fix(config): route plugin providers before config_provider bare-passthrough

Gate found the plugin-routing branch ran AFTER the provider==config_provider
early-return, so when an ACTIVE plugin provider was also the configured default,
model_with_provider_context returned a bare model and dropped the '@plugin:'
hint -> wrong backend. Moved the _is_plugin_model_provider() branch above the
config_provider passthrough. Regression test (GMI + anthropic/claude-sonnet-4.6
as the active plugin+configured provider) added. Co-authored-by: alexfoxtm.

api/config.py

@@ -2960,6 +2960,16 @@ def model_with_provider_context(model_id: str, model_provider: str | None = None
     if provider in _ACP_SUBPROCESS_PROVIDERS:
         return f"@{provider}:{model}"
 
+    # Plugin-only model providers (e.g. 9router, and other model plugins whose
+    # slugs are not in the static provider tables) route through the plugin, not
+    # the default provider. This MUST come before the `provider == config_provider`
+    # bare-passthrough below: when a plugin provider is ALSO the configured
+    # provider, returning a bare model would drop the '@plugin:' hint and the model
+    # would be sent to the wrong backend. Emit the explicit hint so it stays
+    # routable to the plugin that surfaced it. (#5909 gate finding)
+    if _is_plugin_model_provider(provider):
+        return f"@{provider}:{model}"
+
     # If the selected provider is already the configured provider, leaving the
     # model bare preserves provider-specific base_url/proxy settings.
     if provider == config_provider:
@@ -2979,16 +2989,8 @@ def model_with_provider_context(model_id: str, model_provider: str | None = None
     if isinstance(providers_cfg, dict) and provider in providers_cfg:
         return f"@{provider}:{model}"
 
-    # Plugin-only model providers (e.g. 9router, and other model plugins whose
-    # slugs are not in the static provider tables) route through the plugin,
-    # not the default provider. A surfaced plugin-only model such as
-    # 'gh/claude-sonnet-4.5' carries a '/' in its ID, so without this branch it
-    # would fall through to the bare-passthrough below and inherit the default
-    # provider. Emit the explicit '@plugin:model' hint so the model stays
-    # routable to the plugin that surfaced it. This mirrors the explicit
-    # configured-provider handling above.
-    if _is_plugin_model_provider(provider):
-        return f"@{provider}:{model}"
+    # (Plugin-only provider routing handled above, before the config_provider
+    # bare-passthrough.)
 
     # For non-OpenRouter slash IDs without an explicit configured provider,
     # keep the ID intact so existing custom/proxy base_url routing and

tests/test_plugin_model_providers.py

@@ -430,3 +430,45 @@ class TestPluginModelProviderRouting:
             config.cfg.clear()
             config.cfg.update(old_cfg)
             invalidate_plugin_model_provider_cache()
+
+    def test_plugin_provider_routes_even_when_it_is_the_configured_provider(self, monkeypatch):
+        # #5909 gate finding: the plugin-routing branch must run BEFORE the
+        # `provider == config_provider` bare-passthrough. When the ACTIVE plugin
+        # provider is also the configured default, returning a bare model would
+        # drop the '@plugin:' hint and route to the wrong backend.
+        profile = SimpleNamespace(
+            name="gmi",
+            display_name="GMI",
+            env_vars=("GMI_API_KEY",),
+            auth_type="api_key",
+            aliases=(),
+            fallback_models=("anthropic/claude-sonnet-4.6",),
+        )
+
+        def _fake_list_providers():
+            return [profile]
+
+        fake_providers = types.ModuleType("providers")
+        fake_providers.list_providers = _fake_list_providers
+        monkeypatch.setitem(sys.modules, "providers", fake_providers)
+        invalidate_plugin_model_provider_cache()
+
+        old_cfg = dict(config.cfg)
+        config.cfg.clear()
+        # The plugin IS the configured provider now.
+        config.cfg["model"] = {"provider": "gmi", "default": "anthropic/claude-sonnet-4.6"}
+        config.cfg["providers"] = {}
+        try:
+            assert config._is_plugin_model_provider("gmi")
+            routed = config.model_with_provider_context(
+                "anthropic/claude-sonnet-4.6", "gmi"
+            )
+            assert routed == "@gmi:anthropic/claude-sonnet-4.6", (
+                "an active plugin provider must keep its '@plugin:' routing hint "
+                "even when it equals the configured provider, got "
+                f"{routed!r}"
+            )
+        finally:
+            config.cfg.clear()
+            config.cfg.update(old_cfg)
+            invalidate_plugin_model_provider_cache()