[BUG] WorktreeCreate hook returning a path outside the repository is always refused: "git could not be run to resolve it"

What's Wrong?

A WorktreeCreate hook that creates a valid git worktree outside the repository and prints its path is always refused by Claude Code's git-identity verification:

Refusing to use /Users/me/workspace/worktrees/my-repo/<name> as an isolation worktree: git could not be run to resolve it, so its git identity could not be verified. Isolation is refused rather than assumed — recreate the worktree (or remove the corrupt .git entry) and retry.

The worktree itself is healthy: it is registered in git worktree list, git -C <path> status works, the path contains no symlinks and no ./.. segments. The hook's stdout is clean (only the path on the last line; git output redirected to stderr).

Control test: the identical hook returning a path inside the repository ($repo_root/.claude/worktrees/$name) is accepted, and the session runs in it. So the hook mechanics and output parsing are fine — the external location is the trigger.

The refusal reproduces identically for all three creation paths: claude --worktree, the EnterWorktree tool, and Agent(isolation: "worktree") subagents, and in completely fresh sessions.

What Should Happen?

Per https://code.claude.com/docs/en/worktrees.md and hooks.md, a WorktreeCreate hook "replaces default git behavior" and may return any directory; paths outside .claude/worktrees/ are documented as accepted with a one-time approval when entered. Instead, verification hard-fails before any approval prompt, and the failure message ("git could not be run to resolve it") is wrong — git runs fine against the directory.

Steps to Reproduce

1. ~/.claude/settings.json:

{
  "hooks": {
    "WorktreeCreate": [
      { "hooks": [ { "type": "command", "command": "~/.claude/hooks/worktree-create.sh" } ] }
    ]
  }
}

1. ~/.claude/hooks/worktree-create.sh (chmod +x):

#!/bin/bash
set -euo pipefail
input=$(cat)
name=$(jq -r '.name' <<<"$input")
cwd=$(jq -r '.cwd' <<<"$input")
repo_root=$(git -C "$cwd" rev-parse --show-toplevel)
repo=$(basename "$repo_root")
dir="$HOME/workspace/worktrees/$repo/$name"
mkdir -p "$(dirname "$dir")"
git -C "$repo_root" worktree add -b "$name" "$dir" >&2
echo "$dir"

1. From any git repo: claude --worktree mytest -p "pwd"
2. Observe the refusal. Then git worktree list shows the worktree was created and is valid.
3. Change the script's dir= to "$repo_root/.claude/worktrees/$name" and repeat — it works.

Ruled out (each re-tested in a fresh headless session)

• permissions.additionalDirectories: ["~/workspace/worktrees"] in user settings — same refusal
• --add-dir ~/workspace/worktrees — same refusal
• --settings '{"sandbox":{"enabled":false}}' — same refusal
• symlinks in the path — none (realpath identical); no ./.. segments
• --debug logs contain nothing beyond the refusal message; the underlying git spawn error is not logged

Error Messages/Logs

Error creating worktree: Refusing to use /Users/me/workspace/worktrees/my-repo/mytest as an isolation worktree: git could not be run to resolve it, so its git identity could not be verified. Isolation is refused rather than assumed — recreate the worktree (or remove the corrupt .git entry) and retry.

Claude Code Version

2.1.241

Platform

Anthropic API / macOS (Darwin 25.5.0), git 2.53.0 (homebrew), shell zsh

Is this a regression?

Unknown — first attempt at an external-path WorktreeCreate hook on this machine.