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(() => {})