diff --git a/packages/overlay/src/app.stop.test.ts b/packages/overlay/src/app.stop.test.ts
new file mode 100644
index 0000000..02710b3
--- /dev/null
+++ b/packages/overlay/src/app.stop.test.ts
@@ -0,0 +1,189 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { AirshipApp, type Stage } from "./app";
+import { ChromeLayer } from "./chrome-layer";
+import { cls } from "./dom";
+import { keys } from "./keys/registry";
+import { InlineResolver } from "./surface";
+
+/*
+ * Send, while a turn is running, has to become Stop.
+ *
+ * The daemon has supported cancelling a job since `{ type: "cancel", jobId }` landed in the
+ * protocol (`server/src/index.ts`'s `case "cancel": jobs.get(parsed.jobId)?.abort?.abort()`), and
+ * `keepVisual` even explains that a cancelled turn keeps its pending deltas queued "so Send tries
+ * again rather than starting from nothing" — cancelling was designed in from the start. What never
+ * existed was a way to *ask* for it: the composer's Send button just disabled itself the moment a
+ * turn began (`beginJob`) and stayed that way until `job:done`. This file pins the fix — the
+ * button now stays live and flips to Stop, wired to that same cancel message, instead of going
+ * inert for however long the agent takes.
+ */
+
+function stubStage(): Stage {
+  const layer = new ChromeLayer();
+  return {
+    destroy() {
+      // Nothing to release beyond what `AirshipApp.destroy` already does.
+    },
+    layer,
+    mount() {
+      layer.mount(document.body);
+    },
+    onLayoutChange() {
+      // Nothing moves under a stage with no content.
+    },
+    resolver: new InlineResolver(),
+    swallowPresses: true,
+  };
+}
+
+function stubStorage(): void {
+  const store = new Map<string, string>();
+  Object.defineProperty(window, "localStorage", {
+    configurable: true,
+    value: {
+      clear: () => store.clear(),
+      getItem: (k: string) => store.get(k) ?? null,
+      key: () => null,
+      length: 0,
+      removeItem: (k: string) => store.delete(k),
+      setItem: (k: string, v: string) => store.set(k, v),
+    },
+  });
+}
+
+/** A WebSocket stand-in that is "open" from the moment it is constructed (so `AirshipSocket.send`
+ * actually forwards), records every message sent through it, and lets a test push a server event
+ * straight at the app the way a real frame would. */
+class FakeSocket {
+  static readonly OPEN = 1;
+  readyState = FakeSocket.OPEN;
+  sent: unknown[] = [];
+  onmessage: ((ev: { data: string }) => void) | null = null;
+  onclose: (() => void) | null = null;
+  onerror: (() => void) | null = null;
+  constructor() {
+    sockets.push(this);
+  }
+  addEventListener(
+    kind: string,
+    handler: (ev: { data: string }) => void
+  ): void {
+    if (kind === "message") {
+      this.onmessage = handler;
+    }
+  }
+  close(): void {
+    this.onclose?.();
+  }
+  send(data: string): void {
+    this.sent.push(JSON.parse(data));
+  }
+  emit(event: unknown): void {
+    this.onmessage?.({ data: JSON.stringify(event) });
+  }
+}
+
+const apps: AirshipApp[] = [];
+let sockets: FakeSocket[] = [];
+
+function mount(): { app: AirshipApp; socket: FakeSocket } {
+  const stage = stubStage();
+  const app = new AirshipApp(
+    { mode: "inline", wsPath: "/__airship/ws" },
+    stage
+  );
+  app.mount();
+  apps.push(app);
+  return { app, socket: sockets.at(-1) as FakeSocket };
+}
+
+function sendBtn(): HTMLButtonElement {
+  const btn = document.querySelector(`.${cls("send")}`);
+  if (!btn) {
+    throw new Error("sendBtn: composer has not been mounted");
+  }
+  return btn as HTMLButtonElement;
+}
+
+function typeAndSubmit(text: string): void {
+  const input = document.querySelector(
+    `.${cls("input")}`
+  ) as HTMLTextAreaElement;
+  input.value = text;
+  input.dispatchEvent(new Event("input", { bubbles: true }));
+  sendBtn().dispatchEvent(new Event("click", { bubbles: true }));
+}
+
+beforeEach(() => {
+  stubStorage();
+  sockets = [];
+  vi.stubGlobal("WebSocket", FakeSocket);
+});
+
+afterEach(() => {
+  for (const app of apps.splice(0)) {
+    app.destroy();
+  }
+  keys.destroy();
+  document.body.replaceChildren();
+  vi.unstubAllGlobals();
+});
+
+describe("stopping an in-progress chat response", () => {
+  it("turns Send into Stop once a turn is running, and Stop cancels the running job by id", () => {
+    const { socket } = mount();
+
+    typeAndSubmit("add a footer");
+    expect(socket.sent).toEqual([{ request: expect.anything(), type: "edit" }]);
+
+    // The turn is running but the daemon has not answered `job:created` yet — there is nothing
+    // to cancel, so the button must not pretend otherwise.
+    expect(sendBtn().disabled).toBe(false);
+    expect(sendBtn().getAttribute("aria-label")).toBe("Stop");
+
+    socket.emit({
+      job: { createdAt: Date.now(), jobId: "job-1", status: "running" },
+      type: "job:created",
+    });
+
+    sendBtn().dispatchEvent(new Event("click", { bubbles: true }));
+
+    // Exactly one more message went out, and it is the cancel — not a second edit.
+    expect(socket.sent).toEqual([
+      { request: expect.anything(), type: "edit" },
+      { jobId: "job-1", type: "cancel" },
+    ]);
+  });
+
+  it("reverts to Send once the job ends, ready to submit the next turn", () => {
+    const { socket } = mount();
+
+    typeAndSubmit("add a footer");
+    socket.emit({
+      job: { createdAt: Date.now(), jobId: "job-2", status: "running" },
+      type: "job:created",
+    });
+    expect(sendBtn().getAttribute("aria-label")).toBe("Stop");
+
+    socket.emit({
+      bundle: {
+        basedOn: null,
+        jobId: "job-2",
+        parentJobId: null,
+        status: "done",
+        summary: "",
+      },
+      jobId: "job-2",
+      type: "job:done",
+    });
+
+    expect(sendBtn().disabled).toBe(false);
+    expect(sendBtn().getAttribute("aria-label")).toBe("Send");
+
+    typeAndSubmit("one more change");
+    expect(socket.sent.at(-1)).toEqual({
+      request: expect.anything(),
+      type: "edit",
+    });
+  });
+});
diff --git a/packages/overlay/src/app.ts b/packages/overlay/src/app.ts
index 2a1bfdf..11fdff6 100644
--- a/packages/overlay/src/app.ts
+++ b/packages/overlay/src/app.ts
@@ -2675,7 +2675,7 @@ export class AirshipApp {
         "aria-label": "Send",
         class: `${cls("action")} ${cls("action-icon")} ${cls("primary")} ${cls("send")}`,
         ...tip("Send", "chat.send"),
-        onClick: () => this.submit(),
+        onClick: () => this.onSendClick(),
         type: "button",
       },
       [icon("chev-up", "sm")]
@@ -3646,6 +3646,36 @@ export class AirshipApp {
 
   // -- Submit — the single outbox --------------------------------------------
 
+  /**
+   * What Send does — submit a new turn, or stop the one already running.
+   *
+   * The button used to just disable itself for `awaiting`'s whole span, which
+   * left no way back from a turn that was taking too long or was typed wrong:
+   * the daemon has supported `{ type: "cancel", jobId }` since the protocol
+   * added it (`server/src/index.ts`'s `case "cancel"`), but nothing in the
+   * composer ever sent one. `syncSendBtn` is what repaints the button between
+   * the two meanings; this is what a click means once it has.
+   */
+  private onSendClick(): void {
+    if (this.awaiting) {
+      this.cancelActive();
+      return;
+    }
+    this.submit();
+  }
+
+  /** Stop the running turn so its composer state can be edited and resent —
+   *  `keepVisual` is what leaves the pending deltas queued for that resend. */
+  private cancelActive(): void {
+    if (!this.activeJobId) {
+      // `job:created` has not landed yet; there is nothing on the daemon to
+      // cancel. The button still reads "Stop" (see `syncSendBtn`), but a
+      // click this early is a no-op rather than a request with no target.
+      return;
+    }
+    this.socket.send({ jobId: this.activeJobId, type: "cancel" });
+  }
+
   /**
    * Ship one edit turn from the left composer: the typed instruction plus any
    * pasted images and any pending direct-manipulation deltas (style tweaks +
@@ -3907,7 +3937,7 @@ export class AirshipApp {
   private beginJob(): void {
     this.awaiting = true;
     this.activeJobId = null;
-    this.sendBtn.disabled = true;
+    this.syncSendBtn();
     this.syncApplyGroup();
     this.syncJobChip();
     const turn = assistantTurn();
@@ -3915,6 +3945,30 @@ export class AirshipApp {
     this.pushBubble(turn.root);
   }
 
+  /**
+   * Repaint Send between its two meanings.
+   *
+   * Never disabled: disabling it during `awaiting` is what this replaces —
+   * the button stays live throughout a turn, it just means something else
+   * while one is running.
+   */
+  private syncSendBtn(): void {
+    this.sendBtn.disabled = false;
+    this.sendBtn.replaceChildren(
+      icon(this.awaiting ? "square" : "chev-up", "sm")
+    );
+    const label = this.awaiting ? "Stop" : "Send";
+    this.sendBtn.setAttribute("aria-label", label);
+    this.sendBtn.setAttribute("data-tip", label);
+    // `chat.send`'s ⌘⏎ hint belongs on Send, not on Stop — Enter never cancels
+    // a turn, only `submit`'s own early return while `awaiting` is set.
+    if (this.awaiting) {
+      this.sendBtn.removeAttribute("data-key");
+    } else {
+      this.sendBtn.setAttribute("data-key", "chat.send");
+    }
+  }
+
   /**
    * Reconcile a latched `awaiting` against what the daemon actually has.
    *
@@ -3960,7 +4014,7 @@ export class AirshipApp {
     this.awaiting = false;
     this.activeJobId = null;
     this.applyingVisual = false;
-    this.sendBtn.disabled = false;
+    this.syncSendBtn();
     this.syncApplyGroup();
     this.syncJobChip();
 
@@ -4169,7 +4223,7 @@ export class AirshipApp {
 
   private onDone(bundle: JobDiffBundle): void {
     this.awaiting = false;
-    this.sendBtn.disabled = false;
+    this.syncSendBtn();
     this.syncApplyGroup();
     this.syncJobChip();
     this.reportOffscreenTurn(bundle);