feat: add evidence-gated verification to check phase and reviewers

skills/check-phase/SKILL.md

@@ -179,6 +179,51 @@ When the Act phase routes findings back to the Maker and the Maker applies fixes
 
 ---
 
+## Evidence Requirements
+
+Every CRITICAL or WARNING finding must include concrete evidence. Findings without evidence are downgraded to INFO.
+
+### Evidence Types
+
+| Type | Example | When Required |
+|------|---------|---------------|
+| Command output | `npm test` output showing failure | Test-related findings |
+| Exit code | `exit code 1 from eslint` | Tool-based validation |
+| Code citation | `src/auth.ts:48 — \`if (token) { ... }\`` | Logic or security findings |
+| Git diff | `+  db.query(userInput)` (unsanitized) | Implementation review |
+| Reproduction steps | "1. Send POST with empty body, 2. Observe 500" | Runtime behavior findings |
+
+### Banned Phrases
+
+The following phrases are not permitted in CRITICAL or WARNING findings. They indicate speculation, not evidence:
+
+- "might be"
+- "could potentially"
+- "appears to"
+- "seems like"
+- "may not"
+
+A finding using these phrases must either be rewritten with evidence or downgraded to INFO.
+
+### Verification Protocol
+
+For each CRITICAL or WARNING finding, state:
+
+1. **What was tested** — the specific code path, input, or scenario examined
+2. **What was observed** — the actual behavior or code construct found
+3. **What correct behavior should be** — the expected alternative
+
+### Downgrade Rule
+
+If a reviewer produces a CRITICAL or WARNING finding without any of the evidence types above, the orchestrator downgrades it to INFO and emits a `decision` event:
+
+```bash
+./lib/archeflow-event.sh "$RUN_ID" decision check "" \
+  '{"what":"evidence_downgrade","from":"CRITICAL","to":"INFO","finding":"<description>","reviewer":"<archetype>","reason":"no evidence provided"}'
+```
+
+---
+
 ## Why Structured Findings Matter
 
 The standardized format enables: