Updated devcontainer, seamless switching between build environments

.devcontainer/devcontainer-lock.json

@@ -0,0 +1,34 @@
+{
+  "features": {
+    "ghcr.io/devcontainers-extra/features/apt-packages:1": {
+      "version": "1.0.6",
+      "resolved": "ghcr.io/devcontainers-extra/features/apt-packages@sha256:55c54412112da81b9381e470cdbbe55278564950d1ff536ce925b1e8e096babd",
+      "integrity": "sha256:55c54412112da81b9381e470cdbbe55278564950d1ff536ce925b1e8e096babd"
+    },
+    "ghcr.io/devcontainers-extra/features/cmake:1": {
+      "version": "1.0.0",
+      "resolved": "ghcr.io/devcontainers-extra/features/cmake@sha256:86e25502f6b1213a68d88e4e55c969eba0b5016b9666d216ab65f5047808bc90",
+      "integrity": "sha256:86e25502f6b1213a68d88e4e55c969eba0b5016b9666d216ab65f5047808bc90"
+    },
+    "ghcr.io/devcontainers-extra/features/uv:1": {
+      "version": "1.0.2",
+      "resolved": "ghcr.io/devcontainers-extra/features/uv@sha256:1ac5b9f17a9e9e745933d0ac2ecf758e06ed3da4423cd22c94cce4d482fd2dd8",
+      "integrity": "sha256:1ac5b9f17a9e9e745933d0ac2ecf758e06ed3da4423cd22c94cce4d482fd2dd8"
+    },
+    "ghcr.io/devcontainers/features/docker-outside-of-docker:1": {
+      "version": "1.10.0",
+      "resolved": "ghcr.io/devcontainers/features/docker-outside-of-docker@sha256:c2c2cf829505ead8e4892c88c31b6594ae94a2bbb209e16e1fac456c1a3a624e",
+      "integrity": "sha256:c2c2cf829505ead8e4892c88c31b6594ae94a2bbb209e16e1fac456c1a3a624e"
+    },
+    "ghcr.io/devcontainers/features/git-lfs:1": {
+      "version": "1.2.5",
+      "resolved": "ghcr.io/devcontainers/features/git-lfs@sha256:71c2b371cf12ab7fcec47cf17369c6f59156100dad9abf9e4c593049d789de72",
+      "integrity": "sha256:71c2b371cf12ab7fcec47cf17369c6f59156100dad9abf9e4c593049d789de72"
+    },
+    "ghcr.io/devcontainers/features/git:1": {
+      "version": "1.3.8",
+      "resolved": "ghcr.io/devcontainers/features/git@sha256:fd75977de13a9979000e0e78baf949adb0ca71d2398995fa22e0a36d7e7e7fe2",
+      "integrity": "sha256:fd75977de13a9979000e0e78baf949adb0ca71d2398995fa22e0a36d7e7e7fe2"
+    }
+  }
+}

.devcontainer/devcontainer.json

@@ -6,14 +6,17 @@
     "ghcr.io/devcontainers/features/git-lfs:1": {},
     "ghcr.io/devcontainers/features/docker-outside-of-docker:1": {},
     "ghcr.io/devcontainers-extra/features/apt-packages:1": {
-      "packages": "clang-format-14,libx11-dev,libxrandr-dev,libxxf86vm-dev,libgl1-mesa-dev"
+      "packages": "clang-format-14,libx11-dev,libxrandr-dev,libxxf86vm-dev,libgl1-mesa-dev,patchelf"
     },
     "ghcr.io/devcontainers-extra/features/cmake:1": {},
     "ghcr.io/devcontainers-extra/features/uv:1": {}
   },
   "postCreateCommand": "uv tool install pre-commit && pre-commit install",
   "customizations": {
     "vscode": {
+      "settings": {
+        "cmake.buildDirectory": "${workspaceFolder}/build-devcontainer"
+      },
       "extensions": [
         "ms-vscode.cpptools",
         "ms-vscode.cmake-tools",

.gitignore

@@ -10,6 +10,7 @@ package-lock.json
 
 # Build directories
 build/
+build-devcontainer/
 _build/
 **/build/
 install/

cmake/SetupPython.cmake

@@ -150,15 +150,46 @@ if(BUILD_PYTHON_BINDINGS)
         else()
             set(_venv_python "${_build_venv}/bin/python")
         endif()
-        # Reuse an existing venv when possible. If the directory exists but the
-        # interpreter is missing, fail fast and require explicit cleanup.
-        if(EXISTS "${_build_venv}" AND NOT EXISTS "${_venv_python}")
-            message(FATAL_ERROR
-                "Found stale build venv directory at ${_build_venv}, but no interpreter at ${_venv_python}. "
-                "Please remove ${_build_venv} and reconfigure."
+        # Reuse the venv when its interpreter still runs. bin/python is an absolute
+        # symlink into a uv-managed Python, so it is only valid in the environment
+        # that created the venv.
+        set(_venv_usable FALSE)
+        if(EXISTS "${_venv_python}")
+            execute_process(
+                COMMAND "${_venv_python}" --version
+                RESULT_VARIABLE _venv_python_ok
+                OUTPUT_QUIET
+                ERROR_QUIET
             )
+            if(_venv_python_ok EQUAL 0)
+                set(_venv_usable TRUE)
+            endif()
         endif()
-        if(NOT EXISTS "${_venv_python}")
+
+        if(_venv_usable)
+            message(STATUS "Reusing existing build venv at ${_build_venv}")
+        elseif(EXISTS "${_build_venv}")
+            # Directory is present but its interpreter is not usable. Describe the
+            # actual failure: a dangling bin/python symlink (the common case when the
+            # venv was created in a different environment, e.g. a dev container vs the
+            # host, whose uv-managed Python lives elsewhere) versus an interpreter that
+            # is present but does not run. Only the former means the target is missing.
+            if(IS_SYMLINK "${_venv_python}" AND NOT EXISTS "${_venv_python}")
+                file(READ_SYMLINK "${_venv_python}" _venv_link_target)
+                string(CONCAT _venv_detail
+                    "Its interpreter symlink is broken: ${_venv_python} -> "
+                    "${_venv_link_target} (target does not exist). This build venv was "
+                    "created in a different environment whose uv-managed Python lives "
+                    "elsewhere.")
+            else()
+                set(_venv_detail "Its interpreter ${_venv_python} is missing or does not run.")
+            endif()
+            message(FATAL_ERROR
+                "Build venv at ${_build_venv} has no working Python interpreter. "
+                "${_venv_detail}\n"
+                "Remove the build directory ${CMAKE_BINARY_DIR} (or run 'cmake --fresh') "
+                "and reconfigure to recreate the venv for this environment.")
+        else()
             execute_process(
                 COMMAND "${UV_EXECUTABLE}" venv --python "${Python3_EXECUTABLE}" "${_build_venv}"
                 RESULT_VARIABLE _venv_ok
@@ -167,8 +198,6 @@ if(BUILD_PYTHON_BINDINGS)
             if(NOT _venv_ok EQUAL 0)
                 message(FATAL_ERROR "Failed to create build venv: ${_venv_err}")
             endif()
-        else()
-            message(STATUS "Reusing existing build venv at ${_build_venv}")
         endif()
         execute_process(
             COMMAND "${UV_EXECUTABLE}" pip install --python "${_venv_python}" "numpy>=2.0"