v0.2.0

0.2.0

spawn_workspace refuses to attach a new session onto a cow worktree a live
session is still using (ADR 0004). The tool records occupancy itself: on both
the create and attach flows it writes .cow-session.json at the worktree root
(kept out of git status through .git/info/exclude), and at attach time it
probes the recorded session through the session API. Only a positive proof
that the session is gone lets attach proceed: a 404, or silence past a
60-minute window. A live session, a malformed marker, or a probe failure that
proves nothing refuses the attach and names the occupying session plus the
three recoveries (pick another name, delete the session out of band, remove a
known-stale marker). Legacy worktrees without a marker keep today's fail-open
behavior and gain a marker; the git fallback is untouched. A failed marker
write never fails the call; the result carries an "unguarded" warning.

Verified against a real opencode2 serve (0.0.0-next-20260912.3): the
attach scenario refuses on a live session, proceeds after the occupying
session is deleted, and backfills markers onto legacy worktrees
(docs/e2e/run-2026-09-16.md). Unit suite: 307 tests, coverage gate at 100%
lines on all 21 shipped files.

Also in this release:

• The e2e harness stays runnable across the 20260915 nightly split; its
  readiness probe polls /api/plugin because the nightly answers 404 on
  /api/health. The pinned 0.0.0-next-20260912.3 is unaffected.
• Docs: ADR 0004, the announcement draft, the ecosystem listing draft, and
  upstream filing candidates 6-8 (the nightly's /api/health 404, its
  projectID requirement that breaks plugin worktree creates, and the
  realpath-first Worktree.remove that strands dangling rows).