feat(x): one model-selection experience — unified settings, provider lifecycle, split-view picker

Task slots (config + runtime):
- taskModels gains backgroundTask and subagent; getBackgroundTaskAgentModel
  resolves its own override instead of mirroring live-notes (migration
  materializes the old mirror rule so effective models are unchanged)
- spawn-agent precedence: explicit per-spawn args > configured subagent
  override > parent turn's model
- repo.setProvider rejects auth-derived flavors (rowboat/codex) and merges
  over existing entries so key rotation keeps contextLength/reasoningEffort

Models settings, rebuilt:
- ModelSelectionSection: ONE Assistant model picker (with an Unavailable
  badge when the saved model drops off its provider's live list) + all
  seven tasks defaulting to "Same as Assistant" with resolve subtext and a
  clear-override link. Replaces both the signed-in and BYOK screens; the
  "Auto (recommended)" sentinel and both hardcoded preferredDefaults maps
  are gone — connect-time resolution uses backend recommendations
- ProvidersSection replaces the old ModelSettings card grid: status cards
  (Connected · N models / error + Retry), an add-provider dialog
  (choose → creds → loading → first-vs-more result states → error with
  manual-model fallback), and a manage dialog (masked key + Replace,
  endpoint, Refresh models, Used-by list, disconnect with consequences
  spelled out). Rowboat and ChatGPT are cards in the same list
- connecting a provider seeds the assistant ONLY when none is configured —
  never replaces a saved choice
- models:getConfig IPC serves selections + credential-free provider
  metadata; the probe machinery (use-provider-models, liveCredentials)
  is deleted — the add flow validates credentials click-driven

Onboarding:
- screen 2 is the same ProvidersSection (onboarding variant) for BOTH
  paths: "Add more providers" after sign-in, "Connect a model provider"
  otherwise; Continue gates on an assistant model existing. The tile grid,
  per-provider key forms, and ~350 lines of duplicate state are deleted;
  one step sequence replaces the two path-dependent indicators

Picker:
- split-view browse (Popover + cmdk Command): providers left with counts
  and error dots, selected provider's models right, ←/→ switches provider,
  ↑/↓ navigates, typing collapses to a flat cross-provider list that
  matches provider NAMES as well as model ids (searching "rowboat" now
  works). Scoped/static pickers stay flat; public API unchanged

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/x/packages/shared/src/ipc.ts

@@ -656,7 +656,7 @@ const ipcSchemas = {
     }).nullable(),
     res: z.object({
       providers: z.array(z.object({
-        // Provider INSTANCE id — what ModelRef.provider / defaultSelection /
+        // Provider INSTANCE id — what ModelRef.provider / assistantModel /
         // refreshProvider reference. One instance per flavor today, so it
         // always equals the flavor key; kept distinct so a future
         // multi-instance setup ("openai-work") is additive.
@@ -748,6 +748,33 @@ const ipcSchemas = {
       success: z.literal(true),
     }),
   },
+  // Current model selections plus credential-FREE provider metadata (the
+  // renderer never needs keys to render pickers or provider cards). Null
+  // assistantModel = not configured yet.
+  'models:getConfig': {
+    req: z.null(),
+    res: z.object({
+      // Configured BYOK provider entries, secrets stripped: enough to
+      // render manage/edit surfaces (masked key indicator, endpoint).
+      providers: z.array(z.object({
+        id: z.string(),
+        flavor: z.string(),
+        baseURL: z.string().optional(),
+        hasApiKey: z.boolean(),
+      })),
+      assistantModel: ModelRef.nullable(),
+      taskModels: z.object({
+        knowledgeGraph: ModelRef.nullable(),
+        meetingNotes: ModelRef.nullable(),
+        liveNoteAgent: ModelRef.nullable(),
+        autoPermissionDecision: ModelRef.nullable(),
+        chatTitle: ModelRef.nullable(),
+        backgroundTask: ModelRef.nullable(),
+        subagent: ModelRef.nullable(),
+      }),
+      deferBackgroundTasks: z.boolean(),
+    }),
+  },
   // Partial merge of model selections into models.json. Omitted keys are
   // untouched; null clears a key (a cleared task override inherits the
   // assistant model again). taskModels merges per-key.
@@ -760,6 +787,8 @@ const ipcSchemas = {
         liveNoteAgent: ModelRef.nullable().optional(),
         autoPermissionDecision: ModelRef.nullable().optional(),
         chatTitle: ModelRef.nullable().optional(),
+        backgroundTask: ModelRef.nullable().optional(),
+        subagent: ModelRef.nullable().optional(),
       }).optional(),
       deferBackgroundTasks: z.boolean().nullable().optional(),
     }),

apps/x/packages/shared/src/models.ts

@@ -41,13 +41,17 @@ export const ModelRef = z.object({
   model: z.string(),
 });
 
-// The per-task model override slots. Absence = inherit the assistant model.
+// The per-task model override slots. Absence = inherit the assistant model
+// (except `subagent`, whose default is the PARENT turn's model — which is
+// the assistant for a top-level chat).
 export const TaskModels = z.object({
   knowledgeGraph: ModelRef.optional(),
   meetingNotes: ModelRef.optional(),
   liveNoteAgent: ModelRef.optional(),
   autoPermissionDecision: ModelRef.optional(),
   chatTitle: ModelRef.optional(),
+  backgroundTask: ModelRef.optional(),
+  subagent: ModelRef.optional(),
 });
 export type TaskModelKey = keyof z.infer<typeof TaskModels>;