fix(deepseek): backfill v4 assistant reasoning replay

src/plugin-sdk/provider-stream-shared.test.ts

@@ -2,6 +2,7 @@ import type { StreamFn } from "@mariozechner/pi-agent-core";
 import { describe, expect, it } from "vitest";
 import {
   buildCopilotDynamicHeaders,
+  createDeepSeekV4OpenAICompatibleThinkingWrapper,
   createHtmlEntityToolCallArgumentDecodingWrapper,
   createAnthropicThinkingPrefillPayloadWrapper,
   createPayloadPatchStreamWrapper,
@@ -104,6 +105,37 @@ describe("isOpenAICompatibleThinkingEnabled", () => {
   });
 });
 
+describe("createDeepSeekV4OpenAICompatibleThinkingWrapper", () => {
+  it("backfills reasoning_content on every replayed assistant message when thinking is enabled", () => {
+    const payload = {
+      messages: [
+        { role: "user", content: "read file" },
+        { role: "assistant", tool_calls: [{ id: "call_1", name: "read" }] },
+        { role: "tool", content: "ok" },
+        { role: "assistant", content: "done" },
+        { role: "assistant", content: "kept", reasoning_content: "native reasoning" },
+      ],
+    };
+    const baseStreamFn: StreamFn = (_model, _context, options) => {
+      options?.onPayload?.(payload as never, _model as never);
+      return {} as ReturnType<StreamFn>;
+    };
+
+    const wrapped = createDeepSeekV4OpenAICompatibleThinkingWrapper({
+      baseStreamFn,
+      thinkingLevel: "high",
+      shouldPatchModel: () => true,
+    });
+    void wrapped?.({} as never, {} as never, {});
+
+    expect(payload.messages[0]).not.toHaveProperty("reasoning_content");
+    expect(payload.messages[1]).toHaveProperty("reasoning_content", "");
+    expect(payload.messages[2]).not.toHaveProperty("reasoning_content");
+    expect(payload.messages[3]).toHaveProperty("reasoning_content", "");
+    expect(payload.messages[4]).toHaveProperty("reasoning_content", "native reasoning");
+  });
+});
+
 describe("buildCopilotDynamicHeaders", () => {
   it("matches Copilot IDE-style request headers without the legacy Openai-Intent", () => {
     expect(

src/plugin-sdk/provider-stream-shared.ts

@@ -259,7 +259,7 @@ function stripDeepSeekV4ReasoningContent(payload: Record<string, unknown>): void
   }
 }
 
-function ensureDeepSeekV4ToolCallReasoningContent(payload: Record<string, unknown>): void {
+function ensureDeepSeekV4AssistantReasoningContent(payload: Record<string, unknown>): void {
   if (!Array.isArray(payload.messages)) {
     return;
   }
@@ -268,7 +268,7 @@ function ensureDeepSeekV4ToolCallReasoningContent(payload: Record<string, unknow
       continue;
     }
     const record = message as Record<string, unknown>;
-    if (record.role !== "assistant" || !Array.isArray(record.tool_calls)) {
+    if (record.role !== "assistant") {
       continue;
     }
     if (!("reasoning_content" in record)) {
@@ -302,7 +302,7 @@ export function createDeepSeekV4OpenAICompatibleThinkingWrapper(params: {
 
       payload.thinking = { type: "enabled" };
       payload.reasoning_effort = resolveDeepSeekV4ReasoningEffort(params.thinkingLevel);
-      ensureDeepSeekV4ToolCallReasoningContent(payload);
+      ensureDeepSeekV4AssistantReasoningContent(payload);
     });
   };
 }