fix(tiles): page a hollow tile only from the live screen, review follow-up

A tile counts as hollow when every row above its screen is its own overflow
(baseY minus _overflowRows is 0), so unlike the primary pane, whose hollow
buffer has baseY 0, its viewport can sit above the bottom while it is hollow:
Shift+PageUp, a scrollbar drag or a wheel during the first replay leave it up
there. _maybePageCliTranscript never looked at the viewport, so every wheel,
wheel-down included, was turned into PageUp/PageDown and swallowed. xterm never
scrolled back, the stale rows stayed on screen while the CLI paged out of
view, and clicks were dropped too, because the click report refuses an
off-bottom viewport.

The tile now pages only while _terminalViewportAtBottom holds for its own
terminal, checked before the pending travel is touched. Off the bottom the
wheel stays with xterm, so a wheel-down brings the viewport home and paging
resumes from there. The primary pane is unchanged: its hollow test already
implies a viewport at the bottom, which the twin comment now says.

Tests: a unit case for a tile hollow by the discount with its viewport above
the bottom (no page key, no preventDefault, and no travel carried over once
back home), and the real-browser case now scrolls a hollow tile up and proves
a real wheel-down scrolls xterm home with no page key sent, then pages again.
Both go red with the gate removed, and the unit case also with the gate moved
below the pending-travel update.

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

src/web/public/terminal-tile.js

@@ -24,7 +24,8 @@
  *    so the wheel pages the CLI's own transcript with PageUp/PageDown
  *    (_maybePageCliTranscript) through the primary pane's gates, plus an
  *    overflow-row discount for this pane's capture-before-resize load
- *    (_localRows).
+ *    (_localRows), and only while the viewport is on the live screen (a
+ *    wheel-down from those overflow rows is xterm's, and brings it home).
  *  - The desktop click report: a plain left-click hand-encoded as SGR while
  *    the session's CLI has mouse tracking on (cliMouseTracking), for the modes
  *    whose mouse DECSETs the server strips (_installClickListener).
@@ -41,7 +42,7 @@
  *
  * @dependency vendor/xterm.js, vendor/xterm-addon-fit.js
  * @dependency constants.js (window.CodemanTerminalFont, window.CodemanFetchDeadline, DEFAULT_SCROLLBACK, TERMINAL_TAIL_SIZE, TERMINAL_CHUNK_SIZE)
- * @dependency terminal-ui.js (codemanCurrentXtermTheme, codemanCurrentSkinIsLight, CodemanTerminalInput.shouldSuppressTerminalQueryResponse/isTerminalFocusOrMouseReport/wheelDeltaLines/pageKeysForTravel, app._shouldForwardWheelToApp/_localScrollbackIsHollow/_handleDesktopTerminalClick)
+ * @dependency terminal-ui.js (codemanCurrentXtermTheme, codemanCurrentSkinIsLight, CodemanTerminalInput.shouldSuppressTerminalQueryResponse/isTerminalFocusOrMouseReport/wheelDeltaLines/pageKeysForTravel, app._shouldForwardWheelToApp/_localScrollbackIsHollow/_terminalViewportAtBottom/_handleDesktopTerminalClick)
  * @dependency terminal-keycode229-recovery.js (window.CodemanKeyCode229Recovery, optional: absent, xterm's own textarea handling stands)
  * @loadorder 7.4 of 16, loaded after terminal-ui.js and before terminal-split.js
  */
@@ -887,6 +888,17 @@
       // follow-up 4), so the wheel stays with xterm, as before.
       if (app._shouldForwardWheelToApp?.(ev, target)) return false;
       if (!app._localScrollbackIsHollow?.({ ...target, localRows: this._localRows() })) return false;
+      // Only from the live screen. The one gate the primary pane never needs: a
+      // primary hollow buffer has baseY 0, so its viewport is always at the
+      // bottom, while a tile's is hollow with its own overflow rows still above
+      // the screen, and Shift+PageUp, a scrollbar drag or a wheel during the
+      // first replay can leave the viewport up there. Paging from there would
+      // swallow every wheel (wheel-down included) and keep the stale rows on
+      // screen while the CLI pages out of view; left to xterm, a wheel-down
+      // brings the viewport home and paging resumes from there. The click
+      // report refuses an off-bottom viewport for the same reason
+      // (_terminalViewportAtBottom).
+      if (!app._terminalViewportAtBottom?.(this.terminal)) return false;
       const lines = input.wheelDeltaLines(ev, this.terminal.rows);
       if (!lines) return false;
       const step = input.pageKeysForTravel(this._pageKeyPending, lines, this.terminal.rows);