[BUG] PreToolUse hook with permissionDecision: "allow" causes intermittent "undefined is not an object (evaluating 'H.includes')" error

Description

When a PreToolUse hook returns permissionDecision: "allow", Claude Code intermittently crashes with:

Error: undefined is not an object (evaluating 'H.includes')

The permissionDecision: "deny" path works correctly every time. The error appears to be in the client-side rendering code, not in the hook execution itself.

Environment

• Platform: Linux (Ubuntu)
• Claude Code version: 2.0.76
• Node.js version: v22.x

Steps to Reproduce

1. Create a PreToolUse hook that returns:

{
  "hookSpecificOutput": {
    "hookEventName": "PreToolUse",
    "permissionDecision": "allow",
    "permissionDecisionReason": ""
  }
}

Or install this: https://github.com/fprochazka/claude-code-plugins/tree/3b81c70464f0fcffc89ccef7b457e363b66657e1/plugins/no-background-tasks

1. Trigger multiple parallel Bash tool calls

1. The first tool that gets "allow" intermittently fails with the error

Hook Script (minimal reproduction)

#!/usr/bin/env python3
import json
import sys

hook_input = json.load(sys.stdin)

# Always allow
output = {
    "hookSpecificOutput": {
        "hookEventName": "PreToolUse",
        "permissionDecision": "allow",
        "permissionDecisionReason": ""
    }
}
print(json.dumps(output))
sys.exit(0)

Expected Behavior

The tool should execute normally when the hook returns permissionDecision: "allow".

Actual Behavior

Claude Code throws undefined is not an object (evaluating 'H.includes') intermittently.

<img width="1559" height="404" alt="Image" src="https://github.com/user-attachments/assets/d1ddc009-ba2a-4ec0-b43c-c9135444abec" />

Debug Logs

When the hook works correctly, debug logs show:

Hook result has permissionBehavior=allow
Hook approved tool use for Bash, bypassing permission check

When it fails, the error is not logged in ~/.claude/debug/ - suggesting it's a client-side rendering error.

Notes

• The error is intermittent - sometimes it works, sometimes it fails
• permissionDecision: "deny" always works correctly
• Adding permissionDecisionReason: "" (empty string) seems to reduce but not eliminate the error
• The minified variable H suggests this is in bundled/minified Claude Code JavaScript

Workaround

None found. The error prevents reliable use of PreToolUse hooks that need to allow tool execution.