Diagnose Benchmark Failure

Why this skill exists

When a benchmark fails, the natural reflex is to edit the SKILL.md and re-run. That is guessing. The run artifacts (judge-evidence.md, sandbox SKILL.md, the scenario mod.ts) contain the actual chain of cause and effect: what the agent saw, what it emitted, what the judge measured. This skill enforces an evidence-first diagnosis so each iteration moves on facts, not hopes.

Rules

Inputs

• A scenario ID (e.g. plan-interactive). Inferred from the user prompt or from the most recent failure in the bench output.

Step-by-step

<step_by_step>

1. Locate the run dir

   • Default path: acceptance-tests/runs/latest/<scenario-id>/run-1/.
   • If latest is missing, list acceptance-tests/runs/ and pick the most recently modified directory containing <scenario-id>.
   • Required files inside: judge-evidence.md, sandbox/. If either is missing → fail closed (rule 4).

2. Read judge-evidence.md end to end

   • Identify the three sections: <user_query>, <agent_logs>, <file_diffs>.
   • From <agent_logs>, extract the last assistant turn that the user would have seen. This is the agent's actual emitted output.
   • From <user_query>, copy the verbatim query the agent received.
   • Note any tool calls the agent made (## Tool: <name>) — especially Skill, Read, Bash, TodoWrite. The presence/absence of specific tool calls is itself evidence.

3. Read the scenario mod.ts

   • Path: framework/<pack>/{skills,commands,agents}/<primitive>/benchmarks/<scenario>/mod.ts. Find via find framework -path "*/benchmarks/<scenario>/mod.ts".
   • Extract: userQuery, userPersona, checklist[] (with id, description, critical).
   • Also extract: interactive, any setup() body, agentsTemplateVars.

4. Read the sandbox SKILL.md — BOTH copies, side by side

   There are two different SKILL.md files for the same primitive, in two different locations. You MUST read both and compare them. Confusing them leads to the wrong classification.

   • (a) The failing-agent's view (inside the run dir): <run-dir>/sandbox/.claude/skills/<primitive>/SKILL.md (Cursor sandbox uses .cursor/skills/; OpenCode uses .opencode/skills/.) This is the static snapshot the failing agent read. Read this first.

   • (b) The current framework source: framework/<pack>/{skills,commands}/<primitive>/SKILL.md This is the live source on disk now — it may differ from (a).

   Do NOT read .claude/skills/<primitive>/SKILL.md at the project root and call that "the sandbox copy" — it is the current source, identical (or nearly so) to (b), and tells you nothing about what the failing agent saw.

   After reading both, diff (a) vs (b):

   • Identical → the failure cannot be a stale-skill issue; eliminate STALE-SKILL-IN-SANDBOX from candidates.
   • Significantly different → potential STALE-SKILL-IN-SANDBOX; verify by correlating the diff with the failure mode.

   The classification depends on what (a) said vs. what the agent actually emitted in <agent_logs> — not on what (b) currently says.

5. Re-derive the verdict

   • The judge verdict (which checklist items failed and why) is in the bench stdout, not in judge-evidence.md. If you don't have it, re-run the scenario with --no-cache and capture stdout. Otherwise, check each checklist[].description against the agent's last turn from step 2 and judge yourself before continuing — this catches LLM-judge calibration drift.

6. Match symptoms to the failure-mode taxonomy (next section). Pick the most likely mode based on the quoted evidence. If two modes fit equally, list both; do not collapse them.

7. Write the diagnostic report (template below). Every claim cites a quoted line from step 2/3/4.

</step_by_step>

Failure-mode taxonomy

A symptom-to-cause map. Use the symptom column to match what you observed in judge-evidence.md; the cause column gives the most likely root cause; the fix-direction column points the next iteration at a real lever, not a guess. Do not invent new modes unless the evidence rules out every one listed.

• MD-PRIOR-BULLETS (markdown-prior-wins-over-instruction)

  • Symptom: SKILL.md says options must be numbered (1., 2., …); agent emits bulleted dashes (- **X** —) for option lists with rich descriptions.
  • Cause: model's training prior on bulleted-options-with-descriptions overrides plain-prose MUST instructions in SKILL.md context.
  • Fix-direction: scope the SRS clause down to what is enforceable through SKILL.md alone, OR add a runtime mechanism (helper script the agent invokes, post-process hook). Adding more imperative prose has been empirically rejected for this mode.

• HEADING-INSTEAD-OF-ITEM

  • Symptom: SKILL.md says the question must be a numbered list item; agent emits ### Variant A, ### Variant B, or **1. Title** (bold heading).
  • Cause: instruction was read but not internalised at format time; agent reverts to its default for "labelled chunks of related content".
  • Fix-direction: add an explicit anti-pattern example in SKILL.md showing ### Variant A is wrong; demonstrate the correct shape with the EXACT surface form expected.

• STALE-SKILL-IN-SANDBOX

  • Symptom: agent's behaviour matches an older version of SKILL.md; the sandbox copy diffs against the source.
  • Cause: bench cache hit on a scenario whose primitive was edited after the cached run. Or --no-cache was forgotten on a quick re-run.
  • Fix-direction: re-run with --no-cache. If the issue persists, check scripts/acceptance-tests/lib/cache.ts cache-key inputs vs. what changed.

• SKILL-NOT-MOUNTED

  • Symptom: Agent finished with exit code 0 but 0 agent steps, or judge reports "Unknown skill" / agent never invokes the skill.
  • Cause: bench infrastructure didn't copy the primitive into the sandbox .claude/skills/<name>/ (most common: missing pack in Copying packs line; check scenario.skill matches an existing primitive).
  • Fix-direction: fix the bench runner / scenario skill: field, NOT the SKILL.md.

• COMPOSITE-DELEGATION-BYPASS

  • Symptom: composite skill (e.g. review-and-commit) was invoked, but <agent_logs> shows an early ## Tool: Skill { skill: "<source-skill>" } re-entering one of the inlined sources, bypassing the composite's gate.
  • Cause: the composite's frontmatter description names the source skills, or the body lacks a "no-delegation" rule. See framework CLAUDE.md "Composite Skill Authoring".
  • Fix-direction: rename the description (no source-skill names), add the no-delegation rule, harden the verdict gate.

• PERSONA-MISMATCH

  • Symptom: agent asks one question; the simulated user persona answers something the agent did not ask. The trace shows [USER INPUT] <reply> that doesn't fit.
  • Cause: persona scripted for an older skill version, or for a different question structure.
  • Fix-direction: align the persona with the current SKILL.md flow — but ONLY after confirming the skill itself is correct. Persona changes that smuggle in the right answer ("test-fitting") are forbidden.

• TEST-FITTING-PERSONA

  • Symptom: persona contains the literal target output (e.g. dictates the exact format). The benchmark passes only because the persona scripts the answer.
  • Cause: scenario author worked backwards from a green run.
  • Fix-direction: rewrite the persona to be neutral. The scenario's benchmark value is now suspect — review the checklist items too.

• CROSS-PACK-REFERENCE-MISSING

  • Symptom: SKILL.md text references another skill by name, but that skill is not in the sandbox. Agent reads the reference, can't act on it.
  • Cause: the source skill is in a different pack and the scenario doesn't copy that pack (look at the Copying packs: line in bench stdout).
  • Fix-direction: drop the cross-pack reference, OR add the pack to the scenario's copied packs (rare; usually drop the reference).

Output template

Produce exactly this structure. Every bullet ends with a (<file>:<line-range>) citation.

# Diagnostic Report: <scenario-id>

## Run inspected
- Run dir: <path>
- Verdict line: "<paste>"
- Failed checklist items (id + critical?): <list>

## Evidence collected (paths)
- judge-evidence.md — <bytes>, <line count>
- sandbox SKILL.md — <path>, <bytes>
- scenario mod.ts — <path>

## Agent's last assistant turn (verbatim, ≤30 lines)

What the SKILL.md actually said about this point (verbatim, ≤15 lines)

<paste>

(:-)

Diff sandbox SKILL.md vs source SKILL.md

• <"identical" or summary of significant diffs with line refs>

Failure-mode classification

• Primary:
• Why this code:
• Alternatives ruled out: <code(s) considered + the evidence that rules them out>

Proposed next iteration

• <one-sentence fix-direction action, drawn from the taxonomy fix-direction column>
• Files to edit:
• Anti-actions (do NOT try): <bullets, each with the prior failure that disqualified it if applicable>

Confidence

• <High|Medium|Low> —