,7 @@ TEST_CASE("from_unique_ptr_with_deleter+as_unique_ptr", "[E]") {
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(),
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
                         "Incompatible unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -305,7 +306,7 @@ TEST_CASE("from_unique_ptr_with_deleter+as_unique_ptr_with_deleter1", "[S]") {
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> new_owner
-        = hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>();
+        = poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld);
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -314,7 +315,7 @@ TEST_CASE("from_unique_ptr_with_deleter+as_unique_ptr_with_deleter2", "[E]") {
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_other_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_other_delete<int>>(hld)),
                         "Incompatible unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -330,27 +331,27 @@ TEST_CASE("from_unique_ptr_with_deleter+as_shared_ptr", "[S]") {
 TEST_CASE("from_shared_ptr+as_lvalue_ref", "[S]") {
     std::shared_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_shared_ptr(orig_owner);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_shared_ptr+as_raw_ptr_release_ownership", "[E]") {
     std::shared_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_shared_ptr(orig_owner);
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown external shared_ptr (as_raw_ptr_release_ownership).");
 }
 
 TEST_CASE("from_shared_ptr+as_unique_ptr", "[E]") {
     std::shared_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_shared_ptr(orig_owner);
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(),
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
                         "Cannot disown external shared_ptr (as_unique_ptr).");
 }
 
 TEST_CASE("from_shared_ptr+as_unique_ptr_with_deleter", "[E]") {
     std::shared_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_shared_ptr(orig_owner);
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld)),
                         "Missing unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -362,19 +363,19 @@ TEST_CASE("from_shared_ptr+as_shared_ptr", "[S]") {
 
 TEST_CASE("error_unpopulated_holder", "[E]") {
     smart_holder hld;
-    REQUIRE_THROWS_WITH(hld.as_lvalue_ref<int>(), "Unpopulated holder (as_lvalue_ref).");
+    REQUIRE_THROWS_WITH(poc::as_lvalue_ref<int>(hld), "Unpopulated holder (as_lvalue_ref).");
 }
 
 TEST_CASE("error_disowned_holder", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    hld.as_unique_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_lvalue_ref<int>(), "Disowned holder (as_lvalue_ref).");
+    poc::as_unique_ptr<int>(hld);
+    REQUIRE_THROWS_WITH(poc::as_lvalue_ref<int>(hld), "Disowned holder (as_lvalue_ref).");
 }
 
 TEST_CASE("error_cannot_disown_nullptr", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    hld.as_unique_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(), "Cannot disown nullptr (as_unique_ptr).");
+    poc::as_unique_ptr<int>(hld);
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld), "Cannot disown nullptr (as_unique_ptr).");
 }
 
 TEST_CASE("indestructible_int-from_raw_ptr_unowned+as_raw_ptr_unowned", "[S]") {
diff --git a/tests/test_callbacks.cpp b/tests/test_callbacks.cpp
index 2fd05dec7..e303e7656 100644
--- a/tests/test_callbacks.cpp
+++ b/tests/test_callbacks.cpp
@@ -148,7 +148,7 @@ TEST_SUBMODULE(callbacks, m) {
     m.def("dummy_function2", [](int i, int j) { return i + j; });
     m.def(
         "roundtrip",
-        [](std::function<int(int)> f, bool expect_none = false) {
+        [](std::function<int(int)> f, bool expect_none) {
             if (expect_none && f) {
                 throw std::runtime_error("Expected None to be converted to empty std::function");
             }
diff --git a/tests/test_class_sh_basic.cpp b/tests/test_class_sh_basic.cpp
index 9602387b3..ac19a750b 100644
--- a/tests/test_class_sh_basic.cpp
+++ b/tests/test_class_sh_basic.cpp
@@ -120,6 +120,17 @@ std::string get_mtxt(atyp const &obj) { return obj.mtxt; }
 std::ptrdiff_t get_ptr(atyp const &obj) { return reinterpret_cast<std::ptrdiff_t>(&obj); }
 
 std::unique_ptr<atyp> unique_ptr_roundtrip(std::unique_ptr<atyp> obj) { return obj; }
+
+std::string pass_unique_ptr_cref(const std::unique_ptr<atyp> &obj) { return obj->mtxt; }
+
+const std::unique_ptr<atyp> &rtrn_unique_ptr_cref(const std::string &mtxt) {
+    static std::unique_ptr<atyp> obj{new atyp{"static_ctor_arg"}};
+    if (!mtxt.empty()) {
+        obj->mtxt = mtxt;
+    }
+    return obj;
+}
+
 const std::unique_ptr<atyp> &unique_ptr_cref_roundtrip(const std::unique_ptr<atyp> &obj) {
     return obj;
 }
@@ -217,6 +228,9 @@ TEST_SUBMODULE(class_sh_basic, m) {
     m.def("get_ptr", get_ptr);   // pass_cref
 
     m.def("unique_ptr_roundtrip", unique_ptr_roundtrip); // pass_uqmp, rtrn_uqmp
+
+    m.def("pass_unique_ptr_cref", pass_unique_ptr_cref);
+    m.def("rtrn_unique_ptr_cref", rtrn_unique_ptr_cref);
     m.def("unique_ptr_cref_roundtrip", unique_ptr_cref_roundtrip);
 
     py::classh<SharedPtrStash>(m, "SharedPtrStash")
diff --git a/tests/test_class_sh_basic.py b/tests/test_class_sh_basic.py
index 87f1f8f09..7db7d31b7 100644
--- a/tests/test_class_sh_basic.py
+++ b/tests/test_class_sh_basic.py
@@ -151,19 +151,31 @@ def test_unique_ptr_roundtrip(num_round_trips=1000):
         id_orig = id_rtrn
 
 
-# This currently fails, because a unique_ptr is always loaded by value
-# due to pybind11/detail/smart_holder_type_casters.h:689
-# I think, we need to provide more cast operators.
-@pytest.mark.skip()
-def test_unique_ptr_cref_roundtrip():
-    orig = m.atyp("passenger")
-    id_orig = id(orig)
-    mtxt_orig = m.get_mtxt(orig)
+def test_pass_unique_ptr_cref():
+    obj = m.atyp("ctor_arg")
+    assert re.match("ctor_arg(_MvCtor)*_MvCtor", m.get_mtxt(obj))
+    assert re.match("ctor_arg(_MvCtor)*_MvCtor", m.pass_unique_ptr_cref(obj))
+    assert re.match("ctor_arg(_MvCtor)*_MvCtor", m.get_mtxt(obj))
 
-    recycled = m.unique_ptr_cref_roundtrip(orig)
-    assert m.get_mtxt(orig) == mtxt_orig
-    assert m.get_mtxt(recycled) == mtxt_orig
-    assert id(recycled) == id_orig
+
+def test_rtrn_unique_ptr_cref():
+    obj0 = m.rtrn_unique_ptr_cref("")
+    assert m.get_mtxt(obj0) == "static_ctor_arg"
+    obj1 = m.rtrn_unique_ptr_cref("passed_mtxt_1")
+    assert m.get_mtxt(obj1) == "passed_mtxt_1"
+    assert m.get_mtxt(obj0) == "passed_mtxt_1"
+    assert obj0 is obj1
+
+
+def test_unique_ptr_cref_roundtrip(num_round_trips=1000):
+    # Multiple roundtrips to stress-test implementation.
+    orig = m.atyp("passenger")
+    mtxt_orig = m.get_mtxt(orig)
+    recycled = orig
+    for _ in range(num_round_trips):
+        recycled = m.unique_ptr_cref_roundtrip(recycled)
+        assert recycled is orig
+        assert m.get_mtxt(recycled) == mtxt_orig
 
 
 @pytest.mark.parametrize(
diff --git a/tests/test_class_sh_module_local.py b/tests/test_class_sh_module_local.py
deleted file mode 100644
index 9f4230052..000000000
--- a/tests/test_class_sh_module_local.py
+++ /dev/null
@@ -1,30 +0,0 @@
-from __future__ import annotations
-
-import class_sh_module_local_0 as m0
-import class_sh_module_local_1 as m1
-import class_sh_module_local_2 as m2
-import pytest
-
-if not m0.defined_PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
-
-def test_cross_module_get_mtxt():
-    obj1 = m1.atyp("A")
-    assert obj1.tag() == 1
-    obj2 = m2.atyp("B")
-    assert obj2.tag() == 2
-    assert m1.get_mtxt(obj1) == "A"
-    assert m2.get_mtxt(obj2) == "B"
-    assert m1.get_mtxt(obj2) == "B"
-    assert m2.get_mtxt(obj1) == "A"
-    assert m0.get_mtxt(obj1) == "A"
-    assert m0.get_mtxt(obj2) == "B"
-
-
-def test_m0_rtrn_valu_atyp():
-    with pytest.raises(TypeError) as exc_info:
-        m0.rtrn_valu_atyp()
-    assert str(exc_info.value).startswith(
-        "Unable to convert function return value to a Python type!"
-    )
diff --git a/tests/test_class_sh_trampoline_shared_from_this.cpp b/tests/test_class_sh_trampoline_shared_from_this.cpp
index e5d688af6..9c2e4ec76 100644
--- a/tests/test_class_sh_trampoline_shared_from_this.cpp
+++ b/tests/test_class_sh_trampoline_shared_from_this.cpp
@@ -87,7 +87,12 @@ long pass_shared_ptr(const std::shared_ptr<Sft> &obj) {
     return sft.use_count();
 }
 
-void pass_unique_ptr(const std::unique_ptr<Sft> &) {}
+std::string pass_unique_ptr_cref(const std::unique_ptr<Sft> &obj) {
+    return obj ? obj->history : "<NULLPTR>";
+}
+void pass_unique_ptr_rref(std::unique_ptr<Sft> &&) {
+    throw std::runtime_error("Expected to not be reached.");
+}
 
 Sft *make_pure_cpp_sft_raw_ptr(const std::string &history_seed) { return new Sft{history_seed}; }
 
@@ -135,7 +140,8 @@ TEST_SUBMODULE(class_sh_trampoline_shared_from_this, m) {
 
     m.def("use_count", use_count);
     m.def("pass_shared_ptr", pass_shared_ptr);
-    m.def("pass_unique_ptr", pass_unique_ptr);
+    m.def("pass_unique_ptr_cref", pass_unique_ptr_cref);
+    m.def("pass_unique_ptr_rref", pass_unique_ptr_rref);
     m.def("make_pure_cpp_sft_raw_ptr", make_pure_cpp_sft_raw_ptr);
     m.def("make_pure_cpp_sft_unq_ptr", make_pure_cpp_sft_unq_ptr);
     m.def("make_pure_cpp_sft_shd_ptr", make_pure_cpp_sft_shd_ptr);
diff --git a/tests/test_class_sh_trampoline_shared_from_this.py b/tests/test_class_sh_trampoline_shared_from_this.py
index a074b20a1..7c5ee0e8e 100644
--- a/tests/test_class_sh_trampoline_shared_from_this.py
+++ b/tests/test_class_sh_trampoline_shared_from_this.py
@@ -137,11 +137,14 @@ def test_pass_released_shared_ptr_as_unique_ptr():
     obj = PySft("PySft")
     stash1 = m.SftSharedPtrStash(1)
     stash1.Add(obj)  # Releases shared_ptr to C++.
+    assert m.pass_unique_ptr_cref(obj) == "PySft_Stash1Add"
+    assert obj.history == "PySft_Stash1Add"
     with pytest.raises(ValueError) as exc_info:
-        m.pass_unique_ptr(obj)
+        m.pass_unique_ptr_rref(obj)
     assert str(exc_info.value) == (
         "Python instance is currently owned by a std::shared_ptr."
     )
+    assert obj.history == "PySft_Stash1Add"
 
 
 @pytest.mark.parametrize(
diff --git a/tests/test_cmake_build/installed_embed/CMakeLists.txt b/tests/test_cmake_build/installed_embed/CMakeLists.txt
index 2be0aa659..5c6267c72 100644
--- a/tests/test_cmake_build/installed_embed/CMakeLists.txt
+++ b/tests/test_cmake_build/installed_embed/CMakeLists.txt
@@ -1,13 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
-
-# The `cmake_minimum_required(VERSION 3.5...3.29)` syntax does not work with
-# some versions of VS that have a patched CMake 3.11. This forces us to emulate
-# the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.29)
-  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-  cmake_policy(VERSION 3.29)
-endif()
+cmake_minimum_required(VERSION 3.15...3.30)
 
 project(test_installed_embed CXX)
 
diff --git a/tests/test_cmake_build/installed_function/CMakeLists.txt b/tests/test_cmake_build/installed_function/CMakeLists.txt
index fa7795e1e..2945b3d2e 100644
--- a/tests/test_cmake_build/installed_function/CMakeLists.txt
+++ b/tests/test_cmake_build/installed_function/CMakeLists.txt
@@ -1,14 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
-project(test_installed_module CXX)
-
-# The `cmake_minimum_required(VERSION 3.5...3.29)` syntax does not work with
-# some versions of VS that have a patched CMake 3.11. This forces us to emulate
-# the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.29)
-  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-  cmake_policy(VERSION 3.29)
-endif()
+cmake_minimum_required(VERSION 3.15...3.30)
 
 project(test_installed_function CXX)
 
diff --git a/tests/test_cmake_build/installed_target/CMakeLists.txt b/tests/test_cmake_build/installed_target/CMakeLists.txt
index 7e73f4243..344c8bc69 100644
--- a/tests/test_cmake_build/installed_target/CMakeLists.txt
+++ b/tests/test_cmake_build/installed_target/CMakeLists.txt
@@ -1,13 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
-
-# The `cmake_minimum_required(VERSION 3.5...3.29)` syntax does not work with
-# some versions of VS that have a patched CMake 3.11. This forces us to emulate
-# the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.29)
-  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-  cmake_policy(VERSION 3.29)
-endif()
+cmake_minimum_required(VERSION 3.15...3.30)
 
 project(test_installed_target CXX)
 
diff --git a/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt b/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt
index 33a366472..d0ae0798e 100644
--- a/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt
+++ b/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt
@@ -1,13 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
-
-# The `cmake_minimum_required(VERSION 3.5...3.29)` syntax does not work with
-# some versions of VS that have a patched CMake 3.11. This forces us to emulate
-# the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.29)
-  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-  cmake_policy(VERSION 3.29)
-endif()
+cmake_minimum_required(VERSION 3.15...3.30)
 
 project(test_subdirectory_embed CXX)
 
diff --git a/tests/test_cmake_build/subdirectory_function/CMakeLists.txt b/tests/test_cmake_build/subdirectory_function/CMakeLists.txt
index 76418a71f..a521f33df 100644
--- a/tests/test_cmake_build/subdirectory_function/CMakeLists.txt
+++ b/tests/test_cmake_build/subdirectory_function/CMakeLists.txt
@@ -1,13 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
-
-# The `cmake_minimum_required(VERSION 3.5...3.29)` syntax does not work with
-# some versions of VS that have a patched CMake 3.11. This forces us to emulate
-# the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.29)
-  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-  cmake_policy(VERSION 3.29)
-endif()
+cmake_minimum_required(VERSION 3.15...3.30)
 
 project(test_subdirectory_function CXX)
 
diff --git a/tests/test_cmake_build/subdirectory_target/CMakeLists.txt b/tests/test_cmake_build/subdirectory_target/CMakeLists.txt
index 28e903187..4a5a7f2be 100644
--- a/tests/test_cmake_build/subdirectory_target/CMakeLists.txt
+++ b/tests/test_cmake_build/subdirectory_target/CMakeLists.txt
@@ -1,13 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
-
-# The `cmake_minimum_required(VERSION 3.5...3.29)` syntax does not work with
-# some versions of VS that have a patched CMake 3.11. This forces us to emulate
-# the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.29)
-  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-  cmake_policy(VERSION 3.29)
-endif()
+cmake_minimum_required(VERSION 3.15...3.30)
 
 project(test_subdirectory_target CXX)
 
diff --git a/tests/test_eigen_matrix.cpp b/tests/test_eigen_matrix.cpp
index 21261bfc2..cb8e8c625 100644
--- a/tests/test_eigen_matrix.cpp
+++ b/tests/test_eigen_matrix.cpp
@@ -55,7 +55,7 @@ void reset_refs() {
 }
 
 // Returns element 2,1 from a matrix (used to test copy/nocopy)
-double get_elem(const Eigen::Ref<const Eigen::MatrixXd> &m) { return m(2, 1); };
+double get_elem(const Eigen::Ref<const Eigen::MatrixXd> &m) { return m(2, 1); }
 
 // Returns a matrix with 10*r + 100*c added to each matrix element (to help test that the matrix
 // reference is referencing rows/columns correctly).
@@ -76,7 +76,7 @@ struct CustomOperatorNew {
     Eigen::Matrix4d a = Eigen::Matrix4d::Zero();
     Eigen::Matrix4d b = Eigen::Matrix4d::Identity();
 
-    EIGEN_MAKE_ALIGNED_OPERATOR_NEW;
+    EIGEN_MAKE_ALIGNED_OPERATOR_NEW
 };
 
 TEST_SUBMODULE(eigen_matrix, m) {
diff --git a/tests/test_opaque_types.cpp b/tests/test_opaque_types.cpp
index 154d0a8d3..da3866cd0 100644
--- a/tests/test_opaque_types.cpp
+++ b/tests/test_opaque_types.cpp
@@ -18,7 +18,7 @@
 // This also deliberately doesn't use the below StringList type alias to test
 // that MAKE_OPAQUE can handle a type containing a `,`.  (The `std::allocator`
 // bit is just the default `std::vector` allocator).
-PYBIND11_MAKE_OPAQUE(std::vector<std::string, std::allocator<std::string>>);
+PYBIND11_MAKE_OPAQUE(std::vector<std::string, std::allocator<std::string>>)
 
 using StringList = std::vector<std::string, std::allocator<std::string>>;
 
diff --git a/tests/test_pytypes.cpp b/tests/test_pytypes.cpp
index ecb44939a..19f65ce7e 100644
--- a/tests/test_pytypes.cpp
+++ b/tests/test_pytypes.cpp
@@ -13,6 +13,14 @@
 
 #include <utility>
 
+//__has_include has been part of C++17, no need to check it
+#if defined(PYBIND11_CPP20) && __has_include(<ranges>)
+#    if !defined(PYBIND11_COMPILER_CLANG) || __clang_major__ >= 16 // llvm/llvm-project#52696
+#        define PYBIND11_TEST_PYTYPES_HAS_RANGES
+#        include <ranges>
+#    endif
+#endif
+
 namespace external {
 namespace detail {
 bool check(PyObject *o) { return PyFloat_Check(o) != 0; }
@@ -923,4 +931,59 @@ TEST_SUBMODULE(pytypes, m) {
 #else
     m.attr("defined_PYBIND11_TYPING_H_HAS_STRING_LITERAL") = false;
 #endif
+
+#if defined(PYBIND11_TEST_PYTYPES_HAS_RANGES)
+
+    // test_tuple_ranges
+    m.def("tuple_iterator_default_initialization", []() {
+        using TupleIterator = decltype(std::declval<py::tuple>().begin());
+        static_assert(std::random_access_iterator<TupleIterator>);
+        return TupleIterator{} == TupleIterator{};
+    });
+
+    m.def("transform_tuple_plus_one", [](py::tuple &tpl) {
+        py::list ret{};
+        for (auto it : tpl | std::views::transform([](auto &o) { return py::cast<int>(o) + 1; })) {
+            ret.append(py::int_(it));
+        }
+        return ret;
+    });
+
+    // test_list_ranges
+    m.def("list_iterator_default_initialization", []() {
+        using ListIterator = decltype(std::declval<py::list>().begin());
+        static_assert(std::random_access_iterator<ListIterator>);
+        return ListIterator{} == ListIterator{};
+    });
+
+    m.def("transform_list_plus_one", [](py::list &lst) {
+        py::list ret{};
+        for (auto it : lst | std::views::transform([](auto &o) { return py::cast<int>(o) + 1; })) {
+            ret.append(py::int_(it));
+        }
+        return ret;
+    });
+
+    // test_dict_ranges
+    m.def("dict_iterator_default_initialization", []() {
+        using DictIterator = decltype(std::declval<py::dict>().begin());
+        static_assert(std::forward_iterator<DictIterator>);
+        return DictIterator{} == DictIterator{};
+    });
+
+    m.def("transform_dict_plus_one", [](py::dict &dct) {
+        py::list ret{};
+        for (auto it : dct | std::views::transform([](auto &o) {
+                           return std::pair{py::cast<int>(o.first) + 1,
+                                            py::cast<int>(o.second) + 1};
+                       })) {
+            ret.append(py::make_tuple(py::int_(it.first), py::int_(it.second)));
+        }
+        return ret;
+    });
+
+    m.attr("defined_PYBIND11_TEST_PYTYPES_HAS_RANGES") = true;
+#else
+    m.attr("defined_PYBIND11_TEST_PYTYPES_HAS_RANGES") = false;
+#endif
 }
diff --git a/tests/test_pytypes.py b/tests/test_pytypes.py
index 218092b43..1c6335f75 100644
--- a/tests/test_pytypes.py
+++ b/tests/test_pytypes.py
@@ -1048,3 +1048,45 @@ def test_typevar(doc):
     assert doc(m.annotate_listT_to_T) == "annotate_listT_to_T(arg0: list[T]) -> T"
 
     assert doc(m.annotate_object_to_T) == "annotate_object_to_T(arg0: object) -> T"
+
+
+@pytest.mark.skipif(
+    not m.defined_PYBIND11_TEST_PYTYPES_HAS_RANGES,
+    reason="<ranges> not available.",
+)
+@pytest.mark.parametrize(
+    ("tested_tuple", "expected"),
+    [((1,), [2]), ((3, 4), [4, 5]), ((7, 8, 9), [8, 9, 10])],
+)
+def test_tuple_ranges(tested_tuple, expected):
+    assert m.tuple_iterator_default_initialization()
+    assert m.transform_tuple_plus_one(tested_tuple) == expected
+
+
+@pytest.mark.skipif(
+    not m.defined_PYBIND11_TEST_PYTYPES_HAS_RANGES,
+    reason="<ranges> not available.",
+)
+@pytest.mark.parametrize(
+    ("tested_list", "expected"), [([1], [2]), ([3, 4], [4, 5]), ([7, 8, 9], [8, 9, 10])]
+)
+def test_list_ranges(tested_list, expected):
+    assert m.list_iterator_default_initialization()
+    assert m.transform_list_plus_one(tested_list) == expected
+
+
+@pytest.mark.skipif(
+    not m.defined_PYBIND11_TEST_PYTYPES_HAS_RANGES,
+    reason="<ranges> not available.",
+)
+@pytest.mark.parametrize(
+    ("tested_dict", "expected"),
+    [
+        ({1: 2}, [(2, 3)]),
+        ({3: 4, 5: 6}, [(4, 5), (6, 7)]),
+        ({7: 8, 9: 10, 11: 12}, [(8, 9), (10, 11), (12, 13)]),
+    ],
+)
+def test_dict_ranges(tested_dict, expected):
+    assert m.dict_iterator_default_initialization()
+    assert m.transform_dict_plus_one(tested_dict) == expected
diff --git a/tests/test_sequences_and_iterators.cpp b/tests/test_sequences_and_iterators.cpp
index 4a1d37f4d..c997b7300 100644
--- a/tests/test_sequences_and_iterators.cpp
+++ b/tests/test_sequences_and_iterators.cpp
@@ -86,8 +86,8 @@ private:
 };
 using NonCopyableIntPair = std::pair<NonCopyableInt, NonCopyableInt>;
 
-PYBIND11_MAKE_OPAQUE(std::vector<NonCopyableInt>);
-PYBIND11_MAKE_OPAQUE(std::vector<NonCopyableIntPair>);
+PYBIND11_MAKE_OPAQUE(std::vector<NonCopyableInt>)
+PYBIND11_MAKE_OPAQUE(std::vector<NonCopyableIntPair>)
 
 template <typename PythonType>
 py::list test_random_access_iterator(PythonType x) {
diff --git a/tests/test_smart_ptr.cpp b/tests/test_smart_ptr.cpp
index 496073b3c..4ab43953f 100644
--- a/tests/test_smart_ptr.cpp
+++ b/tests/test_smart_ptr.cpp
@@ -11,6 +11,9 @@
 #include "object.h"
 #include "pybind11_tests.h"
 
+// This breaks on PYBIND11_DECLARE_HOLDER_TYPE
+PYBIND11_WARNING_DISABLE_GCC("-Wpedantic")
+
 namespace {
 
 // This is just a wrapper around unique_ptr, but with extra fields to deliberately bloat up the
@@ -279,13 +282,13 @@ struct holder_helper<ref<T>> {
 } // namespace PYBIND11_NAMESPACE
 
 // Make pybind aware of the ref-counted wrapper type (s):
-PYBIND11_DECLARE_HOLDER_TYPE(T, ref<T>, true);
+PYBIND11_DECLARE_HOLDER_TYPE(T, ref<T>, true)
 // The following is not required anymore for std::shared_ptr, but it should compile without error:
-PYBIND11_DECLARE_HOLDER_TYPE(T, std::shared_ptr<T>);
-PYBIND11_DECLARE_HOLDER_TYPE(T, huge_unique_ptr<T>);
-PYBIND11_DECLARE_HOLDER_TYPE(T, custom_unique_ptr<T>);
-PYBIND11_DECLARE_HOLDER_TYPE(T, shared_ptr_with_addressof_operator<T>);
-PYBIND11_DECLARE_HOLDER_TYPE(T, unique_ptr_with_addressof_operator<T>);
+PYBIND11_DECLARE_HOLDER_TYPE(T, std::shared_ptr<T>)
+PYBIND11_DECLARE_HOLDER_TYPE(T, huge_unique_ptr<T>)
+PYBIND11_DECLARE_HOLDER_TYPE(T, custom_unique_ptr<T>)
+PYBIND11_DECLARE_HOLDER_TYPE(T, shared_ptr_with_addressof_operator<T>)
+PYBIND11_DECLARE_HOLDER_TYPE(T, unique_ptr_with_addressof_operator<T>)
 
 TEST_SUBMODULE(smart_ptr, m) {
     // Please do not interleave `struct` and `class` definitions with bindings code,
diff --git a/tests/test_stl.cpp b/tests/test_stl.cpp
index 48c907ff3..dd93d51d0 100644
--- a/tests/test_stl.cpp
+++ b/tests/test_stl.cpp
@@ -59,7 +59,7 @@ struct visit_helper<boost::variant> {
 } // namespace PYBIND11_NAMESPACE
 #endif
 
-PYBIND11_MAKE_OPAQUE(std::vector<std::string, std::allocator<std::string>>);
+PYBIND11_MAKE_OPAQUE(std::vector<std::string, std::allocator<std::string>>)
 
 /// Issue #528: templated constructor
 struct TplCtorClass {
@@ -167,6 +167,14 @@ struct type_caster<ReferenceSensitiveOptional<T>>
 } // namespace detail
 } // namespace PYBIND11_NAMESPACE
 
+int pass_std_vector_int(const std::vector<int> &v) {
+    int zum = 100;
+    for (const int i : v) {
+        zum += 2 * i;
+    }
+    return zum;
+}
+
 TEST_SUBMODULE(stl, m) {
     // test_vector
     m.def("cast_vector", []() { return std::vector<int>{1}; });
@@ -193,6 +201,23 @@ TEST_SUBMODULE(stl, m) {
     m.def("cast_array", []() { return std::array<int, 2>{{1, 2}}; });
     m.def("load_array", [](const std::array<int, 2> &a) { return a[0] == 1 && a[1] == 2; });
 
+    struct NoDefaultCtor {
+        explicit constexpr NoDefaultCtor(int val) : val{val} {}
+        int val;
+    };
+
+    struct NoDefaultCtorArray {
+        explicit constexpr NoDefaultCtorArray(int i)
+            : arr{{NoDefaultCtor(10 + i), NoDefaultCtor(20 + i)}} {}
+        std::array<NoDefaultCtor, 2> arr;
+    };
+
+    // test_array_no_default_ctor
+    py::class_<NoDefaultCtor>(m, "NoDefaultCtor").def_readonly("val", &NoDefaultCtor::val);
+    py::class_<NoDefaultCtorArray>(m, "NoDefaultCtorArray")
+        .def(py::init<int>())
+        .def_readwrite("arr", &NoDefaultCtorArray::arr);
+
     // test_valarray
     m.def("cast_valarray", []() { return std::valarray<int>{1, 4, 9}; });
     m.def("load_valarray", [](const std::valarray<int> &v) {
@@ -546,4 +571,30 @@ TEST_SUBMODULE(stl, m) {
         []() { return new std::vector<bool>(4513); },
         // Without explicitly specifying `take_ownership`, this function leaks.
         py::return_value_policy::take_ownership);
+
+    m.def("pass_std_vector_int", pass_std_vector_int);
+    m.def("pass_std_vector_pair_int", [](const std::vector<std::pair<int, int>> &v) {
+        int zum = 0;
+        for (const auto &ij : v) {
+            zum += ij.first * 100 + ij.second;
+        }
+        return zum;
+    });
+    m.def("pass_std_array_int_2", [](const std::array<int, 2> &a) {
+        return pass_std_vector_int(std::vector<int>(a.begin(), a.end())) + 1;
+    });
+    m.def("pass_std_set_int", [](const std::set<int> &s) {
+        int zum = 200;
+        for (const int i : s) {
+            zum += 3 * i;
+        }
+        return zum;
+    });
+    m.def("pass_std_map_int", [](const std::map<int, int> &m) {
+        int zum = 500;
+        for (const auto &p : m) {
+            zum += p.first * 1000 + p.second;
+        }
+        return zum;
+    });
 }
diff --git a/tests/test_stl.py b/tests/test_stl.py
index 65fda54cc..6f548789e 100644
--- a/tests/test_stl.py
+++ b/tests/test_stl.py
@@ -48,6 +48,13 @@ def test_array(doc):
     )
 
 
+def test_array_no_default_ctor():
+    lst = m.NoDefaultCtorArray(3)
+    assert [e.val for e in lst.arr] == [13, 23]
+    lst.arr = m.NoDefaultCtorArray(4).arr
+    assert [e.val for e in lst.arr] == [14, 24]
+
+
 def test_valarray(doc):
     """std::valarray <-> list"""
     lst = m.cast_valarray()
@@ -381,3 +388,129 @@ def test_return_vector_bool_raw_ptr():
     v = m.return_vector_bool_raw_ptr()
     assert isinstance(v, list)
     assert len(v) == 4513
+
+
+@pytest.mark.parametrize(
+    ("fn", "offset"), [(m.pass_std_vector_int, 0), (m.pass_std_array_int_2, 1)]
+)
+def test_pass_std_vector_int(fn, offset):
+    assert fn([7, 13]) == 140 + offset
+    assert fn({6, 2}) == 116 + offset
+    assert fn({"x": 8, "y": 11}.values()) == 138 + offset
+    assert fn({3: None, 9: None}.keys()) == 124 + offset
+    assert fn(i for i in [4, 17]) == 142 + offset
+    assert fn(map(lambda i: i * 3, [8, 7])) == 190 + offset  # noqa: C417
+    with pytest.raises(TypeError):
+        fn({"x": 0, "y": 1})
+    with pytest.raises(TypeError):
+        fn({})
+
+
+def test_pass_std_vector_pair_int():
+    fn = m.pass_std_vector_pair_int
+    assert fn({1: 2, 3: 4}.items()) == 406
+    assert fn(zip([5, 17], [13, 9])) == 2222
+
+
+def test_list_caster_fully_consumes_generator_object():
+    def gen_invalid():
+        yield from [1, 2.0, 3]
+
+    gen_obj = gen_invalid()
+    with pytest.raises(TypeError):
+        m.pass_std_vector_int(gen_obj)
+    assert not tuple(gen_obj)
+
+
+def test_pass_std_set_int():
+    fn = m.pass_std_set_int
+    assert fn({3, 15}) == 254
+    assert fn({5: None, 12: None}.keys()) == 251
+    with pytest.raises(TypeError):
+        fn([])
+    with pytest.raises(TypeError):
+        fn({})
+    with pytest.raises(TypeError):
+        fn({}.values())
+    with pytest.raises(TypeError):
+        fn(i for i in [])
+
+
+def test_set_caster_dict_keys_failure():
+    dict_keys = {1: None, 2.0: None, 3: None}.keys()
+    # The asserts does not really exercise anything in pybind11, but if one of
+    # them fails in some future version of Python, the set_caster load
+    # implementation may need to be revisited.
+    assert tuple(dict_keys) == (1, 2.0, 3)
+    assert tuple(dict_keys) == (1, 2.0, 3)
+    with pytest.raises(TypeError):
+        m.pass_std_set_int(dict_keys)
+    assert tuple(dict_keys) == (1, 2.0, 3)
+
+
+class FakePyMappingMissingItems:
+    def __getitem__(self, _):
+        raise RuntimeError("Not expected to be called.")
+
+
+class FakePyMappingWithItems(FakePyMappingMissingItems):
+    def items(self):
+        return ((1, 3), (2, 4))
+
+
+class FakePyMappingBadItems(FakePyMappingMissingItems):
+    def items(self):
+        return ((1, 2), (3, "x"))
+
+
+class FakePyMappingItemsNotCallable(FakePyMappingMissingItems):
+    @property
+    def items(self):
+        return ((1, 2), (3, 4))
+
+
+class FakePyMappingItemsWithArg(FakePyMappingMissingItems):
+    def items(self, _):
+        return ((1, 2), (3, 4))
+
+
+class FakePyMappingGenObj(FakePyMappingMissingItems):
+    def __init__(self, gen_obj):
+        super().__init__()
+        self.gen_obj = gen_obj
+
+    def items(self):
+        yield from self.gen_obj
+
+
+def test_pass_std_map_int():
+    fn = m.pass_std_map_int
+    assert fn({1: 2, 3: 4}) == 4506
+    with pytest.raises(TypeError):
+        fn([])
+    assert fn(FakePyMappingWithItems()) == 3507
+    with pytest.raises(TypeError):
+        fn(FakePyMappingMissingItems())
+    with pytest.raises(TypeError):
+        fn(FakePyMappingBadItems())
+    with pytest.raises(TypeError):
+        fn(FakePyMappingItemsNotCallable())
+    with pytest.raises(TypeError):
+        fn(FakePyMappingItemsWithArg())
+
+
+@pytest.mark.parametrize(
+    ("items", "expected_exception"),
+    [
+        (((1, 2), (3, "x"), (4, 5)), TypeError),
+        (((1, 2), (3, 4, 5), (6, 7)), ValueError),
+    ],
+)
+def test_map_caster_fully_consumes_generator_object(items, expected_exception):
+    def gen_invalid():
+        yield from items
+
+    gen_obj = gen_invalid()
+    with pytest.raises(expected_exception):
+        m.pass_std_map_int(FakePyMappingGenObj(gen_obj))
+    assert not tuple(gen_obj)
diff --git a/tests/test_tagbased_polymorphic.cpp b/tests/test_tagbased_polymorphic.cpp
index 24b49021b..13e5ed319 100644
--- a/tests/test_tagbased_polymorphic.cpp
+++ b/tests/test_tagbased_polymorphic.cpp
@@ -145,4 +145,4 @@ TEST_SUBMODULE(tagbased_polymorphic, m) {
         .def(py::init<std::string>())
         .def("purr", &Panther::purr);
     m.def("create_zoo", &create_zoo);
-};
+}
diff --git a/tests/test_type_caster_std_function_specializations.cpp b/tests/test_type_caster_std_function_specializations.cpp
new file mode 100644
index 000000000..89213ddb1
--- /dev/null
+++ b/tests/test_type_caster_std_function_specializations.cpp
@@ -0,0 +1,46 @@
+#include <pybind11/functional.h>
+#include <pybind11/pybind11.h>
+
+#include "pybind11_tests.h"
+
+namespace py = pybind11;
+
+namespace {
+
+struct SpecialReturn {
+    int value = 99;
+};
+
+} // namespace
+
+namespace pybind11 {
+namespace detail {
+namespace type_caster_std_function_specializations {
+
+template <typename... Args>
+struct func_wrapper<SpecialReturn, Args...> : func_wrapper_base {
+    using func_wrapper_base::func_wrapper_base;
+    SpecialReturn operator()(Args... args) const {
+        gil_scoped_acquire acq;
+        SpecialReturn result;
+        try {
+            result = hfunc.f(std::forward<Args>(args)...).template cast<SpecialReturn>();
+        } catch (error_already_set &) {
+            result.value += 1;
+        }
+        result.value += 100;
+        return result;
+    }
+};
+
+} // namespace type_caster_std_function_specializations
+} // namespace detail
+} // namespace pybind11
+
+TEST_SUBMODULE(type_caster_std_function_specializations, m) {
+    py::class_<SpecialReturn>(m, "SpecialReturn")
+        .def(py::init<>())
+        .def_readwrite("value", &SpecialReturn::value);
+    m.def("call_callback_with_special_return",
+          [](const std::function<SpecialReturn()> &func) { return func(); });
+}
diff --git a/tests/test_type_caster_std_function_specializations.py b/tests/test_type_caster_std_function_specializations.py
new file mode 100644
index 000000000..9e45d4f59
--- /dev/null
+++ b/tests/test_type_caster_std_function_specializations.py
@@ -0,0 +1,15 @@
+from __future__ import annotations
+
+from pybind11_tests import type_caster_std_function_specializations as m
+
+
+def test_callback_with_special_return():
+    def return_special():
+        return m.SpecialReturn()
+
+    def raise_exception():
+        raise ValueError("called raise_exception.")
+
+    assert return_special().value == 99
+    assert m.call_callback_with_special_return(return_special).value == 199
+    assert m.call_callback_with_special_return(raise_exception).value == 200
diff --git a/tests/test_virtual_functions.cpp b/tests/test_virtual_functions.cpp
index 93b136ad3..a6164eb81 100644
--- a/tests/test_virtual_functions.cpp
+++ b/tests/test_virtual_functions.cpp
@@ -589,4 +589,4 @@ void initialize_inherited_virtuals(py::module_ &m) {
     // Fix issue #1454 (crash when acquiring/releasing GIL on another thread in Python 2.7)
     m.def("test_gil", &test_gil);
     m.def("test_gil_from_thread", &test_gil_from_thread);
-};
+}
diff --git a/tools/pybind11Common.cmake b/tools/pybind11Common.cmake
index 8467b45d2..450a14156 100644
--- a/tools/pybind11Common.cmake
+++ b/tools/pybind11Common.cmake
@@ -2,7 +2,7 @@
 
 Adds the following targets::
 
-    pybind11::pybind11 - link to headers and pybind11
+    pybind11::pybind11 - link to Python headers and pybind11::headers
     pybind11::module - Adds module links
     pybind11::embed - Adds embed links
     pybind11::lto - Link time optimizations (only if CMAKE_INTERPROCEDURAL_OPTIMIZATION is not set)
@@ -18,11 +18,7 @@ Adds the following functions::
 
 #]======================================================]
 
-# CMake 3.10 has an include_guard command, but we can't use that yet
-# include_guard(global) (pre-CMake 3.10)
-if(TARGET pybind11::pybind11)
-  return()
-endif()
+include_guard(GLOBAL)
 
 # If we are in subdirectory mode, all IMPORTED targets must be GLOBAL. If we
 # are in CONFIG mode, they should be "normal" targets instead.
@@ -75,26 +71,36 @@ set_property(
   APPEND
   PROPERTY INTERFACE_LINK_LIBRARIES pybind11::pybind11)
 
+# -------------- emscripten requires exceptions enabled -------------
+# _pybind11_no_exceptions is a private mechanism to disable this addition.
+# Please open an issue if you need to use it; it will be removed if no one
+# needs it.
+if(CMAKE_SYSTEM_NAME MATCHES Emscripten AND NOT _pybind11_no_exceptions)
+  if(is_config)
+    set(_tmp_config_target pybind11::pybind11_headers)
+  else()
+    set(_tmp_config_target pybind11_headers)
+  endif()
+
+  set_property(
+    TARGET ${_tmp_config_target}
+    APPEND
+    PROPERTY INTERFACE_LINK_OPTIONS -fexceptions)
+  set_property(
+    TARGET ${_tmp_config_target}
+    APPEND
+    PROPERTY INTERFACE_COMPILE_OPTIONS -fexceptions)
+  unset(_tmp_config_target)
+endif()
+
 # --------------------------- link helper ---------------------------
 
 add_library(pybind11::python_link_helper IMPORTED INTERFACE ${optional_global})
 
-if(CMAKE_VERSION VERSION_LESS 3.13)
-  # In CMake 3.11+, you can set INTERFACE properties via the normal methods, and
-  # this would be simpler.
-  set_property(
-    TARGET pybind11::python_link_helper
-    APPEND
-    PROPERTY INTERFACE_LINK_LIBRARIES "$<$<PLATFORM_ID:Darwin>:-undefined dynamic_lookup>")
-else()
-  # link_options was added in 3.13+
-  # This is safer, because you are ensured the deduplication pass in CMake will not consider
-  # these separate and remove one but not the other.
-  set_property(
-    TARGET pybind11::python_link_helper
-    APPEND
-    PROPERTY INTERFACE_LINK_OPTIONS "$<$<PLATFORM_ID:Darwin>:LINKER:-undefined,dynamic_lookup>")
-endif()
+set_property(
+  TARGET pybind11::python_link_helper
+  APPEND
+  PROPERTY INTERFACE_LINK_OPTIONS "$<$<PLATFORM_ID:Darwin>:LINKER:-undefined,dynamic_lookup>")
 
 # ------------------------ Windows extras -------------------------
 
@@ -110,22 +116,14 @@ if(MSVC) # That's also clang-cl
 
   # /MP enables multithreaded builds (relevant when there are many files) for MSVC
   if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC") # no Clang no Intel
-    if(CMAKE_VERSION VERSION_LESS 3.11)
-      set_property(
-        TARGET pybind11::windows_extras
-        APPEND
-        PROPERTY INTERFACE_COMPILE_OPTIONS $<$<NOT:$<CONFIG:Debug>>:/MP>)
-    else()
-      # Only set these options for C++ files.  This is important so that, for
-      # instance, projects that include other types of source files like CUDA
-      # .cu files don't get these options propagated to nvcc since that would
-      # cause the build to fail.
-      set_property(
-        TARGET pybind11::windows_extras
-        APPEND
-        PROPERTY INTERFACE_COMPILE_OPTIONS
-                 $<$<NOT:$<CONFIG:Debug>>:$<$<COMPILE_LANGUAGE:CXX>:/MP>>)
-    endif()
+    # Only set these options for C++ files.  This is important so that, for
+    # instance, projects that include other types of source files like CUDA
+    # .cu files don't get these options propagated to nvcc since that would
+    # cause the build to fail.
+    set_property(
+      TARGET pybind11::windows_extras
+      APPEND
+      PROPERTY INTERFACE_COMPILE_OPTIONS $<$<NOT:$<CONFIG:Debug>>:$<$<COMPILE_LANGUAGE:CXX>:/MP>>)
   endif()
 endif()
 
@@ -329,7 +327,7 @@ function(_pybind11_generate_lto target prefer_thin_lto)
 
     if(CMAKE_SYSTEM_PROCESSOR MATCHES "ppc64le" OR CMAKE_SYSTEM_PROCESSOR MATCHES "mips64")
       # Do nothing
-    elseif(CMAKE_SYSTEM_PROCESSOR MATCHES emscripten)
+    elseif(CMAKE_SYSTEM_NAME MATCHES Emscripten)
       # This compile is very costly when cross-compiling, so set this without checking
       set(PYBIND11_LTO_CXX_FLAGS "-flto${thin}${cxx_append}")
       set(PYBIND11_LTO_LINKER_FLAGS "-flto${thin}${linker_append}")
@@ -371,11 +369,7 @@ function(_pybind11_generate_lto target prefer_thin_lto)
     set(is_debug "$<OR:$<CONFIG:Debug>,$<CONFIG:RelWithDebInfo>>")
     set(not_debug "$<NOT:${is_debug}>")
     set(cxx_lang "$<COMPILE_LANGUAGE:CXX>")
-    if(MSVC AND CMAKE_VERSION VERSION_LESS 3.11)
-      set(genex "${not_debug}")
-    else()
-      set(genex "$<AND:${not_debug},${cxx_lang}>")
-    endif()
+    set(genex "$<AND:${not_debug},${cxx_lang}>")
     set_property(
       TARGET ${target}
       APPEND
@@ -390,17 +384,10 @@ function(_pybind11_generate_lto target prefer_thin_lto)
   endif()
 
   if(PYBIND11_LTO_LINKER_FLAGS)
-    if(CMAKE_VERSION VERSION_LESS 3.11)
-      set_property(
-        TARGET ${target}
-        APPEND
-        PROPERTY INTERFACE_LINK_LIBRARIES "$<${not_debug}:${PYBIND11_LTO_LINKER_FLAGS}>")
-    else()
-      set_property(
-        TARGET ${target}
-        APPEND
-        PROPERTY INTERFACE_LINK_OPTIONS "$<${not_debug}:${PYBIND11_LTO_LINKER_FLAGS}>")
-    endif()
+    set_property(
+      TARGET ${target}
+      APPEND
+      PROPERTY INTERFACE_LINK_OPTIONS "$<${not_debug}:${PYBIND11_LTO_LINKER_FLAGS}>")
   endif()
 endfunction()
 
diff --git a/tools/pybind11Config.cmake.in b/tools/pybind11Config.cmake.in
index 304f1d907..2d9fa94f6 100644
--- a/tools/pybind11Config.cmake.in
+++ b/tools/pybind11Config.cmake.in
@@ -84,7 +84,7 @@ you can either use the basic targets, or use the FindPython tools:
 
   # Python method:
   Python_add_library(MyModule2 src2.cpp)
-  target_link_libraries(MyModule2 pybind11::headers)
+  target_link_libraries(MyModule2 PUBLIC pybind11::headers)
   set_target_properties(MyModule2 PROPERTIES
                                   INTERPROCEDURAL_OPTIMIZATION ON
                                   CXX_VISIBILITY_PRESET ON
diff --git a/tools/pybind11GuessPythonExtSuffix.cmake b/tools/pybind11GuessPythonExtSuffix.cmake
index c5fb3b42c..b550f3935 100644
--- a/tools/pybind11GuessPythonExtSuffix.cmake
+++ b/tools/pybind11GuessPythonExtSuffix.cmake
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.15...3.30)
 
 function(pybind11_guess_python_module_extension python)
 
diff --git a/tools/pybind11NewTools.cmake b/tools/pybind11NewTools.cmake
index 444f3aaf5..d3e938fab 100644
--- a/tools/pybind11NewTools.cmake
+++ b/tools/pybind11NewTools.cmake
@@ -5,10 +5,6 @@
 # All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-if(CMAKE_VERSION VERSION_LESS 3.12)
-  message(FATAL_ERROR "You cannot use the new FindPython module with CMake < 3.12")
-endif()
-
 include_guard(DIRECTORY)
 
 get_property(
@@ -236,7 +232,6 @@ if(TARGET ${_Python}::Python)
     PROPERTY INTERFACE_LINK_LIBRARIES ${_Python}::Python)
 endif()
 
-# CMake 3.15+ has this
 if(TARGET ${_Python}::Module)
   set_property(
     TARGET pybind11::module
diff --git a/tools/pybind11Tools.cmake b/tools/pybind11Tools.cmake
index 021038d95..d91e7670c 100644
--- a/tools/pybind11Tools.cmake
+++ b/tools/pybind11Tools.cmake
@@ -5,13 +5,7 @@
 # All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-# include_guard(global) (pre-CMake 3.10)
-if(TARGET pybind11::python_headers)
-  return()
-endif()
-
-# Built-in in CMake 3.5+
-include(CMakeParseArguments)
+include_guard(GLOBAL)
 
 if(pybind11_FIND_QUIETLY)
   set(_pybind11_quiet QUIET)
@@ -116,36 +110,19 @@ if(PYTHON_IS_DEBUG)
     PROPERTY INTERFACE_COMPILE_DEFINITIONS Py_DEBUG)
 endif()
 
-# The <3.11 code here does not support release/debug builds at the same time, like on vcpkg
-if(CMAKE_VERSION VERSION_LESS 3.11)
-  set_property(
-    TARGET pybind11::module
-    APPEND
-    PROPERTY
-      INTERFACE_LINK_LIBRARIES
-      pybind11::python_link_helper
-      "$<$<OR:$<PLATFORM_ID:Windows>,$<PLATFORM_ID:Cygwin>>:$<BUILD_INTERFACE:${PYTHON_LIBRARIES}>>"
-  )
+# The IMPORTED INTERFACE library here is to ensure that "debug" and "release" get processed outside
+# of a generator expression - https://gitlab.kitware.com/cmake/cmake/-/issues/18424, as they are
+# target_link_library keywords rather than real libraries.
+add_library(pybind11::_ClassicPythonLibraries IMPORTED INTERFACE)
+target_link_libraries(pybind11::_ClassicPythonLibraries INTERFACE ${PYTHON_LIBRARIES})
+target_link_libraries(
+  pybind11::module
+  INTERFACE
+    pybind11::python_link_helper
+    "$<$<OR:$<PLATFORM_ID:Windows>,$<PLATFORM_ID:Cygwin>>:pybind11::_ClassicPythonLibraries>")
 
-  set_property(
-    TARGET pybind11::embed
-    APPEND
-    PROPERTY INTERFACE_LINK_LIBRARIES pybind11::pybind11 $<BUILD_INTERFACE:${PYTHON_LIBRARIES}>)
-else()
-  # The IMPORTED INTERFACE library here is to ensure that "debug" and "release" get processed outside
-  # of a generator expression - https://gitlab.kitware.com/cmake/cmake/-/issues/18424, as they are
-  # target_link_library keywords rather than real libraries.
-  add_library(pybind11::_ClassicPythonLibraries IMPORTED INTERFACE)
-  target_link_libraries(pybind11::_ClassicPythonLibraries INTERFACE ${PYTHON_LIBRARIES})
-  target_link_libraries(
-    pybind11::module
-    INTERFACE
-      pybind11::python_link_helper
-      "$<$<OR:$<PLATFORM_ID:Windows>,$<PLATFORM_ID:Cygwin>>:pybind11::_ClassicPythonLibraries>")
-
-  target_link_libraries(pybind11::embed INTERFACE pybind11::pybind11
-                                                  pybind11::_ClassicPythonLibraries)
-endif()
+target_link_libraries(pybind11::embed INTERFACE pybind11::pybind11
+                                                pybind11::_ClassicPythonLibraries)
 
 function(pybind11_extension name)
   # The prefix and extension are provided by FindPythonLibsNew.cmake
diff --git a/tools/test-pybind11GuessPythonExtSuffix.cmake b/tools/test-pybind11GuessPythonExtSuffix.cmake
index 0de2c0169..ac90e039b 100644
--- a/tools/test-pybind11GuessPythonExtSuffix.cmake
+++ b/tools/test-pybind11GuessPythonExtSuffix.cmake
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.15...3.30)
 
 # Tests for pybind11_guess_python_module_extension
 # Run using `cmake -P tools/test-pybind11GuessPythonExtSuffix.cmake`