Coder Agents chats could get stuck showing "Thinking" forever when a
title regenerate/propose request ran while a generation was in flight.
Manual title generation recorded token cost by inserting a hidden
assistant message into `chat_messages` and immediately soft-deleting it.
Triggers on that table sync `chats.history_version` to
`snapshot_version`, so this out-of-band write broke the
`history_version` fence of an in-flight generation task, killing it
without a replacement and leaving the chat stuck in `running`.
Remove the accounting path entirely; AI Gateway already records
title-call usage in `aibridge_interceptions`/`aibridge_token_usages`.
The manual title endpoints no longer write to `chat_messages` at all,
and new regression tests assert `history_version` stays untouched. Note
this intentionally drops title-generation cost from chatd's chat-level
cost surfaces; it still counts against the user's AI budget via AI
Gateway.
Closes CODAGT-595
Ethan
ea4554025e