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ScinoScino/fstack/skills/principle-make-operations-idempotent/SKILL.md

principle-make-operations-idempotent

Skill18 starsChanged 54 days agoMITView on GitHub

Apply when designing commands, lifecycle steps, or processing loops that run amid crashes, restarts, and retries. Converge to the same end state regardless of partial prior runs.

47 other projects use a version of this, 44 of them edited.

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Projects with it also use principle-explain-the-number, setup-pstack and 10 more.

Other files people use alongside this one.

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The file

We split this skill into the rules it gives an agent

1 rule. 1 is common, 0 are distinctive, and 0 are very specific to this project.

  • 1

    Common

    Most of the 47 edited versions we read keep these.

  • 0

    Distinctive

    This author's own choices. Worth a look.

  • 0

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Common:

    If any answer is "it depends on what state was left behind," the operation needs a reconciliation step.

    line 25

“Common” is measured: kept by at least 6 in 10 of the 47 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Make Operations Idempotent

Design operations so they converge to the correct state regardless of how many times they run or where they start from. Every state-mutating operation should answer: "What happens if this runs twice? What happens if the previous run crashed halfway?"

Why: Commands, lifecycle operations, and processing loops run where crashes, restarts, and retries are normal. If partial state changes the next run's outcome, every restart becomes a debugging session.

The pattern:

  • Convergent startup: scan for existing state, clean stale artifacts, adopt live sessions
  • Content-based cleanup: compare by content equivalence, not creation order
  • Self-healing locks: use PID-based stale lock detection
  • Idempotent scheduling: failed work respawns cleanly, fresh input regenerated after each cycle

The test:

  1. What happens if this runs twice in a row?
  2. What happens if the previous run crashed at every possible point?
  3. Does re-execution converge to the same end state?

If any answer is "it depends on what state was left behind," the operation needs a reconciliation step.

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