TASK
Investigate a fictional publishing failure using only the evidence below.
Explain the likely cause, what each record proves, and how a correction
should be verified. Do not perform changes or claim a test has run.

EVIDENCE
[E1] POST /posts/publish returns HTTP 500 for test post P42.
[E2] The matching server log reports that column published_at is missing.
[E3] The failed request was served by release R12. Its publishing code
writes the publication timestamp to posts.published_at.
[E4] The R12 deployment guide requires migration M12, which creates that column.
[E5] The database used by the running application has migrations M1–M11.
Its posts table does not contain published_at.
[E6] A saved note from an earlier incident says an application release
succeeded while its database migration step was skipped.

OUTPUT
1. A short diagnosis citing E1–E6 where relevant.
2. Separate current evidence from the historical lead.
3. The correction to review and the checks that would confirm it worked.
4. Identify where a skill, MCP-connected tools, RAG and memory could help.

VARIATION
If E5 were unavailable, explain what remains unverified and what to inspect next.