Agent Teams ignore isolation: "worktree" — worktree never created, WorktreeCreate hook never called

Bug Description

When launching an agent with both team_name and isolation: "worktree", the worktree is never created and the WorktreeCreate hook is never called. The agent silently runs in the main repository directory instead of an isolated worktree.

Reproduction Steps

1. Enable Agent Teams:

``json
{ "env": { "CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS": "1" } }
``

1. Create a team and launch an agent with isolation: "worktree":

``
TeamCreate({ team_name: "test-team" })
TaskCreate({ subject: "Test task", description: "..." })
Agent({
name: "member-1",
team_name: "test-team",
isolation: "worktree",
run_in_background: true,
prompt: "Run pwd && git branch --show-current && ls -la .git, then report via SendMessage"
})
``

1. Agent reports:

• pwd → main repo path
• git branch --show-current → main
• .git is a directory (not a worktree file)

Expected Behavior

• WorktreeCreate hook is called
• Agent runs inside an isolated git worktree
• .git is a file pointing to .git/worktrees/...
• Agent has its own branch

Actual Behavior

• WorktreeCreate hook is never called (verified via debug logging)
• Agent runs in the main repository on main branch
• .git is a full directory
• No worktree is created anywhere on disk (git worktree list shows only main)
• No error or warning is emitted — the failure is completely silent

Verification Matrix

We tested all combinations systematically:

| subagent_type | team_name | isolation | WorktreeCreate hook called | Agent in worktree |
|---|---|---|---|---|
| (none) | (none) | "worktree" | Yes | Yes ✅ |
| custom agent | team | "worktree" | No | No ❌ |
| custom agent (with frontmatter isolation: worktree) | team | "worktree" | No | No ❌ |
| (none) | team | "worktree" | No | No ❌ |

Conclusion: team_name is the deciding factor. Any agent launched with team_name silently ignores isolation: "worktree".

Additional Context: WorktreeCreate Hook stdout issue

During investigation, we also discovered a separate issue: git worktree add outputs HEAD is now at ... to stdout, which contaminates the hook's stdout that Claude Code reads as the worktree path. This caused worktree isolation failures even without team_name until we redirected both stdout and stderr:

- git worktree add -b "$NAME" "$WORKTREE_PATH" 2>>"$DEBUG_LOG"
+ git worktree add -b "$NAME" "$WORKTREE_PATH" >>"$DEBUG_LOG" 2>&1

This is a footgun for anyone writing a custom WorktreeCreate hook — the docs should note that git worktree add writes to stdout and the hook must ensure only the path appears on stdout.

Environment

• Claude Code: v2.1.83
• OS: macOS (Darwin 23.6.0)
• Git: worktree feature works correctly outside Claude Code

Related Issues

• #33045 — isolation: "worktree" has no effect for team agents
• #37549 — isolation: "worktree" silently fails when combined with team_name
• #34645 — Parallel subagents with worktree fail due to git config lock contention

🤖 Generated with Claude Code