fix(gemini): honor custom model ids instead of falling back to default (#227) (#317)

* fix(gemini): honor custom model ids instead of falling back to default (#227)

Selecting a custom Gemini model id not present in geminiModels (e.g.
gemini-3.5-flash) silently invoked geminiDefaultModelId. The settings
ModelPicker exposes a 'use custom model' option and useSelectedModel keeps
the configured id, so the UI and the actual request disagreed.

getModel() now honors a custom id when it looks like a Gemini model
(gemini- prefix), using the default model's structural info as a baseline
with pricing/tiers dropped so cost shows as unknown rather than the default
model's rates. Ids that don't look like Gemini still fall back to default.

* test(gemini): assert cache prices are cleared for custom models (#227)

* fix(gemini): use own-property check for known model ids (#227)

modelId in geminiModels also matches inherited Object.prototype keys
(e.g. "toString"), resolving info to a function. Use Object.hasOwn so only
real model keys match; prototype-key ids fall through to the default.

---------

Co-authored-by: Armando Vaquera <263793884+proyectoauraorg@users.noreply.github.com>

Author: proyectoauraorg

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

@@ -174,6 +174,38 @@ describe("GeminiHandler", () => {
 			expect(modelInfo.id).toBe(geminiDefaultModelId) // Default model
 		})
 
+		it("should honor a custom gemini model id not present in geminiModels (#227)", () => {
+			const customHandler = new GeminiHandler({
+				apiModelId: "gemini-3.5-flash",
+				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).not.toBe(geminiDefaultModelId)
+			// A baseline ModelInfo is provided so downstream params resolve.
+			expect(modelInfo.info).toBeDefined()
+			// Pricing is unknown for a custom model, so cost should not be reported
+			// against the default model's rates.
+			expect(modelInfo.info.inputPrice).toBeUndefined()
+			expect(modelInfo.info.outputPrice).toBeUndefined()
+			expect(modelInfo.info.cacheReadsPrice).toBeUndefined()
+			expect(modelInfo.info.cacheWritesPrice).toBeUndefined()
+			expect(modelInfo.info.tiers).toBeUndefined()
+		})
+
+		it("should not treat Object prototype keys as known models", () => {
+			// `"toString" in geminiModels` is true via the prototype chain, which would
+			// otherwise resolve `info` to a function. An own-property check avoids this.
+			const protoHandler = new GeminiHandler({
+				apiModelId: "toString",
+				geminiApiKey: "test-key",
+			})
+			const modelInfo = protoHandler.getModel()
+			expect(modelInfo.id).toBe(geminiDefaultModelId)
+			expect(modelInfo.info).toBeDefined()
+		})
+
 		it("should exclude apply_diff and include edit in tool preferences", () => {
 			const modelInfo = handler.getModel()
 			expect(modelInfo.info.excludedTools).toContain("apply_diff")

src/api/providers/gemini.ts

@@ -490,8 +490,35 @@ export class GeminiHandler extends BaseProvider implements SingleCompletionHandl
 
 	override getModel() {
 		const modelId = this.options.apiModelId
-		let id = modelId && modelId in geminiModels ? (modelId as GeminiModelId) : geminiDefaultModelId
-		let info: ModelInfo = geminiModels[id]
+		let id: string
+		let info: ModelInfo
+
+		if (modelId && Object.hasOwn(geminiModels, modelId)) {
+			id = modelId
+			info = geminiModels[modelId as GeminiModelId]
+		} else if (modelId && modelId.toLowerCase().startsWith("gemini-")) {
+			// Honor a custom/unlisted Gemini model id (e.g. a newly released model
+			// not yet in `geminiModels`) instead of silently falling back to the
+			// default. This mirrors the settings UI's "use custom model" option and
+			// the `useSelectedModel` hook, which both keep the configured id. Ids
+			// that don't look like Gemini models still fall back below.
+			id = modelId
+			// Use the default model's structural info as a baseline, but drop the
+			// pricing fields we can't verify for an unknown model so cost reporting
+			// shows "unknown" (calculateCost returns undefined) instead of charging
+			// the default model's rates against a different model.
+			info = {
+				...geminiModels[geminiDefaultModelId],
+				inputPrice: undefined,
+				outputPrice: undefined,
+				cacheReadsPrice: undefined,
+				cacheWritesPrice: undefined,
+				tiers: undefined,
+			}
+		} else {
+			id = geminiDefaultModelId
+			info = geminiModels[geminiDefaultModelId]
+		}
 
 		const params = getModelParams({
 			format: "gemini",