Fix email template loading and error handling for infrastructure alerts

[Retr0-XD]

Enhancements to the EmailService improve the loading of email templates and error handling. The changes ensure that when a template fails to load or compile, the error is logged and re-thrown, preventing the sending of empty emails. This addresses the issue of empty infrastructure alert emails.

Fixes #3054

Summary by CodeRabbit

• Improvements
  • Enhanced email template reliability with improved error handling and reporting.
  • Optimized email template initialization for faster performance.
  • Added template caching and lazy-loading for consistent email delivery.

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Walkthrough

The EmailService class was refactored to use synchronous initialization with template preloading instead of asynchronous initialization. A new loadTemplate() method loads and compiles templates, while buildEmail() now supports lazy-loading and caching of templates with enhanced error handling for templating failures.

Changes

Cohort / File(s)	Summary
Template initialization and caching server/src/service/v1/infrastructure/emailService.js	Changed init method from async to synchronous with preloaded templates; added loadTemplate() method for loading and compiling templates; introduced templateLookup object for caching compiled templates; enhanced buildEmail() with lazy-loading fallback and template validation; improved error handling with descriptive logging and re-throws

Sequence Diagram

sequenceDiagram
    participant Client
    participant EmailService
    participant TemplateSystem
    
    Note over Client,TemplateSystem: Initialization Phase
    Client->>EmailService: new EmailService()
    EmailService->>EmailService: init() [synchronous]
    EmailService->>TemplateSystem: loadTemplate() for each
    TemplateSystem-->>EmailService: compiled functions cached
    Note over EmailService: templateLookup populated
    
    Note over Client,TemplateSystem: Email Building Phase
    Client->>EmailService: buildEmail(templateName, ...)
    EmailService->>EmailService: Check templateLookup
    alt Template Found
        EmailService->>TemplateSystem: Use cached template
    else Template Not Found
        EmailService->>TemplateSystem: loadTemplate() with fallback logic
        TemplateSystem-->>EmailService: compiled function or null
        alt Load Success
            EmailService->>EmailService: Cache in templateLookup
        else Load Fails
            EmailService->>EmailService: Log & throw error
            EmailService-->>Client: Error
        end
    end
    EmailService->>TemplateSystem: Generate MJML → HTML
    EmailService-->>Client: HTML or empty string

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Areas requiring attention:
  • Logic in buildEmail() for template fallback resolution and lazy-loading behavior
  • Error handling paths and their impact on caller expectations
  • Verify all templates that should be preloaded are covered in init()
  • Confirm synchronous initialization doesn't block the application startup

Poem

🐰 Templates now load without a wait,
No empty emails, their proper fate!
Preloaded and cached, they're ready to go,
Infrastructure alerts will always show! 📧✨

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description provides context and includes the issue reference, but it lacks details on verification steps and doesn't follow the provided template with required checklist items.	Add a completed checklist from the template showing local deployment, self-review, and testing verification to confirm the fix resolves the empty email issue.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing email template loading and error handling for infrastructure alerts, which directly addresses the linked issue.
Linked Issues check	✅ Passed	The code changes directly address all key requirements from issue #3054: fixing template loading errors, preventing empty emails, and improving error handling through synchronous initialization and lazy-loading with caching.
Out of Scope Changes check	✅ Passed	All changes are focused on the EmailService template loading mechanism and error handling, directly scoped to fixing the infrastructure alert email issue with no unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

• [ ] 📝 Generate docstrings

🧪 Generate unit tests (beta)

• [ ] Create PR with unit tests
• [ ] Post copyable unit tests in a comment

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[ajhollid]

Closing as inactive