feat(firestore-genai-chatbot): add responseMimeType param

[CorieW]

Resolves #646

[Copilot]

Pull Request Overview

This PR adds a new responseMimeType parameter to allow callers to specify the MIME type of generated responses.

• Extended type definitions and Zod override schema with responseMimeType
• Propagated the new field through Vertex, Google, and Genkit client calls and config loading
• Exposed the parameter in the extension manifest, README, tests, and bumped the @google/generative-ai dependency

Reviewed Changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
functions/src/types.ts	Added responseMimeType to GenerateMessageOptions
functions/src/overrides.ts	Included responseMimeType in Zod overridesSchema
functions/src/generative-client/vertex_ai.ts	Passed responseMimeType into Vertex AI client options
functions/src/generative-client/google_ai.ts	Passed responseMimeType into Google AI client options
functions/src/generative-client/genkit.ts	Passed responseMimeType into Genkit client configuration
functions/src/config.ts	Added responseMimeType to Config interface and loaded from env
functions/package.json	Bumped @google/generative-ai from ^0.1.1 to ^0.11.0
tests/vertex_ai/index.test.ts	Increased wait time in the no-op integration test
tests/unit/overrides.test.ts	Updated unit test to include responseMimeType override
extension.yaml	Exposed RESPONSE_MIME_TYPE parameter in extension parameters
README.md	Documented the new Response MIME Type parameter
CHANGELOG.md	Added version 0.0.15 entry for responseMimeType feature

Files not reviewed (1)

• firestore-genai-chatbot/functions/package-lock.json: Language not supported

Comments suppressed due to low confidence (1)

firestore-genai-chatbot/functions/src/generative-client/vertex_ai.ts:90

• There are currently no unit tests asserting that responseMimeType is correctly included in the generated API request. Adding a test to verify this propagation would help prevent regressions.

responseMimeType: options.responseMimeType,

[Copilot]

[nitpick] The JSDoc comment for responseMimeType is quite generic. Consider specifying allowed or common MIME types (e.g., text/plain, application/json) or linking to a standard reference to clarify expected values.

[Copilot]

[nitpick] Using a real timeout to wait for asynchronous behavior can slow down the test suite. Consider using Jest's fake timers or mocking the relevant API call instead of increasing the delay.

Suggested change

	await new Promise(resolve => setTimeout(resolve, 1000));
	jest.advanceTimersByTime(1000);