selfupdate: the staging folder keeps what it needs and no more (R-1368 part 2) — not released

Each good update left its staged binary in <state dir>/selfupdate for ever
(49 files / 740 MB on demo-hp). After the wrapper's commit returned success,
MaybeCommit now removes every staged binary but the running version's.

Nothing is removed while a pending marker exists or cannot be read, at a
plain start, or after a rollback. Only a regular file with the exact name
Execute writes is removed. The rollback reads pending.json and
felhom-agent.prev, no staged binary: pinned by a test on the wrapper's text
and by a test that runs the wrapper's real commit and rollback verbs in a
sandbox. Red seen three times.

No version bump, no build, no vouch. /usr/local/bin/felhom-agent.bak-* is
not reached (root-owned; R-1368 part 4).

Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

internal/selfupdate/commit.go

@@ -128,4 +128,11 @@ func (m *Manager) MaybeCommit(ctx context.Context) {
 	if m.onCommitted != nil {
 		m.onCommitted(ctx)
 	}
+	// R-1368 part 2: the update ended healthy — the folder keeps the running version's binary and no other
+	// (prune.go). A refusal or a failed removal is logged and changes nothing about the commit.
+	if removed, err := pruneStaged(m.stateDir, m.runningVersion, m.logger); err != nil {
+		m.logger.Warn("selfupdate: old staged binaries NOT removed after the commit", "err", err)
+	} else if len(removed) > 0 {
+		m.logger.Info("selfupdate: old staged binaries removed after the commit", "count", len(removed), "kept", "felhom-agent-"+m.runningVersion)
+	}
 }