fix(api): preserve provider reasoning across tool calls

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

@@ -182,6 +182,34 @@ describe("AwsBedrockHandler", () => {
 		},
 	)
 
+	it.each([
+		["anthropic.claude-sonnet-4-5-20250929-v1:0", false],
+		["minimax.minimax-m2", true],
+	] as const)("replays stored thinking to %s only when the model preserves reasoning", async (apiModelId, kept) => {
+		const provider = new AwsBedrockHandler({ apiModelId, awsRegion: "us-east-1" })
+		provider["client"].send = vi.fn().mockResolvedValue({ stream: asyncStreamFrom([]) })
+		// A MiniMax-signed thinking block survives a mid-task switch to Bedrock.
+		const history = [
+			{ role: "user", content: "hello" },
+			{
+				role: "assistant",
+				content: [
+					{ type: "thinking", thinking: "Signed by MiniMax.", signature: "minimax-signature" },
+					{ type: "text", text: "Done." },
+					{ type: "tool_use", id: "t1", name: "read_file", input: {} },
+				],
+			},
+			{ role: "user", content: [{ type: "tool_result", tool_use_id: "t1", content: "ok" }] },
+		] as Anthropic.Messages.MessageParam[]
+		await collectStream(provider.createMessage("system", history))
+		const [{ messages }] = mockConverseStreamCommand.mock.lastCall!
+		expect(messages?.[1].content).toStrictEqual([
+			...(kept ? [{ reasoningContent: { reasoningText: { text: "Signed by MiniMax." } } }] : []),
+			{ text: "Done." },
+			{ toolUse: { toolUseId: "t1", name: "read_file", input: {} } },
+		])
+	})
+
 	describe("getModel", () => {
 		it("should return the correct model info for a standard model", () => {
 			const modelInfo = handler.getModel()

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

@@ -436,6 +436,85 @@ describe("MiniMaxHandler", () => {
 			expect(firstChunk.value).toEqual({ type: "reasoning", text: thinkingContent })
 		})
 
+		it("captures thinking signatures for the next tool-loop request", async () => {
+			mockCreate.mockResolvedValueOnce(
+				asyncStreamFrom([
+					{
+						type: "content_block_delta",
+						index: 0,
+						delta: { type: "thinking_delta", thinking: "Inspect the file." },
+					},
+					{
+						type: "content_block_delta",
+						index: 0,
+						delta: { type: "signature_delta", signature: "signed-reasoning" },
+					},
+				]),
+			)
+
+			const chunks = await collectStream(handler.createMessage("system prompt", []))
+
+			expect(chunks).toEqual([{ type: "reasoning", text: "Inspect the file." }])
+			expect(handler.getThoughtSignature()).toBe("signed-reasoning")
+		})
+
+		it("clears stale thinking signatures before the next request", async () => {
+			mockCreate
+				.mockResolvedValueOnce(
+					asyncStreamFrom([
+						{
+							type: "content_block_delta",
+							index: 0,
+							delta: { type: "signature_delta", signature: "signed-reasoning" },
+						},
+					]),
+				)
+				.mockResolvedValueOnce(
+					asyncStreamFrom([
+						{
+							type: "content_block_delta",
+							index: 0,
+							delta: { type: "thinking_delta", thinking: "Continue without a signature." },
+						},
+					]),
+				)
+
+			await collectStream(handler.createMessage("system prompt", []))
+			expect(handler.getThoughtSignature()).toBe("signed-reasoning")
+
+			await collectStream(handler.createMessage("system prompt", []))
+			expect(handler.getThoughtSignature()).toBeUndefined()
+		})
+
+		it("filters legacy reasoning blocks while preserving signed thinking blocks", async () => {
+			mockCreate.mockResolvedValueOnce(asyncStreamFrom([]))
+			// The Anthropic SDK does not model Zoo Code's legacy internal reasoning block,
+			// which can still be present in persisted conversation history.
+			const messages = [
+				{
+					role: "assistant",
+					content: [
+						{ type: "reasoning", text: "legacy unsigned reasoning", summary: [] },
+						{ type: "thinking", thinking: "signed reasoning", signature: "signature" },
+						{ type: "text", text: "I will inspect the file." },
+					],
+				},
+			] as unknown as Anthropic.Messages.MessageParam[]
+
+			await collectStream(handler.createMessage("system prompt", messages))
+
+			const request = mockCreate.mock.calls[0][0] as Anthropic.Messages.MessageCreateParams
+			expect(request.messages).toEqual([
+				{
+					role: "assistant",
+					content: [
+						{ type: "thinking", thinking: "signed reasoning", signature: "signature" },
+						{ type: "text", text: "I will inspect the file." },
+					],
+				},
+			])
+		})
+
 		it("should handle tool calls in stream", async () => {
 			mockCreate.mockResolvedValueOnce(
 				asyncStreamFrom([

src/api/providers/bedrock.ts

@@ -984,7 +984,9 @@
 		conversationId?: string, // Optional conversation ID to track cache points across messages
 	): { system: SystemContentBlock[]; messages: Message[] } {
 		// First convert messages using shared converter for proper image handling
-		const convertedMessages = sharedConverter(anthropicMessages as Anthropic.Messages.MessageParam[])
+		const convertedMessages = sharedConverter(anthropicMessages as Anthropic.Messages.MessageParam[], {
+			preserveReasoning: modelInfo?.preserveReasoning === true,
+		})
 
 		// If prompt caching is disabled, return the converted messages directly
 		if (!usePromptCache) {

src/api/providers/minimax.ts

@@ -11,6 +11,7 @@ import type { ApiHandlerOptions } from "../../shared/api"
 import { ApiStream } from "../transform/stream"
 import { getModelParams } from "../transform/model-params"
 import { mergeEnvironmentDetailsForMiniMax } from "../transform/minimax-format"
+import { filterNonAnthropicBlocks } from "../transform/anthropic-filter"
 
 import { BaseProvider } from "./base-provider"
 import { bridgeExternalAbortSignal, hasUsableTimeout, toSdkTimeoutMs } from "./utils/abort-signal"
@@ -55,6 +56,7 @@ function convertOpenAIToolChoice(
 export class MiniMaxHandler extends BaseProvider implements SingleCompletionHandler {
 	private options: ApiHandlerOptions
 	private client: Anthropic
+	private lastThoughtSignature?: string
 
 	constructor(options: ApiHandlerOptions) {
 		super()
@@ -86,6 +88,7 @@ export class MiniMaxHandler extends BaseProvider implements SingleCompletionHand
 	): ApiStream {
 		const cacheControl: CacheControlEphemeral = { type: "ephemeral" }
 		const { id: modelId, info, maxTokens, temperature } = this.getModel()
+		this.lastThoughtSignature = undefined
 
 		// Bridge the external abort signal from request metadata into a per-request
 		// controller so the SDK call is cancelled when the owning request is aborted
@@ -103,7 +106,7 @@ export class MiniMaxHandler extends BaseProvider implements SingleCompletionHand
 		// into the tool_result content. This preserves reasoning continuity for
 		// thinking models by preventing user messages from interrupting the
 		// reasoning context after tool use (similar to r1-format's mergeToolResultText).
-		const processedMessages = mergeEnvironmentDetailsForMiniMax(messages)
+		const processedMessages = filterNonAnthropicBlocks(mergeEnvironmentDetailsForMiniMax(messages))
 
 		// Build the system blocks array
 		const systemBlocks: Anthropic.Messages.TextBlockParam[] = [
@@ -213,6 +216,9 @@ export class MiniMaxHandler extends BaseProvider implements SingleCompletionHand
 						case "thinking_delta":
 							yield { type: "reasoning", text: chunk.delta.thinking }
 							break
+						case "signature_delta":
+							this.lastThoughtSignature = chunk.delta.signature
+							break
 						case "text_delta":
 							yield { type: "text", text: chunk.delta.text }
 							break
@@ -255,6 +261,10 @@ export class MiniMaxHandler extends BaseProvider implements SingleCompletionHand
 		}
 	}
 
+	getThoughtSignature(): string | undefined {
+		return this.lastThoughtSignature
+	}
+
 	/**
 	 * Add cache control to the last two user messages for prompt caching
 	 */

src/api/transform/__tests__/bedrock-converse-format.spec.ts

@@ -1,6 +1,6 @@
 // npx vitest run src/api/transform/__tests__/bedrock-converse-format.spec.ts
 
-import { convertToBedrockConverseMessages } from "../bedrock-converse-format"
+import { convertToBedrockConverseMessages, REASONING_ONLY_PLACEHOLDER } from "../bedrock-converse-format"
 import { Anthropic } from "@anthropic-ai/sdk"
 import { ContentBlock, ToolResultContentBlock } from "@aws-sdk/client-bedrock-runtime"
 import { OPENAI_CALL_ID_MAX_LENGTH } from "../../../utils/tool-id"
@@ -26,6 +26,121 @@ describe("convertToBedrockConverseMessages", () => {
 		])
 	})
 
+	it("converts internal reasoning blocks to Bedrock reasoning content", () => {
+		// The Anthropic SDK does not model Zoo Code's internal reasoning block,
+		// though this converter receives it from persisted conversation history.
+		const messages = [
+			{
+				role: "assistant",
+				content: [{ type: "reasoning", text: "I should inspect the file first.", summary: [] }],
+			},
+		] as unknown as Anthropic.Messages.MessageParam[]
+
+		expect(convertToBedrockConverseMessages(messages, { preserveReasoning: true })).toEqual([
+			{
+				role: "assistant",
+				content: [
+					{
+						reasoningContent: {
+							reasoningText: { text: "I should inspect the file first." },
+						},
+					},
+				],
+			},
+		])
+	})
+
+	it("replays reasoning into a tool_result continuation but drops it before a new user message", () => {
+		const reasoning = { type: "reasoning", text: "Plan.", summary: [] }
+		const messages = [
+			{ role: "assistant", content: [reasoning, { type: "tool_use", id: "t1", name: "read", input: {} }] },
+			{ role: "user", content: [{ type: "tool_result", tool_use_id: "t1", content: "ok" }] },
+			{ role: "assistant", content: [reasoning, { type: "text", text: "Done." }] },
+			{ role: "user", content: [{ type: "text", text: "next" }] },
+		] as unknown as Anthropic.Messages.MessageParam[]
+
+		const result = convertToBedrockConverseMessages(messages, { preserveReasoning: true })
+
+		expect(result[0].content?.[0]).toEqual({ reasoningContent: { reasoningText: { text: "Plan." } } })
+		expect(result[2].content).toEqual([{ text: "Done." }])
+	})
+
+	it("drops reasoning and thinking blocks for models that do not preserve reasoning", () => {
+		// Signed thinking bypasses Task's reasoning filter, so the converter must not send it to e.g. Claude.
+		const messages = [
+			{
+				role: "assistant",
+				content: [
+					{ type: "thinking", thinking: "Signed elsewhere.", signature: "minimax-signature" },
+					{ type: "text", text: "Reading the file." },
+				],
+			},
+			{
+				role: "assistant",
+				content: [{ type: "reasoning", text: "Reasoning only.", summary: [] }],
+			},
+		] as unknown as Anthropic.Messages.MessageParam[]
+
+		expect(convertToBedrockConverseMessages(messages)).toStrictEqual([
+			{ role: "assistant", content: [{ text: "Reading the file." }] },
+			// Bedrock rejects blank text blocks, so a reasoning-only turn keeps a non-blank placeholder.
+			{ role: "assistant", content: [{ text: REASONING_ONLY_PLACEHOLDER }] },
+		])
+		expect(REASONING_ONLY_PLACEHOLDER.trim()).not.toBe("")
+	})
+
+	it("drops signatures issued by another provider when converting thinking blocks", () => {
+		const messages: Anthropic.Messages.MessageParam[] = [
+			{
+				role: "assistant",
+				content: [
+					{
+						type: "thinking",
+						thinking: "I should inspect the file first.",
+						signature: "signed-reasoning",
+					},
+				],
+			},
+		]
+
+		// Bedrock never records signatures, so a stored one would fail Bedrock's verification.
+		expect(convertToBedrockConverseMessages(messages, { preserveReasoning: true })).toStrictEqual([
+			{
+				role: "assistant",
+				content: [
+					{
+						reasoningContent: {
+							reasoningText: { text: "I should inspect the file first." },
+						},
+					},
+				],
+			},
+		])
+	})
+
+	it("converts unsigned thinking blocks without adding a signature", () => {
+		// Persisted provider output can omit a signature even though the Anthropic SDK requires one.
+		const messages = [
+			{
+				role: "assistant",
+				content: [{ type: "thinking", thinking: "I should inspect the file first." }],
+			},
+		] as unknown as Anthropic.Messages.MessageParam[]
+
+		expect(convertToBedrockConverseMessages(messages, { preserveReasoning: true })).toStrictEqual([
+			{
+				role: "assistant",
+				content: [
+					{
+						reasoningContent: {
+							reasoningText: { text: "I should inspect the file first." },
+						},
+					},
+				],
+			},
+		])
+	})
+
 	it("converts messages with images correctly", () => {
 		const messages: Anthropic.Messages.MessageParam[] = [
 			{