fix: prefix non-default provider model IDs for correct routing (#142)

* fix: prefix non-default provider model IDs for correct routing

When multiple providers are configured, models from non-default providers
(e.g. MiniMax when Anthropic is default) were sent as bare names without
provider context. resolve_model_provider() couldn't determine the target
provider and routed them to the default provider's API, which failed.

Fix: get_available_models() now prefixes model IDs with the provider name
(e.g. minimax/MiniMax-M2.7) for providers that are NOT the active config
provider. The default provider's models keep bare names for direct API
routing. This matches the existing pattern for OpenRouter models.

Added 2 tests to test_model_resolver.py for cross-provider routing.

Closes #138
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: model prefix — null-guard, case normalization, mutation safety, tests

Four fixes on top of original PR:
- active_provider=None guard: without a confirmed provider all models were
  being prefixed. Only prefix when active_provider is set.
- Case normalisation: compare pid against active_provider.lower() so
  config.yaml entries like 'Anthropic' match pid 'anthropic'.
- Mutation safety: default branch used raw reference to _PROVIDER_MODELS[pid];
  the default_model injector later calls list.insert() on that reference,
  permanently mutating the shared constant. Both branches now use a copy.
- Already-prefixed model IDs pass through as-is (no double-prefix).

Added 3 tests for get_available_models() prefix behaviour:
- Non-default provider models are prefixed
- Active provider's own entries remain bare
- No double-prefix when active_provider is absent

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/config.py

@@ -585,9 +585,26 @@ def get_available_models() -> dict:
                     'models': [{'id': m['id'], 'label': m['label']} for m in _FALLBACK_MODELS],
                 })
             elif pid in _PROVIDER_MODELS:
+                # For non-default providers, prefix model IDs with provider name
+                # so resolve_model_provider() can route them correctly (e.g.
+                # \"minimax/MiniMax-M2.7\" instead of bare \"MiniMax-M2.7\").
+                # The default provider's models keep bare names for direct API routing.
+                # Guard: only prefix when we have a confirmed active_provider, and
+                # normalise case before comparing (config.yaml may use 'Anthropic').
+                raw_models = _PROVIDER_MODELS[pid]
+                _active = (active_provider or '').lower()
+                if _active and pid != _active:
+                    # Shallow copy — don't mutate the shared _PROVIDER_MODELS list.
+                    # Bare IDs get prefixed; already-prefixed IDs pass through as-is.
+                    models = []
+                    for m in raw_models:
+                        mid = m['id']
+                        models.append({'id': mid if '/' in mid else f'{pid}/{mid}', 'label': m['label']})
+                else:
+                    models = list(raw_models)  # shallow copy to protect against insert() mutations
                 groups.append({
                     'provider': provider_name,
-                    'models': _PROVIDER_MODELS[pid],
+                    'models': models,
                 })
             else:
                 # Unknown provider -- use auto-detected models if available,