diff --git a/packages/agent/src/pi/upstream.ts b/packages/agent/src/pi/upstream.ts
index a162b6d3..b60771b9 100644
--- a/packages/agent/src/pi/upstream.ts
+++ b/packages/agent/src/pi/upstream.ts
@@ -356,7 +356,14 @@ export class PiUpstreamClient {
         res = await this.models.completeSimple(
           { ...model, maxTokens: Math.min(model.maxTokens || 16, 16) },
           { messages: [{ role: "user", content: "Reply with: ok", timestamp: Date.now() }] },
-          { maxTokens: 16, ...(opts.signal ? { signal: opts.signal } : {}), timeoutMs: 30_000, maxRetries: 0 },
+          {
+            maxTokens: 16,
+            ...(opts.signal ? { signal: opts.signal } : {}),
+            timeoutMs: 30_000,
+            maxRetries: 0,
+            // OpenCode(Zen / Go)按会话路由,缺 x-opencode-session 会被拒;其余 provider 用它做缓存键,无副作用
+            sessionId: `umt-upstream-test-${crypto.randomUUID()}`,
+          },
         );
       } catch (err) {
         throw classifyUpstreamError(err);
diff --git a/packages/agent/test/upstream.test.ts b/packages/agent/test/upstream.test.ts
index d662bcf8..4c856651 100644
--- a/packages/agent/test/upstream.test.ts
+++ b/packages/agent/test/upstream.test.ts
@@ -133,6 +133,31 @@ describe("按上游装配", () => {
     expect(t).toMatchObject({ model: "claude-future-9", inCatalog: false, source: "stored credential" });
   });
 
+  it("测试补全带 sessionId:OpenCode Go 请求头有 x-opencode-session", async () => {
+    const seen: { url: string; headers: Headers }[] = [];
+    const orig = globalThis.fetch;
+    globalThis.fetch = (async (input: RequestInfo | URL, init?: RequestInit) => {
+      const req = new Request(input, init);
+      seen.push({ url: req.url, headers: req.headers });
+      return new Response(JSON.stringify({ error: { message: "stubbed" } }), {
+        status: 500,
+        headers: { "content-type": "application/json" },
+      });
+    }) as typeof fetch;
+    try {
+      const c = new PiUpstreamClient(
+        spec({ provider: "opencode-go", authKind: "api_key" }),
+        memStore({ type: "api_key", key: "sk-opencode-test" }),
+      );
+      await expect(c.test({ mode: "completion" })).rejects.toBeInstanceOf(UpstreamError);
+    } finally {
+      globalThis.fetch = orig;
+    }
+    const call = seen.find((x) => x.headers.get("x-opencode-session"));
+    expect(call, `请求:${seen.map((x) => x.url).join(", ")}`).toBeDefined();
+    expect(call?.headers.get("x-opencode-session")).toMatch(/^umt-upstream-test-/);
+  });
+
   it("自定义兼容端点:baseUrl/模型必填;authKind none 不需要 key", async () => {
     expect(() => new PiUpstreamClient(spec({ provider: "openai-compatible", authKind: "none" }), memStore())).toThrow(
       UpstreamError,