ThePalaceProject / web-patron / 24572737845 / 1

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Fix registry cache race condition (PP-4102) (#122)

## Description

Fixes a registry cache race condition by tracking the in-progress crawl
instead of returning an empty cache immediately. Duplicate overlapping
calls now await the in-progress call.

## Motivation and Context

After `npm run build && npm run start` (I did not see this bug with `npm
run dev`), the first navigation to a registry-sourced library page
intermittently returned a 404 ("No authentication document url is
configured"). A subsequent visit would succeed.

ISR was firing two near-simultaneous `getStaticProps` calls on a cold
page load. The first call set `lastAttemptedFetch` synchronously before
its async crawl completed. The second call hit the `shouldRefresh`
min-interval guard, returned immediately with an empty cache, and caused
the 404. The error page would set revalidation, so subsequent visits
worked once the first crawl had finished.

The fix tracks in-progress crawl promises, so subsequent requests await
the active crawl rather than bailing early.

[Jira PP-4102]

## How Has This Been Tested?

- Manual local testing with both `npm run build-and-start` and `npm run
dev`.
- New tests (happy path, failure path) specifically for that condition.
Happy path test failed against the pre-fix code.
- All checks pass locally.
- [CI
checks](https://github.com/ThePalaceProject/web-patron/actions/runs/24567733387)
pass.

## Checklist:

- [x] I have updated the documentation accordingly.
- [x] All new and existing tests passed.

155 of 195 branches covered (79.49%)

Branch coverage included in aggregate %.

283 of 345 relevant lines covered (82.03%)

10.77 hits per line