competition-race-condition-state-drift

Competition Race Condition State Drift

Use this skill only as a downstream specialization after $ctf-sandbox-orchestrator is already active and has established sandbox assumptions, node ownership, and evidence priorities. If that has not happened yet, return to $ctf-sandbox-orchestrator first.

Use this skill when the decisive behavior depends on request timing, async ordering, lock gaps, or stale state.

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Quick Start

1. Identify mutable state first: rows, cache keys, queue payloads, session fields, counters, or files.
2. Reproduce with smallest concurrent sequence and fixed timing assumptions.
3. Capture one baseline run and one racing run with only one variable changed.
4. Track read, check, write, enqueue, and commit boundaries separately.
5. Prove final state drift from a clean reset.

Workflow

1. Map Mutable Boundaries

• Record transaction scope, lock behavior, retry logic, idempotency keys, cache invalidation, and queue handoff.
• Note where read-check-write is split across requests, workers, or services.
• Keep each boundary tied to exact timestamps or sequence numbers.

2. Reproduce Timing Window

• Build deterministic concurrent inputs with controlled delay, duplicate requests, or reordered worker execution.
• Compare accepted and rejected paths under identical payloads.
• Record which condition flips when ordering changes.

3. Reduce To Decisive Race Chain

• Compress to: request A and B ordering -> stale check or lock gap -> conflicting writes -> resulting capability or artifact.
• State whether root cause is missing lock, weak idempotency, stale cache read, delayed async commit, or retry side effect.
• If the path becomes queue-dominant, hand off to queue worker drift skill.

Read This Reference

• Load references/race-condition-state-drift.md for race harness ideas, evidence blocks, and parity checks.

What To Preserve

• Mutable keys, transaction boundaries, lock behavior, and idempotency markers
• Timestamped or sequenced traces for baseline and race runs
• One minimal replayable concurrent sequence proving drift