[SatyamKumarCS]

References

Fixes #294

Code changes

When the package.json of a federated extension could not be fetched, the Packages tab silently showed that extension with almost no information, and it never retried until the whole page was reloaded. This PR makes the failure visible and recoverable.

src/known-modules.ts

• discoverFederatedKnownModules now resolves with the names of the extensions whose metadata could not be loaded (an empty list when everything worked). Previously a failed fetch returned null and nothing reported it.
• The "discovery complete" flag is only set when nothing failed. Extensions that failed are retried on the next call, even without force; force still refreshes everything.
• The extension package.json files are now fetched with bounded concurrency (6 at a time) instead of one after another.
• Added listFederatedDiscoveryFailures() which returns the names of the extensions that failed in the last run.

src/token-sidebar.tsx

• Added a Refresh button to the Packages view. It uses the existing force path of discoverKnownModules, which no part of the UI called before.
• When some extensions fail, the view shows a message such as "4 extensions could not be loaded: ... Refresh to retry."
• A partially failed discovery is no longer remembered as done, so switching back to the Packages tab retries the failures.
• discoverKnownModules in TokenSidebar.IOptions now returns Promise<ReadonlyArray<string>> (the failed names). The only caller is in src/index.ts, and its code did not need to change.

style/base.css: small layout rules for the message and the button.

ui-tests/tests/plugin-playground.spec.ts: new test, "packages view reports failed extension discovery and recovers on refresh". It blocks the extension package.json requests, checks that the message appears, unblocks, clicks Refresh, and checks that the extension recovers its real description.

User-facing changes

Before this change, if the package.json request failed (for example a flaky network), an entry like jupyterlab-tour went from having Docs / GitHub / package.json links and its real description to showing only an npm link and "Discovered federated extension package". The packages it shares (ajv, react-joyride) disappeared from the list too. There was no message, and the entry stayed broken even after the network recovered, until a full reload.

Before

The request for package.json is blocked, then restored without reloading:

Discovery fails silently	Still broken after the network recovers

After

Failure is reported, Refresh is offered	Recovered after clicking Refresh

The Refresh button shows as an icon in the narrow sidebar (the text label is hidden by existing styles at that width). It has the tooltip and aria-label "Refresh packages".

How I tested it

• Reproduced the problem in a clean environment with jupyterlab-tour and jupyterlab-js-logs installed, by blocking *extensions*package.json in the browser, then checked all three scenarios on the fixed build:
  • blocked: the message names the failed extensions;
  • unblocked, then switching to another tab and back: the entries recover without a reload;
  • blocked, reload, unblocked, click Refresh: the entries recover and the message disappears.
• jlpm playwright test tests/plugin-playground.spec.ts -g packages passes locally on JupyterLab 4.6.4: the new test and the existing Packages-view test.
• tsc --noEmit, ESLint and Prettier pass on the changed files.

AI usage

• Some or all of the content of this PR was generated by AI.
• The human author has carefully reviewed this PR and run this code.
• AI tools and models used: Claude (via Claude Code)

Backwards-incompatible changes

None for users. discoverFederatedKnownModules now returns the failed extension names instead of void, and TokenSidebar.IOptions.discoverKnownModules has the matching return type. Neither is part of the public IPluginPlayground API, and no other code in the repo used the old return value.

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