fix(app): synchronize chat submission and keyboard state

Render optimistic turn feedback before host acknowledgement and roll it back on rejection. Reconcile iOS keyboard offsets from the native transition end event so JS contention cannot leave the composer displaced.

packages/app/src/composer/actions.test.ts

@@ -333,6 +333,26 @@ describe("pickAndPersistImages", () => {
 });
 
 describe("dispatchComposerAgentMessage", () => {
+  it("removes the optimistic prompt when the host rejects it", async () => {
+    const rejection = new Error("Host rejected prompt");
+    const client = createFakeSendClient({ rejection });
+    const stream = createFakeStream();
+
+    await expect(
+      dispatchComposerAgentMessage({
+        client,
+        agentId: "agent",
+        text: "rejected prompt",
+        attachments: [],
+        encodeImages: passthroughEncodeImages,
+        stream,
+      }),
+    ).rejects.toBe(rejection);
+
+    expect(stream.head.get("agent")).toBeUndefined();
+    expect(stream.tail.get("agent") ?? []).toEqual([]);
+  });
+
   it("sends text + image data + structured attachments and appends user_message to the tail when head is empty", async () => {
     const client = createFakeSendClient();
     const stream = createFakeStream();