Empty submission was producing a blank user_turn event in the log and
firing the LLM stream anyway — the bot would invent a response from the
kickoff context alone, producing a monologue with no user input. Two-
layer fix:
- Browser: add `required` to the prose textarea in chat.html so the
form refuses to submit empty.
- Server: 400 in post_turn when prose.strip() is empty. Defense in
depth — if a client bypasses the textarea attribute (custom UI,
curl, etc.), the server still rejects.
Verified live: POST with empty body returns 400; POST with whitespace-
only returns 400; chat shell renders the textarea with required.
Full suite: 168 passed.
Joseph Doherty
52555e0455