Summary of Changes

Hello @bkendall, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the robustness of backend loading within the Firebase CLI by transitioning from a simple boolean flag to a promise-based caching system. This change is crucial for preventing race conditions and ensuring data consistency when multiple parts of the deployment process concurrently attempt to access or initialize backend configurations, particularly during complex deployments involving multiple Hosting sites and Functions.

Highlights

• Improved Parallelism: Refactored the existingBackend loading logic to use a promise-based pattern, ensuring safer parallel calls and preventing race conditions where multiple callers might receive inconsistent values.
• Race Condition Fix: Addressed an issue where deploying multiple Hosting sites with Functions could encounter a race condition, as noted in the changelog.
• API Change: Replaced the loadedExistingBackend boolean flag in the Context interface with an existingBackendPromise to facilitate the new asynchronous caching mechanism.
• Backend Loading Refactor: Modified existingBackend and loadExistingBackend functions to leverage the existingBackendPromise, ensuring that the backend is loaded only once and its result is shared across concurrent requests.