Address review: unknown platforms raise, the filter pin asserts equality

An unknown or misspelled platform name yielded an empty set - the file
would be filtered out of every build (link failure at the end of a long
compile) and the subset guard passed vacuously.

esphome/config_helpers.py

@@ -105,6 +105,9 @@ def frameworks_for_platforms(platforms: Collection[str]) -> set[PlatformFramewor
     registry: deriving the framework set here means a platform added to the
     registry cannot validate and then fail at link on a filtered-out file.
     """
+    known = {pf.value[0].value for pf in PlatformFramework}
+    if unknown := set(platforms) - known:
+        raise ValueError(f"unknown platform(s): {sorted(unknown)}")
     return {pf for pf in PlatformFramework if pf.value[0].value in platforms}
 
 

tests/component_tests/bluetooth_proxy/test_platform_gates.py

@@ -189,7 +189,7 @@ def test_hub_source_filter_covers_every_hub_platform() -> None:
     hub_frameworks = bluetooth_connection.SOURCE_FILE_FRAMEWORKS[
         "bluetooth_connection_hub.cpp"
     ]
-    assert expected <= hub_frameworks
+    assert expected == hub_frameworks
 
 
 def test_bluetooth_connection_auto_load_covers_its_includes() -> None: