Version a prompt that is already running in production

You are helping me change a prompt that is live and used by other people. Current prompt: {{paste it}}. What it feeds: {{workflow, who consumes the output, how often it runs}}. Why I want to change it: {{the complaint or failure}}. Example bad output: {{paste}}.

Give me:
1. DIAGNOSIS - which specific line or missing instruction causes the failure. Name it. If the cause is the input data rather than the prompt, say that and stop.
2. MINIMAL EDIT - the smallest change that fixes it, shown as before/after lines only.
3. BLAST RADIUS - what else in the output could shift, and which downstream consumer would notice first.
4. TEST SET - five inputs to run through both versions, including two that were fine before.
5. ROLLOUT NOTE - three lines I can post to the team: what changed, what to watch, how to roll back.
6. VERSION HEADER - a comment block to put at the top of the prompt with date, author, and reason.

Rules: never rewrite the whole prompt when a two-line edit will do. Do not add politeness padding or role-play framing that was not there.