diff --git a/packages/app/src/components/agent-input-area.tsx b/packages/app/src/components/agent-input-area.tsx
index 750bb68eb..a44f30bb3 100644
--- a/packages/app/src/components/agent-input-area.tsx
+++ b/packages/app/src/components/agent-input-area.tsx
@@ -45,6 +45,7 @@ import { markScrollInvestigationRender } from "@/utils/scroll-jank-investigation
 import { useKeyboardShiftStyle } from "@/hooks/use-keyboard-shift-style";
 import { useKeyboardActionHandler } from "@/hooks/use-keyboard-action-handler";
 import type { KeyboardActionDefinition } from "@/keyboard/keyboard-action-dispatcher";
+import { submitAgentInput } from "@/components/agent-input-submit";
 
 type QueuedMessage = {
   id: string;
@@ -342,43 +343,31 @@ export function AgentInputArea({
     imageAttachments?: ImageAttachment[],
     forceSend?: boolean,
   ) {
-    const trimmedMessage = message.trim();
-    if (!trimmedMessage && !imageAttachments?.length) return;
-    // When the parent controls submission (e.g. draft agent creation), let it
-    // decide what to do even if the socket is currently disconnected (so we
-    // don't no-op and lose deterministic error handling in the UI/tests).
-    if (!sendAgentMessageRef.current && !onSubmitMessageRef.current) return;
-
-    if (agent?.status === "running" && !forceSend) {
-      queueMessage(trimmedMessage, imageAttachments);
-      return;
-    }
-
-    // Clear input optimistically before awaiting server ack.
-    // Save values so we can restore on error.
-    const savedImages = imageAttachments;
-    if (!onSubmitMessageRef.current) {
-      setUserInput("");
-      setSelectedImages([]);
-    }
-    setSendError(null);
-    setIsProcessing(true);
-
-    try {
-      await submitMessage(trimmedMessage, imageAttachments);
-      clearDraft("sent");
-    } catch (error) {
-      console.error("[AgentInput] Failed to send message:", error);
-      // Restore input so the user never loses their message
-      if (!onSubmitMessageRef.current) {
-        setUserInput(trimmedMessage);
-      }
-      if (savedImages) {
-        setSelectedImages(savedImages);
-      }
-      setSendError(error instanceof Error ? error.message : "Failed to send message");
-      setIsProcessing(false);
-    }
+    await submitAgentInput({
+      message,
+      imageAttachments,
+      forceSend,
+      isAgentRunning: agent?.status === "running",
+      // Parent-managed submits are still valid submit paths even when the
+      // transport is disconnected, because the parent decides the failure mode.
+      canSubmit: Boolean(sendAgentMessageRef.current || onSubmitMessageRef.current),
+      queueMessage: ({ message, imageAttachments }) => {
+        queueMessage(message, imageAttachments);
+      },
+      submitMessage: async ({ message, imageAttachments }) => {
+        await submitMessage(message, imageAttachments);
+      },
+      clearDraft,
+      setUserInput,
+      setSelectedImages: (images) => {
+        setSelectedImages(images);
+      },
+      setSendError,
+      setIsProcessing,
+      onSubmitError: (error) => {
+        console.error("[AgentInput] Failed to send message:", error);
+      },
+    });
   }
 
   function handleSubmit(payload: MessagePayload) {
diff --git a/packages/app/src/components/agent-input-submit.test.ts b/packages/app/src/components/agent-input-submit.test.ts
new file mode 100644
index 000000000..7008f725a
--- /dev/null
+++ b/packages/app/src/components/agent-input-submit.test.ts
@@ -0,0 +1,140 @@
+import { describe, expect, it, vi } from "vitest";
+import { submitAgentInput } from "./agent-input-submit";
+
+function createDeferredPromise<T>() {
+  let resolve!: (value: T | PromiseLike<T>) => void;
+  let reject!: (reason?: unknown) => void;
+  const promise = new Promise<T>((nextResolve, nextReject) => {
+    resolve = nextResolve;
+    reject = nextReject;
+  });
+  return {
+    promise,
+    resolve,
+    reject,
+  };
+}
+
+describe("submitAgentInput", () => {
+  it("clears the composer before an in-flight submit resolves", async () => {
+    const deferred = createDeferredPromise<void>();
+    const queueMessage = vi.fn();
+    const submitMessage = vi.fn(async () => {
+      await deferred.promise;
+    });
+    const clearDraft = vi.fn();
+    const setUserInput = vi.fn();
+    const setSelectedImages = vi.fn();
+    const setSendError = vi.fn();
+    const setIsProcessing = vi.fn();
+
+    const submitPromise = submitAgentInput({
+      message: "  hello world  ",
+      isAgentRunning: false,
+      canSubmit: true,
+      queueMessage,
+      submitMessage,
+      clearDraft,
+      setUserInput,
+      setSelectedImages,
+      setSendError,
+      setIsProcessing,
+    });
+
+    expect(queueMessage).not.toHaveBeenCalled();
+    expect(submitMessage).toHaveBeenCalledWith({
+      message: "hello world",
+      imageAttachments: undefined,
+    });
+    expect(setUserInput).toHaveBeenCalledWith("");
+    expect(setSelectedImages).toHaveBeenCalledWith([]);
+    expect(setSendError).toHaveBeenCalledWith(null);
+    expect(setIsProcessing).toHaveBeenCalledWith(true);
+    expect(clearDraft).not.toHaveBeenCalled();
+
+    deferred.resolve();
+
+    await expect(submitPromise).resolves.toBe("submitted");
+    expect(clearDraft).toHaveBeenCalledWith("sent");
+  });
+
+  it("queues while the agent is running and clears the composer immediately", async () => {
+    const queueMessage = vi.fn();
+    const submitMessage = vi.fn();
+    const clearDraft = vi.fn();
+    const setUserInput = vi.fn();
+    const setSelectedImages = vi.fn();
+    const setSendError = vi.fn();
+    const setIsProcessing = vi.fn();
+
+    await expect(
+      submitAgentInput({
+        message: "  queued message  ",
+        imageAttachments: [{ id: "img-1" }],
+        isAgentRunning: true,
+        canSubmit: true,
+        queueMessage,
+        submitMessage,
+        clearDraft,
+        setUserInput,
+        setSelectedImages,
+        setSendError,
+        setIsProcessing,
+      }),
+    ).resolves.toBe("queued");
+
+    expect(queueMessage).toHaveBeenCalledWith({
+      message: "queued message",
+      imageAttachments: [{ id: "img-1" }],
+    });
+    expect(submitMessage).not.toHaveBeenCalled();
+    expect(setUserInput).toHaveBeenCalledWith("");
+    expect(setSelectedImages).toHaveBeenCalledWith([]);
+    expect(setSendError).not.toHaveBeenCalled();
+    expect(setIsProcessing).not.toHaveBeenCalled();
+    expect(clearDraft).not.toHaveBeenCalled();
+  });
+
+  it("restores the composer when submit fails", async () => {
+    const submitError = new Error("No host selected");
+    const queueMessage = vi.fn();
+    const submitMessage = vi.fn(async () => {
+      throw submitError;
+    });
+    const clearDraft = vi.fn();
+    const setUserInput = vi.fn();
+    const setSelectedImages = vi.fn();
+    const setSendError = vi.fn();
+    const setIsProcessing = vi.fn();
+    const onSubmitError = vi.fn();
+    const imageAttachments = [{ id: "img-1" }];
+
+    await expect(
+      submitAgentInput({
+        message: "  hello world  ",
+        imageAttachments,
+        isAgentRunning: false,
+        canSubmit: true,
+        queueMessage,
+        submitMessage,
+        clearDraft,
+        setUserInput,
+        setSelectedImages,
+        setSendError,
+        setIsProcessing,
+        onSubmitError,
+      }),
+    ).resolves.toBe("failed");
+
+    expect(onSubmitError).toHaveBeenCalledWith(submitError);
+    expect(setUserInput).toHaveBeenNthCalledWith(1, "");
+    expect(setUserInput).toHaveBeenNthCalledWith(2, "hello world");
+    expect(setSelectedImages).toHaveBeenNthCalledWith(1, []);
+    expect(setSelectedImages).toHaveBeenNthCalledWith(2, imageAttachments);
+    expect(setSendError).toHaveBeenNthCalledWith(1, null);
+    expect(setSendError).toHaveBeenNthCalledWith(2, "No host selected");
+    expect(setIsProcessing).toHaveBeenNthCalledWith(1, true);
+    expect(setIsProcessing).toHaveBeenNthCalledWith(2, false);
+    expect(clearDraft).not.toHaveBeenCalled();
+  });
+});
diff --git a/packages/app/src/components/agent-input-submit.ts b/packages/app/src/components/agent-input-submit.ts
new file mode 100644
index 000000000..deabff19b
--- /dev/null
+++ b/packages/app/src/components/agent-input-submit.ts
@@ -0,0 +1,58 @@
+export type AgentInputSubmitResult = "noop" | "queued" | "submitted" | "failed";
+
+export interface AgentInputSubmitActionInput<TImage> {
+  message: string;
+  imageAttachments?: TImage[];
+  forceSend?: boolean;
+  isAgentRunning: boolean;
+  canSubmit: boolean;
+  queueMessage: (input: { message: string; imageAttachments?: TImage[] }) => void;
+  submitMessage: (input: { message: string; imageAttachments?: TImage[] }) => Promise<void>;
+  clearDraft: (lifecycle: "sent" | "abandoned") => void;
+  setUserInput: (text: string) => void;
+  setSelectedImages: (images: TImage[]) => void;
+  setSendError: (message: string | null) => void;
+  setIsProcessing: (isProcessing: boolean) => void;
+  onSubmitError?: (error: unknown) => void;
+}
+
+export async function submitAgentInput<TImage>(
+  input: AgentInputSubmitActionInput<TImage>,
+): Promise<AgentInputSubmitResult> {
+  const trimmedMessage = input.message.trim();
+  const imageAttachments = input.imageAttachments;
+
+  if (!trimmedMessage && !imageAttachments?.length) {
+    return "noop";
+  }
+
+  if (!input.canSubmit) {
+    return "noop";
+  }
+
+  if (input.isAgentRunning && !input.forceSend) {
+    input.queueMessage({ message: trimmedMessage, imageAttachments });
+    input.setUserInput("");
+    input.setSelectedImages([]);
+    return "queued";
+  }
+
+  // Clear immediately so optimistic stream updates and composer state stay in sync.
+  input.setUserInput("");
+  input.setSelectedImages([]);
+  input.setSendError(null);
+  input.setIsProcessing(true);
+
+  try {
+    await input.submitMessage({ message: trimmedMessage, imageAttachments });
+    input.clearDraft("sent");
+    return "submitted";
+  } catch (error) {
+    input.onSubmitError?.(error);
+    input.setUserInput(trimmedMessage);
+    input.setSelectedImages(imageAttachments ?? []);
+    input.setSendError(error instanceof Error ? error.message : "Failed to send message");
+    input.setIsProcessing(false);
+    return "failed";
+  }
+}