[quirogas]

Description

Reuse the PubSub GoogleAuth instance across underlying GAPIC clients and JSDocs.

Impact

Prevents duplicate GoogleAuth instantiations and duplicate credential deprecation warnings in PubSub.

Changes

• Reuse this.options.auth in PubSub constructor if provided, and pass this.options.auth ??= this.auth in getClientConfig() so PublisherClient, SubscriberClient, and SchemaServiceClient share the same GoogleAuth instance.
• Sync GAPIC JWT properties (defaultServicePath, useJWTAccessWithScope, defaultScopes) onto this.auth.cachedCredential in getClientAsync_() and getSchemaClient() when getProjectId() has already cached a JWT client prior to GAPIC client initialization.
• Add @deprecated notices to ClientConfig JSDoc properties keyFilename and credentials in handwritten/pubsub/src/pubsub.ts.

Testing

• Added unit tests in handwritten/pubsub/test/pubsub.ts verifying options.auth reuse in new PubSub({auth}) and getClientAsync_().
• Added unit tests in handwritten/pubsub/test/pubsub.ts verifying GAPIC JWT property synchronization on this.auth.cachedCredential in getClientAsync_() and getSchemaClient().

Alternatives

• Leaving PubSub to create a separate GoogleAuth instance per underlying GAPIC client causes duplicate GoogleAuth constructor warnings when keyFilename or credentials is passed and reloads credentials unnecessarily.

[gemini-code-assist]

Code Review

This pull request updates the PubSub class to support reusing an existing GoogleAuth instance if provided in the options, and marks the keyFilename and credentials options as deprecated in the JSDoc. It also introduces logic to sync GAPIC JWT values on the cached credential when instantiating clients, ensuring existing properties are not overwritten. Corresponding unit tests have been added to verify these changes. There are no review comments, so I have no feedback to provide.