[FEATURE] Warn user immediately when session opens inside a worktree before allowing any file edits

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Summary

When Claude Code opens a new session inside a worktree (.claude/worktrees/*),
it begins editing files there without warning the user. Worktrees are branched
from older commits, so edits silently overwrite the user's real working code
with an outdated version — destroying recent uncommitted work.

Proposed Solution

Requested behaviour

When cwd is detected inside .claude/worktrees/*, warn before any file edit:

⚠️ This session opened inside a worktree which may be based on an older
branch. Before I edit anything — should I work here or in your main project
folder?

Then wait for explicit confirmation before touching any file.

Why this matters

Silent data-loss risk. One sentence at session start eliminates it entirely.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

Real incident

A user had months of production code including 2000+ lines of automation that
had never been committed. A new session landed in a worktree based on an old
branch. Claude edited files there and copied them to the main project folder,
wiping out all uncommitted work. The user spent hours re-debugging issues that
had already been solved.

Root cause

• Claude has no awareness it is in a worktree vs the real project
• No session-start warning exists
• CLAUDE.md helps only if the user already knows to create it

Additional Context

Summary

When Claude Code opens a new session inside a worktree (.claude/worktrees/*),
it begins editing files there without warning the user. Worktrees are branched
from older commits, so edits silently overwrite the user's real working code
with an outdated version — destroying recent uncommitted work.

Real incident

A user had months of production code including 2000+ lines of automation that
had never been committed. A new session landed in a worktree based on an old
branch. Claude edited files there and copied them to the main project folder,
wiping out all uncommitted work. The user spent hours re-debugging issues that
had already been solved.

Root cause

• Claude has no awareness it is in a worktree vs the real project
• No session-start warning exists
• CLAUDE.md helps only if the user already knows to create it

Requested behaviour

When cwd is detected inside .claude/worktrees/*, warn before any file edit:

⚠️ This session opened inside a worktree which may be based on an older
branch. Before I edit anything — should I work here or in your main project
folder?

Then wait for explicit confirmation before touching any file.

Why this matters

Silent data-loss risk. One sentence at session start eliminates it entirely.