- Replace all catch(err: any) with catch(err: unknown) across 8 source files
- Add errorMessage() and errorCode() helpers for safe error property access
- Type nodemailer transport config as SMTPTransport.Options (was any)
- Type health endpoint databaseStatus (was any)
- Type convert route margin param (was any)
- Change queryWithRetry params from any[] to unknown[]
- Update isTransientError to require Error instances (was accepting plain objects)
- 19 new TDD tests (error-type-safety.test.ts)
- Updated existing tests to use proper Error instances
- 598 tests total, all passing, zero type errors
