fix(agent-runtime): backfill reasoning_content for relayed DeepSeek models

packages/agent-runtime/src/reasoning-content-backfill.test.ts

@@ -0,0 +1,88 @@
+import { describe, expect, it } from "vitest";
+import { convertMessages } from "@earendil-works/pi-ai/api/openai-completions";
+
+// Guards the pnpm patch on @earendil-works/pi-ai (patches/@earendil-works__pi-ai@0.85.1.patch):
+// DeepSeek-style endpoints accept a history where either every assistant message
+// carries reasoning_content or none does, and reject a mix. A relayed model that
+// is not in the catalogue has `reasoning: false`, so pi's per-message backfill
+// never ran and a mixed history was sent as is (#223).
+
+const compat = {
+  supportsDeveloperRole: false,
+  supportsOpenAIGrammarTools: false,
+  requiresToolResultName: false,
+  requiresAssistantAfterToolResult: false,
+  requiresThinkingAsText: false,
+  requiresReasoningContentOnAssistantMessages: true,
+  thinkingFormat: "deepseek",
+  deferredToolsMode: "none",
+} as never;
+
+function model(reasoning: boolean) {
+  return {
+    id: "deepseek-relay",
+    name: "deepseek-relay",
+    api: "openai-completions",
+    provider: "custom-relay",
+    baseUrl: "https://relay.example/v1",
+    reasoning,
+    input: ["text"],
+    contextWindow: 128_000,
+    maxTokens: 8_192,
+    cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+    compat: {},
+  } as never;
+}
+
+function assistant(content: unknown[]) {
+  return {
+    role: "assistant",
+    api: "openai-completions",
+    provider: "custom-relay",
+    model: "deepseek-relay",
+    usage: {
+      input: 1,
+      output: 1,
+      cacheRead: 0,
+      cacheWrite: 0,
+      totalTokens: 2,
+      cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+    },
+    stopReason: "stop",
+    timestamp: 1,
+    content,
+  };
+}
+
+const user = (text: string) => ({ role: "user", content: text, timestamp: 1 });
+
+function assistantParams(messages: unknown[]) {
+  return convertMessages(model(false), { systemPrompt: "", messages, tools: [] } as never, compat)
+    .filter((message) => message.role === "assistant")
+    .map((message) => (message as { reasoning_content?: unknown }).reasoning_content);
+}
+
+describe("reasoning_content backfill for non-catalogue DeepSeek models", () => {
+  it("fills an empty reasoning_content on assistant turns without thinking once any turn has it", () => {
+    const reasoning = assistantParams([
+      user("first"),
+      assistant([
+        { type: "thinking", thinking: "let me think", thinkingSignature: "reasoning_content" },
+        { type: "text", text: "thought answer" },
+      ]),
+      user("second"),
+      assistant([{ type: "text", text: "plain answer" }]),
+    ]);
+    expect(reasoning).toEqual(["let me think", ""]);
+  });
+
+  it("leaves a history without any thinking untouched", () => {
+    const reasoning = assistantParams([
+      user("first"),
+      assistant([{ type: "text", text: "one" }]),
+      user("second"),
+      assistant([{ type: "text", text: "two" }]),
+    ]);
+    expect(reasoning).toEqual([undefined, undefined]);
+  });
+});

patches/@earendil-works__pi-ai@0.85.1.patch

@@ -1,3 +1,30 @@
+diff --git a/dist/api/openai-completions.js b/dist/api/openai-completions.js
+index 48464f2bf56b9369d5c202e4f02fc4f13d35b412..fd36bd0f3daab13023c0220bb44c475503ec0c28 100644
+--- a/dist/api/openai-completions.js
++++ b/dist/api/openai-completions.js
+@@ -1141,6 +1141,22 @@ export function convertMessages(model, context, compat, options) {
+         }
+         lastRole = msg.role;
+     }
++    // DeepSeek-style endpoints reject a history in which only some assistant
++    // messages carry reasoning_content, while all-or-none is accepted. The
++    // per-message backfill above only runs for models flagged `reasoning`,
++    // which a relayed model outside the catalogue is not, even though its
++    // persisted turns still carry thinking. Whenever any assistant message
++    // ends up with reasoning_content, give the rest an empty one.
++    if (compat.requiresReasoningContentOnAssistantMessages &&
++        params.some((m) => m.role === "assistant" &&
++            typeof m.reasoning_content === "string" &&
++            m.reasoning_content.length > 0)) {
++        for (const m of params) {
++            if (m.role === "assistant" && m.reasoning_content === undefined) {
++                m.reasoning_content = "";
++            }
++        }
++    }
+     return params;
+ }
+ function convertTools(tools, compat) {
 diff --git a/dist/api/openai-responses-shared.js b/dist/api/openai-responses-shared.js
 index 43e463dbfd1e6cc437ebc680468036f47678de26..364c8c0426d12543c1b64daa8e6eaa22f35f6f60 100644
 --- a/dist/api/openai-responses-shared.js