fix: external datasets are dropped from the atlas datasets tab when it has no hca datasets (#3236)

[frano-m]

Summary

Closes #3236

In getContentStaticProps, the append of atlas.externalDatasets lived inside the if (atlas.datasets.length > 0) guard, so an atlas with only external datasets rendered an empty datasets tab.

The guard now gates only the Azul fetch, which has moved into a fetchAtlasProjects helper. That helper returns [] early when the atlas has no HCA datasets, and a comment explains why the guard has to stay: filterProjectId([]) would send an empty filter that Azul doesn't define. External datasets are always merged. The merged list is sorted by title, ignoring case, the same as on main, where the old if (datasets) check on the always-present array was always true. So the order of HCA-only atlases doesn't change.

The Azul and CELLxGENE fetches now run in parallel.

Verification

• Lint, tsc --noEmit, prettier and npm run build-prod:data-portal pass.
• Probe: with the eye retina atlas's HCA datasets temporarily emptied, the built datasets.html listed the external dataset and no HCA project. Config restored afterwards.
• Normal build: the mixed eye retina atlas shows both HCA and external datasets.

Notes from review

• No test runner exists in the repo, so no regression test was added.
• Tracker atlases never get a datasets tab (datasets.tsx uses getNonTrackerStaticPaths), so the hard-coded projectsResponses: [] on the tracker path can't cause this bug.
• The non-tracker Overview page still fetches and embeds projectsResponses, which it never renders. Tracked in refactor: the non-tracker atlas overview page fetches azul projects it never renders #3249.

🤖 Generated with Claude Code

[NoopDog]

I'm requesting changes mainly because the branch needs a rebase (see eslint.config.mjs). The fix itself is correct: externalDatasets is a required ProjectsResponse[], so the old if (datasets) check isn't needed. Inline comments cover the rest. Two more findings are on lines outside this diff:

• utils/trackerAtlasPages.ts:87: tracker atlases have the same bug. The tracker path hard-codes projectsResponses: [] and never reads atlas.externalDatasets. A tracker-sourced atlas (breast, gut, liver and others) that gets a non-empty externalDatasets would show "No Source Studies" on its datasets tab, the same symptom #3236 fixes for non-tracker atlases. Merging externalDatasets in one shared place, or ruling it out in the type for tracker atlases, would close both paths.
• utils/atlasPages.ts: the Overview and Source Datasets pages fetch data they never show. They still go through this builder, so they make the Azul round trips and embed projectsResponses in __NEXT_DATA__ (now including external datasets), but only the Datasets main column reads it. A per-page option like the existing TrackerDataOptions could skip building it on those pages. Lower priority.

No page today is affected by the bug or by the ordering change, because every non-tracker atlas with external datasets also has HCA datasets.

[frano-m]

Replies to the two findings outside the diff:

• Tracker atlases (utils/trackerAtlasPages.ts:87): no change. Tracker atlases never get a Datasets tab, because datasets.tsx builds its pages with getNonTrackerStaticPaths. That tab's main column is the only thing that reads projectsResponses, so the hard-coded [] never reaches a page. None of the tracker atlases (breast, gut, liver) has any external datasets today either. If we want this guarded in the type, we can do it as a follow-on.
• Overview and Source Datasets fetch data they don't show: opened refactor: the non-tracker atlas overview page fetches azul projects it never renders #3249. Only the non-tracker Overview is affected. /source-datasets only builds for tracker atlases, and those take the tracker path, which makes no Azul request. refactor: the non-tracker atlas overview page fetches azul projects it never renders #3249 covers the non-tracker side of the same problem refactor: the atlas overview page fetches source datasets and source studies it never renders #3205 fixed for tracker atlases.

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused change satisfies the acceptance criteria without introducing unresolved issues.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes atlas dataset tabs so external-only atlases display their datasets.

Changes:

• Separates guarded Azul fetching into fetchAtlasProjects.
• Always merges and sorts external datasets.
• Runs Azul and CELLxGENE requests concurrently.

File	Description
utils/​atlasPages.ts	Corrects dataset merging and refactors concurrent fetching.

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