fix(ci): restore green lint gate on main

Merges of #564/#555 landed lint regressions that the old HF-429-masked CI hid:
- I001 unsorted imports in tests/repro_unsendable_panic.py (#564)
- ruff-format drift in helpers.py and code_compressor.py
- mypy arg-type on get_language() in code_compressor.py (#564 dropped the
  type: ignore the old get_parser() call had)

ruff check + ruff format --check + mypy headroom all green.

headroom/proxy/helpers.py

@@ -841,9 +841,7 @@ def decide_compression_failure_action(
             frame_bytes=frame_bytes,
         )
 
-    if (client or "").strip().lower() == "codex" and isinstance(
-        exception, asyncio.TimeoutError
-    ):
+    if (client or "").strip().lower() == "codex" and isinstance(exception, asyncio.TimeoutError):
         return CompressionFailureAction(
             refuse=False,
             reason="client_override:codex",

headroom/transforms/code_compressor.py

@@ -117,7 +117,9 @@ def _get_parser(language: str) -> Any:
             from tree_sitter_language_pack import get_language
 
             parser = Parser()
-            parser.language = get_language(language)
+            # `language` is a validated runtime str; get_language types its arg
+            # as a Literal of supported names, which a dynamic str can't satisfy.
+            parser.language = get_language(language)  # type: ignore[arg-type]
             parsers[language] = parser
             logger.debug(
                 "Loaded tree-sitter parser for %s (thread %s)",
@@ -163,7 +165,9 @@ def unload_tree_sitter() -> bool:
     if parsers:
         count = len(parsers)
         parsers.clear()
-        logger.info("Unloaded %d tree-sitter parsers (thread %s)", count, threading.current_thread().name)
+        logger.info(
+            "Unloaded %d tree-sitter parsers (thread %s)", count, threading.current_thread().name
+        )
         return True
     return False
 

tests/repro_unsendable_panic.py

@@ -12,8 +12,8 @@ Usage:
     python repro_unsendable_panic.py
 """
 
-import threading
 import concurrent.futures
+import threading
 
 CODE = b"def hello():\n    return 42\n"