Claude Code Plugin Hacker

Specialist skill for debugging and fixing Claude Code plugin system issues.

When to Use

• SessionStart:startup hook error or any hook error on launch
• Plugin behavior after enable/disable doesn't match expectations
• Investigating how plugins, hooks, and skills interact
• Fixing broken plugin hooks across projects
• Auditing which plugins inject what into sessions

Critical Knowledge

enabledPlugins: false Is NOT a Kill Switch

Component	When false	When true
hooks	Still execute	Execute
skills	Still accessible via Skill tool	Accessible
CLAUDE.md	Likely not loaded	Loaded
agents	Likely not registered	Registered

To truly stop a hook: edit hooks.json in cache, delete cache dir, or fix the script.

Plugin Cache Is Versioned

~/.claude/plugins/cache/<marketplace>/<plugin>/<hash>/

• <hash> = git commit hash of ~/.claude repo (when it's a git repo)
• New commit → new cache directory → new copy of hooks/skills
• Fixing ONE cached version does NOT fix others
• Always use find ... -exec for bulk fixes

Hook Execution Environment

Claude Code runs hooks in a minimal environment:

• Restricted PATH (may lack timeout, jq, etc.)
• Minimal environment variables (many unset)
• Short timeout on hook execution
• stdin receives JSON with hook context
• stdout must emit valid JSON for context injection
• Non-zero exit code → "hook error" displayed to user

Phase 1: Audit

Enumerate ALL hook sources. Run these diagnostics:

# 1. List ALL plugin hooks.json files
find ~/.claude/plugins/cache -name "hooks.json" -path "*/hooks/*" \
  -exec echo "=== {} ===" \; -exec cat {} \;

# 2. Find ALL SessionStart hooks specifically
find ~/.claude/plugins/cache -name "hooks.json" -path "*/hooks/*" \
  -exec grep -l "SessionStart" {} \;

# 3. User-defined hooks in settings.json
grep -A5 '"SessionStart"' ~/.claude/settings.json

# 4. List enabled plugins
grep -A1 'enabledPlugins' ~/.claude/settings.json | head -30

# 5. Count cached versions per plugin
for d in ~/.claude/plugins/cache/*/*/; do
  plugin=$(echo "$d" | rev | cut -d/ -f3-2 | rev)
  echo "$plugin: $(ls -d ${d}*/ 2>/dev/null | wc -l) versions"
done

Output: Complete map of hooks × plugins × versions.

Phase 2: Diagnose

Test each suspicious hook in isolation:

# Test a hook script directly
echo '{"source":"startup","session_id":"diag-test"}' | \
  CLAUDE_PLUGIN_ROOT="<plugin_root>" \
  <hook_command> 2>&1
echo "EXIT: $?"

Known Failure Patterns

Pattern	Signature	Root Cause	Fix
Permission denied	EACCES, exit 126/127	.sh script missing +x	chmod +x all copies
Unset variable	exit 1 with no output	set -u in bash script	Remove -u from set
Node module mismatch	NODE_MODULE_VERSION N vs M	Native addon for wrong Node.js	npm rebuild <module>
Database locked	SqliteError: database is locked	Concurrent DB access	Retry logic or skip
Command not found	timeout: not found	Minimal PATH	Use builtins or full paths
JSON parse error	SyntaxError: Unexpected token	Hook outputs non-JSON to stdout	Fix script output

Permission Check (bulk)

# Find ALL hook scripts without execute permission
find ~/.claude/plugins/cache -name "*.sh" ! -perm -u+x \
  -exec echo "BROKEN: {}" \;

Bash Safety Check

# Find dangerous set -u in hook scripts
grep -rn "set.*-u" ~/.claude/plugins/cache/*/hooks/ \
  ~/.claude/plugins/cache/*/*/hooks/ 2>/dev/null

Node.js Native Addon Check

# Find better-sqlite3 or other native addons
find ~/.claude/plugins/cache -name "*.node" -exec sh -c \
  'echo "=== $1 ==="; file "$1"' _ {} \;

Phase 3: Fix

Fix 1: Bulk chmod (permission denied)

find ~/.claude/plugins/cache/<plugin> -name "<script>.sh" \
  ! -perm -u+x -exec chmod +x {} \; -exec echo "FIXED: {}" \;

Fix 2: Remove set -u (unset variable errors)

find ~/.claude/plugins/cache/<plugin> -name "<script>" \
  -exec sed -i '' 's/set -euo pipefail/set -eo pipefail 2>\/dev\/null || true/' {} \; \
  -exec echo "FIXED: {}" \;

Fix 3: Rebuild native addons

cd ~/.claude/plugins/cache/<plugin>/<version>
npm rebuild <module-name>

Fix 4: Remove problematic hook entirely

Edit hooks.json to empty the event:

{ "hooks": { "SessionStart": [] } }

Apply to ALL cached versions with find ... -exec.

Fix 5: Nuclear option — delete plugin cache

rm -rf ~/.claude/plugins/cache/<marketplace>/<plugin>/

Plugin will be re-cached on next session start.

Phase 4: Verify

# Re-test all hooks after fixes
find ~/.claude/plugins/cache -name "hooks.json" -path "*/hooks/*" \
  -exec grep -l "SessionStart" {} \; | while read f; do
    dir=$(dirname "$f")
    root=$(dirname "$dir")
    echo "=== Testing: $root ==="
    # Extract command from hooks.json and test it
    cmd=$(python3 -c "
import json, sys
h=json.load(open('$f'))
for entry in h.get('hooks',{}).get('SessionStart',[]):
  for hook in entry.get('hooks',[]):
    print(hook['command'].replace('\${CLAUDE_PLUGIN_ROOT}','$root'))
" 2>/dev/null)
    if [ -n "$cmd" ]; then
      echo '{"source":"startup"}' | CLAUDE_PLUGIN_ROOT="$root" eval "$cmd" >/dev/null 2>&1
      echo "EXIT: $?"
    fi
  done

Decision Tree

Hook error on startup?
├─ Run Phase 1 Audit
│  └─ Which plugins have SessionStart hooks?
│     ├─ Test each hook (Phase 2)
│     │  ├─ Permission denied → Fix 1 (chmod, ALL copies)
│     │  ├─ Exit 1, no output → Fix 2 (remove set -u)
│     │  ├─ NODE_MODULE_VERSION → Fix 3 (npm rebuild)
│     │  ├─ All pass locally but still errors →
│     │  │  Check if there are MORE cached versions
│     │  │  you didn't fix (Phase 1, count versions)
│     │  └─ Unknown error → Fix 4 (remove hook) or Fix 5 (nuke cache)
│     └─ Verify all hooks pass (Phase 4)
│
Plugin behavior unexpected after disable?
├─ Remember: `false` doesn't stop hooks/skills
├─ To stop hooks: edit hooks.json or delete cache
└─ To stop skills: delete cache (no other way)

Anti-Patterns

Don't	Why	Do Instead
Set enabledPlugins: false to stop hooks	Doesn't work — hooks still run	Edit hooks.json or delete cache
Fix one cached version	Other versions still broken	Use find -exec for ALL versions
Add set -euo pipefail to hook scripts	-u kills script in minimal runtime	Use set -e or set -eo pipefail
Test hooks only from your shell	Your shell has richer env than CC runtime	Test with minimal PATH and env
Assume manual test = CC runtime	CC may pipe stdin differently, set timeout	Always verify with actual CC launch