fix(webui): keep #1855 fast-path window and Copilot gpt-4o regression tests green

- Extract the MoA @moa:/moa/ prefix-stripping branch of
  _resolve_compatible_session_model_state into a new
  _moa_fast_path_model_state() helper. Inlining it had pushed
  `catalog = get_available_models()` just past the 6000-char
  source window that
  tests/test_issue1855_resolve_model_provider_fast_path.py::
  TestFastPathSourceShape scans to guard the #1855 fast-path/
  catalog-call ordering, breaking that regression test after
  rebasing onto current master.
- Re-add gpt-4o to the refreshed Copilot static fallback list.
  It's a real Copilot-served model and
  tests/test_issues_373_374_375.py::TestStaleModelListCleanup::
  test_copilot_list_unchanged asserts the Copilot list keeps it
  even as #374 removes it from the generic OpenAI list. The live
  Copilot catalog probe remains authoritative; this only affects
  the cold-start/probe-miss fallback.

Verification:
  ./scripts/test.sh tests/test_issue1855_resolve_model_provider_fast_path.py tests/test_issues_373_374_375.py tests/test_issue5057_moa_webui_route.py tests/test_copilot_provider_model_settings_not_allowlist.py tests/test_moa_model_picker_provider.py tests/test_pr1970_lmstudio_base_url_fallback.py -q
  -> 73 passed in 3.60s

  ./scripts/test.sh tests/ -k "config or provider or model or copilot or moa or lmstudio" -q
  -> 1745 passed, 2 skipped, 9775 deselected, 1 xpassed in 68.57s

api/config.py

@@ -1703,6 +1703,7 @@ _PROVIDER_MODELS = {
         {"id": "gemini-3.5-flash", "label": "Gemini 3.5 Flash"},
         {"id": "gemini-2.5-pro", "label": "Gemini 2.5 Pro"},
         {"id": "mai-code-1-flash-picker", "label": "MAI Code 1 Flash"},
+        {"id": "gpt-4o", "label": "GPT-4o"},
     ],
     # Cursor ACP — models served via Cursor CLI agent acp
     "cursor-acp": [

api/routes.py

@@ -5888,6 +5888,23 @@ def _read_profile_model_config(
     return _provider, _default
 
 
+def _moa_fast_path_model_state(model: str) -> tuple[str, str, bool]:
+    """Strip an optional ``@moa:``/``moa/`` prefix from an MoA-routed model.
+
+    Split out of ``_resolve_compatible_session_model_state`` so the MoA
+    fast-path stays a single-line call in that function body (see
+    ``test_issue1855_resolve_model_provider_fast_path.py``, the fast-path/
+    catalog-call ordering check scans a bounded window of that function's
+    source, and inlining this here previously pushed the catalog call just
+    past that window).
+    """
+    if model.startswith("@moa:"):
+        return model.split(":", 1)[1].strip(), "moa", True
+    if model.lower().startswith("moa/"):
+        return model.split("/", 1)[1].strip(), "moa", True
+    return model, "moa", False
+
+
 def _resolve_compatible_session_model_state(
     model_id: str | None,
     model_provider: str | None = None,
@@ -5914,7 +5931,7 @@ def _resolve_compatible_session_model_state(
     after paying the full catalog-build cost. Avoiding the catalog here keeps
     ``POST /api/chat/start`` snappy even when the model catalog is cold and the
     rebuild has to make network calls (custom OpenAI-compat endpoints,
-    OpenRouter ``/models``, LM Studio ``/models``, credential pool refresh) —
+    OpenRouter ``/models``, LM Studio ``/models``, credential pool refresh),
     those used to wedge the handler for >100s and trigger 502s on default-60s
     reverse proxies, even though the WebUI itself eventually responded.
 
@@ -5922,7 +5939,7 @@ def _resolve_compatible_session_model_state(
     non-blocking: it resolves from the warm/disk cache or a network-free
     minimal catalog and NEVER triggers a live per-provider rebuild (the
     Copilot token-exchange HTTPS call that hangs a server-initiated wakeup
-    turn — see rebase report §1/§3/model-resolve-hang). Human-initiated
+    turn, see rebase report §1/§3/model-resolve-hang). Human-initiated
     chat/start leaves this False to keep full live discovery; a session that
     already has a persisted model still resolves correctly because the
     persisted model wins over the catalog and the catalog is only consulted
@@ -5931,11 +5948,7 @@ def _resolve_compatible_session_model_state(
     model = str(model_id or "").strip()
     requested_provider = _clean_session_model_provider(model_provider)
     if model and requested_provider == "moa":
-        if model.startswith("@moa:"):
-            return model.split(":", 1)[1].strip(), "moa", True
-        if model.lower().startswith("moa/"):
-            return model.split("/", 1)[1].strip(), "moa", True
-        return model, "moa", False
+        return _moa_fast_path_model_state(model)
     if model and requested_provider and model.startswith(f"@{requested_provider}:"):
         try:
             from api.config import cfg as _active_cfg