Link to Issue or Description of Change

Problem:
The AuthConfig type in EventActions (defined in core/src/events/event_actions.ts) was typed as any with a TODO: b/425992518. This lacked proper type safety and permitted incorrect assignments elsewhere in the codebase.

Solution:
Replaced any with the proper AuthConfig import from ../auth/auth_tool.js.
To resolve resulting TypeScript compiler errors:

• Initialized requestedAuthConfigs as an empty object {} instead of an empty array [] inside the default actions block of token_based_context_compactor.ts.
• Imported AuthConfig and cast actions.requestedAuthConfigs as Record<string, AuthConfig> (rather than Record<string, unknown>) in vertex_ai_session_service.ts.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Summary of passed npm test results:

• Ran npm run test:unit locally.
• All 142 test files and 1782/1782 tests passed successfully.

Manual End-to-End (E2E) Tests:

Verified that compiling the workspaces via npm run build succeeds without any TypeScript diagnostic errors (which previously failed on tsc with TS2322).

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

Addresses TODO: b/425992518 - Replace 'any' with a proper AuthConfig.