feat(cache): add persistent smartdata-backed cache with LocalTsmDb, cache cleaner, and DcRouter integration

readme.hints.md

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+- Nested objects with visual indentation
+
+## Smartdata Cache System (2026-02-03)
+
+### Overview
+DcRouter now uses smartdata + LocalTsmDb for persistent caching. Data is stored at `/etc/dcrouter/tsmdb`.
+
+### Technology Stack
+| Layer | Package | Purpose |
+|-------|---------|---------|
+| ORM | `@push.rocks/smartdata` | Document classes, decorators, queries |
+| Database | `@push.rocks/smartmongo` (LocalTsmDb) | Embedded TsmDB via Unix socket |
+
+### TC39 Decorators
+The project uses TC39 Stage 3 decorators (not experimental decorators). The tsconfig was updated:
+- Removed `experimentalDecorators: true`
+- Removed `emitDecoratorMetadata: true`
+
+This is required for smartdata v7+ compatibility.
+
+### Cache Document Classes
+Located in `ts/cache/documents/`:
+
+| Class | Purpose | Default TTL |
+|-------|---------|-------------|
+| `CachedEmail` | Email queue items | 30 days |
+| `CachedIPReputation` | IP reputation lookups | 24 hours |
+| `CachedBounce` | Bounce records | 30 days |
+| `CachedSuppression` | Suppression list | 30 days / permanent |
+| `CachedDKIMKey` | DKIM key pairs | 90 days |
+
+### Usage Pattern
+```typescript
+// Document classes use smartdata decorators
+@plugins.smartdata.Collection(() => getDb())
+export class CachedEmail extends CachedDocument<CachedEmail> {
+  @plugins.smartdata.svDb()
+  public createdAt: Date = new Date();
+
+  @plugins.smartdata.svDb()
+  public expiresAt: Date = new Date(Date.now() + TTL.DAYS_30);
+
+  @plugins.smartdata.unI()
+  @plugins.smartdata.svDb()
+  public id: string;
+  // ...
+}
+
+// Query examples
+const email = await CachedEmail.getInstance({ id: 'abc123' });
+const pending = await CachedEmail.getInstances({ status: 'pending' });
+await email.save();
+await email.delete();
+```
+
+### Configuration
+```typescript
+const dcRouter = new DcRouter({
+  cacheConfig: {
+    enabled: true,
+    storagePath: '/etc/dcrouter/tsmdb',
+    dbName: 'dcrouter',
+    cleanupIntervalHours: 1,
+    ttlConfig: {
+      emails: 30,       // days
+      ipReputation: 1,  // days
+      bounces: 30,      // days
+      dkimKeys: 90,     // days
+      suppression: 30   // days
+    }
+  }
+});
+```
+
+### Cache Cleaner
+- Runs hourly by default (configurable via `cleanupIntervalHours`)
+- Finds and deletes documents where `expiresAt < now()`
+- Uses smartdata's `getInstances()` + `delete()` pattern
+
+### Key Files
+- `ts/cache/classes.cachedb.ts` - CacheDb singleton wrapper
+- `ts/cache/classes.cached.document.ts` - Base class with TTL support
+- `ts/cache/classes.cache.cleaner.ts` - Periodic cleanup service
+- `ts/cache/documents/*.ts` - Document class definitions