From f3404227d29344e59e164ee93bc6bd6dc387f867 Mon Sep 17 00:00:00 2001
From: Tushar Agarwal <76201310+Tushar49@users.noreply.github.com>
Date: Fri, 29 May 2026 09:26:16 +0530
Subject: [PATCH] fix(deepseek-web): return 400 when client sends tools[] -
 chat.deepseek.com has no tool support (#2854)

Integrated into release/v3.8.6.
---
 open-sse/executors/deepseek-web.ts | 24 +++++++++++++
 tests/unit/deepseek-web.test.ts    | 57 ++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/open-sse/executors/deepseek-web.ts b/open-sse/executors/deepseek-web.ts
index 376bafbab2..0076126ddb 100644
--- a/open-sse/executors/deepseek-web.ts
+++ b/open-sse/executors/deepseek-web.ts
@@ -683,6 +683,30 @@ export class DeepSeekWebExecutor extends BaseExecutor {
 
   async execute({ model, body, stream, credentials, signal, log }: ExecuteInput) {
     const bodyObj = (body || {}) as Record<string, unknown>;
+
+    // chat.deepseek.com's web API only accepts {prompt, ref_file_ids,
+    // thinking_enabled, search_enabled} - no tools field. Silently dropping
+    // tools[] is misleading: models reply as if no tools were ever offered,
+    // causing agentic clients (OpenAI-compatible) to hallucinate "I don't
+    // have that tool". Fail fast with a clear error so callers route to the
+    // official DeepSeek API (provider: 'deepseek') or a different provider
+    // for tool-using requests. See #2848.
+    const requestedTools = bodyObj.tools;
+    if (Array.isArray(requestedTools) && requestedTools.length > 0) {
+      return {
+        response: errorResponse(
+          400,
+          "deepseek-web upstream (chat.deepseek.com) does not support function calling. " +
+            "The web interface only accepts text + thinking_enabled + search_enabled flags. " +
+            "Use provider 'deepseek' (official api.deepseek.com) for tool-using requests, " +
+            "or route through a different provider."
+        ),
+        url: COMPLETION_URL,
+        headers: {},
+        transformedBody: body,
+      };
+    }
+
     const messages = (Array.isArray(bodyObj.messages) ? bodyObj.messages : []) as Array<{
       role: string;
       content: string;
diff --git a/tests/unit/deepseek-web.test.ts b/tests/unit/deepseek-web.test.ts
index bfc7ab0738..3271b65c96 100644
--- a/tests/unit/deepseek-web.test.ts
+++ b/tests/unit/deepseek-web.test.ts
@@ -58,6 +58,63 @@ test("execute returns 400 with empty apiKey", async () => {
   assert.equal(result.response.status, 400);
 });
 
+test("execute returns 400 when client sends non-empty tools[] (chat.deepseek.com has no tool support) - issue #2848", async () => {
+  const executor = new DeepSeekWebExecutor();
+  const result = await executor.execute({
+    model: "default",
+    body: {
+      messages: [{ role: "user", content: "call my_tool" }],
+      tools: [
+        {
+          type: "function",
+          function: {
+            name: "my_tool",
+            description: "test",
+            parameters: { type: "object", properties: {} },
+          },
+        },
+      ],
+    },
+    stream: false,
+    credentials: { apiKey: "any-valid-looking-token" },
+    signal: AbortSignal.timeout(5000),
+  });
+  assert.equal(result.response.status, 400);
+  const text = await result.response.text();
+  assert.ok(
+    /does not support function calling/i.test(text),
+    `expected explanatory error body, got: ${text}`
+  );
+  assert.ok(
+    /provider 'deepseek'|api\.deepseek\.com/i.test(text),
+    `expected guidance to use official deepseek provider, got: ${text}`
+  );
+});
+
+test("execute does NOT 400 on tools[]=[] (empty array, equivalent to no tools)", async () => {
+  const executor = new DeepSeekWebExecutor();
+  const result = await executor.execute({
+    model: "default",
+    body: {
+      messages: [{ role: "user", content: "hi" }],
+      tools: [],
+    },
+    stream: false,
+    credentials: {},
+    signal: AbortSignal.timeout(5000),
+  });
+  assert.equal(
+    result.response.status,
+    400,
+    "still returns 400 but for missing userToken, NOT for tools[]"
+  );
+  const text = await result.response.text();
+  assert.ok(
+    text.includes("userToken"),
+    `expected userToken error (not tools error) for empty tools[], got: ${text}`
+  );
+});
+
 // ─── Test connection ─────────────────────────────────────────────────────
 
 test("testConnection returns false with empty credentials", async () => {