fix(gemini-cli): surface MODEL_CAPACITY_EXHAUSTED cleanly + drop retired gemma-4-26b (#11833)

Google-side 429 Code Assist errors now flow through Hermes' normal rate-limit
path (status_code on the exception, Retry-After preserved via error.response)
instead of being opaque RuntimeErrors. User sees a one-line capacity message
instead of a 500-char JSON dump.

Changes
- CodeAssistError grows status_code / response / retry_after / details attrs.
  _extract_status_code in error_classifier picks up status_code and classifies
  429 as FailoverReason.rate_limit, so fallback_providers triggers the same
  way it does for SDK errors. run_agent.py line ~10428 already walks
  error.response.headers for Retry-After — preserving the response means that
  path just works.
- _gemini_http_error parses the Google error envelope (error.status +
  error.details[].reason from google.rpc.ErrorInfo, retryDelay from
  google.rpc.RetryInfo). MODEL_CAPACITY_EXHAUSTED / RESOURCE_EXHAUSTED / 404
  model-not-found each produce a human-readable message; unknown shapes fall
  back to the previous raw-body format.
- Drop gemma-4-26b-it from hermes_cli/models.py, hermes_cli/setup.py, and
  agent/model_metadata.py — Google returned 404 for it today in local repro.
  Kept gemma-4-31b-it (capacity-constrained but not retired).

Validation
|                           | Before                         | After                                     |
|---------------------------|--------------------------------|-------------------------------------------|
| Error message             | 'Code Assist returned HTTP 429: {500 chars JSON}' | 'Gemini capacity exhausted for gemini-2.5-pro (Google-side throttle...)' |
| status_code on error      | None (opaque RuntimeError)     | 429                                       |
| Classifier reason         | unknown (string-match fallback) | FailoverReason.rate_limit                |
| Retry-After honored       | ignored                        | extracted from RetryInfo or header        |
| gemma-4-26b-it picker     | advertised (404s on Google)    | removed                                   |

Unit + E2E tests cover non-streaming 429, streaming 429, 404 model-not-found,
Retry-After header fallback, malformed body, and classifier integration.
Targeted suites: tests/agent/test_gemini_cloudcode.py (81 tests), full
tests/hermes_cli (2203 tests) green.

Co-authored-by: teknium1 <teknium@nousresearch.com>

hermes_cli/models.py

@@ -135,7 +135,6 @@ _PROVIDER_MODELS: dict[str, list[str]] = {
         "gemini-2.5-flash-lite",
         # Gemma open models (also served via AI Studio)
         "gemma-4-31b-it",
-        "gemma-4-26b-it",
     ],
     "google-gemini-cli": [
         "gemini-2.5-pro",

hermes_cli/setup.py

@@ -91,7 +91,7 @@ _DEFAULT_PROVIDER_MODELS = {
     "gemini": [
         "gemini-3.1-pro-preview", "gemini-3-flash-preview", "gemini-3.1-flash-lite-preview",
         "gemini-2.5-pro", "gemini-2.5-flash", "gemini-2.5-flash-lite",
-        "gemma-4-31b-it", "gemma-4-26b-it",
+        "gemma-4-31b-it",
     ],
     "zai": ["glm-5.1", "glm-5", "glm-4.7", "glm-4.5", "glm-4.5-flash"],
     "kimi-coding": ["kimi-k2.5", "kimi-k2-thinking", "kimi-k2-turbo-preview"],