fix(skills): capture worktree path before Step 5 changes directory

Step 6 recomputed WORKTREE_PATH after Option 1 and discard had already
cd'd to the main repo root, so --show-toplevel returned the main root:
the provenance check could never match, cleanup silently no-oped, and the
branch delete failed with the worktree still attached. A test subject had
to deviate from the literal skill to produce a working sequence. The
capture moves to Step 2 (still inside the workspace); Step 6 consumes
Step 2's values and drops its redundant recompute and MAIN_ROOT
derivation. Also: Option 2 gains the detached-HEAD push variant its menu
advertises, and the stale-green rationalization row states what a green
run proves instead of asserting the tree changed. Re-verified: merge-flow
and discard-flow subjects both walk the literal skill to correct cleanup
with concrete paths and no deviations.

skills/finishing-a-development-branch/SKILL.md

@@ -30,6 +30,9 @@ Tests failing (<N> failures). Must fix before completing:
 ```bash
 GIT_DIR=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
 GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
+# Capture now, while still inside the workspace — Step 5 changes directory
+# before cleanup (Step 6) needs this value
+WORKTREE_PATH=$(git rev-parse --show-toplevel)
 ```
 
 This determines which menu to show and how cleanup works:
@@ -111,6 +114,8 @@ git branch -d <feature-branch>
 
 ```bash
 git push -u origin <feature-branch>
+# From a detached HEAD, name the new branch on the remote:
+# git push origin HEAD:refs/heads/<new-branch>
 ```
 
 Then create the pull/merge request against <base-branch> with the forge's
@@ -154,23 +159,17 @@ git branch -D <feature-branch>
 ## Step 6: Cleanup Workspace
 
 **Runs for Option 1 and confirmed discards.** Options 2 and 3 always
-preserve the worktree.
-
-```bash
-GIT_DIR=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
-GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
-WORKTREE_PATH=$(git rev-parse --show-toplevel)
-```
+preserve the worktree. Both callers have already changed directory to the
+main repo root — worktree removal must run from outside the worktree —
+and use the `GIT_DIR`/`GIT_COMMON`/`WORKTREE_PATH` values captured in
+Step 2, from before that directory change.
 
 **If `GIT_DIR == GIT_COMMON`:** Normal repo, no worktree to clean up. Done.
 
-**If worktree path is under `.worktrees/` or `worktrees/`:** Superpowers
-created this worktree — we own cleanup. Run it from the main repo root
-(removal fails from inside the worktree being removed):
+**If `WORKTREE_PATH` is under `.worktrees/` or `worktrees/`:** Superpowers
+created this worktree — we own cleanup:
 
 ```bash
-MAIN_ROOT=$(git -C "$(git rev-parse --git-common-dir)/.." rev-parse --show-toplevel)
-cd "$MAIN_ROOT"
 git worktree remove "$WORKTREE_PATH"
 git worktree prune  # Self-healing: clean up any stale registrations
 ```
@@ -191,7 +190,7 @@ place. If your platform provides a workspace-exit tool, use it.
 
 | Excuse | Reality |
 |--------|---------|
-| "Tests passed earlier this session" | Run the suite now. The tree changed since the last green run. |
+| "Tests passed earlier this session" | Run the suite on the tree you are about to integrate. A green run only proves the tree it ran on. |
 | "They obviously want it merged" | Integration is your human partner's decision. Present the menu and wait. |
 | "They seem done with this feature — I'll offer to discard it" | The menu is complete as written. Discard happens only when your human partner asks for it in so many words. |
 | "'Yeah, get rid of it' counts as confirmation" | Only the typed word `discard` authorizes deletion. |