fix(ai-sdk): preserve reasoning parts in message conversion (RooCodeInc#11217)

* fix(ai-sdk): preserve reasoning parts in message conversion

* fix(ai-sdk): convert message-level reasoning_content to reasoning part

* fix(task): remove invalid openai-compatible from reasoning allowlist

* feat: add isAiSdkProvider() method for dynamic AI SDK provider detection

- Add isAiSdkProvider() method to ApiHandler interface
- Default implementation in BaseProvider returns false
- Override to return true in 11 AI SDK providers:
  deepseek, fireworks, mistral, groq, xai, cerebras,
  sambanova, huggingface, gemini, vertex, openai-compatible
- Update Task.ts to use dynamic detection instead of hardcoded Set
- Add method to FakeAIHandler and update test mocks

* fix: handle reasoning parts in flattenAiSdkMessagesToStringContent

- Strip reasoning parts when flattening messages for string-only models
- Allow flattening when message contains only text and reasoning parts
- Add tests for reasoning part handling in string-only model contexts

This addresses the review feedback about ensuring flattenAiSdkMessagesToStringContent
works correctly when reasoning parts are present (e.g., SambaNova DeepSeek).

---------

Co-authored-by: daniel-lxs <ricciodaniel98@gmail.com>

Author: hannesrudolph

src/api/index.ts

@@ -117,6 +117,15 @@ export interface ApiHandler {
 	 * @returns A promise resolving to the token count
 	 */
 	countTokens(content: Array<Anthropic.Messages.ContentBlockParam>): Promise<number>
+
+	/**
+	 * Indicates whether this provider uses the Vercel AI SDK for streaming.
+	 * AI SDK providers handle reasoning blocks differently and need to preserve
+	 * them in conversation history for proper round-tripping.
+	 *
+	 * @returns true if the provider uses AI SDK, false otherwise
+	 */
+	isAiSdkProvider(): boolean
 }
 
 export function buildApiHandler(configuration: ProviderSettings): ApiHandler {

src/api/providers/base-provider.ts

@@ -119,4 +119,12 @@ export abstract class BaseProvider implements ApiHandler {
 
 		return countTokens(content, { useWorker: true })
 	}
+
+	/**
+	 * Default implementation returns false.
+	 * AI SDK providers should override this to return true.
+	 */
+	isAiSdkProvider(): boolean {
+		return false
+	}
 }

src/api/providers/cerebras.ts

@@ -156,4 +156,8 @@ export class CerebrasHandler extends BaseProvider implements SingleCompletionHan
 
 		return text
 	}
+
+	override isAiSdkProvider(): boolean {
+		return true
+	}
 }

src/api/providers/deepseek.ts

@@ -166,4 +166,8 @@ export class DeepSeekHandler extends BaseProvider implements SingleCompletionHan
 
 		return text
 	}
+
+	override isAiSdkProvider(): boolean {
+		return true
+	}
 }

src/api/providers/fake-ai.ts

@@ -78,4 +78,8 @@ export class FakeAIHandler implements ApiHandler, SingleCompletionHandler {
 	completePrompt(prompt: string): Promise<string> {
 		return this.ai.completePrompt(prompt)
 	}
+
+	isAiSdkProvider(): boolean {
+		return false
+	}
 }

src/api/providers/fireworks.ts

@@ -172,4 +172,8 @@ export class FireworksHandler extends BaseProvider implements SingleCompletionHa
 
 		return text
 	}
+
+	override isAiSdkProvider(): boolean {
+		return true
+	}
 }

src/api/providers/gemini.ts

@@ -397,4 +397,8 @@ export class GeminiHandler extends BaseProvider implements SingleCompletionHandl
 
 		return totalCost
 	}
+
+	override isAiSdkProvider(): boolean {
+		return true
+	}
 }

src/api/providers/groq.ts

@@ -174,4 +174,8 @@ export class GroqHandler extends BaseProvider implements SingleCompletionHandler
 
 		return text
 	}
+
+	override isAiSdkProvider(): boolean {
+		return true
+	}
 }

src/api/providers/huggingface.ts

@@ -208,4 +208,8 @@ export class HuggingFaceHandler extends BaseProvider implements SingleCompletion
 
 		return text
 	}
+
+	override isAiSdkProvider(): boolean {
+		return true
+	}
 }

src/api/providers/mistral.ts

@@ -198,4 +198,8 @@ export class MistralHandler extends BaseProvider implements SingleCompletionHand
 
 		return text
 	}
+
+	override isAiSdkProvider(): boolean {
+		return true
+	}
 }