v0.270.0: no update for a current app (R-679); an interrupted install is reported (R-681); a restore brings back the pinned version's health check (R-669); R-674

Five red-proofs. MinAgent 0.131.0 unchanged.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/stacks/ladder.go

@@ -136,6 +136,13 @@ func nextLadderStep(templateDir string, pinned map[string]string) (LadderStep, e
 		}
 	}
 	if idx < 0 {
+		// R-674 (v0.270.0): a pin equal to the newest entry's `to` is AT THE HEAD, not "older than the
+		// ladder" — the old sentence sent an operator looking for a missing record. Pinned by
+		// TestR674_HeadIsNotCalledOlder.
+		if sameRefs(ladder[len(ladder)-1].To, pinned) {
+			return LadderStep{Index: -1, Source: current, Meta: currentMeta,
+				Why: fmt.Sprintf("the installed version %s is AT THE HEAD of the update_ladder (%d entries) — the catalog's current definition", summarisePin(pinned), len(ladder))}, nil
+		}
 		return LadderStep{Index: -1, Source: current, Meta: currentMeta,
 			Why: fmt.Sprintf("the installed version %s matches no update_ladder entry (%d entries) — an app older than the ladder has no record to climb; the catalog's current definition", summarisePin(pinned), len(ladder))}, nil
 	}