fix: respect model.default from config.yaml for openai-codex provider (#1896)

When config.yaml had a non-default model (e.g. gpt-5.3-codex) and the
provider was openai-codex, _normalize_model_for_provider() would replace
it with the latest available codex model because _model_is_default only
checked the CLI argument, not the config value.

Now _model_is_default is False when config.yaml has a model that differs
from the global fallback (anthropic/claude-opus-4.6), so the user's
explicit config choice is preserved.

Fixes #1887

Co-authored-by: Test <test@test.com>

cli.py

@@ -1044,11 +1044,17 @@ class HermesCLI:
         # env vars would stomp each other.
         _model_config = CLI_CONFIG.get("model", {})
         _config_model = _model_config.get("default", "") if isinstance(_model_config, dict) else (_model_config or "")
-        self.model = model or _config_model or "anthropic/claude-opus-4.6"
+        _FALLBACK_MODEL = "anthropic/claude-opus-4.6"
+        self.model = model or _config_model or _FALLBACK_MODEL
         # Track whether model was explicitly chosen by the user or fell back
         # to the global default.  Provider-specific normalisation may override
         # the default silently but should warn when overriding an explicit choice.
-        self._model_is_default = not model
+        # A config model that matches the global fallback is NOT considered an
+        # explicit choice — the user just never changed it.  But a config model
+        # like "gpt-5.3-codex" IS explicit and must be preserved.
+        self._model_is_default = not model and (
+            not _config_model or _config_model == _FALLBACK_MODEL
+        )
 
         self._explicit_api_key = api_key
         self._explicit_base_url = base_url

tests/test_cli_provider_resolution.py

@@ -312,6 +312,49 @@ def test_codex_provider_uses_config_model(monkeypatch):
     assert shell.model != "should-be-ignored"
 
 
+def test_codex_config_model_not_replaced_by_normalization(monkeypatch):
+    """When the user sets model.default in config.yaml to a specific codex
+    model, _normalize_model_for_provider must NOT replace it with the latest
+    available model from the API.  Regression test for #1887."""
+    cli = _import_cli()
+
+    monkeypatch.delenv("LLM_MODEL", raising=False)
+    monkeypatch.delenv("OPENAI_MODEL", raising=False)
+
+    # User explicitly configured gpt-5.3-codex in config.yaml
+    monkeypatch.setitem(cli.CLI_CONFIG, "model", {
+        "default": "gpt-5.3-codex",
+        "provider": "openai-codex",
+        "base_url": "https://chatgpt.com/backend-api/codex",
+    })
+
+    def _runtime_resolve(**kwargs):
+        return {
+            "provider": "openai-codex",
+            "api_mode": "codex_responses",
+            "base_url": "https://chatgpt.com/backend-api/codex",
+            "api_key": "fake-key",
+            "source": "env/config",
+        }
+
+    monkeypatch.setattr("hermes_cli.runtime_provider.resolve_runtime_provider", _runtime_resolve)
+    monkeypatch.setattr("hermes_cli.runtime_provider.format_runtime_provider_error", lambda exc: str(exc))
+    # API returns a DIFFERENT model than what the user configured
+    monkeypatch.setattr(
+        "hermes_cli.codex_models.get_codex_model_ids",
+        lambda access_token=None: ["gpt-5.4", "gpt-5.3-codex"],
+    )
+
+    shell = cli.HermesCLI(compact=True, max_turns=1)
+
+    # Config model is NOT the global default — user made a deliberate choice
+    assert shell._model_is_default is False
+    assert shell._ensure_runtime_credentials() is True
+    assert shell.provider == "openai-codex"
+    # Model must stay as user configured, not replaced by gpt-5.4
+    assert shell.model == "gpt-5.3-codex"
+
+
 def test_codex_provider_preserves_explicit_codex_model(monkeypatch):
     """If the user explicitly passes a Codex-compatible model, it must be
     preserved even when the provider resolves to openai-codex."""