SDLC Agent-Skill Wiki

Pattern: Idempotent operations

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Design commands, lifecycle steps, and processing loops to converge to the same end state regardless of partial prior runs. Re-running is always safe; a crash, a restart, or a retry mid-way leaves no half-state the next run has to reason about.

This is classic operational engineering, but it acquires a specific edge in agent work, which is why it earns a pattern page here rather than staying an implementation detail. Agent runs are interrupted far more often than human ones — context compaction, a session ending, a killed subagent, a cloud worker dropping out, an operator pressing stop. Every long-horizon capability in this wiki therefore depends on its steps being re-enterable, and the frameworks that run unattended lean on it hardest. It is the precondition that makes pattern-autonomous-loop and pattern-session-handoff safe: a resumed session can re-run the last step rather than having to determine exactly how far the dead one got.

Its most visible expression is a setup or configuration command that overwrites its whole output rather than patching it, so a second run cannot accumulate drift from the first.

pstack:

  • pstack-principle-make-operations-idempotent — the principle statement, scoped to commands, lifecycle steps, and loops that run amid crashes and retries.
  • pstack-setup-pstack — overwrites the whole model-role rule file on every run so re-runs stay idempotent.
  • pstack-benny-setup — a re-runnable install that preserves destination-only files and reviews conflicts instead of overwriting local edits.

Tessl:

  • tessl-environment — an update replaces an environment’s values rather than merging them, so a re-run converges on exactly the supplied set. Safety over convenience, and the right default for a secret store.
  • tessl-schedule — recurring unattended runs, which only make sense if each run is safe to repeat.

builder-skills:

  • builder-factory-recover — the resumption side. Recheck external state before retrying an uncertain action, and “do not repeat completed writes, replies, approvals, merges, or deployments.”

Matt Pocock — Skills for Real Engineers:

  • mp-wizard — generated wizards upsert values into .env files idempotently and write gh secret/gh variable with graceful degradation, so a re-run is safe (v1.2.0).

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