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F2: Template Store, Registry & Versioning (NTF-002, NTF-009, NTF-028, NTF-029) ​

1. Technical Summary & Behavior ​

Versioned notification template catalog supporting subject and body templates, language tagging, and multi-tenant isolation.

  • Feature ID: F2
  • Source Files: backend/src/models/store.py, backend/src/templates/engine.py
  • Key Implementation Lines: store.py:89-125 (TemplateRecord), templates/engine.py:39-74 (register_template, get_template_version)
  • Data & Schema: templates (id, tenant_id, name, channel, version, language, body_template, subject_template, status, is_active, approved_by, approved_at, deactivated_by, deactivated_at, created_at)

2. Architecture & Data Flow ​

3. Sequence Flow Diagram ​

4. Failure Path & Resilience Diagram ​

5. Security & Edge Case Considerations ​

  • Tenant Isolation: Every query and operation scopes explicitly to tenant_id. Cross-tenant data leakage is structurally prevented.
  • Data Sanitization & Encryption: Sensitive recipient tokens and provider secrets are encrypted with Fernet and masked on all outputs.
  • Idempotency: Requests enforce unique constraint hashes to prevent duplicate dispatch under network retries.

6. Say It Out Loud (Spoken Interview Script) ​

"I designed the template registry to allow engineering and product teams to manage notification copy independently of application deployments. In backend/src/templates/engine.py, templates are identified by tenant, template name, version, and language code. When selecting a template, the engine queries the latest active version or a pinned version number. I rejected storing templates in static JSON files or code constants because business requirements demand zero-downtime copy updates and multilingual support. If a requested template does not exist, the engine raises an explicit ValueError and logs the missing template name. One limitation is that templates are fetched per delivery request; in a high-volume production environment, I would add a local in-memory LRU cache with Redis Pub/Sub invalidation to eliminate database read overhead."