fix(terminal): the history notice waits for the pull already in flight (#583 merge-time fix)

_smoothScrollBy and the touch paths call _maybeLoadMoreHistoryOnScroll on
every frame. Once the viewport sat at row 0, the next frame hit the real
pull's in-flight early return, so its reveal ran at once and the notice
showed the pre-pull tail state for the whole pull. A later frame now leaves
the reveal to the call that started the pull.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/public/terminal-ui.js

@@ -3681,6 +3681,9 @@ Object.assign(CodemanApp.prototype, {
       return;
     }
     if (lines === 0 || this.terminal?.buffer?.active?.viewportY !== 0) return;
+    // An earlier frame of this gesture already started the pull; its own
+    // completion reveals the notice, so do not flash the pre-pull state now.
+    if (this._fullHistoryRepullInFlight || this._isLoadingBuffer) return;
     const sessionId = this.activeSessionId;
     Promise.resolve(this._maybeRefetchFullHistory?.())
       .catch(() => {})

test/history-notice-reveal.test.ts

@@ -184,6 +184,32 @@ describe('partial-history notice: lazy reveal', () => {
     expect(loadButton(bar)?.textContent).toBe('Load full history');
   });
 
+  it('a later frame of the same gesture does not flash the pre-pull state while the pull runs', async () => {
+    const { app, bar, buffer } = makeApp();
+    app._setHistoryTruncation('s1', TAIL);
+    // Like the real pull: it marks itself in flight and returns at once to every later caller.
+    const pull = { release: () => {} };
+    app._maybeRefetchFullHistory.mockImplementation(() => {
+      if (app._fullHistoryRepullInFlight) return Promise.resolve();
+      app._fullHistoryRepullInFlight = true;
+      return new Promise<void>((res) => {
+        pull.release = () => {
+          app._fullHistoryRepullInFlight = false;
+          res();
+        };
+      });
+    });
+    buffer.viewportY = 0;
+    app._maybeLoadMoreHistoryOnScroll(-500);
+    app._maybeLoadMoreHistoryOnScroll(-1); // the next animation frame, still at row 0
+    for (let i = 0; i < 5; i++) await Promise.resolve();
+    expect(bar.hidden).toBe(true);
+
+    pull.release();
+    for (let i = 0; i < 5; i++) await Promise.resolve();
+    expect(bar.hidden).toBe(false);
+  });
+
   it('shows what the pull left: nothing, when the pull brought everything back', async () => {
     const { app, bar, buffer } = makeApp();
     app._setHistoryTruncation('s1', TAIL);