fix(gateway): resolve reattach URL and key as one pair; fail fast on 401/403

Drop the persisted base_url: pairing a saved URL with the profile's current key could poll the
old gateway with a new credential. Both now come from the session profile's current config, and
an auth rejection settles the turn at once with an explicit error instead of 150 retries.

api/gateway_chat.py

@@ -895,6 +895,8 @@ def _await_gateway_run_result(
         except urllib.error.HTTPError as exc:
             if exc.code == 404:
                 raise RuntimeError("Gateway no longer has this run; its result could not be recovered after the WebUI restart.") from exc
+            if exc.code in (401, 403):
+                raise RuntimeError(f"Gateway rejected the WebUI credentials (HTTP {exc.code}) while reattaching to a run after the restart.") from exc
             failures += 1
             status = None
         except (urllib.error.URLError, OSError, ValueError):
@@ -982,18 +984,15 @@ def _sidecars_with_active_stream(session_dir) -> list[str]:
     return ids
 
 
-def _gateway_endpoint_for_reattach(session, run: dict) -> tuple[str, str]:
+def _gateway_endpoint_for_reattach(session) -> tuple[str, str]:
-    """Resolve the gateway that owns ``run`` using the session's profile, not the process default."""
+    """Resolve gateway URL and key together from the session's profile, never the process default."""
     from api import profiles as _profiles
     from api.config import get_config
 
     with _profiles.profile_scope_for_detached_worker(
         getattr(session, "profile", None), "gateway reattach", logger_override=logger,
     ):
-        base_url = _gateway_base_url(get_config())
+        return _gateway_base_url(get_config()), _gateway_api_key()
-        api_key = _gateway_api_key()
-    # The run lives on the gateway that accepted it, even if config changed since.
-    return str(run.get("base_url") or base_url).rstrip("/"), api_key
 
 
 def _resume_gateway_run_for_session(session) -> bool:
@@ -1005,7 +1004,7 @@ def _resume_gateway_run_for_session(session) -> bool:
     if not stream_id or not run_id or run.get("stream_id") != stream_id:
         return False
     sid = session.session_id
-    endpoint = _gateway_endpoint_for_reattach(session, run)
+    endpoint = _gateway_endpoint_for_reattach(session)
     with STREAMS_LOCK:
         if stream_id in STREAMS:
             return False
@@ -1318,7 +1317,6 @@ def _run_gateway_chat_streaming(
                         active_provider=(model_provider or ""),
                         on_run_id=lambda run_id: _record_gateway_run(
                             session_id, stream_id, run_id,
-                            base_url=base_url,
                             regeneration=bool(regeneration),
                             goal_related=bool(goal_related),
                         ),

tests/test_gateway_run_reattach_after_restart.py

@@ -113,7 +113,7 @@ def test_runs_api_start_sends_idempotency_key_and_persists_run_id(isolated_sessi
     assert captured["post_headers"]["Idempotency-key"] == f"webui-{stream_id}"
     assert captured["persisted_at_events"]["run_id"] == "run_live"
     assert captured["persisted_at_events"]["stream_id"] == stream_id
-    assert captured["persisted_at_events"]["base_url"] == "http://gateway.local"
+    assert "api_key" not in captured["persisted_at_events"]
     saved = json.loads((isolated_sessions / f"{s.session_id}.json").read_text())
     assert saved["gateway_run"] is None
     assert saved["active_stream_id"] is None
@@ -348,16 +348,20 @@ def test_reattach_resolves_gateway_from_the_session_profile(isolated_sessions, m
     assert saved["messages"][-1]["content"] == "answer"
 
 
-def test_reattach_polls_the_gateway_that_accepted_the_run(isolated_sessions, monkeypatch):
+@pytest.mark.parametrize("code", [401, 403])
-    sid, stream_id = _orphaned_gateway_turn()
+def test_reattach_auth_rejection_fails_fast_with_an_auth_error(isolated_sessions, monkeypatch, code):
-    s = models.Session.load(sid)
+    sid, _stream_id = _orphaned_gateway_turn()
-    s.gateway_run = {**s.gateway_run, "base_url": "http://accepted-gateway:8642/"}
+    calls = []
-    s.save(touch_updated_at=False)
-    models.SESSIONS.clear()
-    seen = []
-    _poll_until_completed(monkeypatch, seen)
 
+    def rejected(base_url, api_key, run_id):
+        calls.append(run_id)
+        raise urllib.error.HTTPError("http://gateway.local/v1/runs/x", code, "denied", Message(), io.BytesIO(b""))
+
+    monkeypatch.setattr(gateway_chat, "_get_gateway_run_status", rejected)
     gateway_chat.resume_gateway_runs_after_restart()
     _wait_for_reattach_threads()
 
-    assert {b for b, _k, _r in seen} == {"http://accepted-gateway:8642"}
+    assert len(calls) == 1
+    saved = json.loads((isolated_sessions / f"{sid}.json").read_text())
+    assert saved["active_stream_id"] is None and saved["gateway_run"] is None
+    assert f"HTTP {code}" in json.dumps(saved["messages"][-1])