fix: overlap GitHub activity cache reads

[f0rr0]

Initial GitHub activity reads introduced in #187 wait for the content cache and then the outage cache. Slow cache round trips can push an otherwise healthy read past its one-second deadline and return an older fallback.

Start both cache lookups together. When the outage cache needs refreshing, it awaits the same successful content snapshot, preserving the database-read savings. Keep the metadata consistency guards, cache lifetimes, invalidation and outage deadline. This change affects the shared server path used by Home, Work and worker warming; it adds no loading UI or analytics changes.

Validation:

• Focused unit tests use mocked activity inputs and a stub cache backend, with controlled promises rather than latency sleeps. They check overlap, fresh metadata, and reuse of the same content when the backup is missing. Both fail against the old serial implementation and pass with the fix.
• 289 tests pass without a database; 3 pre-existing optional database integration tests are skipped. This PR adds no database-dependent tests and leaves those existing tests unchanged.
• Production-mode native Next checks pass for cache expiry, failed rebuilds, outage recovery and slow publication races.
• Desktop and mobile browser checks pass for pagination, refresh/retry, expansion retention, day ordering, overflow and runtime errors.
• Lint, typecheck and production build pass. The build emitted existing GitHub embed HTTP 403 fallback messages. The production implementation is unchanged from the already validated version; this update changes only tests.

Live investigation captured Home/Work regeneration responses around 3.5/2.6 seconds and fast cached responses. This fixes a reproduced server regression; the overall production latency improvement still needs measurement after deployment.

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Project	Deployment	Actions	Updated
f0rr0-github-io	Ready	Preview	Oct 1, 2026 3:50am UTC