Preflight Checklist

• I have searched existing issues and this hasn't been reported yet
• This is a single bug report (please file separate reports for different bugs)
• I am using the latest version of Claude Code

What's Wrong?

[Bug] v2.1.142 VSCode extension: PostToolUse Bash hook does NOT fire for LLM-initiated Bash tool calls (stream-json mode)

Environment

• Claude Code VSCode extension: 2.1.142-darwin-arm64 (upgraded from 2.1.141)
• VSCode: 1.120.0 (Electron 39.8.8)
• macOS: Darwin 25.2.0 (Sequoia 14.6+)
• Hardware: Mac Mini ARM (Apple Silicon M-series)
• Mode: stream-json (VSCode native integration default — --output-format stream-json --input-format stream-json --include-partial-messages --debug --debug-to-stderr)
• Permission mode: default

Summary

PostToolUse hook with matcher: "Bash" configured in .claude/settings.json does NOT fire when the LLM (assistant) uses the Bash tool to execute commands. This affects ALL LLM-initiated Bash tool calls, including git commit, ls, cat, grep, etc.

SessionStart and SessionEnd hooks fire correctly. Only PostToolUse specifically does not fire for LLM-initiated tool calls.

Symptoms

• LLM runs git commit --allow-empty -m "..." via Bash tool → commit succeeds in git history → PostToolUse hook never invoked
• Hook command (notify-telegram.sh, /tmp/minimal-hook.sh, anything) never executes
• No error in VSCode Output panel "Claude Code" channel
• Manual invocation of hook script works perfectly (script logic is fine)

100% Reproducer (Minimal)

Step 1: Create minimal hook script

cat > /tmp/minimal-hook.sh <<'EOF'
#!/bin/bash
echo "[$(date +'%H:%M:%S')] MINIMAL_HOOK_FIRED event=${1:-unknown}" >> /tmp/minimal-hook-fired.log
EOF
chmod +x /tmp/minimal-hook.sh

Step 2: Configure .claude/settings.json

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "/tmp/minimal-hook.sh post-tool-use-bash",
            "timeout": 8
          }
        ]
      }
    ]
  }
}

(Note: minimal — no ${CLAUDE_PROJECT_DIR} expansion, no path-with-space, no env var, simplest possible 1-line echo to file)

Step 3: Restart VSCode (to ensure settings.json hot-reload)

Step 4: Have LLM run a Bash command (e.g., git commit --allow-empty -m "test" or any Bash tool call)

Step 5: Check log file

cat /tmp/minimal-hook-fired.log

Expected: Log file contains MINIMAL_HOOK_FIRED event=post-tool-use-bash entry per LLM Bash tool call

Actual: File never created (hook never invoked) → confirms PostToolUse never fires for LLM-initiated tool calls

What Works (SessionStart / SessionEnd)

In the same .claude/settings.json, SessionStart and SessionEnd hooks work correctly:

{
  "hooks": {
    "SessionStart": [
      {
        "matcher": "startup|resume|clear|compact",
        "hooks": [
          {
            "type": "command",
            "command": "/tmp/minimal-hook.sh session-start",
            "timeout": 8
          }
        ]
      }
    ],
    "SessionEnd": [
      {
        "matcher": "*",
        "hooks": [
          {
            "type": "command",
            "command": "/tmp/minimal-hook.sh session-end",
            "timeout": 8
          }
        ]
      }
    ]
  }
}

After Cmd+Q quit + restart VSCode:

• SessionEnd fires for terminated sessions
• SessionStart fires for restarted sessions
• Log file /tmp/minimal-hook-fired.log contains entries

Verified via Telegram TOPIC_GOVERNANCE receiving SessionStart/End notifications correctly when hook script also includes curl to Telegram API.

What Does NOT Work (PostToolUse Bash)

In the same setup, PostToolUse Bash hook does NOT fire:

• 4 empty git commit calls via LLM Bash tool: 5d78718 / 992d924 / 8f8904a / c6f223a
• None triggered the hook (log file not created)
• Verified across multiple session restarts (PID 9525 / 9709 / 11264 etc., all v2.1.142)

Related Output panel logs (no error visible)

[DEBUG] Registered 0 hooks from 0 plugins  ← plugin hooks (irrelevant, we use project hooks)
[WARN] [3P telemetry] Event dropped (no event logger initialized): hook_registered  ← hooks ARE registered
[DEBUG] Watching for changes in setting files /Users/.../.claude/settings.json

No Hook fire / PostToolUse invoked log visible.

Suspected Root Causes (speculation)

1. v2.1.142 stream-json mode IPC path may not invoke PostToolUse hook for tool calls from LLM (only invokes for human-typed Bash commands via slash commands)
2. Hook event firing pathway in v2.1.142 may have regression for Bash tool specifically (other tool matchers untested)
3. Race condition / timing issue with stream-json --include-partial-messages flag (default in VSCode integration)

Workaround

None functional. Currently rely on SessionStart + SessionEnd hooks for session lifecycle audit, plus .githooks/pre-commit (git native, fires for ALL commits including LLM-initiated) for syntax check and commit audit fallback.

Severity

Medium — does not block development but breaks audit/observability hooks for LLM-initiated tool calls (especially git commit notifications, command logging, etc.). PostToolUse is documented as firing for ALL tool calls including built-in tools.

Reference

• Local project sink: /Users/weihuafu/Documents/Ai Project/DevPlan/LESSONS_LEARNED.md LL-012 Case 21
• Local project commit: 60a8773 docs(infra+lessons): W1-D9 morning ... LL-004 cumulative 18→21
• Confirmed via claude-code-guide agent: matcher "Bash" is correct, PostToolUse should fire for all tool calls per docs, no --include-hook-events / disableAllHooks setting active

What Should Happen?

Claude code should fix this issue which PostToolUse Bash hook should fire for LLM-initiated Bash tool calls (stream-json mode).

Error Messages/Logs

Steps to Reproduce

100% Reproducer (Minimal)

Step 1: Create minimal hook script

cat > /tmp/minimal-hook.sh <<'EOF'
#!/bin/bash
echo "[$(date +'%H:%M:%S')] MINIMAL_HOOK_FIRED event=${1:-unknown}" >> /tmp/minimal-hook-fired.log
EOF
chmod +x /tmp/minimal-hook.sh

Step 2: Configure .claude/settings.json

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "/tmp/minimal-hook.sh post-tool-use-bash",
            "timeout": 8
          }
        ]
      }
    ]
  }
}

(Note: minimal — no ${CLAUDE_PROJECT_DIR} expansion, no path-with-space, no env var, simplest possible 1-line echo to file)

Step 3: Restart VSCode (to ensure settings.json hot-reload)

Step 4: Have LLM run a Bash command (e.g., git commit --allow-empty -m "test" or any Bash tool call)

Step 5: Check log file

cat /tmp/minimal-hook-fired.log

Expected: Log file contains MINIMAL_HOOK_FIRED event=post-tool-use-bash entry per LLM Bash tool call

Actual: File never created (hook never invoked) → confirms PostToolUse never fires for LLM-initiated tool calls

What Works (SessionStart / SessionEnd)

In the same .claude/settings.json, SessionStart and SessionEnd hooks work correctly:

{
  "hooks": {
    "SessionStart": [
      {
        "matcher": "startup|resume|clear|compact",
        "hooks": [
          {
            "type": "command",
            "command": "/tmp/minimal-hook.sh session-start",
            "timeout": 8
          }
        ]
      }
    ],
    "SessionEnd": [
      {
        "matcher": "*",
        "hooks": [
          {
            "type": "command",
            "command": "/tmp/minimal-hook.sh session-end",
            "timeout": 8
          }
        ]
      }
    ]
  }
}

After Cmd+Q quit + restart VSCode:

• SessionEnd fires for terminated sessions
• SessionStart fires for restarted sessions
• Log file /tmp/minimal-hook-fired.log contains entries

Verified via Telegram TOPIC_GOVERNANCE receiving SessionStart/End notifications correctly when hook script also includes curl to Telegram API.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

2.1.142 (Claude code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

No response