POST /api/ai-chat/bound-chat 500'd with Postgres 22P02 because the client
sends a page slugId (10-char nanoid) in the request `pageId` field, which the
server passed straight into the UUID `page_id` column. The chat-to-document
binding silently broke (client fail-softs to a new chat) and every slug-URL
page open logged a 500.
Fix: resolve the incoming id to a real page UUID on the server. PageRepo.findById
already accepts both a uuid and a slugId (isValidUUID→slugId fallback), so
boundChat now resolves the page first, guards it against a foreign/unknown
workspace (returns {chatId:null} before any chat lookup — no cross-workspace
probe), and looks up the latest chat by the resolved page.id (real uuid).
Client: renamed the local pageId→slugId for clarity (the value is a slugId);
the wire body key stays `pageId` so the DTO is unchanged. DTO left @IsString()
(a @IsUUID() would only turn the 500 into a 400 and still break binding).
Test: bound-chat spec asserts a slugId resolves and findLatestByPage is called
with the real uuid; a foreign-workspace page → {chatId:null} without a chat
lookup (no leak); an unknown id → {chatId:null}, no throw.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
claude code agent 227