Skip the doomed gch compile after header-generation failure, self-heal the placeholder from CMake

tests/unit_tests/build_helpers/test_pch.py

@@ -244,6 +244,8 @@ def test_pch_cmake_consumer_substitutes_target_and_sources(
     assert '"$<$<COMPILE_LANGUAGE:CXX>:esphome_pch.h>"' in block
     assert "set_source_files_properties(${APP_SOURCES} PROPERTIES" in block
     assert 'OBJECT_DEPENDS "${CMAKE_BINARY_DIR}/esphome_pch.h"' in block
+    # Placeholder guard: survives a build-system-side pristine wipe
+    assert 'file(TOUCH "${CMAKE_BINARY_DIR}/esphome_pch.h")' in block
 
 
 def test_pch_cmake_consumer_strict_escalates(

tests/unit_tests/components/nrf52/test_pch.py

@@ -230,7 +230,8 @@ class TestRunCompilePhases:
         with pytest.raises(EsphomeError, match="nRF52 native build failed"):
             self._run()
         assert "Zephyr header generation failed" in caplog.text
-        assert prepare.called
+        # The doomed .gch compile is skipped: it would latch .gch.failed
+        assert not prepare.called
 
     def test_generated_headers_failure_strict_raises(
         self, monkeypatch: pytest.MonkeyPatch, compile_ctx: CompileCtx