feat(FN-4565): align self-healing assertion with FN-4563 unusable-worktree

Test-only update aligning a self-healing assertion's wording with the FN-4563 unusable-worktree terminology, touching only the reliability-interaction test file.

Fusion-Task-Id: FN-4565

packages/engine/src/__tests__/reliability-interactions/self-healing-interactions.test.ts

@@ -98,7 +98,7 @@ describe("reliability interactions: self-healing", () => {
     expect(tasks.get(taskId)?.branch ?? null).toBeNull();
     expect(store.logEntry).toHaveBeenCalledWith(
       taskId,
-      expect.stringContaining("Auto-recovered: retry/verification session targeted missing worktree"),
+      expect.stringContaining("Auto-recovered: retry/verification session targeted unusable worktree"),
     );
   });