refactor(chat): route browser chat through one runtime (P3 Slice-Zero Task 5) (#1172)

Co-authored-by: shaggy <[email protected]>

apps/web/src/spa/chat/use-harness-selection.spec.tsx

@@ -226,7 +226,10 @@ describe('useHarnessSelection', () => {
       modelId: 'gpt-5',
     });
     expect(value().canSend).toBe(true);
-    expect(value().projection).toEqual({ provider: 'openai', modelId: 'gpt-5' });
+    // Task Five: the composer sends the nested `persistedSelection` tuple directly.
+    // The Task-Four compat flat `projection` ({provider, modelId}) is removed — the
+    // harnessId must never be dropped on the way to the wire.
+    expect('projection' in value()).toBe(false);
   });
 
   it('keeps a stale/unavailable persisted selection visibly displayed rather than silently dropping it', async () => {
@@ -386,7 +389,8 @@ describe('useHarnessSelection', () => {
       providerId: 'anthropic',
       modelId: 'claude',
     });
-    expect(value().projection).toEqual({ provider: 'anthropic', modelId: 'claude' });
+    // Task Five: no compat flat projection — the nested persistedSelection is the wire tuple.
+    expect('projection' in value()).toBe(false);
   });
 
   it('does not enable send on a model pick until the PUT for that exact new tuple resolves', async () => {
@@ -420,7 +424,8 @@ describe('useHarnessSelection', () => {
     });
     await flush();
     expect(value().canSend).toBe(true);
-    expect(value().projection).toEqual({ provider: 'anthropic', modelId: 'claude' });
+    // Task Five: no compat flat projection — the nested persistedSelection is the wire tuple.
+    expect('projection' in value()).toBe(false);
   });
 
   it('never requests any /api/providers* endpoint across the whole flow', async () => {