feat: add circuit breaker to prevent Stop hook infinite loop

- Track block attempts per session in .attempts file
- After 3 attempts (configurable via REVIEW_MAX_ATTEMPTS), trip breaker
- Circuit breaker allows exit with warning instead of crashing
- Clear attempts on approve or when breaker trips
- Add 3 new tests for circuit breaker behavior (46 total)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

skills/review-gate/scripts/review-gate

@@ -40,24 +40,44 @@ get_state_file() {
     echo "${STATE_DIR}/${session_id}.json"
 }
 
+# Circuit breaker settings
+MAX_BLOCK_ATTEMPTS="${REVIEW_MAX_ATTEMPTS:-3}"
+
 # Commands
 cmd_check() {
     local session_id=$(get_session_id "${1:-}")
     local state_file=$(get_state_file "$session_id")
+    local attempts_file="${STATE_DIR}/${session_id}.attempts"
 
-    # Check for stop_hook_active to prevent infinite loops
-    # Claude Code passes JSON on stdin with this flag when we're in a continuation
+    # Check for stop_hook_active (continuation after previous block)
     local hook_input=""
+    local stop_hook_active="false"
     if [[ ! -t 0 ]]; then
-        # stdin is not a terminal, try to read hook input
         hook_input=$(cat 2>/dev/null || true)
     fi
 
     if [[ -n "$hook_input" ]]; then
-        local stop_hook_active=$(echo "$hook_input" | jq -r '.stop_hook_active // false' 2>/dev/null || echo "false")
+        stop_hook_active=$(echo "$hook_input" | jq -r '.stop_hook_active // false' 2>/dev/null || echo "false")
+    fi
+
+    # Track block attempts for circuit breaker
+    local attempts=0
+    if [[ -f "$attempts_file" ]]; then
+        attempts=$(cat "$attempts_file" 2>/dev/null || echo "0")
+    fi
+
+    # Circuit breaker: if we've hit max attempts, allow exit
     if [[ "$stop_hook_active" == "true" ]]; then
-            # Already in a Stop hook continuation - allow exit to prevent infinite loop
-            echo "Stop hook continuation detected - allowing exit to prevent loop"
+        attempts=$((attempts + 1))
+        echo "$attempts" > "$attempts_file"
+
+        if [[ $attempts -ge $MAX_BLOCK_ATTEMPTS ]]; then
+            # Circuit breaker tripped
+            echo "⚠ CIRCUIT BREAKER: Max block attempts ($MAX_BLOCK_ATTEMPTS) reached"
+            echo "Review was not completed. Allowing exit to prevent infinite loop."
+            echo "Session: $session_id"
+            # Reset attempts for next time
+            rm -f "$attempts_file"
             exit 0
         fi
     fi
@@ -124,6 +144,7 @@ EOF
 cmd_approve() {
     local session_id=$(get_session_id "${1:-}")
     local state_file=$(get_state_file "$session_id")
+    local attempts_file="${STATE_DIR}/${session_id}.attempts"
 
     if [[ ! -f "$state_file" ]]; then
         echo "No review state for session: $session_id"
@@ -140,6 +161,9 @@ cmd_approve() {
 }
 EOF
 
+    # Clear circuit breaker attempts
+    rm -f "$attempts_file"
+
     echo "✓ Review approved for session: $session_id"
 }
 

skills/review-gate/tests/test-review-gate.sh

@@ -290,6 +290,34 @@ output=$(run_gate check reset-session)
 exit_code=$?
 assert_exit_code "Check blocks after re-enable" "2" "$exit_code"
 
+# --- Circuit Breaker ---
+echo ""
+echo "## Circuit Breaker (Prevents Infinite Loop)"
+
+# Enable a review
+run_gate enable test-circuit > /dev/null
+
+# Simulate multiple stop_hook_active=true continuations
+# Default MAX_BLOCK_ATTEMPTS is 3
+echo '{"stop_hook_active": true}' | run_gate check test-circuit > /dev/null 2>&1 || true  # attempt 1
+echo '{"stop_hook_active": true}' | run_gate check test-circuit > /dev/null 2>&1 || true  # attempt 2
+
+# Third attempt should trip circuit breaker
+output=$(echo '{"stop_hook_active": true}' | run_gate check test-circuit 2>&1)
+exit_code=$?
+
+assert_exit_code "Circuit breaker trips after max attempts" "0" "$exit_code"
+assert_output_contains "Circuit breaker message shown" "CIRCUIT BREAKER" "$output"
+
+# Attempts file should be cleaned up
+if [[ ! -f "$TEST_STATE_DIR/test-circuit.attempts" ]]; then
+    echo -e "${GREEN}PASS${NC}: Attempts file cleaned after circuit breaker"
+    ((PASSED++))
+else
+    echo -e "${RED}FAIL${NC}: Attempts file should be cleaned after circuit breaker"
+    ((FAILED++))
+fi
+
 # --- Clean Command ---
 echo ""
 echo "## Clean Command"