Skill: /adversarial-diff-verify [file] [builder claim]

Read what the builder actually did, not what it said it did — a claim and a diff disagreeing is the single most common failure in parallel agent work, and it is invisible unless someone reads both.

Don't: accept a claim because it is detailed and confident; the fabricated ones are the most detailed. Don't read only the diff — a diff shows what moved, not what the file now says, and claims about preservation are only checkable against the whole file. Don't return a verdict per file; return one per assertion, because builders are usually right about most of them and wrong about one.

Inputs

• file — the path the builder edited.
• builder claim — its structured report. Typically JSON with fields like changes[], contentPreserved, buildPassed, plus task-specific assertions.

If either is missing, ask. Do not infer the claim from the diff — that defeats the check.

Steps

1. Read the file IN FULL. Not a grep, not a range. Preservation claims are unfalsifiable without the whole text.
2. Read the whole diff: cd <repo> && git diff -- <file>. If the builder already committed, use git show <sha> -- <file>.
3. Decompose the claim into assertions. Each one gets its own verdict. A typical builder report yields 5–15.
4. Test each assertion against the evidence, in this order of suspicion:
   • Preservation claims ("kept verbatim: …") — check each named item is present and unchanged. This is where claims fail most often.
   • Negative claims ("no new fact, no invented number", "zero figures shipped") — these need a search to confirm, not a reading. Run the grep. A negative asserted without a grep is unverified, not true.
   • Build/test claims (buildPassed: true) — re-run it. Do not take the flag.
   • Change claims ("wrapped in the shell, added X") — confirm the diff actually contains them.
   • Reasoning claims ("every figure type fails its entry requirement") — check the reasoning against the stated rule, not against plausibility.
5. Return a verdict per assertion: confirmed, refuted, or unverifiable — with the evidence line or diff hunk that decided it. When uncertain, refuted, matching the fact-check default.

Output

<file>
  confirmed:    <n>
  refuted:      <n>   ← list each with the contradicting evidence
  unverifiable: <n>   ← list each with what would settle it

Lead with the refuted ones. A clean run reports zero refuted and still lists what was unverifiable — silence on unverifiable assertions reads as confirmation.

Fan-out

One verifier per file, dispatched in parallel, each blind to the others' results. Do not let one agent verify several files — it starts pattern-matching the second file against the first and stops reading.