feat(ai-gemini): expose stateful Interactions API (previous_interaction_id)

[tombeckenham]

Problem

The @google/genai SDK (v1.43+) exposes a preview Interactions API that provides server-side conversation state — the Gemini equivalent of OpenAI's Responses API (previous_response_id / conversation). This lets callers skip storing and replaying message history on their side.

// @google/genai
const interaction1 = await ai.interactions.create({
  model: 'gemini-2.5-flash',
  input: 'Hi, my name is Amir.',
})

const interaction2 = await ai.interactions.create({
  model: 'gemini-2.5-flash',
  input: 'What is my name?',
  previous_interaction_id: interaction1.id, // server-side state
})

Today the ai-gemini text adapter routes through the stateless client.models.generateContent / generateContentStream path (packages/typescript/ai-gemini/src/adapters/text.ts:131,177), so there's no way to take advantage of this — even via providerOptions.

For comparison, ai-openai already supports the equivalent pattern: it uses the Responses API (client.responses.create) and exposes previous_response_id / conversation via providerOptions (packages/typescript/ai-openai/src/text/text-provider-options.ts:30,49).

Proposal

Add first-class support for Gemini's Interactions API. Two reasonable shapes:

1. New tree-shakeable adapter — e.g. geminiInteractions() alongside geminiText(), calling client.interactions.create under the hood. Matches the existing tree-shakeable adapter convention.
2. Opt-in via providerOptions — e.g. providerOptions.previous_interaction_id on the existing text adapter, with the adapter routing to client.interactions.create when that option (or a dedicated flag) is present.

Option 1 is probably cleaner given the Interactions API has a different request/response shape than generateContent, and it keeps the stateless path simple.

Notes / caveats

• The Interactions API is currently marked preview/experimental in @google/genai — worth flagging in docs and JSDoc.
• Response-id capture: callers need a way to read the interaction id off the returned response to pass back next turn. Needs a small addition to the chat result shape, or a provider-specific metadata field.
• Tool calling, streaming, and multimodal input parity with the existing text adapter should be confirmed against the Interactions API surface before shipping.

Context

Came up in discussion — users want to avoid plumbing conversation history through their own storage when the provider already offers it server-side. OpenAI side is already covered; Gemini side is the gap.

[nilsingwersen]

Now with the release of @google/genai version 2 that package should also be updated. Interactions API is the way forward for the gemini api