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/composer.tsx

@@ -1,8 +1,9 @@
 import { useState, type KeyboardEvent, type ReactElement } from 'react';
+import type { HarnessSelection } from '@/lib/types';
 import type { HarnessSelectionValue } from './use-harness-selection';
 
 interface ComposerProps {
-  onSend: (input: { content: string; provider?: string; modelId?: string }) => void;
+  onSend: (input: { content: string; selection: HarnessSelection }) => boolean;
   onStop: () => void;
   streaming: boolean;
   /** True from local send time through server turn startup/ack and
@@ -44,11 +45,17 @@ export function Composer({
     if (busy) return;
     // Send is gated on a validated, persisted catalog tuple — a draft or unset
     // selection can never emit, so provider/model never travel as free text.
-    if (!harness.canSend) return;
+    if (!harness.canSend || harness.persistedSelection === null) return;
     const trimmed = content.trim();
     if (!trimmed) return;
-    onSend({ content: trimmed, ...harness.projection });
-    setContent('');
+    // Pass the validated, persisted selection tuple only. The hook derives the
+    // wire projection (legacy `message` provider/model, or `turn:send`) from the
+    // negotiated `chat:send-capability` protocol — never from flat caller input.
+    const selection = harness.persistedSelection;
+    const ok = onSend({ content: trimmed, selection });
+    // Clear the input only when the send was accepted — a refused turn (e.g. a
+    // failed idempotency mint) must retain the user's text so it is not lost.
+    if (ok) setContent('');
   }
 
   function handleKeyDown(event: KeyboardEvent<HTMLTextAreaElement>): void {