fix(model-switch): preserve per-model metadata dict in _save_discovered_models_to_config (#67841)

When custom_providers[].models uses the mapping form to store
per-model metadata (e.g. context_length), _save_discovered_models_to_config
must not replace it with a flat list of strings.  Add a guard that skips
entries whose models value is a dict, preserving the user's curated
metadata.

The regression was introduced by PR #65652, which added the auto-save
helper without considering the dict form.

hermes_cli/model_switch.py

@@ -133,6 +133,11 @@ def _save_discovered_models_to_config(
             if entry_url.rstrip("/").lower() != norm_url:
                 continue
             existing = entry.get("models")
+            # Preserve per-model metadata: when ``models`` is a mapping
+            # (e.g. ``{"model-a": {"context_length": 8192}}``), the user
+            # has curated metadata per model — do not replace it.
+            if isinstance(existing, dict):
+                continue
             # Only update when models are stale — avoids unnecessary
             # config writes on every picker open.
             if isinstance(existing, list) and existing == model_ids:

tests/hermes_cli/test_model_switch_custom_providers.py

@@ -1479,3 +1479,40 @@ def test_save_discovered_models_noop_on_empty_args(monkeypatch):
     _save_discovered_models_to_config("", [])
 
     assert load_calls == 0, "load_config must not be called for empty args"
+
+
+def test_save_discovered_models_preserves_dict_form(monkeypatch):
+    """``_save_discovered_models_to_config`` must not replace a dict-form
+    ``models`` mapping (per-model metadata like ``context_length``) with
+    a flat list of strings (#67841)."""
+    from hermes_cli.model_switch import _save_discovered_models_to_config
+
+    save_calls = []
+
+    def fake_save(config):
+        save_calls.append(dict(config))
+
+    monkeypatch.setattr("hermes_cli.config.save_config", fake_save)
+    monkeypatch.setattr(
+        "hermes_cli.config.load_config",
+        lambda: {
+            "custom_providers": [
+                {
+                    "name": "my-gateway",
+                    "base_url": "https://gateway.example.com/v1",
+                    "models": {
+                        "configured-model": {"context_length": 8192},
+                    },
+                }
+            ]
+        },
+    )
+
+    # Dict-form models must NOT be overwritten by discovered models
+    _save_discovered_models_to_config(
+        "https://gateway.example.com/v1",
+        ["configured-model", "discovered-model"],
+    )
+    assert save_calls == [], (
+        "Dict-form models must not be replaced with a flat list"
+    )