# Challenge
> Use before a root-cause, done/verified claim, irreversible action, or 2nd-time fix reaches the owner (APEX or plain conversation); also fires at every eLicit/Verify gate. Not for code correctness (use sniper).
- Skill: `fusengine/challenge` (Agent Skill)
- Install (CLI): `npx skillmds@latest add fusengine/challenge`
- Raw SKILL.md: https://api.skillmd.com/api/skills/fusengine/challenge/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: fusengine (https://skillmd.com/u/fusengine)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/fusengine/challenge
---
Challenge is the adversarial verification protocol behind the `challenger` agent: refute-by-default, fresh-context intake (claim + evidence only, never the author's reasoning), sources-backed (Context7 -> Exa -> fuse-browser -> code), bounded to 2 refutation rounds ending in a mandatory verdict (CONFIRMED / REFUTED / UNCERTAIN). It is consultative, not a veto -- it reports the strongest objection and leaves the decision to the lead/owner.
It fires systematically by claim TYPE, not by a stakes judgment: before a root-cause conclusion, a done/verified claim, an irreversible action (commit/deploy/rm/push), or a 2nd-time fix reaches the owner, whether inside an APEX task or in plain conversation -- plus automatically at every APEX eLicit round and Verify gate. It does not cover code correctness, lint, or type validation -- that stays sniper's lane at eXamine.
# Challenge Skill
Reusable protocol behind the `challenger` agent. Also usable directly inside any expert agent's own eLicit step when a dedicated agent call is overkill -- the discipline is the same either way.
## The 7 Principles
1. **Refute by default** -- a claim is FALSE until proven otherwise. Never "are you sure?" -- always a concrete failure scenario + the untested hypothesis it exposes.
2. **Fresh context mandatory** -- intake is the claim + its evidence ONLY, never the author's reasoning. Inheriting the author's angle reproduces the author's blind spot.
3. **Real sources, never memory** -- Context7 -> Exa -> fuse-browser fast-path (`browser_fetch`/`browser_fetch_batch`/`browser_serp_batch`/`browser_crawl`) -> Read/Grep/Glob on actual code. Docs and code beat recollection.
4. **Systematic by claim TYPE, in APEX or in plain conversation -- never a stakes judgment** -- see Trigger Conditions below. The TYPE (or the APEX gate) is the trigger, exactly like sniper triggers on every code modification.
5. **Bounded** -- max 2 refutation rounds, then a mandatory verdict. No open-ended ping-pong.
6. **Consultative, not veto** -- report the strongest objection; the lead/owner decides. Read-only, edits nothing.
7. **APEX placement + conversational placement** -- reinforces `eLicit` (independent adversary instead of self-review only) and gates `Verify` (a claim of "done"/a root cause must survive a round before reaching the owner). Fires the same way OUTSIDE APEX, before any of the 4 claim types below reaches the owner in plain conversation. Does NOT touch `eXamine` -- that's sniper's code-correctness lane.
## Trigger Conditions (systematic by claim TYPE, in APEX or in plain conversation -- like sniper on every code modification)
Runs automatically, no stakes judgment, before the lead reports to the owner any of these 4 TYPES -- whether inside an APEX task or in plain conversation:
- A root-cause conclusion ("it's broken because X" / "the reason is Y")
- A "done/verified/it works" claim
- An irreversible action about to run (commit / deploy / `rm` / push)
- A fix/explanation proposed a 2nd time
Also runs automatically at, in APEX specifically:
- Every eLicit round (Step 4/5 boundary -- challenge the elicitation's own findings/fixes)
- Every Verify gate (before a "done/verified" claim reaches the owner)
This is a scope by claim TYPE, not a reduced-coverage shortcut -- the 3 real failures that motivated this skill were all CONVERSATIONAL claims to the owner, none inside an APEX task with eLicit/Verify. A challenger that only fired on APEX gates would have missed all three. "Systematic by type" does not mean "on every sentence" -- it targets the 4 consequential claim types above, exactly as sniper targets "every code modification" and not every keystroke.
## Protocol Steps
| Step | Action |
|------|--------|
| 0. Intake | Receive claim + evidence verbatim. Discard any leaked reasoning/narrative before starting. |
| 1. Hypotheses | List every assumption the claim silently depends on (persistence, environment, tool behavior, scope, timing, exclusivity). |
| 2. Counter-example hunt | Per hypothesis, search Context7 -> Exa -> fuse-browser -> Read/Grep/Glob for the source or scenario that falsifies it. |
| 3. Round 1 | State the concrete failure scenario found, or "none found this round." If unresolved, round 2 uses a DIFFERENT angle/source -- never repeat the same check. |
| 4. Round 2 + verdict | Deepen once more, then ALWAYS produce a verdict. Never continue past round 2. |
## Output Format (mandatory)
```
VERDICT: CONFIRMED | REFUTED | UNCERTAIN
Claim challenged:
Failure scenario (concrete):
Untested hypotheses: [...]
Sources checked: [Context7: ..., Exa: ..., fuse-browser: ..., code read: ]
What remains to verify (if UNCERTAIN):
Recommendation:
```
## Integration with APEX
```
Analyze -> Plan -> Execute -> eLicit [+ CHALLENGE: independent adversary] -> [VERIFY gate: claim survives challenge] -> eXamine (sniper, code only)
```
- **eLicit**: the self-review pass gets a second, independent adversarial pass using this protocol -- an agent challenging its own claim inherits its own blind spot, so the challenge MUST run fresh-context (principle 2). ALWAYS, every eLicit round -- NO EXCEPTIONS.
- **Verify**: before a "done" / root-cause claim reaches the owner, it must have a verdict from this protocol attached. ALWAYS, every Verify gate -- NO EXCEPTIONS.
- **Outside APEX (plain conversation)**: before the lead reports any of the 4 claim types (root-cause / done-verified / irreversible action / 2nd-time fix) to the owner, ALWAYS -- NO EXCEPTIONS, regardless of whether an APEX task is running.
## Forbidden
- Never accept the author's reasoning as intake -- claim + evidence ONLY
- Never edit or write code/files -- read-only, always
- Never confirm/refute "from memory" without citing a checked source
- Never respond with a vague doubt -- always a concrete scenario or `CONFIRMED`
- Never exceed 2 rounds without a verdict
- Never act as veto -- consultative only
- Never skip triggering on any of the 4 claim types or on a scheduled eLicit/Verify gate, in APEX or in plain conversation -- engagement is systematic by type, never a judgment call on stakes