tasks: 59 also clears the workspaces a phase leaves behind

complete_task works from the stem of the card it is completing, so a
finished phase leaves every member's worktree, local branch and remote
branch in place — measured on 53: three worktrees at 3.8M each and two
member branches still on origin. The sweep now removes them, with the
existing rule intact for a member that never merged: there is work in
that worktree, so it stays.

tasks/backlog/59-finishing-a-phase-finishes-its-cards.md

@@ -1,14 +1,17 @@
-# 59 — Finishing a phase finishes its cards
+# 59 — Finishing a phase finishes its cards, and clears up after them
 
 **Status:** Backlog
 **Priority:** Medium — without it a phase ends by handing you a pile of
-cards you have already judged
+cards you have already judged and a heap of checkouts nobody will
+remember to delete
 **Type:** Feature
 
 When a phase's PR merges into `main`, its members' work is in `main` too —
 but their cards are sitting in `review/`, where the board says they are
-waiting on you. **Merge & clean up** on a phase card should move its
-members to `done/` in the same operation that moves the phase.
+waiting on you, and every one of them has left a worktree and three
+branches behind. **Merge & clean up** on a phase card should finish its
+members too: move them to `done/`, and clear the workspaces they are done
+with.
 
 ## Context
 
@@ -29,6 +32,16 @@ members to `done/` in the same operation that moves the phase.
 - Board-made moves commit themselves under `BOARD_COMMIT_MOVES` and, in
   team mode, push — so a sweep of five cards is five commits or one, and
   which it is deserves a decision rather than an accident.
+- **The cleanup half is missing entirely.** `complete_task` works from
+  `stem = filename[:-3]`, so it removes the worktree and branch of the
+  card being completed and knows nothing about members. Measured on phase
+  53 after it finished: three worktrees still on disk
+  (`.worktrees/47-…`, `.worktrees/52-…`, `.worktrees/53-…`, 3.8M each),
+  both member branches still local, and both still on origin. A grep of
+  `phases.py` finds worktrees created and never removed.
+- An ordinary card already gets the full treatment on completion —
+  worktree removed, local branch deleted, remote branch deleted after the
+  push. Members should get exactly that, from the same place.
 
 **Affected areas:** `manager/core/github.py` (`complete_task`), and
 whatever narrates the result.
@@ -38,9 +51,17 @@ whatever narrates the result.
 - **The sweep, inside the merge.** When a phase card is completed, every
   member the phase lists moves to `done/` as part of the same operation —
   after the merge into `main` has actually succeeded, never before.
+- **Clear each merged member's workspace**, the way completing an
+  ordinary card clears its own: remove the worktree, delete the local
+  branch, delete the branch on the remote. The member's work is in `main`
+  by then, so there is nothing in any of them worth keeping.
 - **Only what the phase merged.** A member that never reached the phase
-  branch — halted, held, walked back — is not swept. It stays where it
-  is, and it is the reason a person will look at the phase afterwards.
+  branch — halted, held, walked back — is neither moved nor cleared. Its
+  card stays where it is, and so do its worktree and its branch: there is
+  work in them, and it is the reason a person will look at the phase
+  afterwards. The board already applies this rule to a failed run that
+  committed something, and removing a worktree with work in it is the one
+  unrecoverable thing in this card.
 - **Narrate it as one thing.** The ticker should say a phase finished and
   how many cards went with it, not five separate moves scrolling past. A
   person watching should see one event, because one thing happened.
@@ -73,8 +94,13 @@ whatever narrates the result.
       number of cards.
 - [ ] Given the merge fails or conflicts, nothing moves — not the phase
       card, not one member.
-- [ ] Given a member that never reached the phase branch, it is left
-      exactly where it is.
+- [ ] Given a member that never reached the phase branch, its card, its
+      worktree and its branch are all left exactly as they are.
+- [ ] Given the phase completes, no merged member leaves a worktree,
+      a local branch or a branch on the remote behind — `git worktree
+      list` and `git branch` name only what was there before the phase.
+- [ ] Removing a worktree never discards uncommitted changes: a member
+      with a dirty worktree is reported and kept, not forced.
 - [ ] Given "just move the card" instead, no member moves.
 - [ ] Given the phase card is archived rather than merged, its members
       reappear on the board in their own stages and none of them is
@@ -97,3 +123,10 @@ The reason it is separate from card 56 rather than folded in: 56 is about
 what the *Board view draws*, and this is about what the *board does*. One
 is a rendering rule, the other moves files and commits them. Keeping them
 apart also keeps 56 shippable on its own.
+
+**Why the cleanup is not cosmetic.** A stale worktree is not just disk —
+`start_agent` refuses to launch a card whose worktree already exists on
+the wrong branch, so a leftover from a finished phase is a trap laid for
+whoever reopens that card. And the accumulation is per member per phase:
+five-card phases leave five checkouts and fifteen branches each time,
+until somebody notices and does it by hand.