refactor: remove redundant local imports already available at module level

Sweep ~74 redundant local imports across 21 files where the same module
was already imported at the top level. Also includes type fixes and lint
cleanups on the same branch.

agent/context_compressor.py

@@ -807,7 +807,7 @@ The user has requested that this compaction PRIORITISE preserving all informatio
                 )
                 self.summary_model = ""  # empty = use main model
                 self._summary_failure_cooldown_until = 0.0  # no cooldown
-                return self._generate_summary(messages, summary_budget)  # retry immediately
+                return self._generate_summary(turns_to_summarize)  # retry immediately
 
             # Transient errors (timeout, rate limit, network) — shorter cooldown
             _transient_cooldown = 60

agent/copilot_acp_client.py

@@ -386,6 +386,8 @@ class CopilotACPClient:
         stderr_tail: deque[str] = deque(maxlen=40)
 
         def _stdout_reader() -> None:
+            if proc.stdout is None:
+                return
             for line in proc.stdout:
                 try:
                     inbox.put(json.loads(line))

agent/gemini_cloudcode_adapter.py

@@ -799,7 +799,8 @@ def _gemini_http_error(response: httpx.Response) -> CodeAssistError:
         err_obj = {}
     err_status = str(err_obj.get("status") or "").strip()
     err_message = str(err_obj.get("message") or "").strip()
-    err_details_list = err_obj.get("details") if isinstance(err_obj.get("details"), list) else []
+    _raw_details = err_obj.get("details")
+    err_details_list = _raw_details if isinstance(_raw_details, list) else []
 
     # Extract google.rpc.ErrorInfo reason + metadata.  There may be more
     # than one ErrorInfo (rare), so we pick the first one with a reason.

agent/gemini_native_adapter.py

@@ -613,7 +613,8 @@ def gemini_http_error(response: httpx.Response) -> GeminiAPIError:
         err_obj = {}
     err_status = str(err_obj.get("status") or "").strip()
     err_message = str(err_obj.get("message") or "").strip()
-    details_list = err_obj.get("details") if isinstance(err_obj.get("details"), list) else []
+    _raw_details = err_obj.get("details")
+    details_list = _raw_details if isinstance(_raw_details, list) else []
 
     reason = ""
     retry_after: Optional[float] = None