feat(gemini): Gemini 3.5 Flash Support (#331)

* feat(gemini): gemini-3.5-flash support

* fix(vertex): reaffirm lack of support for reasoning budget

* Update packages/types/src/providers/gemini.ts

Co-authored-by: edelauna <54631123+edelauna@users.noreply.github.com>

* Update packages/types/src/providers/vertex.ts

Co-authored-by: edelauna <54631123+edelauna@users.noreply.github.com>

* fix(gemini): cov tests error

---------

Co-authored-by: edelauna <54631123+edelauna@users.noreply.github.com>

Author: jeanbispo

packages/types/src/providers/gemini.ts

@@ -6,6 +6,19 @@ export type GeminiModelId = keyof typeof geminiModels
 export const geminiDefaultModelId: GeminiModelId = "gemini-3.1-pro-preview"
 
 export const geminiModels = {
+	"gemini-3.5-flash": {
+		maxTokens: 65_536,
+		contextWindow: 1_048_576,
+		supportsImages: true,
+		supportsPromptCache: true,
+		supportsReasoningEffort: ["minimal", "low", "medium", "high"],
+		reasoningEffort: "medium",
+		inputPrice: 1.5,
+		outputPrice: 9,
+		cacheReadsPrice: 0.15,
+		cacheWritesPrice: 1.0,
+		supportsReasoningBudget: false,
+	},
 	"gemini-3.1-pro-preview": {
 		maxTokens: 65_536,
 		contextWindow: 1_048_576,

packages/types/src/providers/vertex.ts

@@ -6,6 +6,19 @@ export type VertexModelId = keyof typeof vertexModels
 export const vertexDefaultModelId: VertexModelId = "claude-sonnet-4-5@20250929"
 
 export const vertexModels = {
+	"gemini-3.5-flash": {
+		maxTokens: 65_536,
+		contextWindow: 1_048_576,
+		supportsImages: true,
+		supportsPromptCache: true,
+		supportsReasoningEffort: ["minimal", "low", "medium", "high"],
+		reasoningEffort: "medium",
+		inputPrice: 1.5,
+		outputPrice: 9,
+		cacheReadsPrice: 0.15,
+		cacheWritesPrice: 1.0,
+		supportsReasoningBudget: false,
+	},
 	"gemini-3.1-pro-preview": {
 		maxTokens: 65_536,
 		contextWindow: 1_048_576,

src/api/providers/__tests__/gemini.spec.ts

@@ -176,12 +176,12 @@ describe("GeminiHandler", () => {
 
 		it("should honor a custom gemini model id not present in geminiModels (#227)", () => {
 			const customHandler = new GeminiHandler({
-				apiModelId: "gemini-3.5-flash",
+				apiModelId: "gemini-9.9-nonexistent",
 				geminiApiKey: "test-key",
 			})
 			const modelInfo = customHandler.getModel()
 			// The configured id must be invoked, not silently swapped for the default.
-			expect(modelInfo.id).toBe("gemini-3.5-flash")
+			expect(modelInfo.id).toBe("gemini-9.9-nonexistent")
 			expect(modelInfo.id).not.toBe(geminiDefaultModelId)
 			// A baseline ModelInfo is provided so downstream params resolve.
 			expect(modelInfo.info).toBeDefined()