fix(ai): normalize opencode go reasoning replay

closes #4251

packages/ai/CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - Fixed Xiaomi MiMo model metadata to use the OpenAI-compatible endpoints and `openai-completions` API, restoring multi-turn thinking/tool-call sessions ([#4505](https://github.com/earendil-works/pi/issues/4505)).
+- Fixed OpenCode Go Kimi reasoning replay by normalizing streamed `reasoning` fields back to `reasoning_content` for OpenCode Go only ([#4251](https://github.com/earendil-works/pi/issues/4251)).
 
 ## [0.75.0] - 2026-05-17
 

packages/ai/src/providers/openai-completions.ts

@@ -326,7 +326,11 @@ export const streamOpenAICompletions: StreamFunction<"openai-completions", OpenA
 					if (foundReasoningField) {
 						const delta = deltaFields[foundReasoningField];
 						if (typeof delta === "string" && delta.length > 0) {
-							const block = ensureThinkingBlock(foundReasoningField);
+							const thinkingSignature =
+								model.provider === "opencode-go" && foundReasoningField === "reasoning"
+									? "reasoning_content"
+									: foundReasoningField;
+							const block = ensureThinkingBlock(thinkingSignature);
 							block.thinking += delta;
 							stream.push({
 								type: "thinking_delta",
@@ -844,7 +848,10 @@ export function convertMessages(
 					}
 
 					// Use the signature from the first thinking block if available (for llama.cpp server + gpt-oss)
-					const signature = nonEmptyThinkingBlocks[0].thinkingSignature;
+					let signature = nonEmptyThinkingBlocks[0].thinkingSignature;
+					if (model.provider === "opencode-go" && signature === "reasoning") {
+						signature = "reasoning_content";
+					}
 					if (signature && signature.length > 0) {
 						(assistantMsg as any)[signature] = nonEmptyThinkingBlocks.map((block) => block.thinking).join("\n");
 					}

packages/ai/test/openai-completions-tool-choice.test.ts

@@ -1,8 +1,9 @@
 import { Type } from "typebox";
 import { beforeEach, describe, expect, it, vi } from "vitest";
 import { getModel } from "../src/models.js";
+import { convertMessages } from "../src/providers/openai-completions.js";
 import { streamSimple } from "../src/stream.js";
-import type { Tool } from "../src/types.js";
+import type { Model, Tool } from "../src/types.js";
 
 const mockState = vi.hoisted(() => ({
 	lastParams: undefined as unknown,
@@ -816,6 +817,114 @@ describe("openai-completions tool_choice", () => {
 		expect(writeCall).not.toHaveProperty("partialArgs");
 	});
 
+	it("normalizes OpenCode Go reasoning deltas to reasoning_content for replay", async () => {
+		mockState.chunks = [
+			{
+				id: "chatcmpl-opencode-go-reasoning",
+				choices: [{ delta: { reasoning: "think" }, finish_reason: "stop" }],
+			},
+		];
+
+		const { compat: _compat, ...baseModel } = getModel("opencode-go", "kimi-k2.6")!;
+		const model = { ...baseModel, api: "openai-completions" } as const;
+		const response = await streamSimple(
+			model,
+			{
+				messages: [{ role: "user", content: "Use reasoning.", timestamp: Date.now() }],
+			},
+			{ apiKey: "test" },
+		).result();
+
+		expect(response.content).toEqual([
+			{
+				type: "thinking",
+				thinking: "think",
+				thinkingSignature: "reasoning_content",
+			},
+		]);
+	});
+
+	it("keeps non-OpenCode Go reasoning deltas on the original reasoning field", async () => {
+		mockState.chunks = [
+			{
+				id: "chatcmpl-reasoning",
+				choices: [{ delta: { reasoning: "think" }, finish_reason: "stop" }],
+			},
+		];
+
+		const { compat: _compat, ...baseModel } = getModel("openai", "gpt-4o-mini")!;
+		const model = { ...baseModel, api: "openai-completions" } as const;
+		const response = await streamSimple(
+			model,
+			{
+				messages: [{ role: "user", content: "Use reasoning.", timestamp: Date.now() }],
+			},
+			{ apiKey: "test" },
+		).result();
+
+		expect(response.content).toEqual([
+			{
+				type: "thinking",
+				thinking: "think",
+				thinkingSignature: "reasoning",
+			},
+		]);
+	});
+
+	it("replays OpenCode Go reasoning thinking blocks as reasoning_content", () => {
+		const { compat: _compat, ...baseModel } = getModel("opencode-go", "kimi-k2.6")!;
+		const model = { ...baseModel, api: "openai-completions" } as Model<"openai-completions">;
+		const messages = convertMessages(
+			model,
+			{
+				messages: [
+					{
+						role: "assistant",
+						api: "openai-completions",
+						provider: "opencode-go",
+						model: "kimi-k2.6",
+						content: [
+							{ type: "thinking", thinking: "think", thinkingSignature: "reasoning" },
+							{ type: "toolCall", id: "call_1", name: "read", arguments: { path: "README.md" } },
+						],
+						usage: {
+							input: 0,
+							output: 0,
+							cacheRead: 0,
+							cacheWrite: 0,
+							totalTokens: 0,
+							cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+						},
+						stopReason: "stop",
+						timestamp: Date.now(),
+					},
+				],
+			},
+			{
+				...model.compat,
+				supportsStore: false,
+				supportsDeveloperRole: false,
+				supportsReasoningEffort: true,
+				supportsUsageInStreaming: true,
+				maxTokensField: "max_completion_tokens",
+				requiresToolResultName: false,
+				requiresAssistantAfterToolResult: false,
+				requiresThinkingAsText: false,
+				requiresReasoningContentOnAssistantMessages: false,
+				thinkingFormat: "openai",
+				openRouterRouting: {},
+				vercelGatewayRouting: {},
+				zaiToolStream: false,
+				supportsStrictMode: true,
+				sendSessionAffinityHeaders: false,
+				supportsLongCacheRetention: true,
+			},
+		);
+
+		expect(messages[0]).toMatchObject({ role: "assistant", reasoning_content: "think" });
+		expect(messages[0]).not.toHaveProperty("reasoning");
+	});
+
 	it("does not double-count reasoning tokens in completion usage", async () => {
 		mockState.chunks = [
 			{