[AI] Rename vertexAI to agentPlatform

[paulb777]

Description

This PR deprecates the Vertex AI backend configuration (Backend.vertexAI) in favor of the Gemini Enterprise Agent Platform (Backend.agentPlatform). In addition to renaming the public builders, this PR updates the internal representation and shifts the default location from "us-central1" to "global".

The internal code is systematically renamed to fully replace all non-public occurrences of the string vertexAI with agentPlatform (including staging endpoints, logging message codes, error configurations, and unit tests).

Backward compatibility is preserved: the deprecated public Backend.vertexAI() methods are kept functional (and verified in BackendTests.swift) by mapping them to the new .agentPlatform service case under the hood.

Note: A few tweaks to the pod_lib_tests are done to bypass warnings so we can continue to test the deprecated API.

---

Changes

Public API & Documentation

• Backend.swift:
  • Deprecated Backend.vertexAI() (without arguments), directing developers to Backend.agentPlatform() and informing them of the default location change to "global".
  • Deprecated Backend.vertexAI(location:), adding the @available(*, deprecated, renamed: "agentPlatform(location:)") compiler attribute for Xcode automatic Fix-It refactoring.
  • Added the new recommended builder: public static func agentPlatform(location: String = "global") -> Backend.
• CHANGELOG.md:
  • Added a change entry detailing the deprecation of Backend.vertexAI in favor of Backend.agentPlatform.

Internal Service & Error Renaming (vertexAI -> agentPlatform)

• APIConfig.swift:
  • Renamed the internal enum case APIConfig.Service.vertexAI to Service.agentPlatform.
  • Renamed the debug staging bypass case Endpoint.vertexAIStagingBypassProxy to Endpoint.agentPlatformStagingBypassProxy.
• FirebaseAI.swift:
  • Renamed internal helper function vertexAIModelResourceName to agentPlatformModelResourceName.
  • Updated pattern match switches to handle .agentPlatform and .agentPlatformStagingBypassProxy.
• GenerativeModel.swift:
  • Updated the debug staging bypass proxy case to .googleAI(endpoint: .agentPlatformStagingBypassProxy).
• AILog.swift & GenerativeAIService.swift:
  • Renamed the logging error code case vertexAIInFirebaseAPIDisabled to agentPlatformInFirebaseAPIDisabled.
• Request & Connection Modules:
  • Updated URL/path compilation matching in TemplateGenerateContentRequest.swift, TemplateImagenGenerationRequest.swift, LiveSessionService.swift, and CountTokensRequest.swift to match on .agentPlatform.

Test Suites & Snippets

• InstanceConfig.swift:
  • Renamed all configuration constants from vertexAI_v1beta... to agentPlatform_v1beta... and updated serviceName display values to "Agent Platform".
• VertexComponentTests.swift:
  • Renamed test cases (testModelResourceName_agentPlatform, testGenerativeModel_deprecatedVertexAI_defaultLocation, testGenerativeModel_deprecatedVertexAI_customLocation) and updated matching logic.
• Test Case Names:
  • Renamed testGenerateContentStream_failure_vertexAIInFirebaseAPINotEnabled() to testGenerateContentStream_failure_agentPlatformInFirebaseAPINotEnabled() in GenerativeModelVertexAITests.swift.
  • Renamed testGenerateContent_success_mapsGrounding_vertexAI() to testGenerateContent_success_mapsGrounding_agentPlatform() in TemplateGenerativeModelTests.swift.
  • Renamed testDecodeCitationMetadata_vertexAIFormat() to testDecodeCitationMetadata_agentPlatformFormat() in CitationMetadataTests.swift.
  • Renamed testEncodeCountTokensRequest_vertexAI_minimal() to testEncodeCountTokensRequest_agentPlatform_minimal() in CountTokensRequestTests.swift.
  • Updated all integration tests and snippets to use agentPlatform configurations instead of vertexAI.

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Verification Plan

Automated Tests

• Verified compilation checks for the deprecated API endpoints remain intact in APITests.swift.
• Verified functional mapping of deprecated methods continues to work in BackendTests.swift.

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[paulb777]

/gemini review

[gemini-code-assist]

Code Review

This pull request deprecates Backend.vertexAI in favor of Backend.agentPlatform (with the default location changing from "us-central1" to "global") and renames references to Vertex AI to Gemini Enterprise Agent Platform across the codebase. The review feedback highlights several unit tests that were incorrectly updated to use the new .agentPlatform backend, which removes test coverage for the deprecated .vertexAI methods they were originally designed to verify.

[paulb777]

/gemini review

[gemini-code-assist]

Code Review

This pull request renames Vertex AI to Gemini Enterprise Agent Platform (using agentPlatform internally) across the codebase, deprecating the old Backend.vertexAI methods in favor of Backend.agentPlatform with a new default location of "global". The review feedback primarily advises against excluding unit test files from the CocoaPods podspec to bypass deprecation warnings. Instead, the reviewer recommends keeping the tests active by marking the deprecated test cases with @available(*, deprecated) and ensuring that backward compatibility for the deprecated vertexAI method is still actively tested.

[paulb777]

/gemin review

[andrewheard]

LGTM. Feel free to ignore the CHANGELOG suggestion.