feat(compaction): add proactive context budget and checkpointing

src/config/schema.test.ts

@@ -1169,6 +1169,12 @@ describe('configSchema — compaction importance threshold', () => {
   it('defaults compaction importance threshold to disabled behavior', () => {
     const result = configSchema.parse(minimalConfig);
     expect(result.compaction.importance_threshold).toBe(1);
+    expect(result.compaction.proactive.enabled).toBe(false);
+    expect(result.compaction.proactive.warn_pct).toBe(75);
+    expect(result.compaction.proactive.checkpoint_pct).toBe(85);
+    expect(result.compaction.proactive.auto_compact_pct).toBe(95);
+    expect(result.compaction.proactive.checkpoint_cooldown_ms).toBe(300000);
+    expect(result.compaction.proactive.memory_namespace).toBe('session/checkpoints');
   });
 
   it('accepts a custom importance threshold', () => {
@@ -1176,9 +1182,23 @@ describe('configSchema — compaction importance threshold', () => {
       ...minimalConfig,
       compaction: {
         importance_threshold: 0.5,
+        proactive: {
+          enabled: true,
+          warn_pct: 70,
+          checkpoint_pct: 82,
+          auto_compact_pct: 93,
+          checkpoint_cooldown_ms: 120000,
+          memory_namespace: 'notes/checkpoints',
+        },
       },
     });
     expect(result.compaction.importance_threshold).toBe(0.5);
+    expect(result.compaction.proactive.enabled).toBe(true);
+    expect(result.compaction.proactive.warn_pct).toBe(70);
+    expect(result.compaction.proactive.checkpoint_pct).toBe(82);
+    expect(result.compaction.proactive.auto_compact_pct).toBe(93);
+    expect(result.compaction.proactive.checkpoint_cooldown_ms).toBe(120000);
+    expect(result.compaction.proactive.memory_namespace).toBe('notes/checkpoints');
   });
 });