cross-worktree-spec-handoff-via-checkout-pathslisted

# Cross-worktree spec handoff via `git checkout <branch> -- <paths>` ## Problem You ran a brainstorming / design session in Claude Code session A. Output: design spec doc, a handoff prompt, a vibe mockup HTML. You committed them on branch `worktree-spec-A` in `.claude/worktrees/spec-A/`. You then started Claude Code session B in a different worktree, on a fresh branch `feat/something-B` branched from `main`. Session B is supposed to consume the design spec — but the spec doc, handoff prompt, and mockup files **don't exist** in B's working tree, because B's branch was cut from main before A's commits landed and the commits never made it to main. Session B reports: "the referenced design spec files don't exist in the handover. Let me look at what's available." → it's blocked. The naive fix is "merge A's branch into main, then B pulls main". That needs a PR review cycle. Slow. ## Context / Trigger Conditions All of: - Two (or more) Claude Code sessions are running in parallel, in **different worktrees** of the same repo. (`git worktree list` shows multiple paths.) - Session A (the producer) committed artefacts — design docs, plans, spec files, mockups, fixtures, prompts — on a branch that is **not** the base branch of session B. - Session B (the consumer) is on a branch branched from `main` (or any ancestor that predates A's commits) and cannot see A's files via `ls` or Read. - B reports a "file not found" / "doesn't exist" / "can't see the spec" symptom re