feat: enable mergeToolResultText for all OpenAI-compatible providers

src/api/providers/base-openai-compatible-provider.ts

@@ -90,7 +90,13 @@ export abstract class BaseOpenAiCompatibleProvider<ModelName extends string>
 			model,
 			max_tokens,
 			temperature,
-			messages: [{ role: "system", content: systemPrompt }, ...convertToOpenAiMessages(messages)],
+			// Enable mergeToolResultText to merge environment_details and other text content
+			// after tool_results into the last tool message. This prevents reasoning/thinking
+			// models from dropping reasoning_content when they see a user message after tool results.
+			messages: [
+				{ role: "system", content: systemPrompt },
+				...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
+			],
 			stream: true,
 			stream_options: { include_usage: true },
 			...(metadata?.tools && { tools: this.convertToolsForOpenAI(metadata.tools) }),

src/api/providers/cerebras.ts

@@ -106,7 +106,7 @@ export class CerebrasHandler extends BaseProvider implements SingleCompletionHan
 			supportsNativeTools && metadata?.tools && metadata.tools.length > 0 && metadata?.toolProtocol !== "xml"
 
 		// Convert Anthropic messages to OpenAI format (Cerebras is OpenAI-compatible)
-		const openaiMessages = convertToOpenAiMessages(messages)
+		const openaiMessages = convertToOpenAiMessages(messages, { mergeToolResultText: true })
 
 		// Prepare request body following Cerebras API specification exactly
 		const requestBody: Record<string, any> = {

src/api/providers/chutes.ts

@@ -44,7 +44,10 @@ export class ChutesHandler extends RouterProvider implements SingleCompletionHan
 		const params: OpenAI.Chat.Completions.ChatCompletionCreateParamsStreaming = {
 			model,
 			max_tokens,
-			messages: [{ role: "system", content: systemPrompt }, ...convertToOpenAiMessages(messages)],
+			messages: [
+				{ role: "system", content: systemPrompt },
+				...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
+			],
 			stream: true,
 			stream_options: { include_usage: true },
 			...(metadata?.tools && { tools: metadata.tools }),

src/api/providers/deepinfra.ts

@@ -72,7 +72,10 @@ export class DeepInfraHandler extends RouterProvider implements SingleCompletion
 
 		const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsStreaming = {
 			model: modelId,
-			messages: [{ role: "system", content: systemPrompt }, ...convertToOpenAiMessages(messages)],
+			messages: [
+				{ role: "system", content: systemPrompt },
+				...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
+			],
 			stream: true,
 			stream_options: { include_usage: true },
 			reasoning_effort,

src/api/providers/featherless.ts

@@ -44,7 +44,10 @@ export class FeatherlessHandler extends BaseOpenAiCompatibleProvider<Featherless
 			model,
 			max_tokens,
 			temperature,
-			messages: [{ role: "system", content: systemPrompt }, ...convertToOpenAiMessages(messages)],
+			messages: [
+				{ role: "system", content: systemPrompt },
+				...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
+			],
 			stream: true,
 			stream_options: { include_usage: true },
 		}

src/api/providers/huggingface.ts

@@ -56,7 +56,10 @@ export class HuggingFaceHandler extends BaseProvider implements SingleCompletion
 		const params: OpenAI.Chat.Completions.ChatCompletionCreateParamsStreaming = {
 			model: modelId,
 			temperature,
-			messages: [{ role: "system", content: systemPrompt }, ...convertToOpenAiMessages(messages)],
+			messages: [
+				{ role: "system", content: systemPrompt },
+				...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
+			],
 			stream: true,
 			stream_options: { include_usage: true },
 		}

src/api/providers/lite-llm.ts

@@ -45,7 +45,7 @@ export class LiteLLMHandler extends RouterProvider implements SingleCompletionHa
 	): ApiStream {
 		const { id: modelId, info } = await this.fetchModel()
 
-		const openAiMessages = convertToOpenAiMessages(messages)
+		const openAiMessages = convertToOpenAiMessages(messages, { mergeToolResultText: true })
 
 		// Prepare messages with cache control if enabled and supported
 		let systemMessage: OpenAI.Chat.ChatCompletionMessageParam

src/api/providers/lm-studio.ts

@@ -44,7 +44,7 @@ export class LmStudioHandler extends BaseProvider implements SingleCompletionHan
 	): ApiStream {
 		const openAiMessages: OpenAI.Chat.ChatCompletionMessageParam[] = [
 			{ role: "system", content: systemPrompt },
-			...convertToOpenAiMessages(messages),
+			...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
 		]
 
 		// LM Studio always supports native tools (https://lmstudio.ai/docs/developer/core/tools)

src/api/providers/openai.ts

@@ -126,7 +126,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 					}
 				}
 
-				convertedMessages = [systemMessage, ...convertToOpenAiMessages(messages)]
+				convertedMessages = [systemMessage, ...convertToOpenAiMessages(messages, { mergeToolResultText: true })]
 
 				if (modelInfo.supportsPromptCache) {
 					// Note: the following logic is copied from openrouter:
@@ -234,7 +234,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 					? convertToR1Format([{ role: "user", content: systemPrompt }, ...messages])
 					: enabledLegacyFormat
 						? [systemMessage, ...convertToSimpleMessages(messages)]
-						: [systemMessage, ...convertToOpenAiMessages(messages)],
+						: [systemMessage, ...convertToOpenAiMessages(messages, { mergeToolResultText: true })],
 				...(metadata?.tools && { tools: this.convertToolsForOpenAI(metadata.tools) }),
 				...(metadata?.tool_choice && { tool_choice: metadata.tool_choice }),
 				...(metadata?.toolProtocol === "native" && {
@@ -349,7 +349,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 						role: "developer",
 						content: `Formatting re-enabled\n${systemPrompt}`,
 					},
-					...convertToOpenAiMessages(messages),
+					...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
 				],
 				stream: true,
 				...(isGrokXAI ? {} : { stream_options: { include_usage: true } }),
@@ -386,7 +386,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 						role: "developer",
 						content: `Formatting re-enabled\n${systemPrompt}`,
 					},
-					...convertToOpenAiMessages(messages),
+					...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
 				],
 				reasoning_effort: modelInfo.reasoningEffort as "low" | "medium" | "high" | undefined,
 				temperature: undefined,

src/api/providers/openrouter.ts

@@ -229,13 +229,15 @@ export class OpenRouterHandler extends BaseProvider implements SingleCompletionH
 
 		// Convert Anthropic messages to OpenAI format.
 		// Pass normalization function for Mistral compatibility (requires 9-char alphanumeric IDs)
+		// Enable mergeToolResultText to merge environment_details after tool_results into the last
+		// tool message, preventing reasoning/thinking models from dropping reasoning_content.
 		const isMistral = modelId.toLowerCase().includes("mistral")
 		let openAiMessages: OpenAI.Chat.ChatCompletionMessageParam[] = [
 			{ role: "system", content: systemPrompt },
-			...convertToOpenAiMessages(
-				messages,
-				isMistral ? { normalizeToolCallId: normalizeMistralToolCallId } : undefined,
-			),
+			...convertToOpenAiMessages(messages, {
+				mergeToolResultText: true,
+				...(isMistral && { normalizeToolCallId: normalizeMistralToolCallId }),
+			}),
 		]
 
 		// DeepSeek highly recommends using user instead of system role.

src/api/providers/qwen-code.ts

@@ -222,7 +222,7 @@ export class QwenCodeHandler extends BaseProvider implements SingleCompletionHan
 			content: systemPrompt,
 		}
 
-		const convertedMessages = [systemMessage, ...convertToOpenAiMessages(messages)]
+		const convertedMessages = [systemMessage, ...convertToOpenAiMessages(messages, { mergeToolResultText: true })]
 
 		const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsStreaming = {
 			model: model.id,

src/api/providers/requesty.ts

@@ -140,7 +140,7 @@ export class RequestyHandler extends BaseProvider implements SingleCompletionHan
 
 		const openAiMessages: OpenAI.Chat.ChatCompletionMessageParam[] = [
 			{ role: "system", content: systemPrompt },
-			...convertToOpenAiMessages(messages),
+			...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
 		]
 
 		// Map extended efforts to OpenAI Chat Completions-accepted values (omit unsupported)

src/api/providers/roo.ts

@@ -100,7 +100,13 @@ export class RooHandler extends BaseOpenAiCompatibleProvider<string> {
 			model,
 			max_tokens,
 			temperature,
-			messages: [{ role: "system", content: systemPrompt }, ...convertToOpenAiMessages(messages)],
+			// Enable mergeToolResultText to merge environment_details and other text content
+			// after tool_results into the last tool message. This prevents reasoning/thinking
+			// models from dropping reasoning_content when they see a user message after tool results.
+			messages: [
+				{ role: "system", content: systemPrompt },
+				...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
+			],
 			stream: true,
 			stream_options: { include_usage: true },
 			...(reasoning && { reasoning }),

src/api/providers/unbound.ts

@@ -86,7 +86,7 @@ export class UnboundHandler extends RouterProvider implements SingleCompletionHa
 
 		const openAiMessages: OpenAI.Chat.ChatCompletionMessageParam[] = [
 			{ role: "system", content: systemPrompt },
-			...convertToOpenAiMessages(messages),
+			...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
 		]
 
 		if (info.supportsPromptCache) {

src/api/providers/vercel-ai-gateway.ts

@@ -45,7 +45,7 @@ export class VercelAiGatewayHandler extends RouterProvider implements SingleComp
 
 		const openAiMessages: OpenAI.Chat.ChatCompletionMessageParam[] = [
 			{ role: "system", content: systemPrompt },
-			...convertToOpenAiMessages(messages),
+			...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
 		]
 
 		if (VERCEL_AI_GATEWAY_PROMPT_CACHING_MODELS.has(modelId) && info.supportsPromptCache) {

src/api/providers/xai.ts

@@ -66,7 +66,7 @@ export class XAIHandler extends BaseProvider implements SingleCompletionHandler
 			temperature: this.options.modelTemperature ?? XAI_DEFAULT_TEMPERATURE,
 			messages: [
 				{ role: "system", content: systemPrompt },
-				...convertToOpenAiMessages(messages),
+				...convertToOpenAiMessages(messages, { mergeToolResultText: true }),
 			] as OpenAI.Chat.ChatCompletionMessageParam[],
 			stream: true as const,
 			stream_options: { include_usage: true },

src/api/transform/__tests__/openai-format.spec.ts

@@ -224,4 +224,181 @@ describe("convertToOpenAiMessages", () => {
 		const assistantMessage = openAiMessages[0] as OpenAI.Chat.ChatCompletionAssistantMessageParam
 		expect(assistantMessage.tool_calls![0].id).toBe("custom_toolu_123")
 	})
+
+	describe("mergeToolResultText option", () => {
+		it("should merge text content into last tool message when mergeToolResultText is true", () => {
+			const anthropicMessages: Anthropic.Messages.MessageParam[] = [
+				{
+					role: "user",
+					content: [
+						{
+							type: "tool_result",
+							tool_use_id: "tool-123",
+							content: "Tool result content",
+						},
+						{
+							type: "text",
+							text: "<environment_details>\nSome context\n</environment_details>",
+						},
+					],
+				},
+			]
+
+			const openAiMessages = convertToOpenAiMessages(anthropicMessages, { mergeToolResultText: true })
+
+			// Should produce only one tool message with merged content
+			expect(openAiMessages).toHaveLength(1)
+			const toolMessage = openAiMessages[0] as OpenAI.Chat.ChatCompletionToolMessageParam
+			expect(toolMessage.role).toBe("tool")
+			expect(toolMessage.tool_call_id).toBe("tool-123")
+			expect(toolMessage.content).toBe(
+				"Tool result content\n\n<environment_details>\nSome context\n</environment_details>",
+			)
+		})
+
+		it("should merge text into last tool message when multiple tool results exist", () => {
+			const anthropicMessages: Anthropic.Messages.MessageParam[] = [
+				{
+					role: "user",
+					content: [
+						{
+							type: "tool_result",
+							tool_use_id: "call_1",
+							content: "First result",
+						},
+						{
+							type: "tool_result",
+							tool_use_id: "call_2",
+							content: "Second result",
+						},
+						{
+							type: "text",
+							text: "<environment_details>Context</environment_details>",
+						},
+					],
+				},
+			]
+
+			const openAiMessages = convertToOpenAiMessages(anthropicMessages, { mergeToolResultText: true })
+
+			// Should produce two tool messages, with text merged into the last one
+			expect(openAiMessages).toHaveLength(2)
+			expect((openAiMessages[0] as OpenAI.Chat.ChatCompletionToolMessageParam).content).toBe("First result")
+			expect((openAiMessages[1] as OpenAI.Chat.ChatCompletionToolMessageParam).content).toBe(
+				"Second result\n\n<environment_details>Context</environment_details>",
+			)
+		})
+
+		it("should NOT merge text when images are present (fall back to user message)", () => {
+			const anthropicMessages: Anthropic.Messages.MessageParam[] = [
+				{
+					role: "user",
+					content: [
+						{
+							type: "tool_result",
+							tool_use_id: "tool-123",
+							content: "Tool result content",
+						},
+						{
+							type: "image",
+							source: {
+								type: "base64",
+								media_type: "image/png",
+								data: "base64data",
+							},
+						},
+					],
+				},
+			]
+
+			const openAiMessages = convertToOpenAiMessages(anthropicMessages, { mergeToolResultText: true })
+
+			// Should produce a tool message AND a user message (because image is present)
+			expect(openAiMessages).toHaveLength(2)
+			expect((openAiMessages[0] as OpenAI.Chat.ChatCompletionToolMessageParam).role).toBe("tool")
+			expect(openAiMessages[1].role).toBe("user")
+		})
+
+		it("should create separate user message when mergeToolResultText is false", () => {
+			const anthropicMessages: Anthropic.Messages.MessageParam[] = [
+				{
+					role: "user",
+					content: [
+						{
+							type: "tool_result",
+							tool_use_id: "tool-123",
+							content: "Tool result content",
+						},
+						{
+							type: "text",
+							text: "<environment_details>\nSome context\n</environment_details>",
+						},
+					],
+				},
+			]
+
+			const openAiMessages = convertToOpenAiMessages(anthropicMessages, { mergeToolResultText: false })
+
+			// Should produce a tool message AND a separate user message (default behavior)
+			expect(openAiMessages).toHaveLength(2)
+			expect((openAiMessages[0] as OpenAI.Chat.ChatCompletionToolMessageParam).role).toBe("tool")
+			expect((openAiMessages[0] as OpenAI.Chat.ChatCompletionToolMessageParam).content).toBe(
+				"Tool result content",
+			)
+			expect(openAiMessages[1].role).toBe("user")
+		})
+
+		it("should work with normalizeToolCallId when mergeToolResultText is true", () => {
+			const anthropicMessages: Anthropic.Messages.MessageParam[] = [
+				{
+					role: "user",
+					content: [
+						{
+							type: "tool_result",
+							tool_use_id: "call_5019f900a247472bacde0b82",
+							content: "Tool result content",
+						},
+						{
+							type: "text",
+							text: "<environment_details>Context</environment_details>",
+						},
+					],
+				},
+			]
+
+			const openAiMessages = convertToOpenAiMessages(anthropicMessages, {
+				mergeToolResultText: true,
+				normalizeToolCallId: normalizeMistralToolCallId,
+			})
+
+			// Should merge AND normalize the ID
+			expect(openAiMessages).toHaveLength(1)
+			const toolMessage = openAiMessages[0] as OpenAI.Chat.ChatCompletionToolMessageParam
+			expect(toolMessage.role).toBe("tool")
+			expect(toolMessage.tool_call_id).toBe(normalizeMistralToolCallId("call_5019f900a247472bacde0b82"))
+			expect(toolMessage.content).toBe(
+				"Tool result content\n\n<environment_details>Context</environment_details>",
+			)
+		})
+
+		it("should handle user messages with only text content (no tool results)", () => {
+			const anthropicMessages: Anthropic.Messages.MessageParam[] = [
+				{
+					role: "user",
+					content: [
+						{
+							type: "text",
+							text: "Hello, how are you?",
+						},
+					],
+				},
+			]
+
+			const openAiMessages = convertToOpenAiMessages(anthropicMessages, { mergeToolResultText: true })
+
+			// Should produce a normal user message
+			expect(openAiMessages).toHaveLength(1)
+			expect(openAiMessages[0].role).toBe("user")
+		})
+	})
 })