add format instructions

Author: sutigit

src/config.ts

@@ -55,3 +55,11 @@ export const DEFAULT_MODEL_ON_ENABLE = 'gpt-5'
 
 export const DEFAULT_ASSISTANT_INSTRUCTIONS = '' // 11th August 2025 we decided it should be empty
 export const DEFAULT_MODEL_TEMPERATURE = 0.5
+
+export const formatInstructions = `
+        Always format responses in plain Markdown.
+        Use Markdown headings (#, ##, ###) for structure, even for normal text.
+        Use lists, tables, and blockquotes where useful.
+        Put math in $$ ... $$ for LaTeX rendering.
+        Wrap code in triple backticks with the correct language tag (js, ts, py, etc.) so syntax highlighting and rendering work.
+      `

src/server/services/langchain/chat.ts

@@ -5,7 +5,7 @@ import type { Runnable } from '@langchain/core/runnables'
 import type { StructuredTool } from '@langchain/core/tools'
 import { concat } from '@langchain/core/utils/stream'
 import { AzureChatOpenAI } from '@langchain/openai'
-import { ValidModelName, validModels } from '../../../config'
+import { formatInstructions, ValidModelName, validModels } from '../../../config'
 import type { ChatEvent } from '../../../shared/chat'
 import type { ChatMessage } from '../../../shared/chat'
 import type { ChatToolDef, ChatToolOutput } from '../../../shared/tools'
@@ -68,6 +68,10 @@ export const streamChat = async ({
   const chatModel = getChatModel(model, tools, temperature)
 
   const messages: BaseMessageLike[] = [
+    {
+      role: 'system',
+      content: formatInstructions,
+    },
     {
       role: 'system',
       content: systemMessage,