From e97d338f3a5128b499c16f6289da2acef29395b5 Mon Sep 17 00:00:00 2001
From: Felix-Ayush <67006255+Ayush7614@users.noreply.github.com>
Date: Thu, 30 Jul 2026 04:08:31 +0530
Subject: [PATCH] fix(ai-chat): preserve max_tokens 0 for Alibaba, DeepSeek,
 and Claude (#3472)

These providers used `max_tokens || default`, so an explicit zero was
replaced by the fallback. Use nullish coalescing so 0 is forwarded.
---
 .../providers/alibaba/AlibabaProvider.test.ts    | 15 +++++++++++++++
 .../ai-chat/providers/alibaba/AlibabaProvider.ts |  2 +-
 .../providers/claude/ClaudeProvider.test.ts      | 16 ++++++++++++++++
 .../ai-chat/providers/claude/ClaudeProvider.ts   |  2 +-
 .../providers/deepseek/DeepSeekProvider.test.ts  | 15 +++++++++++++++
 .../providers/deepseek/DeepSeekProvider.ts       |  2 +-
 6 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/src/backend/drivers/ai-chat/providers/alibaba/AlibabaProvider.test.ts b/src/backend/drivers/ai-chat/providers/alibaba/AlibabaProvider.test.ts
index 5d66e0a2e..d79f9519c 100644
--- a/src/backend/drivers/ai-chat/providers/alibaba/AlibabaProvider.test.ts
+++ b/src/backend/drivers/ai-chat/providers/alibaba/AlibabaProvider.test.ts
@@ -225,6 +225,21 @@ describe('AlibabaProvider.complete request shape', () => {
         expect(createMock.mock.calls[0]![0].max_tokens).toBe(256);
     });
 
+    it('forwards max_tokens 0 instead of substituting the default 1000', async () => {
+        const { provider } = makeProvider();
+        createMock.mockResolvedValueOnce(baseCompletion);
+
+        await withTestActor(() =>
+            provider.complete({
+                model: 'qwen-plus',
+                messages: [{ role: 'user', content: 'hi' }],
+                max_tokens: 0,
+            }),
+        );
+
+        expect(createMock.mock.calls[0]![0].max_tokens).toBe(0);
+    });
+
     it('forwards temperature when supplied', async () => {
         const { provider } = makeProvider();
         createMock.mockResolvedValueOnce(baseCompletion);
diff --git a/src/backend/drivers/ai-chat/providers/alibaba/AlibabaProvider.ts b/src/backend/drivers/ai-chat/providers/alibaba/AlibabaProvider.ts
index 14798ae28..a825e36b1 100644
--- a/src/backend/drivers/ai-chat/providers/alibaba/AlibabaProvider.ts
+++ b/src/backend/drivers/ai-chat/providers/alibaba/AlibabaProvider.ts
@@ -86,7 +86,7 @@ export class AlibabaProvider implements IChatProvider {
             messages,
             model: modelUsed.id,
             ...(tools ? { tools } : {}),
-            max_tokens: max_tokens || 1000,
+            max_tokens: max_tokens ?? 1000,
             temperature,
             stream,
             ...(stream
diff --git a/src/backend/drivers/ai-chat/providers/claude/ClaudeProvider.test.ts b/src/backend/drivers/ai-chat/providers/claude/ClaudeProvider.test.ts
index 63780655d..6e5ac5b51 100644
--- a/src/backend/drivers/ai-chat/providers/claude/ClaudeProvider.test.ts
+++ b/src/backend/drivers/ai-chat/providers/claude/ClaudeProvider.test.ts
@@ -237,6 +237,22 @@ describe('ClaudeProvider.complete request shape', () => {
         });
     });
 
+    it('forwards max_tokens 0 instead of substituting the model default', async () => {
+        const { provider } = makeProvider();
+        messagesCreateMock.mockResolvedValueOnce(baseResponse);
+
+        await withTestActor(() =>
+            provider.complete({
+                model: 'claude-haiku-4-5-20251001',
+                messages: [{ role: 'user', content: 'hello' }],
+                max_tokens: 0,
+            }),
+        );
+
+        const [args] = messagesCreateMock.mock.calls[0]!;
+        expect(args.max_tokens).toBe(0);
+    });
+
     it('extracts system messages and forwards them as the top-level `system` field', async () => {
         const { provider } = makeProvider();
         messagesCreateMock.mockResolvedValueOnce(baseResponse);
diff --git a/src/backend/drivers/ai-chat/providers/claude/ClaudeProvider.ts b/src/backend/drivers/ai-chat/providers/claude/ClaudeProvider.ts
index 01e8c0cd3..309a44133 100644
--- a/src/backend/drivers/ai-chat/providers/claude/ClaudeProvider.ts
+++ b/src/backend/drivers/ai-chat/providers/claude/ClaudeProvider.ts
@@ -320,7 +320,7 @@ export class ClaudeProvider implements IChatProvider {
         } = {
             model: modelUsed.id,
             max_tokens: Math.floor(
-                max_tokens ||
+                max_tokens ??
                     (model === 'claude-3-5-sonnet-20241022' ||
                     model === 'claude-3-5-sonnet-20240620'
                         ? 8192
diff --git a/src/backend/drivers/ai-chat/providers/deepseek/DeepSeekProvider.test.ts b/src/backend/drivers/ai-chat/providers/deepseek/DeepSeekProvider.test.ts
index 5c7903086..423270069 100644
--- a/src/backend/drivers/ai-chat/providers/deepseek/DeepSeekProvider.test.ts
+++ b/src/backend/drivers/ai-chat/providers/deepseek/DeepSeekProvider.test.ts
@@ -216,6 +216,21 @@ describe('DeepSeekProvider.complete request shape', () => {
         expect(createMock.mock.calls[0]![0].max_tokens).toBe(256);
     });
 
+    it('forwards max_tokens 0 instead of substituting the default 1000', async () => {
+        const { provider } = makeProvider();
+        createMock.mockResolvedValueOnce(baseCompletion);
+
+        await withTestActor(() =>
+            provider.complete({
+                model: 'deepseek-v4-flash',
+                messages: [{ role: 'user', content: 'hi' }],
+                max_tokens: 0,
+            }),
+        );
+
+        expect(createMock.mock.calls[0]![0].max_tokens).toBe(0);
+    });
+
     it('omits the `tools` key entirely when no tools are supplied', async () => {
         const { provider } = makeProvider();
         createMock.mockResolvedValueOnce(baseCompletion);
diff --git a/src/backend/drivers/ai-chat/providers/deepseek/DeepSeekProvider.ts b/src/backend/drivers/ai-chat/providers/deepseek/DeepSeekProvider.ts
index 53edb1db5..58b0320fe 100644
--- a/src/backend/drivers/ai-chat/providers/deepseek/DeepSeekProvider.ts
+++ b/src/backend/drivers/ai-chat/providers/deepseek/DeepSeekProvider.ts
@@ -117,7 +117,7 @@ export class DeepSeekProvider implements IChatProvider {
             messages,
             model: modelUsed.id,
             ...(tools ? { tools } : {}),
-            max_tokens: max_tokens || 1000,
+            max_tokens: max_tokens ?? 1000,
             temperature,
             stream,
             ...(stream