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

skills/run/SKILL.md

@@ -477,6 +477,32 @@ Spawn all applicable reviewers in parallel (multiple Agent calls in one message)
 
 After each returns, emit `review.verdict` and save artifact.
 
+#### 3c-ii. Evidence Validation
+
+After all reviewers complete, scan their outputs for banned phrases in CRITICAL/WARNING findings. Downgrade unsupported findings before proceeding to Act.
+
+```bash
+BANNED_PHRASES=("might be" "could potentially" "appears to" "seems like" "may not")
+
+for artifact in .archeflow/artifacts/${RUN_ID}/check-*.md; do
+  REVIEWER=$(basename "$artifact" .md | sed 's/check-//')
+  while IFS= read -r line; do
+    SEVERITY=$(echo "$line" | grep -oE '(CRITICAL|WARNING)' | head -1)
+    [[ -z "$SEVERITY" ]] && continue
+    for phrase in "${BANNED_PHRASES[@]}"; do
+      if echo "$line" | grep -qi "$phrase"; then
+        echo "EVIDENCE DOWNGRADE: $REVIEWER finding uses '$phrase' — downgrading to INFO"
+        ./lib/archeflow-event.sh "$RUN_ID" decision check "" \
+          '{"what":"evidence_downgrade","from":"'"$SEVERITY"'","to":"INFO","reviewer":"'"$REVIEWER"'","reason":"banned phrase: '"$phrase"'"}'
+        # Replace severity in artifact
+        sed -i "s/$line/$(echo "$line" | sed "s/$SEVERITY/INFO/")/" "$artifact"
+        break
+      fi
+    done
+  done < "$artifact"
+done
+```
+
 #### 3d. Phase Transition: Check to Act
 
 Collect all verdict seq numbers for the parent array.