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cost-diff

Snapshot delta between two cost-summary JSON outputs. PR-level cost regression detection — answers "what changed between these two specific snapshots?". Pairs with cost-summary's stable JSON contract.

plugins/ruflo-cost-tracker/skills/cost-diff/SKILL.md

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Nov 7, 2026
License
MIT

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PR-level cost regression detection. Where cost-counterfactual compares
to HYPOTHETICAL baselines (always-haiku/sonnet/opus) and cost-burn
compares latest bucket to PRIOR MEAN, cost-diff compares two SPECIFIC
known-good snapshots.

| Question | Skill |
|---|---|
| "What would we have spent at always-X?" | `cost-counterfactual` |
| "Is daily burn accelerating vs prior mean?" | `cost-burn` |
| "Did THIS PR add spend vs main?" | **`cost-diff`** ← this |

## Algorithm

Implementation: [`scripts/diff.mjs`](../../scripts/diff.mjs). Consumes the