/premortem

name: premortem
description: 'Challenge a rollout plan with one fresh judge before implementation; identify what could make it fail. Not for finished-code judgment. Triggers: "one judge", "challenge this plan".'
practices: [design-by-contract, adr]
hexagonal_role: domain
consumes: []
produces: [premortem-plan-review.v1]
context_rel:
- kind: supplier-to
  with: plan
skill_api_version: 1
user-invocable: true
metadata:
  capabilities: [challenge_plan]
  effects: [write_advisory_plan_review]
  canonical_status: canonical
  disposition: keep_strategy
  graph_root: true
  tier: judgment
  dependencies: []
output_contract: skills/premortem/schemas/premortem-plan-review.v1.schema.json

Premortem

Premortem is an optional plan-challenge strategy. It asks one fresh context to identify concrete ways the resolved bead or caller intent could fail before implementation. It is not part of the required RPI sequence and does not authorize readiness.

The first check: who verifies, and are they fresh?

Before any technical risk, test the plan's EVIDENCE SHAPE: for every unit of work, who verifies it, and is the verifying context distinct from the authoring context? A plan whose closure step is "the implementer runs its own tests and closes" contains no independent judgment anywhere — self-graded green is the classic false-done, and it outranks any single technical risk because it silently converts every other failure into a shipped one.

> Measured 2026-08-04, probe `premortem-self-validation` (gpt-5.6-luna, N=2, > directional): without this doctrine loaded the producer named the planted > self-validation flaw in 1/2 runs; with it loaded, 2/2. Ledger: > `evals/skill-probes/LEDGER.md`. That row is `LEGACY-UNVERIFIED` under the > current capture contract — replay cannot establish producer, configuration, > or reproducibility — so treat this skill as unmeasured until a tier-2 probe > under the current contract re-establishes it.

The second check: which steps are one-way doors?

After evidence shape, test the plan's REVERSIBILITY SHAPE. Walk the plan's steps and mark each one two-way (the plan can back out of it) or one-way (it cannot). For every one-way step, name three things: the exact undo cost, the point of no return, and who is holding the handle when it is crossed — the caller, or an agent auto-deciding inside a batch.

This ranks above every technical risk on a one-way step, because a two-way failure costs a retry and a one-way failure costs the thing itself. It also catches the plan shape that no single-step review sees: nineteen reversible steps followed by an irreversible one, where the reflex trained by the first nineteen answers the twentieth.

A material irreversible action outside existing caller authority is a finding. Trace actual undo cost and authorization using [Plan](../plan/SKILL.md). Prior authorization remains valid; do not demand repeated approval at the crossing or classify every uncertain implementation detail as irreversible.

The named failure mode here is **reversibility asserted, not traced**: a plan that says "fully reversible" in its rollback section while one step revokes a credential, force-pushes, or publishes. Stop condition: every step carries a mark, and every one-way mark carries its undo cost.

Workflow

1. Resolve the existing intent source and derive its digest; inspect acceptance, non-goals, evidence requirements, and declared write scope there. 2. Use one fresh judge with a context ID distinct from the plan author, in the author's model family by default (Codex or Claude). A caller may explicitly select a different-family judge. Follow [model-dispatch](../agent-native/references/model-dispatch.md) for model pins, authorization and caller/native time bounds; no fixed ten-minute cap applies. 3. Test acceptance completeness, edge behavior, scope, dependencies, reversibility, and evidence shape against cited repository facts. 4. Return one complete set of concrete findings and checked/not-checked scope. 5. Stop. The caller decides whether to revise the plan or invoke RPI.

Council or Dueling Idea Genies may be caller-supplied evidence, but Premortem does not require either strategy and cannot turn consensus into approval.

Adversarial defeat attempts

Actively try to construct each failure, not imagine it. For every candidate failure, attempt a concrete defeat: write the input, command sequence, or repository state that would make the plan fail, and run or cite the check that shows whether the plan survives it. A finding is reportable as concrete when it names the defeating construction and what the plan does when it lands; a failure you could not construct is reported as attempted-and-blocked with the obstacle named, which is itself evidence for the plan. The named failure mode is armchair pessimism: a list of imagined risks with no construction attempts, which reads as diligence while testing nothing. Stop condition: every reported finding is backed by a defeat attempt — constructed, or attempted with the blocking fact cited; a finding with neither is deleted, not softened.

Derivation-diff challenge

A challenger that critiques the handed plan is a yes-man with extra steps: it anchors on the author's design and rationalizes it. Derive independently, then diff. Give one fresh context ONLY the intent source and the plan's declared ground truth — the vendor docs and stock behavior for integration work, the repo's patterns and behavior spec for extension — and never the author's design. Have it sketch its own design from that ground truth alone. The diff between that independent design and the working plan is the challenge artifact; each divergence is a finding to defend or adopt. Convergence is weak evidence the plan follows the ground truth; divergence names where it may not.

Two questions the challenger answers with an artifact, not an opinion:

• Cathedral: is this the smallest real thing, or does it rebuild what already