[ci] Keep the venv ninja on PATH, only cmake is missing in a real install

.github/cmake_windows/idf.yaml

@@ -0,0 +1,14 @@
+esphome:
+  name: cmake-idf
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+logger:
+api:
+
+wifi:
+  ssid: cmake
+  password: cmakepassword

.github/workflows/cmake-windows.yml

@@ -0,0 +1,43 @@
+name: Windows cmake lookup check
+
+on:
+  push:
+    branches:
+      - windows_cmake_lookup_ci
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  compile:
+    name: esp-idf native without host cmake
+    runs-on: windows-latest
+    timeout-minutes: 120
+    steps:
+      - name: Check out code from GitHub
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Set up Python
+        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
+        with:
+          python-version: "3.13"
+      # cmd throughout: idf_tools.py refuses to run under MSYS, which the
+      # bash shell announces, and users build from a plain Windows shell
+      - name: Install esphome
+        shell: cmd
+        run: |
+          python -m venv venv
+          call venv\Scripts\activate.bat
+          pip install -r requirements.txt
+          pip install -e .
+      # The runner image has cmake preinstalled on PATH, which would mask
+      # the bug: users of the builder install have no host cmake. Strip
+      # PATH to the interpreter, git and the system dirs, then prove it.
+      # ninja stays reachable through the venv, as in a real install: the
+      # pip ninja package from requirements.txt puts it in Scripts.
+      - name: Compile without cmake on the host PATH
+        shell: cmd
+        run: |
+          set "PATH=%CD%\venv\Scripts;%pythonLocation%;%pythonLocation%\Scripts;C:\Program Files\Git\cmd;%SystemRoot%\system32;%SystemRoot%"
+          where cmake && echo cmake still on PATH, test is invalid && exit /b 1
+          esphome compile .github/cmake_windows/idf.yaml

esphome/espidf/toolchain.py

@@ -138,7 +138,9 @@ def _get_cmake_output(build_dir) -> str:
         if not (Path(build_dir) / "CMakeCache.txt").is_file():
             raise EsphomeError(f"No ESP-IDF build found in {build_dir}")
 
-        cmd = ["cmake", "-LA", "-N", "."]
+        # Resolve to an absolute path: Windows locates a child process
+        # through the parent's PATH, not the env passed to it.
+        cmd = [_get_idf_tool("cmake"), "-LA", "-N", "."]
 
         env = _get_idf_env()
         result = subprocess.run(

tests/unit_tests/test_espidf_toolchain.py

@@ -264,6 +264,7 @@ def test_get_cmake_output_with_configured_build(setup_core: Path) -> None:
     )
     with (
         patch.object(toolchain, "_get_idf_env", return_value={}),
+        patch.object(toolchain, "_get_idf_tool", return_value="/idf/tools/cmake"),
         patch.object(toolchain.subprocess, "run", return_value=completed) as mock_run,
     ):
         assert toolchain._get_cmake_output(build_dir) == completed.stdout
@@ -271,6 +272,9 @@ def test_get_cmake_output_with_configured_build(setup_core: Path) -> None:
         assert toolchain._get_cmake_output(build_dir) == completed.stdout
 
     mock_run.assert_called_once()
+    # The resolved path, never a bare "cmake": Windows locates the child
+    # through the parent's PATH, where the IDF-managed cmake is missing.
+    assert mock_run.call_args.args[0][0] == "/idf/tools/cmake"
     assert toolchain._get_cmake_tool_path("CMAKE_ADDR2LINE") == Path("/tool/addr2line")