fix(cache): evict stale entry on SWR revalidation failure

[pi0]

Summary

• When SWR background revalidation throws (e.g. handler returns 404), the stale cache entry is now evicted from storage
• When SWR background revalidation returns a value that fails validation (e.g. empty/undefined), the stale cache entry is now evicted from storage
• Previously, stale entries persisted indefinitely in both cases, causing the "stale forever" bug

Addresses upstream Nitro issues:

• nitrojs/nitro#3110 — SWR prevents cache expiration
• nitrojs/nitro#1992 — SWR cached routes never update if response is empty or 404
• Related PRs: nitrojs/nitro#2606, nitrojs/nitro#3263, nitrojs/nitro#4060

Changes

src/cache.ts: Added _evictFromStorage helper. Called in two places in _resolve:

1. In the catch block — when resolver throws, evict stale entry
2. After validate(entry) === false — when new value is invalid, evict stale entry

test/index.test.ts: Two regression tests confirming stale entries are evicted from storage after failed SWR revalidation.

Test plan

• Regression test: SWR evicts stale entry when bg revalidation throws
• Regression test: SWR evicts stale entry when bg revalidation result fails validation
• All 86 tests pass

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Configuration used: defaults

Review profile: CHILL

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Run ID: 10d741cd-075f-4f42-b95d-517c07e9f93b

📥 Commits

Reviewing files that changed from the base of the PR and between 58616e0 and 9f75858.

📒 Files selected for processing (2)

• src/cache.ts
• test/index.test.ts

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• Commit unit tests in branch fix/swr-issues

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