Retry transient GitHub initialization failures

[Copilot]

Transient failures fetching the authenticated user or repository metadata cached rejected promises, preventing PR overviews from recovering until reload. The resulting error also obscured which initialization dependency failed.

• Current user

  • Keep currentUser and isEmu on one shared request.
  • Clear both after rejection only when they still reference the failed request.
  • Route direct consumers through retry-aware accessors.

• Repository metadata

  • Clear transient rejected metadata promises with an identity guard.
  • Preserve resolved metadata and intentional non-SAML 404 session caching.

• PR overview errors

  • Add operation context to each parallel initialization request.
  • Replace the misleading description-specific error with a general PR update error.

• Fixes Transient connect timeout on GET /user (or repo metadata) permanently breaks PR overview until reload: rejected promises are cached (setCurrentUser / getMetadata) #8899

[azure-pipelines]

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