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Changes

Closes #7446

When a URL contains an environment identifier that does not correspond to a real environment for the current project (e.g. /project/1/environment/undefined/features), the dashboard previously showed an infinite loading spinner. Root cause:

1. useFeatureListWithApiKey returns skipToken when the env api_key does not resolve, so the features query is permanently skipped and isLoading never flips to false.
2. EnvironmentReadyChecker silently ignored the 404 from useGetEnvironmentQuery and fell through to render its children with the invalid environmentId.

EnvironmentReadyChecker now redirects to /project/:projectId/ when either the loaded environments list does not contain the URL's environmentId, or the per-environment query returns a 404. That route already handles "pick the default environment" via ProjectRedirectPage, so no new default-environment logic is introduced.

The redirect decision is extracted into a pure helper (common/utils/shouldRedirectMissingEnvironment) with unit tests covering nine cases including the ref guard against double-fire, partial loading states, zero-environment projects, and non-404 errors.

Notes for review

• Acknowledging the reverted PR fix: prevent infinite API loop on invalid environment URLs #7284 history: that earlier attempt rendered a NotFoundState UX which was reverted by fix: revert prevent infinite API loop on invalid environment URLs #7312. This PR takes the redirect approach explicitly called out in Features list loops in loading forever #7446's acceptance criterion.
• The checker is also switched from useRouteMatch to useRouteContext to match FeaturesPage/ProjectRedirectPage, and the now-unused match prop from ParameterizedRoute is removed.
• Zero-environment projects are intentionally not redirected so the create-environment flow can still be reached — flagging for UX review.

How did you test this code?

Automated

​ bash cd frontend npx jest common/utils/__tests__/shouldRedirectMissingEnvironment.test.ts ​

Expected: 9 passed. Type-check and lint are clean on the changed files.

Manual reproduction

With a local stack (ENV=local npm run dev against an API on localhost:8000), logged into a project with at least one environment:

1. Visit /project/1/environment/undefined/features - before: infinite spinner + repeating environments/undefined/ 404s; after: URL flips to the default environment, list renders.
2. Visit a valid env URL - no redirect, normal load.
3. Visit /project/1/environment/create - env-create flow loads (checker skipped).
4. Visit /project/99999/environment/undefined/features - bounces through /project/99999/ and inherits ProjectRedirectPage's org-home fallback.