fix(context): implement loose boundary policy for gc backstop. (#26594)

packages/core/src/context/contextManager.barrier.test.ts

@@ -60,9 +60,7 @@ describe('ContextManager Sync Pressure Barrier Tests', () => {
 
     // Verify Episode 0 (System) was pruned, so we now start with a sentinel due to role alternation
     expect(projection[0].role).toBe('user');
-    expect(projection[0].parts![0].text).toBe(
-      '[Continuing from previous AI thoughts...]',
-    );
+    expect(projection[0].parts![0].text).toContain('User turn 17');
 
     // Filter out synthetic Yield nodes (they are model responses without actual tool/text bodies)
     const contentNodes = projection.filter(