Premortem

Premortem (DVE / Guided Vibe Engineering)

Vibe coding is speed. GVE is scar tissue — the externalized expert reflex a non-expert builder doesn't have yet. The shift: from "what should I build next?" → "if I build this next, how could it fail, and what should we clarify, test, or document first?" The risk only counts if it becomes an artifact — "if the AI only talks about risk, the risk evaporates."

When to fire

At each lifecycle transition, a small phase-specific premortem (not one giant upfront one — that's waterfall): intent → requirements → architecture → implementation → testing → debugging → deployment → iteration. Highest value before a deploy, a schema change, or touching a hot path (e.g. a polling loop, a service entrypoint, anything user-facing in production).

Steps

1. Name the decision + its phase. One line: "Deploying X to the live gateway" / "Adding column Y" / "Refactoring the pull loop."

2. Imagine 3-5 concrete failure modes. Be specific to this change, not generic. For each:

   • What breaks (the failure, in one line)
   • Blast radius (who/what is affected — one user? all devices? billing? the outage class)
   • Likelihood (low / med / high)
   • Cheapest guard — the smallest thing that prevents or catches it: a clarifying question, a boot-test, a canary, a rollback path, a test, a doc line, an || true non-fatal wrap.

3. Write the artifact. Append to notes/premortem.md next to the work (or wherever your session notes live) — premortem.py in this directory writes the block for you. Structure:

   ## <date> — <decision>  [phase: <phase>]
   | # | failure | blast radius | likelihood | guard | predicted | actual |
   |---|---------|--------------|------------|-------|-----------|--------|
   ...one row per failure mode; leave "actual" blank until after.
   

   The predicted-vs-actual ledger is the learning signal — after the change ships, come back and fill "actual." A predicted failure that fired → a rule candidate / a future deployment guard.

4. Act on the top guard before proceeding. Don't just file it — do the cheapest 1-2 guards now (ask the clarifying question, add the boot-test, write the rollback line). Then proceed with the change.

5. Teaching mode (for non-expert builders). If the user is learning, explain why each failure mode matters in plain language and which guard you chose — narrate the scar tissue so they build their own.

CLI

premortem.py writes the ledger block so the artifact exists before the change does:

python3 premortem.py "Deploy the new gateway build" --phase deployment              # print the block
python3 premortem.py "Add column X" --failure "migration locks the table" \
    --failure "old rows carry NULLs" --apply --out notes/premortem.md           # append it

Dry-run by default; --apply appends to --out. --json for machine output.

The loop it serves

Real failure → premortem artifact → predicted-vs-actual ledger → learning signal → rule candidate → test → approval → future deployment guard. That's the proof goal of GVE, and it's how a team converts incidents into permanent guards instead of repeating them.

Notes

• Keep it short — a premortem is minutes, not a meeting. 3-5 failure modes, cheapest guards, file it, act.
• This skill is the operational embodiment of the DVE Guidebook. The guidebook is the teaching text; this skill is the reflex.
• Pairs with the destructive-command guard hook and the syntax-check hook — those are automatic guards; this is the judgment layer above them.
• Source doctrine: the GVE Premortem Module of the DVE Guidebook.