fix: Fusion strip stream_options + reasoning model test probe

- combos: strip stream_options from Fusion panel fan-out to avoid DeepSeek 400 (#3024)
- dashboard: raise model-test probe budget to 1024 + soft-pass reasoning-only responses (#3010)

tests/unit/fusion-strip-stream-options-3024.test.js

@@ -0,0 +1,83 @@
+// Issue #3024 — Fusion combo must strip `stream_options` from panel requests
+// when running non-streaming, or DeepSeek rejects with
+// "stream_options should be set along with stream = true".
+
+import { describe, it, expect, vi } from "vitest";
+import { handleFusionChat } from "../../open-sse/services/combo.js";
+
+// Minimal logger stub (combo.js calls log.info/warn).
+const log = { info: () => {}, warn: () => {}, error: () => {} };
+
+function makeBody(extra = {}) {
+  return {
+    model: "combo/gemseek",
+    stream: true,
+    stream_options: { include_usage: true },
+    messages: [{ role: "user", content: "hi" }],
+    ...extra,
+  };
+}
+
+describe("Fusion strips stream_options (#3024)", () => {
+  it("removes stream_options before fanning out to panel models", async () => {
+    let capturedPanelBody = null;
+    const handleSingleModel = vi.fn(async (panelBody, model, isPanel) => {
+      if (isPanel) capturedPanelBody = panelBody;
+      // Simulate a successful non-stream JSON answer for the panel.
+      if (isPanel) {
+        return new Response(JSON.stringify({ choices: [{ message: { content: `ans-${model}` } }] }), {
+          status: 200,
+          headers: { "Content-Type": "application/json" },
+        });
+      }
+      // Judge leg: return a final answer.
+      return new Response(JSON.stringify({ choices: [{ message: { content: "final" } }] }), {
+        status: 200,
+        headers: { "Content-Type": "application/json" },
+      });
+    });
+
+    const res = await handleFusionChat({
+      body: makeBody(),
+      models: ["ds/deepseek-v4-flash", "gemini/gemini-3.5-flash-lite"],
+      handleSingleModel,
+      log,
+      comboName: "GemSeek",
+      judgeModel: "gemini/gemini-3.5-flash-lite",
+    });
+
+    expect(res).toBeInstanceOf(Response);
+    expect(capturedPanelBody).not.toBeNull();
+    // Critical assertion: stream_options must NOT leak into panel requests.
+    expect(capturedPanelBody.stream_options).toBeUndefined();
+    expect(capturedPanelBody.stream).toBe(false);
+    // Ensure the original client body still had it (proves we stripped deliberately).
+    expect(makeBody().stream_options).toBeDefined();
+  });
+
+  it("does not throw for a 2-model fusion with stream_options present", async () => {
+    const handleSingleModel = vi.fn(async (panelBody, model, isPanel) => {
+      if (isPanel) {
+        return new Response(JSON.stringify({ choices: [{ message: { content: "ok" } }] }), {
+          status: 200,
+          headers: { "Content-Type": "application/json" },
+        });
+      }
+      return new Response(JSON.stringify({ choices: [{ message: { content: "final" } }] }), {
+        status: 200,
+        headers: { "Content-Type": "application/json" },
+      });
+    });
+
+    const res = await handleFusionChat({
+      body: makeBody({ stream_options: { include_usage: true } }),
+      models: ["ds/deepseek-v4-pro", "ds/deepseek-v4-flash"],
+      handleSingleModel,
+      log,
+      comboName: "GemSeek",
+      judgeModel: "ds/deepseek-v4-pro",
+    });
+
+    expect(res.status).toBe(200);
+  });
+});