NotFoundError: Message not found: msg_f95b9........

Describe the bug
Session revert cleanup deletes messages without updating child parentID references, leaving orphaned messages that crash the session view with NotFoundError.

To Reproduce

1. Open a project in opencode web
2. In an active session, use /undo to revert to an earlier message
3. Continue the session (new messages created after revert point)
4. Reload the page or reopen the session
5. Session fails to load with: Message not found: msg_XXXXX

Expected behavior
Messages are deleted during revert cleanup without leaving orphaned parentID references. Child messages are either reparented to the nearest surviving ancestor or have their parentID cleared.

Actual behavior
cleanup() in packages/opencode/src/session/revert.ts (lines 100-134) calls sessions.removeMessage() for each message at/after the revert point. Any messages created after the revert that have parentID pointing to a deleted message become orphaned. The API returns 404 when loading these orphaned messages, crashing the session view.

Error

NotFoundError: Message not found: msg_f95b93c2e001CmgY3q2JKDV77E

Environment

• OpenCode version: 1.18.3
• Platform: Linux

Additional context
The orphaned messages can be identified via SQL:

SELECT m.id, json_extract(m.data, '$.parentID') as parent_id
FROM message m
WHERE json_extract(m.data, '$.parentID') IS NOT NULL
  AND json_extract(m.data, '$.parentID') != ''
  AND NOT EXISTS (
    SELECT 1 FROM message m2 WHERE m2.id = json_extract(m.data, '$.parentID')
  );

Manual workaround: reparent orphaned messages to the last surviving user message before the revert point.