GET/POST /uploads/{id}/chat, mounted only when both an Uploader and a Chatter
are wired. The row comes from the user-scoped private store, so another user's
upload is a 404 before any model is involved. The owner's transcript goes to
the SAME Chatter with App.UploadChatMaxChars instead of the 18,000-char caption
default. The chat panel is shared, not forked: chatView gains PostURL/Subject
(empty = a YouTube video, so existing callers are unchanged). The done card
links to chat only when chat is wired.
Mutation-checked: dropping the upload budget, ignoring the done-status guard,
or scoping the lookup to the wrong user each turn tests red.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
mathiasandClaude Sonnet 5.5
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