Seamless local multi-branching: parallel sessions currently conflict on the working tree

Problem
When I run two Claude Code sessions in parallel on the same repo (common: one implementing, one reviewing / exploring), they step on each other's working tree — uncommitted edits collide, one session's branch switch breaks the other, etc. I end up with repo states I didn't intend.

Proposal
Make multi-session the happy path, not something I have to manually plumb with git worktrees. Concretely:

• Launching a second session on the same repo should auto-provision an isolated worktree + branch under a predictable path (.claude/worktrees/<session-id>/).
• The session UI should surface which worktree/branch it's attached to so I never mix them up.
• Merging / discarding a session's worktree back into the main checkout should be a one-command operation.

(I see there's already some EnterWorktree primitive — this ask is about making it the default multi-session experience, not an opt-in advanced mode.)

Why it matters
Parallel sessions are the single biggest productivity unlock of this product, and today they're also the single biggest source of "wait, why is my repo in this state" confusion.