fix(messages): keep a playing row mounted in the channel timeline - #2695

…ently

The playback pin from the previous commit cleared only when React
delivered a pause or ended event from a player still in the attachment
list. Some paths never deliver one, so the row stayed in keptIndices
for the rest of the visit.

A player is now counted as playing only while it is not paused and has
no error. The list also recomputes on emptied, which load(), media read
recovery and src swaps fire instead of pause. It also recomputes on
error, which reaches the list before AudioAttachment or MediaAttachment
swaps in its unavailable state.

React drops the pause a removed player fires. A player is removed
without one when it is edited out, claimed by a message renderer,
swapped by its plugin's ContributionBoundary, or unmounted with the
whole list once no attachment groups remain. While a player plays, a
MutationObserver on the row rechecks the list whenever the row's tree
changes, and it disconnects when playback stops. It watches the row,
not the list, so the list unmounting counts as a change. A recheck after
MessageRow commits would miss boundary swaps, which re-render only the
boundary.

The comment now says that only players inside the list's DOM count, so
a plugin player portalled elsewhere never pins the row.

ChannelTimeline.report.test.tsx adds three tests: a playing a.mp3 that
fails, a playing player edited out, and one claimed by a message
renderer, which empties the list. All three fail on f2889a1, with the
row still pinned after eviction.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Signed-off-by: mtoohey <[email protected]>

…unmounts

The observer from the previous commit watched the row div, so it missed
that div or an ancestor being removed while MessageRowContent stayed
mounted. An agents-audience row renders the message inside
Collapsible.Panel, which Base UI 1.9 unmounts on close by default.
Collapsing a row while its audio played detached the player without a
mutation record inside the row, and React dropped the browser's pause,
so the row stayed pinned for the rest of the visit. The effect also
reran only when mediaPlaying changed, so after the row reopened it kept
watching the detached div.

A stable callback ref on the attachment list now owns the observer. It
watches the list's subtree, rechecks only while a player plays, and its
cleanup disconnects and clears the flag. React 19 runs ref cleanups
whenever the node is deleted, whichever ancestor is removed, so that
covers a claim of the last attachment group as well as the fold. The
callback also keeps the ref the media handlers read in sync.

The review also named MessageActionBar's wrapper swap. That can't happen
today: no production code has provided ConversationPresentation since
89bc099, so it is always true. The ref cleanup would cover it too.

Test changes in ChannelTimeline.report.test.tsx:
- A new test plays audio in an agents row, collapses it and evicts it.
  It fails on the previous commit.
- The error test now uses a voice note with a decode error. Recovery
  retries only network errors, and the card keeps its failed <audio>
  mounted, so only onError and the error check can release the row.
- The playback it.each gains a voice note stopped by emptied.
- That it.each now flushes microtasks after play. The list observer is
  attached for the list's whole life, so records from the play's own
  re-render otherwise arrived after the test set paused, and released
  the row whatever the stop event was.

Each of these fails when its code is removed: onError with the error
check fails the error test, onEmptied fails the emptied case, and
dropping setMediaPlaying(false) from the cleanup fails the agents and
claim tests.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Signed-off-by: mtoohey <[email protected]>

trackMedia read the attachment list through a ref that observeAttachments
set on attach and cleared in its cleanup. A React media event's
currentTarget is already that list div, including events that reach it
from a portalled player. trackMedia now takes the event and rechecks
event.currentTarget, so the attachmentList ref and the two lines that
kept it in sync are gone. playingIn always gets a list now, so it takes
a non-null Element.

No behaviour change. The ref was set before the list could receive
events and cleared only once it was detached, so it always matched
currentTarget when a handler ran. No test changes.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Signed-off-by: mtoohey <[email protected]>