fix: thread allowEmptySubmit through composer submit path

The Create button on the new workspace screen was visible but clicking
it did nothing — submitAgentInput() still rejected empty payloads as
"noop". Thread allowEmptySubmit through Composer into submitAgentInput
so the callback fires and workspace creation + redirect completes.

Adds regression test for the empty-submit path.

packages/app/src/components/agent-input-submit.test.ts

@@ -137,4 +137,37 @@ describe("submitAgentInput", () => {
     expect(setIsProcessing).toHaveBeenNthCalledWith(2, false);
     expect(clearDraft).not.toHaveBeenCalled();
   });
+
+  it("submits when empty submit is explicitly allowed", async () => {
+    const queueMessage = vi.fn();
+    const submitMessage = vi.fn(async () => {});
+    const clearDraft = vi.fn();
+    const setUserInput = vi.fn();
+    const setSelectedImages = vi.fn();
+    const setSendError = vi.fn();
+    const setIsProcessing = vi.fn();
+
+    await expect(
+      submitAgentInput({
+        message: "   ",
+        allowEmptySubmit: true,
+        isAgentRunning: false,
+        canSubmit: true,
+        queueMessage,
+        submitMessage,
+        clearDraft,
+        setUserInput,
+        setSelectedImages,
+        setSendError,
+        setIsProcessing,
+      }),
+    ).resolves.toBe("submitted");
+
+    expect(queueMessage).not.toHaveBeenCalled();
+    expect(submitMessage).toHaveBeenCalledWith({
+      message: "",
+      imageAttachments: undefined,
+    });
+    expect(clearDraft).toHaveBeenCalledWith("sent");
+  });
 });

packages/app/src/components/agent-input-submit.ts

@@ -4,6 +4,7 @@ export interface AgentInputSubmitActionInput<TImage> {
   message: string;
   imageAttachments?: TImage[];
   hasExternalContent?: boolean;
+  allowEmptySubmit?: boolean;
   forceSend?: boolean;
   isAgentRunning: boolean;
   canSubmit: boolean;
@@ -23,7 +24,12 @@ export async function submitAgentInput<TImage>(
   const trimmedMessage = input.message.trim();
   const imageAttachments = input.imageAttachments;
 
-  if (!trimmedMessage && !imageAttachments?.length && !input.hasExternalContent) {
+  if (
+    !trimmedMessage &&
+    !imageAttachments?.length &&
+    !input.hasExternalContent &&
+    !input.allowEmptySubmit
+  ) {
     return "noop";
   }
 

packages/app/src/components/composer.tsx

@@ -359,6 +359,7 @@ export function Composer({
       message,
       imageAttachments,
       hasExternalContent,
+      allowEmptySubmit,
       forceSend,
       isAgentRunning: agentState.status === "running",
       // Parent-managed submits are still valid submit paths even when the