* feat: unarchive tasks with worktree branch recovery
Archived tasks can now be restored. Unarchive works for manual/legacy
archives (empty cascade id, root-only) and cascade archives. Archive
deletes the local branch, so worktree recreate now falls back to
fetching the branch from origin, and unarchive writes the old branch
back as checkout_branch so a fresh session resumes the prior work.
Unrecoverable branches (never pushed) surface a warning. WS archive now
routes through the handoff cascade so it stays stamped and reversible.
UI: unarchive action on /tasks archived rows and the task top bar.
* fix: address PR review feedback on unarchive recovery
Forward PRNumber to the recreate fetch so fork-PR heads (only reachable
via pull/<N>/head) are recoverable, publish task.updated per task in the
cascade unarchive loop so the UI restores without a reload, and
re-publish task.updated after a checkout_branch restore since the
unarchive event goes out with the pre-restore repository rows.
* fix: harden unarchive recovery per review feedback
Propagate branch-probe errors instead of misreporting recoverable work
as gone, and reserve ErrBranchUnrecoverable for a confirmed-missing
remote ref (transient fetch failures keep their own error). Validate
the archive root exists so WS/HTTP archive no longer reports success
for unknown task IDs, CAS-guard manual unarchive on an empty cascade
stamp, detach branch recovery from the request context, and skip
checkout_branch restore for multi-branch repos. UI: in-flight guard on
the list unarchive button, pluralized unrecoverable-branch toast.
* docs: document CAS guard on UnarchiveTask interface contract
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Co-authored-by: Kandev Agent <agent@kandev.dev>
Henry