Fix CDN invalid manifest cache recovery

[cursor]

Summary

• Reset all in-memory CDN manifest state when a persisted manifest cache entry is invalid.
• Clear runtime secrets, artifact mappings, ETag, and last-update metadata together so startup refetches the manifest instead of returning empty definitions.
• Add a regression test for corrupted cached manifest state.

Validation

• git diff --check HEAD~1..HEAD
• Dart/Flutter tests not run: dart/flutter executables are not available on PATH in this environment.

  

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Note

Medium Risk
Changes CDN manifest cache recovery and state-reset behavior, which affects app startup and refresh logic if a persisted cache entry is corrupted or stale.

Overview
Fixes corrupted CDN manifest cache recovery by clearing all in-memory provider state (artifact cache, mappings, config, ETag/_lastUpdatedAt, pending-update flag) and persisted SharedPreferences entry when cached manifest JSON cannot be decoded.

Refactors runtime secret cleanup into _clearRuntimeSecrets() and ensures it is invoked on manifest rebuilds and cache clears so secrets/env entries don’t linger across refreshes. Adds test-only hooks to load cached state and assert freshness metadata, plus a regression test covering invalid persisted cache invalidation.

^{Reviewed by Cursor Bugbot for commit 00ec9cc. Configure here.}