fix: cache merged pull requests immediately

[VedantKhairnar]

Closes #9

Caches a freshly ranked leaderboard after a counted merge, adding the webhook PR when GitHub search has not indexed it yet. If search fails, the old cache is cleared and the merge shoutout still posts.

How I tested this

• npm run typecheck
• npm test (190 tests)

AI assistance

• Used Codex to help implement the scoped cache update and test coverage; reviewed the diff and verified it locally.

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[anurag629]

Thanks @VedantKhairnar, the change itself is right. I tried it on top of current main (213 tests pass, typecheck clean), and both cache checks fail on main's code like they should. Dropping the append, appending every time and skipping the cache write each fail a test too.

One thing before I merge: the issue also asks for a test that the handler makes no more GitHub requests than before, and nothing checks that yet. If I add a second searchMergedPrs call to onPullRequest, every test still passes. One line in the first merged PR test is enough:

expect(fetched.calls.filter((c) => c.url.startsWith("https://api.github.com/"))).toHaveLength(1);

I tried it: it passes with your change and fails with the extra call.

[VedantKhairnar]

Addressed in dee4e5d: the lagging-search regression test now asserts that the handler makes exactly one GitHub API request. npm run typecheck and npm test both pass locally (190 tests).

[anurag629]

Thanks @VedantKhairnar, that's the one. With a second searchMergedPrs call in onPullRequest the first merged PR test fails now, and without it typecheck and all 222 tests pass on top of current develop. Merging.

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