[ci] Fix memory impact build selecting unbuildable platform (#16788)

script/helpers.py

@@ -149,6 +149,31 @@ def get_component_test_files(
     return files
 
 
+def get_component_test_platforms(component: str, *, base_only: bool = True) -> set[str]:
+    """Return the set of platforms a component has compilable test files for.
+
+    Uses the same discovery as ``test_build_components.py`` (``get_component_test_files``
+    + ``parse_test_filename``) so callers agree with what the build runner would
+    actually compile. With ``base_only=True`` (the default, matching the
+    memory-impact build's ``--base-only``), only base ``test.<platform>.yaml``
+    files are considered; variant ``test-<variant>.<platform>.yaml`` files are
+    excluded. The ``"all"`` platform sentinel is excluded.
+
+    Args:
+        component: Component name (e.g. "wifi")
+        base_only: If True, only consider base test files (default).
+
+    Returns:
+        Set of platform identifiers (e.g. {"esp32-idf", "esp8266-ard"}).
+    """
+    platforms: set[str] = set()
+    for test_file in get_component_test_files(component, all_variants=not base_only):
+        platform = parse_test_filename(test_file)[1]
+        if platform != "all":
+            platforms.add(platform)
+    return platforms
+
+
 def is_validate_only_file(test_file: Path) -> bool:
     """Return True if the given path is a config-only validate file.