Desktop sidebar ignores UserPromptSubmit hook `sessionTitle` output

Summary

The documented hookSpecificOutput.sessionTitle from UserPromptSubmit hooks (added in v2.1.94) is honored by the CLI but not by the desktop app's sidebar. The desktop displays its own auto-generated title and ignores the hook output.

Environment

• Claude Code 2.1.121 (desktop)
• macOS 14.x

Repro

1. Add a UserPromptSubmit hook in ~/.claude/settings.json:

``json
{
"hooks": {
"UserPromptSubmit": [
{ "hooks": [ { "type": "command", "command": "/path/to/hook.sh" } ] }
]
}
}
``

1. Have the hook return:

``json
{
"hookSpecificOutput": {
"hookEventName": "UserPromptSubmit",
"sessionTitle": "[ProjectA] Test Title"
}
}
``

1. Submit a first prompt in a desktop session.

Expected

Sidebar entry shows [ProjectA] Test Title.

Actual

• ~/.claude/sessions/<pid>.json → .name = \"[ProjectA] Test Title\" ✅
• Session .jsonl transcript → custom-title records contain \"[ProjectA] Test Title\" ✅
• ~/Library/Application Support/Claude/claude-code-sessions/.../local_*.json → title = \"<auto-generated summary>\", titleSource = \"auto\" ❌

The desktop sidebar reads from the local_*.json file. The hook output never reaches it.

Manual /rename works because it sets titleSource: \"user\", so the field is honored when set through the UI's own path.

Workaround attempted (and why it's not viable)

Patching local_*.json directly to titleSource: \"user\" works briefly but the desktop overwrites it on session-close/app-close — disk state at next app start is what wins, and the in-memory state is what writes last. So patches don't survive a close/reopen reliably without a constantly-running watcher daemon.

Ask

Have the desktop sidebar honor hookSpecificOutput.sessionTitle from UserPromptSubmit hooks — same effect as /rename (i.e. set titleSource: \"user\" in local_*.json and invalidate the in-memory cache).

Use case

Auto-formatting session titles per-project (e.g. [ProjectA] …, [ProjectB] …) for users who work across multiple repos and view sessions in date-sorted mode rather than project mode.