[BUG] Claude Code executes Node.js hooks on Python projects in multi-project workspace

Problem Summary

Claude Code incorrectly executes npm/biome PostToolUse hooks on Python FastAPI projects that don't have a package.json file, causing "ENOENT" errors after every Edit tool use.

Environment

• Platform: macOS (Darwin 24.5.0)
• Claude Code Version: Latest
• Project Type: Python FastAPI ML service
• Working Directory: /Users/devhub/WebstormProjects/polirate/political-fraud-detection-ml

Error Details

Every time the Edit tool is used, the following error appears:

⏺ PostToolUse:Edit [cd "$CLAUDE_PROJECT_DIR" && npm run biome:check] failed with non-blocking status 
  code 254: npm error code ENOENT
  npm error syscall open
  npm error path /Users/devhub/WebstormProjects/polirate/political-fraud-detection-ml/package.json
  npm error errno -2
  npm error enoent Could not read package.json: Error: ENOENT: no such file or directory, open 
  '/Users/devhub/WebstormProjects/polirate/political-fraud-detection-ml/package.json'

Detailed Project Configuration Analysis

I've thoroughly checked all possible hook configuration locations:

Project Hook Configuration

• File: .claude/config/hooks.json
• Content: Only contains Python-specific hooks using code-style-guardian agent
• No npm/biome references found

Settings Files Checked

• ~/.claude/settings.json - Does not exist
• .claude/settings.json - Does not exist
• .claude/settings.local.json - Contains only Python-specific permissions and hook config references
• .claude/config/debug.json - Contains only Python debugging settings

Search Results

• Searched entire .claude directory for "npm", "biome", "PostToolUse" - No matches found
• No package.json file exists in the project (this is a Python project)

Project Context

This is a Python FastAPI ML service with the following characteristics:

• Uses Python 3.11+
• FastAPI framework
• SQLAlchemy + PostgreSQL
• scikit-learn + TensorFlow for ML
• Poetry/pip for dependency management
• Has requirements.txt, pyproject.toml, alembic.ini
• No JavaScript/Node.js components whatsoever

Root Cause Analysis

Claude Code appears to be executing a hardcoded or default npm/biome PostToolUse hook regardless of:

• Project type (Python vs JavaScript)
• Absence of package.json
• Project-specific hook configuration that only defines Python tooling

This suggests cross-project hook inheritance where hooks from sibling Node.js projects are being inappropriately applied to Python projects.

Expected Behavior

Claude Code should:

1. Detect project type correctly - This is clearly a Python FastAPI project with requirements.txt, pyproject.toml, Python files, etc.
2. Not execute JavaScript/Node.js hooks on Python projects
3. Respect project-specific hook configurations that only define Python tooling

Actual Behavior

Claude Code is executing npm/biome hooks despite the project being pure Python with no JavaScript dependencies or configuration.

Reproduction Steps

1. Create or work in a Python project (no package.json)
2. Set up .claude/config/hooks.json with only Python-specific hooks
3. Use the Edit tool to modify any file
4. Observe the npm/biome error in the output

Impact

• Severity: Minor (non-blocking but annoying)
• Frequency: Every Edit tool usage
• User Experience: Creates noise and confusion about project setup

Suggested Fix

Claude Code should:

1. Check for project type before executing language-specific hooks
2. Only run npm/biome hooks when package.json exists or project is explicitly JavaScript/TypeScript
3. Respect user-defined hook configurations and not inject default hooks that conflict with project type
4. Add project type detection logic to prevent cross-language hook contamination

This appears to be a case where a default or hardcoded hook is being applied universally instead of contextually based on project type.

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This issue replaces #5384 with improved structure while preserving all technical details and investigation findings.