menu: do not close on the panel's own scrolling

The dismiss-on-scroll listener is on the capture phase, because `scroll`
does not bubble — so it also heard the menu scrolling itself, and a long
tracklist closed the moment it was wheeled. Filter on the event's origin.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/docs/playlists.md b/docs/playlists.md
index 49b1585..c450815 100644
--- a/docs/playlists.md
+++ b/docs/playlists.md
@@ -808,10 +808,17 @@ The codebase has no context menu and no dropdown outside the account menu in
   button** — `icon.js` already has `dots` (`icon.js:54`). Both affordances, both
   platforms: the button is visible on hover on a fine pointer and always visible
   under `@media (pointer: coarse)`.
-- closes on Escape, on an outside click, and **on scroll**. The last one is not
-  optional here: Music's toolbar is a sticky band and the grid scrolls beneath
-  it, so a menu that survives a scroll is a menu now anchored to a different
-  album than the one it was opened on.
+- closes on Escape, on an outside click, and **on a scroll of the page**. The
+  last one is not optional here: Music's toolbar is a sticky band and the grid
+  scrolls beneath it, so a menu that survives a scroll is a menu now anchored to
+  a different album than the one it was opened on. **Never on a scroll of its
+  own panel** — the panel is `overflow-y: auto` and a tracklist is routinely
+  taller than the window, so the two must be told apart by where the event came
+  from. `scroll` does not bubble, so that listener is on the capture phase,
+  which is also what made it hear the panel's own scrolling: the menu closed the
+  instant it was wheeled or its scrollbar dragged, and no track below the fold
+  could be reached. Measured by `menu_scroll_probe.py`; `playlist_ui_probe.py`
+  cannot see it, because `.click()` scrolls nothing.
 - flips its anchor when it would open past the viewport edge, which on a phone
   is most of the time.
 - submenus **expand in place**, downward, at every width. This is the