fix(app): keep delayed navigation behind user scroll intent

A prompt sent during an active gesture requested the bottom, but the older gesture cancelled that request when momentum ended away. Honor the still-sticky pending request on release while allowing a newer gesture to take ownership.

docs/agent-stream-disclosure.md

@@ -156,8 +156,10 @@ keeps following.
 
 Following resumes only for a gesture that ends within 1 px of the end, either when the finger lifts
 or when momentum stops. A release past the end counts: iOS bounces back to the end, and lines that
-land during the bounce must keep scrolling in. A release anywhere short of the end stays detached
-with the scroll-to-bottom pill, so the rows the user let go of never move.
+land during the bounce must keep scrolling in. A release short of the end stays detached with the scroll-to-bottom pill unless you submitted
+another prompt during that gesture. That submit requests the end after the gesture finishes;
+a new drag after submitting takes ownership again. Rewind and tail-fetch completions do not
+override a scroll away because they can arrive after the action that requested them.
 
 ### Draw distance
 

packages/app/src/agent-stream/bottom-anchor-controller.test.ts

@@ -394,6 +394,56 @@ describe("bottom anchor controller driver", () => {
     expect(harness.scrollAttempts).toHaveLength(0);
   });
 
+  it("honors a submit made during a gesture when that gesture ends away", () => {
+    const harness = createDriverHarness({ isNearBottom: false });
+    harness.driver.beginUserScroll();
+    harness.driver.requestLocalAnchor({ agentId: "agent-1", reason: "message-sent" });
+    harness.scheduler.flushAll();
+    expect(harness.scrollAttempts).toEqual([]);
+
+    harness.driver.endUserScroll({ isAtEnd: false });
+    harness.scheduler.flushAll();
+
+    expect(harness.context.measurementState.offsetY).toBe(
+      harness.context.measurementState.contentHeight -
+        harness.context.measurementState.viewportHeight,
+    );
+    expect(harness.driver.getSnapshot()).toMatchObject({
+      mode: "sticky-bottom",
+      pendingRequest: null,
+    });
+  });
+
+  it.each(["rewind", "jump-to-bottom"] as const)(
+    "lets scrolling away supersede a late %s request",
+    (reason) => {
+      const harness = createDriverHarness({ isNearBottom: false });
+      harness.driver.beginUserScroll();
+      harness.driver.requestLocalAnchor({ agentId: "agent-1", reason });
+      harness.driver.endUserScroll({ isAtEnd: false });
+      harness.scheduler.flushAll();
+
+      expect(harness.scrollAttempts).toEqual([]);
+      expect(harness.driver.getSnapshot()).toMatchObject({
+        mode: "detached",
+        pendingRequest: null,
+      });
+    },
+  );
+
+  it("lets a new gesture supersede a submit requested during the previous gesture", () => {
+    const harness = createDriverHarness({ isNearBottom: false });
+    harness.driver.beginUserScroll();
+    harness.driver.requestLocalAnchor({ agentId: "agent-1", reason: "message-sent" });
+    harness.driver.endUserScroll({ isAtEnd: false });
+    harness.driver.beginUserScroll();
+    harness.driver.endUserScroll({ isAtEnd: false });
+    harness.scheduler.flushAll();
+
+    expect(harness.scrollAttempts).toEqual([]);
+    expect(harness.driver.getSnapshot()).toMatchObject({ mode: "detached", pendingRequest: null });
+  });
+
   it("resumes following when a user scroll ends at the end", () => {
     const harness = createDriverHarness({
       transportBehavior: {

packages/app/src/agent-stream/bottom-anchor-controller.ts

@@ -499,11 +499,16 @@ function createBottomAnchorControllerDriver(
       cancelPendingAttempt();
       setModeInternal("detached");
     },
-    // Following resumes only for a gesture that ends at the end. Resuming from short of it would
-    // scroll the rows the finger just let go of, so a release above the end, or with output that
-    // arrived below it during the gesture, stays detached with the pill.
+    // A gesture ending short stays detached unless a newer prompt submission requested the end.
+    // Passive output must not move the rows the finger just let go of.
     endUserScroll(params) {
       isUserScrollActive = false;
+      // Submit arrives with the user's action; rewind and tail jumps can arrive after a fetch.
+      // A newer gesture would have detached again, so only a still-sticky submit owns release.
+      if (pendingRequest?.reason === "message-sent" && mode === "sticky-bottom") {
+        evaluate(false, "user_scroll_end");
+        return;
+      }
       if (params.isAtEnd) {
         if (mode === "detached") {
           setModeInternal("sticky-bottom");