Bug Report: PreToolUse Hooks Strip Result Data from AskUserQuestion Tool

Summary

When PreToolUse hooks are enabled in Claude Code settings, the AskUserQuestion tool fails to return the user's selected answer in the function results. The answer data is completely missing from the hook result, making it impossible to validate or use user responses. Disabling all PreToolUse hooks resolves the issue immediately.

Severity

Critical - Blocks all interactive workflows that depend on receiving user choices from AskUserQuestion tool.

Reproduction Steps

Step 1: Verify AskUserQuestion Works Without Hooks

Set "disableAllHooks": true in ~/.claude/settings.json
Restart Claude Code
Invoke AskUserQuestion tool with any question
Expected Result: Function returns "User has answered your questions: \"<question>\"=\"<answer>\""
Actual Result: ✅ Works correctly - answer data is present

Step 2: Enable PreToolUse Hooks and Reproduce Bug

Set "disableAllHooks": false in ~/.claude/settings.json
Restart Claude Code
Invoke AskUserQuestion tool with the same question
Expected Result: Function returns "User has answered your questions: \"<question>\"=\"<answer>\""
Actual Result: ✗ Bug reproduced - function returns "User has answered your questions: ." (answer missing)

Step 3: Isolate Which Hook Type Causes Issue

Tested with PreToolUse hooks disabled and PostToolUse hooks enabled:

Result: ✅ AskUserQuestion works correctly
Conclusion: Bug is specifically in PreToolUse hook infrastructure

Step 4: Test Individual PreToolUse Hooks

Tested each of the three PreToolUse hooks individually:

task_required_skills_tracker.py - ✗ Causes bug
prevent_skill_reinvocation.py - ✗ Causes bug
gated_tool_access_control.py - ✗ Causes bug

Conclusion: All PreToolUse hooks cause the bug (not specific to one hook)

Root Cause Analysis

Evidence That Hooks Are Implemented Correctly

All three PreToolUse hooks use cchooks SDK properly
- They correctly call context.output.allow() or context.output.deny()
- They follow the documented PreToolUse hook pattern
- They output valid JSON with correct schema
PreToolUse hooks execute and return properly
- Hook debug logs confirm hooks execute successfully
- Hooks return proper JSON decisions (allow/deny)
- Hooks don't crash or exit with errors
AskUserQuestion tool executes and returns result
- Tool runs without errors
- Tool produces a result object
- Result contains the user's selected answer
The answer data is lost between tool execution and function result
- When hooks disabled: Full answer data returned
- When hooks enabled: Answer data stripped

Root Cause Hypothesis

Claude Code's hook infrastructure has a bug when processing UI-only tools (like AskUserQuestion) in the presence of PreToolUse hooks. The most likely cause is:

Claude Code's internal hook result processing is not properly preserving tool response data for UI tools when PreToolUse hooks are active.

Possible mechanisms:

Claude Code replaces UI tool results with hook responses instead of merging them
The hook infrastructure has a special code path for UI tools that breaks with PreToolUse hooks
Result data is stripped during hook response serialization for UI tools
Hook output transformation doesn't account for UI tool response structures

Expected Behavior

When AskUserQuestion tool executes:

PreToolUse hook executes and returns allow decision
AskUserQuestion tool executes and returns user's selection
Function result includes both the hook decision AND the tool result with answer data
Answer data should be accessible in the function result

Actual Behavior

When AskUserQuestion tool executes:

PreToolUse hook executes and returns allow decision ✓
AskUserQuestion tool executes and returns user's selection ✓
Function result only includes hook decision ✗
Answer data is missing/stripped ✗

Impact

Blocks: Any workflow using AskUserQuestion with PreToolUse hooks enabled
Affects: All users with active PreToolUse hooks who need interactive tool responses
Prevents: Validation of user choices, conditional logic based on selections, interactive task workflows
Workaround: Disable all hooks ("disableAllHooks": true) - not acceptable for production use

Environment

Claude Code Version: Latest (as of Nov 20, 2025)
Model: claude-haiku-4-5-20251001
Platform: Linux (Ubuntu)
Settings Location: ~/.claude/settings.json

Affected Code/Components

Claude Code's PreToolUse hook infrastructure (internal, not cchooks SDK)
Specifically: Hook result processing for UI-only tools
Related: Hook result serialization/deserialization layer

Hook Configuration (Minimal Repro)

{
  "disableAllHooks": false,
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "*",
        "hooks": [
          {
            "type": "command",
            "command": "~/.claude/hooks/production/any-pretooluse-hook.py"
          }
        ]
      }
    ]
  }
}

Workaround

Temporary: Set "disableAllHooks": true in settings.json

⚠️ Not recommended for production (disables all safety hooks)
✅ Confirms bug is in hook infrastructure
⚠️ Removes all hook-based safety and guidance systems

Testing Notes

Tested with 3 different PreToolUse hooks - all cause the bug
Bug is 100% reproducible
Bug appears immediately after restart with hooks enabled
Bug disappears immediately when hooks disabled and restarted
PostToolUse hooks do not cause the issue
All other hook types do not cause the issue

Questions for Claude Code Team

Is there special handling for UI-only tools in the PreToolUse hook infrastructure?
Does the hook result processing preserve tool response data for UI tools?
Is there a serialization/deserialization issue with UI tool responses when PreToolUse hooks are active?
Should UI tools (like AskUserQuestion) be excluded from PreToolUse hook processing?

Related Files for Investigation

Claude Code's internal hook result processing (not public)
Hook infrastructure response handling for UI tools
AskUserQuestion tool implementation's integration with hook system
PreToolUse hook decision handling for non-state-modifying tools

Resolution Suggestions

Preserve UI tool results in PreToolUse hook infrastructure: Ensure that when PreToolUse hooks return an allow decision, the original tool result data (including UI tool responses) is preserved and merged with the hook response
Special handling for UI-only tools: Consider excluding UI-only tools from PreToolUse hook processing, or have a special code path that always preserves tool result data
Validation in hook SDK: Consider adding validation in cchooks SDK to warn developers if PreToolUse hooks are used with UI tools

Reproduction Code

# Test case to reproduce the bug
from cchooks import AskUserQuestion

def test_asksuser_question_with_pretooluse_hooks():
    """
    Setup:
    1. Enable PreToolUse hooks in settings.json
    2. Restart Claude Code
    3. Run this code:
    """
    result = AskUserQuestion(
        questions=[{
            "question": "Is Python a programming language?",
            "header": "Test",
            "options": [
                {"label": "True", "description": "Correct"},
                {"label": "False", "description": "Incorrect"}
            ],
            "multiSelect": False
        }]
    )

    # Expected: result contains answer data like:
    # {"User has answered your questions: \"Is Python a programming language?\"=\"True\""}

    # Actual (with hooks enabled): result is:
    # {"User has answered your questions: ."}

    assert "True" in str(result), "Answer data missing - BUG CONFIRMED"

Additional Context

Testing Matrix

Scenario	AskUserQuestion Returns Answer	Works
All hooks disabled	✅ Yes	✅ YES
PostToolUse only	✅ Yes	✅ YES
SessionStart only	✅ Yes	✅ YES
PreToolUse only	❌ No	❌ NO
PreToolUse + PostToolUse	❌ No	❌ NO
PreToolUse + SessionStart	❌ No	❌ NO

Debug Evidence

Hook debug logs confirm:

PreToolUse hooks execute successfully
Hooks return valid JSON responses
No errors in hook processing
Tool execution appears to complete
Answer data is lost between tool execution and function result return

Code Quality

All hooks follow cchooks SDK best practices
All hooks use proper error handling
All hooks return valid JSON
Issue is NOT in hook implementation
Issue is in Claude Code's hook infrastructure

Submitted by: Christina Date: November 20, 2025 Reproducibility: 100% - Consistent and immediate

Nov 20 '25 15:11 kitaekatt

This issue has been inactive for 30 days. If the issue is still occurring, please comment to let us know. Otherwise, this issue will be automatically closed in 30 days for housekeeping purposes.

Dec 21 '25 10:12 github-actions[bot]

Yes this issue is still occurring

Dec 28 '25 18:12 kitaekatt