fix: do not enforce temperature of 0 for OpenAI compatible provider

When no custom temperature is set and the model is not a DeepSeek
reasoner, the OpenAI compatible provider was hardcoding temperature=0.
This overrode whatever server-side default the provider may have.

Changed the fallback to undefined so the temperature field is omitted
from the API request, letting the remote provider use its own default.

Fixes #12042

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

@@ -632,7 +632,7 @@ describe("OpenAiHandler", () => {
 					],
 					stream: true,
 					stream_options: { include_usage: true },
-					temperature: 0,
+					temperature: undefined,
 					tools: undefined,
 					tool_choice: undefined,
 					parallel_tool_calls: true,

src/api/providers/openai.ts

@@ -154,7 +154,8 @@ 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:
+					this.options.modelTemperature ?? (deepseekReasoner ? DEEP_SEEK_DEFAULT_TEMPERATURE : undefined),
 				messages: convertedMessages,
 				stream: true as const,
 				...(isGrokXAI ? {} : { stream_options: { include_usage: true } }),
@@ -287,7 +288,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 			modelId: id,
 			model: info,
 			settings: this.options,
-			defaultTemperature: 0,
+			defaultTemperature: undefined,
 		})
 		return { id, info, ...params }
 	}

src/api/transform/__tests__/model-params.spec.ts

@@ -123,6 +123,17 @@ describe("getModelParams", () => {
 			expect(result.temperature).toBe(0.3)
 		})
 
+		it("should return undefined temperature when defaultTemperature is undefined and no user/model temperature", () => {
+			const result = getModelParams({
+				...openaiParams,
+				settings: {},
+				model: baseModel,
+				defaultTemperature: undefined,
+			})
+
+			expect(result.temperature).toBeUndefined()
+		})
+
 		it("should use model maxTokens when available", () => {
 			const model: ModelInfo = {
 				...baseModel,

src/api/transform/model-params.ts

@@ -33,7 +33,7 @@ type GetModelParamsOptions<T extends Format> = {
 	modelId: string
 	model: ModelInfo
 	settings: ProviderSettings
-	defaultTemperature: number
+	defaultTemperature: number | undefined
 }
 
 type BaseModelParams = {