fix: use getModel() temperature as single source of truth in OpenAI handler

The OpenAiHandler computed temperature independently in createMessage(),
ignoring defaultTemperature from custom model info. This caused a 400
error with models like kimi-for-coding that only accept specific
temperature values (e.g. 0.6).

Changes:
- getModel() now detects deepseek reasoner models and passes the correct
  defaultTemperature to getModelParams()
- createMessage() streaming path uses temperature from getModel() instead
  of computing it separately
- createMessage() non-streaming path now includes temperature (was missing)
- completePrompt() now includes temperature (was missing)

This makes getModelParams() the single source of truth for temperature,
which respects: user overrides > model defaultTemperature > provider default.

Closes #12142

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

@@ -499,6 +499,87 @@ describe("OpenAiHandler", () => {
 		})
 	})
 
+	describe("temperature handling", () => {
+		const systemPrompt = "You are a helpful assistant."
+		const testMessages: Anthropic.Messages.MessageParam[] = [{ role: "user", content: "Hello!" }]
+
+		it("should use defaultTemperature from custom model info when no user temperature is set", async () => {
+			const handlerWithModelDefault = new OpenAiHandler({
+				...mockOptions,
+				openAiCustomModelInfo: {
+					...openAiModelInfoSaneDefaults,
+					defaultTemperature: 0.6,
+				},
+			})
+			const stream = handlerWithModelDefault.createMessage(systemPrompt, testMessages)
+			for await (const _chunk of stream) {
+			}
+			expect(mockCreate).toHaveBeenCalled()
+			const callArgs = mockCreate.mock.calls[0][0]
+			expect(callArgs.temperature).toBe(0.6)
+		})
+
+		it("should prefer user-set modelTemperature over defaultTemperature from model info", async () => {
+			const handlerWithUserTemp = new OpenAiHandler({
+				...mockOptions,
+				modelTemperature: 0.3,
+				openAiCustomModelInfo: {
+					...openAiModelInfoSaneDefaults,
+					defaultTemperature: 0.6,
+				},
+			})
+			const stream = handlerWithUserTemp.createMessage(systemPrompt, testMessages)
+			for await (const _chunk of stream) {
+			}
+			expect(mockCreate).toHaveBeenCalled()
+			const callArgs = mockCreate.mock.calls[0][0]
+			expect(callArgs.temperature).toBe(0.3)
+		})
+
+		it("should default to 0 when no user temperature and no model defaultTemperature", async () => {
+			const handlerNoTemp = new OpenAiHandler({
+				...mockOptions,
+			})
+			const stream = handlerNoTemp.createMessage(systemPrompt, testMessages)
+			for await (const _chunk of stream) {
+			}
+			expect(mockCreate).toHaveBeenCalled()
+			const callArgs = mockCreate.mock.calls[0][0]
+			expect(callArgs.temperature).toBe(0)
+		})
+
+		it("should use defaultTemperature in non-streaming path", async () => {
+			const handlerNonStreaming = new OpenAiHandler({
+				...mockOptions,
+				openAiStreamingEnabled: false,
+				openAiCustomModelInfo: {
+					...openAiModelInfoSaneDefaults,
+					defaultTemperature: 0.6,
+				},
+			})
+			const stream = handlerNonStreaming.createMessage(systemPrompt, testMessages)
+			for await (const _chunk of stream) {
+			}
+			expect(mockCreate).toHaveBeenCalled()
+			const callArgs = mockCreate.mock.calls[0][0]
+			expect(callArgs.temperature).toBe(0.6)
+		})
+
+		it("should use defaultTemperature in completePrompt", async () => {
+			const handlerWithModelDefault = new OpenAiHandler({
+				...mockOptions,
+				openAiCustomModelInfo: {
+					...openAiModelInfoSaneDefaults,
+					defaultTemperature: 0.6,
+				},
+			})
+			await handlerWithModelDefault.completePrompt("Hello")
+			expect(mockCreate).toHaveBeenCalled()
+			const callArgs = mockCreate.mock.calls[0][0]
+			expect(callArgs.temperature).toBe(0.6)
+		})
+	})
+
 	describe("error handling", () => {
 		const testMessages: Anthropic.Messages.MessageParam[] = [
 			{
@@ -547,6 +628,7 @@ describe("OpenAiHandler", () => {
 			expect(mockCreate).toHaveBeenCalledWith(
 				{
 					model: mockOptions.openAiModelId,
+					temperature: 0,
 					messages: [{ role: "user", content: "Test prompt" }],
 				},
 				{},
@@ -678,6 +760,7 @@ describe("OpenAiHandler", () => {
 			expect(mockCreate).toHaveBeenCalledWith(
 				{
 					model: azureOptions.openAiModelId,
+					temperature: 0,
 					messages: [
 						{ role: "system", content: systemPrompt },
 						{ role: "user", content: "Hello!" },
@@ -701,6 +784,7 @@ describe("OpenAiHandler", () => {
 			expect(mockCreate).toHaveBeenCalledWith(
 				{
 					model: azureOptions.openAiModelId,
+					temperature: 0,
 					messages: [{ role: "user", content: "Test prompt" }],
 				},
 				{ path: "/models/chat/completions" },

src/api/providers/openai.ts

@@ -84,7 +84,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 		messages: Anthropic.Messages.MessageParam[],
 		metadata?: ApiHandlerCreateMessageMetadata,
 	): ApiStream {
-		const { info: modelInfo, reasoning } = this.getModel()
+		const { info: modelInfo, reasoning, temperature } = this.getModel()
 		const modelUrl = this.options.openAiBaseUrl ?? ""
 		const modelId = this.options.openAiModelId ?? ""
 		const enabledR1Format = this.options.openAiR1FormatEnabled ?? false
@@ -154,7 +154,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 
 			const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsStreaming = {
 				model: modelId,
-				temperature: this.options.modelTemperature ?? (deepseekReasoner ? DEEP_SEEK_DEFAULT_TEMPERATURE : 0),
+				temperature,
 				messages: convertedMessages,
 				stream: true as const,
 				...(isGrokXAI ? {} : { stream_options: { include_usage: true } }),
@@ -223,6 +223,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 		} else {
 			const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsNonStreaming = {
 				model: modelId,
+				temperature,
 				messages: deepseekReasoner
 					? convertToR1Format([{ role: "user", content: systemPrompt }, ...messages])
 					: [systemMessage, ...convertToOpenAiMessages(messages)],
@@ -282,12 +283,14 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 	override getModel() {
 		const id = this.options.openAiModelId ?? ""
 		const info: ModelInfo = this.options.openAiCustomModelInfo ?? openAiModelInfoSaneDefaults
+		const enabledR1Format = this.options.openAiR1FormatEnabled ?? false
+		const isDeepSeekReasoner = id.includes("deepseek-reasoner") || enabledR1Format
 		const params = getModelParams({
 			format: "openai",
 			modelId: id,
 			model: info,
 			settings: this.options,
-			defaultTemperature: 0,
+			defaultTemperature: isDeepSeekReasoner ? DEEP_SEEK_DEFAULT_TEMPERATURE : 0,
 		})
 		return { id, info, ...params }
 	}
@@ -300,6 +303,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 
 			const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsNonStreaming = {
 				model: model.id,
+				temperature: model.temperature,
 				messages: [{ role: "user", content: prompt }],
 			}