WorktreeCreate hook payload change causes undefined worktrees on Windows

Summary

Claude Code 2.1.98 appears to send a different WorktreeCreate hook payload than the older sample hook implementation expects. On Windows, a legacy hook that reads worktree_path / branch_name / base_path can end up creating a real worktree named undefined and then throwing when it tries to write undefined to stdout.

The failure I saw was:

WorktreeCreate hook failed: node "C:/Users/panit/.claude/hooks/worktree-create.js": Failed to create worktree: The "chunk" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received undefined

Environment

• Claude Code: 2.1.98
• OS: Windows
• Hook type: WorktreeCreate command hook

Observed behavior

• Claude tries to create an agent worktree.
• The legacy hook reads missing fields as undefined.
• git worktree add still runs, which can register a real worktree at a path like <repo>/undefined on branch undefined.
• The hook then crashes on process.stdout.write(worktreePath) because worktreePath is undefined.
• Claude falls back to sequential execution with no worktrees.

Expected behavior

• The hook contract should be clear and stable, or the sample hook should be updated for the current payload.
• A current-format hook should be able to read cwd and name, create the worktree, and print the absolute worktree path.
• Stale sample hooks should not silently create undefined branches or worktree directories.

Likely root cause

I verified that a working hook for 2.1.98 needs to treat the current payload as cwd + name for create, with legacy fallbacks for older field names.

Minimal fix that worked locally

• Read cwd and name for WorktreeCreate.
• Keep fallbacks for base_path, branch_name, and worktree_path.
• Resolve repo root with git rev-parse --show-toplevel.
• Create the worktree at <repo>/.claude/worktrees/<name>.
• If the branch already exists, run git worktree add <path> <branch>.
• Otherwise, run git worktree add <path> -b <branch>.
• Print only the absolute created path to stdout.

Repro notes

The legacy hook shape that broke looked like this:

const worktreePath = data.worktree_path;
const branchName = data.branch_name;
const basePath = data.base_path;

execSync(`git worktree add "${worktreePath}" -b "${branchName}"`, { cwd: basePath });
process.stdout.write(worktreePath);

Thanks � happy to provide the full working replacement script if useful.

Working replacement hooks

Public gist: https://gist.github.com/pithpusher/8596767975959b8ceac96574b7dd4285