feat: preserve reasoning details for OpenRouter models between conversation turns

- Add preserveReasoning flag to ModelInfo for reasoning-capable models
- Set preserveReasoning=true for OpenRouter models that support reasoning
- Ensure reasoning content is included in conversation history for continuity
- Add comprehensive tests for preserveReasoning functionality

Fixes #9125

src/api/providers/fetchers/__tests__/openrouter.spec.ts

@@ -29,6 +29,7 @@ describe("OpenRouter API", () => {
 				supportsReasoningBudget: false,
 				supportsReasoningEffort: false,
 				supportedParameters: ["max_tokens", "temperature", "reasoning", "include_reasoning"],
+				preserveReasoning: true,
 			})
 
 			expect(models["anthropic/claude-3.7-sonnet:thinking"]).toEqual({
@@ -45,6 +46,7 @@ describe("OpenRouter API", () => {
 				requiredReasoningBudget: true,
 				supportsReasoningEffort: true,
 				supportedParameters: ["max_tokens", "temperature", "reasoning", "include_reasoning"],
+				preserveReasoning: true,
 			})
 
 			expect(models["google/gemini-2.5-flash-preview-05-20"].maxTokens).toEqual(65535)
@@ -97,6 +99,7 @@ describe("OpenRouter API", () => {
 					description: undefined,
 					supportsReasoningEffort: undefined,
 					supportedParameters: undefined,
+					preserveReasoning: true,
 				},
 				"google-ai-studio": {
 					maxTokens: 65536,
@@ -111,6 +114,7 @@ describe("OpenRouter API", () => {
 					description: undefined,
 					supportsReasoningEffort: undefined,
 					supportedParameters: undefined,
+					preserveReasoning: true,
 				},
 			})
 
@@ -236,5 +240,122 @@ describe("OpenRouter API", () => {
 			expect(textResult.maxTokens).toBe(64000)
 			expect(imageResult.maxTokens).toBe(64000)
 		})
+
+		describe("preserveReasoning flag", () => {
+			it("should set preserveReasoning to true for models with reasoning support", () => {
+				const mockModel = {
+					name: "Test Reasoning Model",
+					context_length: 128000,
+					max_completion_tokens: 8192,
+					pricing: {
+						prompt: "0.001",
+						completion: "0.002",
+					},
+				}
+
+				const result = parseOpenRouterModel({
+					id: "test/reasoning-model",
+					model: mockModel,
+					inputModality: ["text"],
+					outputModality: ["text"],
+					maxTokens: 8192,
+					supportedParameters: ["reasoning", "temperature"],
+				})
+
+				expect(result.preserveReasoning).toBe(true)
+			})
+
+			it("should set preserveReasoning to true for models with include_reasoning support", () => {
+				const mockModel = {
+					name: "Test Include Reasoning Model",
+					context_length: 128000,
+					max_completion_tokens: 8192,
+					pricing: {
+						prompt: "0.001",
+						completion: "0.002",
+					},
+				}
+
+				const result = parseOpenRouterModel({
+					id: "test/include-reasoning-model",
+					model: mockModel,
+					inputModality: ["text"],
+					outputModality: ["text"],
+					maxTokens: 8192,
+					supportedParameters: ["include_reasoning", "temperature"],
+				})
+
+				expect(result.preserveReasoning).toBe(true)
+			})
+
+			it("should set preserveReasoning to false for models without reasoning support", () => {
+				const mockModel = {
+					name: "Test Non-Reasoning Model",
+					context_length: 128000,
+					max_completion_tokens: 8192,
+					pricing: {
+						prompt: "0.001",
+						completion: "0.002",
+					},
+				}
+
+				const result = parseOpenRouterModel({
+					id: "test/non-reasoning-model",
+					model: mockModel,
+					inputModality: ["text"],
+					outputModality: ["text"],
+					maxTokens: 8192,
+					supportedParameters: ["temperature", "max_tokens"],
+				})
+
+				expect(result.preserveReasoning).toBe(false)
+			})
+
+			it("should set preserveReasoning to true for claude-3.7-sonnet:thinking", () => {
+				const mockModel = {
+					name: "Claude 3.7 Sonnet Thinking",
+					context_length: 200000,
+					max_completion_tokens: 8192,
+					pricing: {
+						prompt: "0.003",
+						completion: "0.015",
+					},
+				}
+
+				const result = parseOpenRouterModel({
+					id: "anthropic/claude-3.7-sonnet:thinking",
+					model: mockModel,
+					inputModality: ["text"],
+					outputModality: ["text"],
+					maxTokens: 8192,
+					supportedParameters: ["reasoning"],
+				})
+
+				expect(result.preserveReasoning).toBe(true)
+			})
+
+			it("should set preserveReasoning to true for claude-haiku-4.5", () => {
+				const mockModel = {
+					name: "Claude Haiku 4.5",
+					context_length: 200000,
+					max_completion_tokens: 8192,
+					pricing: {
+						prompt: "0.001",
+						completion: "0.005",
+					},
+				}
+
+				const result = parseOpenRouterModel({
+					id: "anthropic/claude-haiku-4.5",
+					model: mockModel,
+					inputModality: ["text"],
+					outputModality: ["text"],
+					maxTokens: 8192,
+					supportedParameters: ["reasoning"],
+				})
+
+				expect(result.preserveReasoning).toBe(true)
+			})
+		})
 	})
 })

src/api/providers/fetchers/openrouter.ts

@@ -205,6 +205,11 @@ export const parseOpenRouterModel = ({
 
 	const supportsPromptCache = typeof cacheReadsPrice !== "undefined" // some models support caching but don't charge a cacheWritesPrice, e.g. GPT-5
 
+	// Check if the model supports reasoning (either through include_reasoning or reasoning parameters)
+	const supportsReasoning = supportedParameters
+		? supportedParameters.includes("reasoning") || supportedParameters.includes("include_reasoning")
+		: false
+
 	const modelInfo: ModelInfo = {
 		maxTokens: maxTokens || Math.ceil(model.context_length * 0.2),
 		contextWindow: model.context_length,
@@ -217,6 +222,8 @@ export const parseOpenRouterModel = ({
 		description: model.description,
 		supportsReasoningEffort: supportedParameters ? supportedParameters.includes("reasoning") : undefined,
 		supportedParameters: supportedParameters ? supportedParameters.filter(isModelParameter) : undefined,
+		// Preserve reasoning in conversation history for models that support reasoning
+		preserveReasoning: supportsReasoning,
 	}
 
 	if (OPEN_ROUTER_REASONING_BUDGET_MODELS.has(id)) {
@@ -239,6 +246,8 @@ export const parseOpenRouterModel = ({
 
 	if (id === "anthropic/claude-3.7-sonnet:thinking") {
 		modelInfo.maxTokens = anthropicModels["claude-3-7-sonnet-20250219:thinking"].maxTokens
+		// Ensure reasoning is preserved for thinking models
+		modelInfo.preserveReasoning = true
 	}
 
 	// Set claude-opus-4.1 model to use the correct configuration
@@ -251,6 +260,14 @@ export const parseOpenRouterModel = ({
 	if (id === "anthropic/claude-haiku-4.5") {
 		modelInfo.supportsReasoningBudget = true
 		modelInfo.supportsReasoningEffort = false
+		// Preserve reasoning for Claude Haiku 4.5
+		modelInfo.preserveReasoning = true
+	}
+
+	// Ensure reasoning preservation for models that support reasoning budget
+	// This includes models like MiniMax-M2 and other reasoning-capable models
+	if (modelInfo.supportsReasoningBudget || modelInfo.requiredReasoningBudget) {
+		modelInfo.preserveReasoning = true
 	}
 
 	// Set horizon-alpha model to 32k max tokens