Anti Hallucination Gates

Anti-Hallucination Gates

The most common agent failure is declaring victory too early. This skill is the gate between "I think it works" and "evidence proves it works".

The Iron Rule

No claim of "done" / "fixed" / "passing" without a concrete artifact path proving it.

A claim like "I fixed the bug" is incomplete. The proper form:

"Fixed by commit abc123. Test tests/foo.test.ts::handles-edge-case now passes (output captured in .harness-anchor/test-2026-05-28.log). Build still passes (.build/last-build.log exit 0)."

The Iron Rule runs both ways

The rule above governs claims that something IS. Claims that something IS NOT are the same failure with the sign flipped, and until v0.17.0 this skill said nothing about them.

No claim that something is absent without stating the scope you actually searched and when you looked.

"clang-tidy isn't installed on this machine" is incomplete in exactly the way "I fixed the bug" is incomplete. The proper form:

"searched PATH + the VS-bundled LLVM and CMake directories, not found (as of 2026-07-29)"

Two classes, two probes

An empty result proves only that your search found nothing. That is a different proposition from the thing is absent, and conflating the two is what this section exists to stop.

The "there is no" detector

The mirror of the "should" detector further down. When you are about to type not installed, doesn't exist, isn't supported, couldn't find, there is no — stop. Either:

• Widen the search, then state the coverage you reached. Capability → run the discovery chain, not just command -v / where. Search → loosen the glob, drop case sensitivity, include ignored files.
• Or scope-and-date the claim in the mandated form above.

Out of scope, deliberately: judgement-shaped negatives

"This is impossible", "that approach won't work", "the library can't do this" are NOT covered here. They carry no executable evidence path, and pulling them in would turn a verifiable contract into unverifiable moralising — softening the very invariant this skill holds (CLAUDE.md #8). State them as the judgements they are, with reasoning. Do not dress them up as findings.

Residual blind spot — read this before trusting the section above

This contract binds only when this skill is loaded, and it loads from its description. A negative assertion made in a turn where the description didn't match is entirely unguarded: no hook, no probe, no test stands behind it. Coverage is strictly narrower than the failure. A session that never triggered this skill is not a session in which negative claims were checked.

The second line of defence is init-verification, which re-checks negative capability conclusions already written into AGENTS.md at the start of the next session. It catches what this section missed — one session late, which is not never, but is also not here.

Default-FAIL Evaluation Contract

Adapted from Anthropic's Code with Claude 2026 reference impl:

"Every criterion starts false; the agent can't mark it passing without opening evidence first."

Standard criteria (adapt to project)

Filling out evidence in feature_list.json

{
  "id": "doc-list-rendering",
  "status": "pass",
  "evidence": {
    "timestamp": "2026-05-28T13:45:21Z",
    "commit": "abc123def456",
    "artifacts": [
      ".harness-anchor/build-2026-05-28T13-44.log",
      ".harness-anchor/test-2026-05-28T13-45.txt"
    ],
    "notes": "All 47 tests pass. Build clean. clang-tidy: 0 warnings on changed files."
  },
  "completedAt": "2026-05-28T13:45:21Z"
}

evidence: null ⇒ status cannot be "pass". This is enforced by feature_list.schema.json.

Calibrated Uncertainty (2026 consensus)

When evidence is missing or partial, do NOT bluff. The 2026 LLM-hallucination research consensus is:

"Aim for calibrated uncertainty: systems that transparently signal doubt and can safely refuse to answer when unsure."

Templates for expressing uncertainty:

• "I am uncertain whether the test passes because I didn't run it. Recommend npm test -- --testPathPattern foo to verify."
• "The build appears to succeed based on no error in the output, but I did not see an explicit success line. Recommend cmake --build .build && echo BUILD_OK."
• "This fix may resolve the issue, but I have not reproduced the original failure. To gain confidence, run ./repro.sh before and after the change."

These statements earn user trust. Confident-but-wrong claims destroy it.

Anti-patterns

Do NOT say:

• "Should work now."
• "The build should pass."
• "Tests should be green."
• "This looks correct."
• "These are old / unrelated changes." (said about uncommitted files without running git diff to confirm — verify before you dismiss; this is how a pass's own source gets left behind)
• "clang-tidy isn't installed on this machine." / "There's no such function." (a negative claim with no search scope and no date)

Say instead:

• "Build passes (evidence: ) / Build pending verification (recommend: )"
• The test status alongside a captured artifact path.
• "searched PATH + , not found (as of )"

The "should" detector

When you find yourself typing "should", "probably", "I think", or "looks like" about a behavioural claim, pause. Either:

• Run the command to verify, then state the observed result, OR
• Explicitly mark the claim as unverified per the templates above.

Pre-claim checklist

Before saying ANY of {"done", "fixed", "ready", "complete", "passing", "working"}:

- [ ] I ran the build/compile, observed exit code 0
- [ ] I ran the test suite, observed N passed / 0 failed
- [ ] the passing tests exercise the spec's edge cases / risk paths — not just the happy path (run `/test-plan` if unsure)
- [ ] if tests changed alongside source: I explained each test change (new coverage vs adjusted expectation)
- [ ] I have a file path for each piece of evidence
- [ ] if I claimed something is **absent** (not installed, no such function, nothing found): I stated the scope I searched and the date — `searched <scope>, not found (as of <date>)`
- [ ] feature_list.json is updated with evidence object + timestamp + commit
- [ ] if I claimed "committed / shipped / delivered": I reviewed the **full** `git status` and confirmed the committed HEAD builds (not just the working tree)

If any box is unchecked: state uncertainty explicitly, do NOT flip status to pass.

When to invoke

• The user asks "is it done?"
• You're about to update feature_list.json status to "pass"
• You're about to say "the fix should work"
• You're about to say a tool/function/file/test doesn't exist or isn't available
• The PostToolUse hook injected warnings — do NOT silently ignore them; surface and address per self-correction-loop

Looking up evidence commands for unfamiliar frameworks

When the project uses a test/lint framework you don't have committed to memory (Catch2, doctest, ruff, deno test, etc.) — invoke the docs-lookup skill before constructing the verification command. The lookup result becomes part of the evidence trail.

Bluffing the command and not actually running it is the anti-pattern this skill exists to prevent — that's why lookup precedes execution here.

Related

• verification-before-completion (superpowers) — the same Iron Law (no completion claim without fresh evidence). This skill is its harness-anchor counterpart and superset: it adds the on-disk evidence record (feature_list.json) and the /verify subagent. One verification run satisfies both gates — capture the evidence once, don't re-verify.
• feature-state-keeper — actual writes to feature_list.json
• test-coverage-design / /test-plan — derive the coverage obligations this gate checks (are the right things tested, and actually run?)
• self-correction-loop — what to do when evidence shows failure
• /verify command — full automated verification pass via verification-runner subagent