[#12] feat(loader): warm and invalidate CloudFront cache on publish

[jameswillis99]

What does this MR do?

Extends the prefillCloudfront worker to warm CloudFront's versioned cache and trigger per-project scoped CreateInvalidation on published loader paths after each project publish. This allows the loader_published CloudFront cache TTL to be safely raised from 30s to 300s — reducing origin load and storefront latency without serving stale content.

Per-project scoping is achieved via a CloudFront Function that embeds sorted project IDs into the code/published URL path at the edge, making cache entries targetable by project.

Changes

• platform/wab/package.json — add @aws-sdk/client-cloudfront dependency
• AppServer.ts — add /api/v1/loader/code/published/:projectIds route alongside the existing one; handles CloudFront-rewritten URLs (e.g. /published/aaa,zzz?projectId=aaa&...) with the same handler — no behaviour change, req.query.projectId is read as normal
• prefill-cloudfront.ts — after bundle generation and isPrefilled: true:
  1. GET each versioned CDN URL to warm CloudFront's versioned cache (Promise.allSettled, 30s timeout per request)
  2. Call CloudFrontClient.CreateInvalidation with per-combination paths for code/published (e.g. /published/p1,p2,p3*) and per-project paths for repr-v2/v3/html (which already have :projectId in the route)
• prefill-cloudfront.spec.ts — tests for ordering (isPrefilled before warming, warming before invalidation), warming URL construction, per-project invalidation paths, env var guard, warming failure handling, and resilience when CloudFront API throws

Design decisions

Ordering is critical: isPrefilled is set before CDN warming so origin serves pre-computed S3 bundles during warm requests. Warming precedes invalidation so clients following the published→versioned redirect always get a cache hit.

Per-project invalidation for code/published: CloudFront invalidations match on URI path only — query strings are ignored. A CloudFront Function rewrites /published?projectId=aaa&projectId=zzz → /published/aaa,zzz?projectId=aaa&... at the edge. Invalidation then targets /published/aaa* which matches all combinations containing aaa without touching other projects.

repr/html already scoped: repr-v2/published/:projectId, repr-v3/published/:projectId, and html/published/:projectId/:component already have the project ID in the path — no CloudFront Function needed for those.

Non-fatal failures: Warming fetches use Promise.allSettled with a 30s timeout; failures are logged with a count but don't block the publish flow. Invalidation errors are also non-fatal.

Environment guard: Everything is skipped when CLOUDFRONT_DISTRIBUTION_ID is unset — local dev and non-CDN environments are unaffected.

Testing

Unit tests cover: correct warming fetch URLs per publishment, isPrefilled set before first fetch, invalidation fired after all warm fetches, per-combination code/published paths (e.g. /published/p1,p2,p3*), per-project repr/html paths, warning logged on warming failures, no-op when env var absent, graceful handling of CloudFront API errors.