perf: parallelize jsDelivr README fallback probes

[trivikr]

🔗 Linked issue

N/A

🧭 Context

README fallback probing in server/utils/readme-loaders.ts was strictly sequential. On cache misses, packages with missing or nonstandard README filenames could pay for several failed jsDelivr requests before the loader found the right file or gave up, which made worst-case README render time noticeably slower than necessary.

📚 Description

This changes the jsDelivr README fallback path to reduce that long-tail latency while keeping the fallback behavior conservative.

• Build a prioritized candidate list that tries the npm registry’s readmeFilename first when it exists.
• Probe jsDelivr candidates in small parallel batches instead of one-by-one.
• Preserve existing fallback semantics for missing, nonstandard, and truncated npm READMEs.
• Add unit coverage for batched probing and candidate prioritization in test/unit/server/utils/readme-loaders.spec.ts.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
npmx.dev	Ready	Preview, Comment	Apr 5, 2026 3:15pm

2 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
docs.npmx.dev	Ignored	Preview	Apr 5, 2026 3:15pm
npmx-lunaria	Ignored		Apr 5, 2026 3:15pm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

📢 Thoughts on this report? Let us know!

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 8bca88e2-a235-400f-964e-0ac2f8ee89f5

📥 Commits

Reviewing files that changed from the base of the PR and between 9048f42 and 36fced5.

📒 Files selected for processing (1)

• server/utils/readme-loaders.ts

✅ Files skipped from review due to trivial changes (1)

• server/utils/readme-loaders.ts

---

📝 Walkthrough

Walkthrough

The PR changes server/utils/readme-loaders.ts to fetch candidate README filenames from jsDelivr in batches of three concurrently using Promise.all. fetchReadmeFromJsdelivr now returns the first successful body found within an earliest successful batch; failed fetches and non-OK responses yield null. A new internal buildReadmeFetchCandidates avoids duplicated candidates when a specific readmeFilename is provided. resolvePackageReadmeSource first tries the explicit readmeFilename alone, then falls back to the batched candidate list. Tests were added/expanded to cover batching, concurrency and candidate ordering. No exported signatures changed.

Possibly related PRs

• fix: use jsdelivr when npm has a truncated readme #1459: Modifies jsDelivr-first README resolution and filename/version handling within the same readme-loaders module.
• perf: load markdown source code on copy instead of on main request #1386: Directly alters fetchReadmeFromJsdelivr and resolvePackageReadmeSource implementations and their tests.

Suggested reviewers

• danielroe

🚥 Pre-merge checks | ✅ 1

✅ Passed checks (1 passed)

Check name	Status	Explanation
Description check	✅ Passed	The pull request description clearly relates to the changeset, detailing the problem (sequential README probing causing long-tail latency), the solution (batched-parallel probing), and the preserved semantics.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[trivikr]

Also updated PR to fetch provided readme before starting the fallback batch in 72bb0b2