---
name: ln-98-mutation-reliability-engineer
description: "Implements transactions, idempotency and interrupted-operation recovery; not schema migration or a mandatory background-job platform."
---

# Mutation Reliability Engineer

**Goal:** Deliver approved mutation reliability while preserving business effects and consumer contracts. Change only scoped operations and required integration boundaries; live replay/compensation requires explicit affected-target authority.

**Execution contract:** Track every checklist item as `PENDING`, `PROVEN` with observed outcome evidence, `CLEARED` with evidence its condition is absent, or `UNPROVEN` with a gap. Reading, delegation, tool failure, zero exit status, and self-reported success are not proof. Reconcile after each section; before returning, resolve all `PENDING`, count only `PROVEN` and `CLEARED`, and apply verdict and approval rules to every gap.
Preserve intent, scope, mode, and existing authorization. Complete authorized work before required external approval; ask only consequential unresolved choices. If nobody can answer, report the exact question and apply the skill's gap verdict without waiting or guessing. Cite any blocking instruction and unresolved boundary; never invent approval gates. Scale depth to material risk; preserve mandatory checks, dependencies, and safety order while choosing verification methods.
Accept equivalent user or repository evidence without requiring another skill, named artifact, or full lifecycle. Preserve source requirement and decision IDs. Bind reused evidence to relevant versions, dirty changes, configuration, environment, and observation windows; invalidate only affected claims.
Choose the primary workflow by outcome and explicit selection. Consume neighboring contracts and valid evidence without duplicating ownership or restarting audits. Split distinct deliverables by scope, not mandatory skill invocation. Broad independent assessments use audit workflows; focused domain reviews remain read-only.
On continuation, reconcile task, authorization, state, and gaps. Return a compact continuation record for long work or update an already authorized artifact; read-only skills do not persist it. Distinguish artifact readiness, verified behavior, and external-action authority.
Before retrieval, define the evidence question; read selectively without skipping applicable instructions. Use tools for mechanical processing; summarize bounded results, errors, coverage, and source paths, keeping full output outside context.
Before technical decisions, establish applicability and actual versions; verify version-dependent assumptions against official documentation or specifications. Search and read primary pages for current external recommendations; snippets are not evidence. Version-matched bundled documentation or valid prior evidence suffices. Record decision, version, source, and limitations. Mark unavailable evidence UNVERIFIED; block only essential dependent work. Prefer native mechanisms, justify added tools or abstractions with evidence, and reuse the existing rule owner.


## Tool Routing

| Need | Preferred capability | Fallback |
|---|---|---|
| Actual stack and owners | Instructions, manifests, lockfiles, focused source/configuration reads and Git state | Supplied artifacts with explicit gaps; never infer versions from examples |
| External semantics | Version-matched official documentation, specifications and maintained upstream source | Bundled official docs or valid prior evidence; mark unsupported conclusions UNVERIFIED |
| Authorized changes | Project-native editor, configuration and maintained runtime tooling | Minimal scoped patch; BLOCKED when no safe mutation capability exists |
| Observable verification | Existing checks and isolated runtime/consumer exercises | Static evidence labeled as such; BLOCKED when essential behavior cannot be established |

## Boundaries

This workflow owns runtime atomicity, concurrency and recovery. Database lifecycle owns schema delivery; errors own safe consumer representation. Choose transactions, replayable requests or durable jobs from operation needs; at-least-once delivery does not guarantee exactly-once effects.

Authorization owns access predicates and their required validity window; enforce them through the operation's atomicity mechanism without redefining grants. For durable audit records, implement only the approved effect-to-record consistency contract; record contents, access and retention remain separate policy inputs.

Review and explanation requests are read-only. Preparation does not authorize remote publication, deployment or shared-state mutation.

## Checklist

### 1. Model failure windows

- [ ] Trace dispatch, each database/file/queue/external effect and acknowledgement; identify authoritative completion evidence.
- [ ] Define protected invariants, concurrent actors, existing retry owners and approved partial-success behavior.
- [ ] Classify request-atomic, replayable request or durable job; prefer existing transactions/constraints before new coordination.

### 2. Implement recovery

- [ ] Align transaction ownership with the business invariant and native isolation; use constraints/conditional writes to close demonstrated races.
- [ ] For replayable requests, scope idempotency key and fingerprint, persist effect/result consistently, and define conflicting reuse and retention from the contract.
- [ ] Lost commit acknowledgement or post-dispatch timeout is not rollback; resolve authoritative state before retry or compensation.
- [ ] Bound attempts, deadlines and backoff with appropriate jitter; retry only classified transient failures and replay-safe effects at one layer.
- [ ] For durable jobs use maintained mechanisms when they fit; define claims, necessary leases, idempotent handlers, retry/poison-item handling and terminal state.
- [ ] Checkpoint resumable work at durable boundaries; worker termination must resume without skipped/duplicated business effects.
- [ ] Model non-atomic database/filesystem/remote windows explicitly; use recoverable stages or existing outbox/inbox mechanisms where justified.
- [ ] Keep authorization context and resource access valid during execution; do not retain stale privileges to simplify replay.

### 3. Exercise interruption

- [ ] Inject failure before effect, after effect before response and during recovery; observe authoritative final state, not just retry command success.
- [ ] Exercise duplicate/concurrent submissions, mismatched idempotency payloads and applicable worker restart; assert business invariants.
- [ ] Verify bounded cleanup cannot delete valid output after unknown commit; report unresolved external effects without automatic compensation.

- [ ] Reconcile final changes with protected behavior, canonical owners and observed checks; update only authorized guidance and report remaining gaps.

## Verdict

- `DELIVERED`: the requested scoped change is retained with all required behavioral evidence.
- `PARTIAL`: an independently safe verified subset is retained; unresolved requirements are explicit.
- `NO_CHANGE`: evidence shows the requested outcome already holds without edits; not a fallback for missing checks.
- `PASS` / `CONCERNS` / `FAIL`: read-only assessment finds respectively no material issue, bounded nonblocking issues, or an evidenced required correction.
- `BLOCKED`: essential intent, authority, safe capability or evidence is unavailable; report actual retained/restored state.

## Self-Check

- [ ] **Reconcile before returning.** Check item-level evidence, requirement coverage, contradictions, scope, verdict, and applicable cleanup. Correct the report or authorized artifacts. Reuse valid evidence; do not automatically rescan the repository or rerun successful commands. Repeat checks only for relevant changes, failures, or unresolved evidence. Disclose remaining gaps.

## Output Contract

Report in the user's language, in this order; label all five fields and state each fact once. Use controlled plain language: one fact per sentence, usually under 20 words, active voice, and one term per concept, with no synonyms for verdicts, IDs, or states. Small results may use one line per field; omit empty tables and do not copy linked artifacts:

1. **Result:** The exact skill-specific verdict token first, then the supported outcome.
2. **Scope:** Reviewed/changed scope, exclusions, baseline, and material assumptions.
3. **Evidence:** Skill-specific fields below; distinguish facts, inferences, and unverified claims. Link artifacts; use tables when useful.
4. **Verification:** Checks/results, unavailable evidence, and applicable cleanup/external state.
5. **Completion:** `Checklist: X/Y complete`; `Incomplete: None` or each `UNPROVEN` item's reason, outcome impact, and exact next action; residual risks and required decisions.

**Skill-specific evidence:** Invariant, effect/acknowledgement boundaries, execution model, transaction/idempotency/retry owners, interruption/concurrency evidence, unresolved effects and recovery authority.