Build branch switching and the popover git surface

GitBranchSwitcher holds 06's sequence as one object: settle editors
explicitly (SessionSettleGate — Save All applies raw buffers with
validation and a refused buffer cancels the whole switch; Discard
reverts buffers AND reconciles the session folders against HEAD;
never silent), flush the pending auto-commit, stamp intent in the
per-board registry, bracketed safe checkout (git_checkout_tree
GIT_CHECKOUT_SAFE + set_head — no path passes FORCE, abort
included), one reload via the async wholesale bracket (failed final
reload engages the existing read-only lock), reseed undo/redo from
the new HEAD with redo empty, clear the stamp. Create-and-switch
keeps the full sequence — the tree-cannot-change proof fails under
concurrent writers. Lock contention shows the 02 in-progress row's
waiting state ("waiting for another writer's git lock"), bounded at
30s then failing cleanly naming the lock path.

GitOperationStamp + GitOperationRecovery: the own-leftovers rule as
a pure conjunction — pause state AND matching stamp = the app's own
interrupted operation, aborted to the pre-operation state with a
banner, stamp cleared on success only; either alone defers to the
pause-and-defer stance. Checked where the committer starts.

BoardGitControls replaces the read-only branch line: branch picker,
inline create-and-switch, the abnormal-state pause note in 06's own
words with controls dimmed, and commit-identity fields that read and
write repo-local .git/config (derived default as placeholder, never
value; unfocused resync, focused keystrokes kept; 2s poll while
visible — .git is watcher-filtered by design).

Also fixes a shipped bug from the undo card: plan(reconciling:)
matched card ids as path prefixes, so the reconcile branch was inert
on every board (<lane>/<card> never matches a bare id) — a session
file the restore diff couldn't name (attachment, comment, draft)
survived Discard and landed in the next flush's commit. One shared
component-exact folder-name resolver now serves both Discard paths;
noteDiscarded takes cardFolderName; regression test verified failing
against the pre-fix code.

41 branch tests + the regression; 2374 tests / 409 suites green;
InertGitTests untouched.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/LiveStore/BannerCenter.swift

@@ -604,6 +604,22 @@ public final class BannerCenter {
         return operation.id
     }
 
+    /// **Relabels a running operation** — the same row, still spinning, now saying something else.
+    ///
+    /// It exists for one sentence in 06-history-undo.md ▸ Interaction with external writers:
+    /// "contention outlasting the brief retry surfaces as a *waiting* state in the operation's
+    /// in-progress banner row ('waiting for another writer's git lock'), retrying on its cadence".
+    /// The waiting state is explicitly *the operation's own row*, not a second row and not a
+    /// replacement — the operation has not restarted, it is explaining itself — so the id is stable
+    /// and the view neither churns nor re-animates.
+    ///
+    /// An unknown id is a no-op: a completion racing a relabel is ordinary, not a bug.
+    public func updateOperation(_ id: UUID, label: String) {
+        guard let index = operations.firstIndex(where: { $0.id == id }) else { return }
+        let existing = operations[index]
+        operations[index] = InProgressOperation(id: existing.id, label: label, cancel: existing.cancel)
+    }
+
     /// Ends one — the row leaves the strip.
     ///
     /// **Completion and failure both come through here.** There is no `failOperation`: a failure is