fix(model-set): persist base_url/api_key on auxiliary slot assignments

Sibling of #65254 (main-slot endpoint preservation): the auxiliary scope of
POST /api/model/set dropped the request's base_url/api_key on the floor, so
an aux slot pinned to a custom/local endpoint silently depended on
model.base_url — and broke the moment the main slot switched away and
cleared it. The aux resolver already reads auxiliary.<task>.base_url/api_key
(_resolve_task_provider_model); this persists them.

Desktop side: setAuxiliaryToMain / applyAuxiliaryDraft now carry the
user-defined provider's api_url as base_url, mirroring applyMainModel.

apps/desktop/src/app/settings/model-settings.test.tsx

@@ -316,6 +316,41 @@ describe('ModelSettings', () => {
     )
   })
 
+  it('carries the user-defined endpoint when an aux slot is set to a local main model', async () => {
+    getGlobalModelOptions.mockResolvedValueOnce({
+      providers: [
+        {
+          name: 'Ollama',
+          slug: 'local-ollama',
+          models: ['qwen3:latest'],
+          authenticated: true,
+          is_user_defined: true,
+          api_url: 'http://localhost:11434/v1'
+        }
+      ]
+    })
+    getGlobalModelInfo.mockResolvedValueOnce({ provider: 'local-ollama', model: 'qwen3:latest' })
+    getAuxiliaryModels.mockResolvedValueOnce({
+      main: { provider: 'local-ollama', model: 'qwen3:latest' },
+      tasks: [{ task: 'vision', provider: 'auto', model: '', base_url: '' }]
+    })
+
+    await renderModelSettings()
+
+    const setToMainButtons = await screen.findAllByRole('button', { name: 'Set to main' })
+    fireEvent.click(setToMainButtons[0])
+
+    await waitFor(() =>
+      expect(setModelAssignment).toHaveBeenCalledWith({
+        model: 'qwen3:latest',
+        provider: 'local-ollama',
+        scope: 'auxiliary',
+        task: 'vision',
+        base_url: 'http://localhost:11434/v1'
+      })
+    )
+  })
+
   it('warns when a main switch leaves auxiliary tasks pinned to another provider', async () => {
     setModelAssignment.mockResolvedValueOnce({
       provider: 'openrouter',

apps/desktop/src/app/settings/model-settings.tsx

@@ -643,6 +643,20 @@ export function ModelSettings({ onMainModelChanged }: ModelSettingsProps) {
     }
   }, [onMainModelChanged, refresh, selectedModel, selectedProvider, selectedProviderRow])
 
+  // Sibling of the applyMainModel endpoint passthrough (#65254): auxiliary
+  // assignments targeting a user-defined provider must carry that provider's
+  // endpoint too, or the backend pins the slot without a base_url and the
+  // aux resolver falls back to the (possibly different, possibly cleared)
+  // main endpoint.
+  const endpointForProvider = useCallback(
+    (provider: string) => {
+      const row = providers.find(entry => entry.slug === provider)
+
+      return row?.api_url ? { base_url: row.api_url } : {}
+    },
+    [providers]
+  )
+
   const setAuxiliaryToMain = useCallback(
     async (task: string) => {
       if (!mainModel) {
@@ -653,7 +667,13 @@ export function ModelSettings({ onMainModelChanged }: ModelSettingsProps) {
       setError('')
 
       try {
-        await setModelAssignment({ model: mainModel.model, provider: mainModel.provider, scope: 'auxiliary', task })
+        await setModelAssignment({
+          model: mainModel.model,
+          provider: mainModel.provider,
+          scope: 'auxiliary',
+          task,
+          ...endpointForProvider(mainModel.provider)
+        })
         await refresh()
       } catch (err) {
         setError(err instanceof Error ? err.message : String(err))
@@ -661,7 +681,7 @@ export function ModelSettings({ onMainModelChanged }: ModelSettingsProps) {
         setApplying(false)
       }
     },
-    [mainModel, refresh]
+    [endpointForProvider, mainModel, refresh]
   )
 
   const applyAuxiliaryDraft = useCallback(
@@ -674,7 +694,13 @@ export function ModelSettings({ onMainModelChanged }: ModelSettingsProps) {
       setError('')
 
       try {
-        await setModelAssignment({ model: auxDraft.model, provider: auxDraft.provider, scope: 'auxiliary', task })
+        await setModelAssignment({
+          model: auxDraft.model,
+          provider: auxDraft.provider,
+          scope: 'auxiliary',
+          task,
+          ...endpointForProvider(auxDraft.provider)
+        })
         setEditingAuxTask(null)
         await refresh()
       } catch (err) {
@@ -683,7 +709,7 @@ export function ModelSettings({ onMainModelChanged }: ModelSettingsProps) {
         setApplying(false)
       }
     },
-    [auxDraft, refresh]
+    [auxDraft, endpointForProvider, refresh]
   )
 
   const beginAuxiliaryEdit = useCallback(

hermes_cli/web_server.py

@@ -1392,17 +1392,18 @@ class ModelAssignment(BaseModel):
     provider: str
     model: str
     task: str = ""
-    # Optional OpenAI-compatible endpoint URL. Only honored for custom/local
-    # providers on the main slot — lets the GUI configure a self-hosted endpoint
-    # (vLLM, llama.cpp, Ollama, …) that needs no API key. The runtime resolver
-    # reads model.base_url from config (it ignores OPENAI_BASE_URL), so this is
-    # the path that actually wires a local endpoint into resolution.
+    # Optional OpenAI-compatible endpoint URL. Honored for custom/local
+    # providers on the main slot AND on auxiliary slots — lets the GUI wire a
+    # self-hosted endpoint (vLLM, llama.cpp, Ollama, …) that needs no API key.
+    # The runtime resolvers read model.base_url / auxiliary.<task>.base_url
+    # from config (they ignore OPENAI_BASE_URL), so this is the path that
+    # actually wires a local endpoint into resolution.
     base_url: str = ""
     # Optional API key for a custom/local endpoint. Persisted to
-    # ``model.api_key`` (where the runtime resolver reads it) so a self-hosted
-    # endpoint that requires auth works from the GUI — mirrors the key the
-    # ``hermes model`` custom flow collects. Honored only on the main slot for
-    # custom/local providers.
+    # ``model.api_key`` (main slot) or ``auxiliary.<task>.api_key`` (aux
+    # slots) — where the runtime resolvers read it — so a self-hosted
+    # endpoint that requires auth works from the GUI. Mirrors the key the
+    # ``hermes model`` custom flow collects.
     api_key: str = ""
     confirm_expensive_model: bool = False
     profile: Optional[str] = None
@@ -7244,7 +7245,19 @@ def _apply_model_assignment_sync(
         new_provider = provider.strip().lower()
         slot_cfg["provider"] = provider
         slot_cfg["model"] = model
-        if new_provider != prev_provider and new_provider != "custom":
+        if base_url:
+            # Sibling of the main-slot endpoint handling (#65254): an aux
+            # assignment for a custom/local endpoint must carry its own
+            # base_url, or the slot silently rebinds to whatever
+            # model.base_url happens to hold — and breaks entirely once the
+            # main slot switches away and clears it. The auxiliary resolver
+            # already reads auxiliary.<task>.base_url/api_key
+            # (_resolve_task_provider_model), so persisting them here is
+            # what actually wires the endpoint in.
+            slot_cfg["base_url"] = base_url
+            if api_key:
+                slot_cfg["api_key"] = api_key
+        elif new_provider != prev_provider and new_provider != "custom":
             slot_cfg.pop("base_url", None)
             clear_model_endpoint_credentials(slot_cfg)
         aux[slot] = slot_cfg

tests/hermes_cli/test_web_server.py

@@ -4616,6 +4616,67 @@ class TestWebServerEndpoints:
         assert model_cfg["provider"] == "openrouter"
         assert model_cfg.get("base_url", "") == ""
 
+    def test_set_model_auxiliary_persists_base_url_and_api_key(self):
+        """Aux assignments for a custom/local endpoint must persist the slot's
+        own base_url/api_key (sibling of the main-slot fix, #65254). Without
+        them the aux resolver falls back to model.base_url — which breaks the
+        moment the main slot switches away and clears it."""
+        from hermes_cli.config import load_config
+
+        resp = self.client.post(
+            "/api/model/set",
+            json={
+                "scope": "auxiliary",
+                "task": "vision",
+                "provider": "custom",
+                "model": "qwen3:latest",
+                "base_url": "http://localhost:11434/v1",
+                "api_key": "sk-local",
+            },
+        )
+        assert resp.status_code == 200
+        assert resp.json()["ok"] is True
+
+        slot = load_config()["auxiliary"]["vision"]
+        assert slot["provider"] == "custom"
+        assert slot["model"] == "qwen3:latest"
+        assert slot["base_url"] == "http://localhost:11434/v1"
+        assert slot["api_key"] == "sk-local"
+
+    def test_set_model_auxiliary_provider_switch_still_clears_stale_endpoint(self):
+        """The existing stale-endpoint scrub on provider switch is preserved
+        when the new assignment carries no base_url."""
+        from hermes_cli.config import load_config, save_config
+
+        cfg = load_config()
+        cfg["auxiliary"] = {
+            "vision": {
+                "provider": "custom",
+                "model": "qwen3:latest",
+                "base_url": "http://localhost:11434/v1",
+                "api_key": "sk-local",
+            },
+        }
+        save_config(cfg)
+
+        resp = self.client.post(
+            "/api/model/set",
+            json={
+                "scope": "auxiliary",
+                "task": "vision",
+                "provider": "openrouter",
+                "model": "google/gemini-2.5-flash",
+            },
+        )
+        assert resp.status_code == 200
+
+        slot = load_config()["auxiliary"]["vision"]
+        assert slot["provider"] == "openrouter"
+        # load_config deep-merges DEFAULT_CONFIG, which re-materializes the
+        # keys as empty strings — assert the stale endpoint VALUES are gone.
+        assert not slot.get("base_url")
+        assert not slot.get("api_key")
+
     def test_custom_endpoints_list_includes_direct_custom_config(self):
         """A bare model.provider=custom config should show up in Desktop even
         before the user has materialized it under providers.