Exclude the prefix wrapper from esphome.h, state the failure-path cost honestly

esphome/components/host/__init__.py

@@ -64,8 +64,9 @@ async def to_code(config: ConfigType) -> None:
         # Curated prefix for the pch (the script folds it plus defines.h):
         # host has no framework force-includes, and the per-TU cost is the
         # STL closure behind the core headers. Measured -43% compile CPU.
-        # Gated so ESPHOME_PCH_ENABLE=0 restores the strict view; a
-        # toolchain that cannot load its own pch hits the script's probe.
+        # Gated so ESPHOME_PCH_ENABLE=0 restores the strict view. When the
+        # .gch fails to build or load, the force-include stays and every TU
+        # parses the closure as text: correct, but slower than no pch.
         cg.add_platformio_option("build_src_flags", f"-include {HOST_PCH_PREFIX}")
 
 

esphome/writer.py

@@ -247,6 +247,7 @@ def copy_src_tree():
         Path(
             "esphome/core/ring_buffer.h"
         ),  # moved to components/ring_buffer/, removed in 2026.11.0
+        Path("esphome/core/pch_prefix.h"),  # build machinery, not user API
     }
     include_l = []
     for target, _ in source_files_l: