refactor: simplify header generation and improve session management logic

Author: cuipengfei

README.md

@@ -360,9 +360,8 @@ copilot-api start --header-mode savings
 
 VS Code Copilot extension compatibility:
 
-- **Headers**: Both `X-Initiator` and `X-Interaction-Id`
-- **Logic**: Replicates VS Code extension's behavior(sort of)
-- **Session Management**: UUID-based session tracking
+- **Headers**: `X-Initiator`
+- **Logic**: If last message is user then it is user, otherwise agent
 - **Use case**: Use this when you want to mimic the behavior of the VS Code extension to avoid potential abuse detection. (I am not sure if they do that, but it's better to be cautious.)
 
 ```bash

src/lib/headers.ts

@@ -1,51 +1,28 @@
-import { randomUUID } from "node:crypto"
-
 import type { ChatCompletionsPayload } from "~/services/copilot/create-chat-completions"
 
 export type HeaderMode = "savings" | "compatible"
 
 export interface RequestHeaders {
   "X-Initiator": "user" | "agent"
-  "X-Interaction-Id"?: string
 }
 
-/**
- * Simple session manager for compatible mode
- */
-class SessionManager {
-  private sessionId: string = randomUUID()
-
-  newSession(): string {
-    this.sessionId = randomUUID()
-    return this.sessionId
-  }
-
-  getCurrentSession(): string {
-    return this.sessionId
-  }
-}
-
-const sessionManager = new SessionManager()
-
 /**
  * Generate headers based on mode
  */
 export function generateSessionHeaders(
   payload: ChatCompletionsPayload,
   mode: HeaderMode,
 ): RequestHeaders {
-  return mode === "savings" ?
-      {
-        "X-Initiator": getSavingsInitiator(payload),
-      }
-    : {
-        "X-Initiator": getCompatibleInitiator(payload),
-        "X-Interaction-Id": getSessionId(payload),
-      }
+  return {
+    "X-Initiator":
+      mode === "savings" ?
+        getSavingsInitiator(payload)
+      : getCompatibleInitiator(payload),
+  }
 }
 
 /**
- * Savings mode: default behavior
+ * Savings mode: if any message is assistant or tool, then it is agent
  */
 function getSavingsInitiator(
   payload: ChatCompletionsPayload,
@@ -58,42 +35,11 @@ function getSavingsInitiator(
 }
 
 /**
- * Compatible mode: replicate VS Code extension logic
+ * Compatible mode: if last message is user then it is user
  */
 function getCompatibleInitiator(
   payload: ChatCompletionsPayload,
 ): "user" | "agent" {
-  // VS Code: userInitiatedRequest = iterationNumber === 0 && !isContinuation
-  const hasAssistantMessage = payload.messages.some(
-    (msg) => msg.role === "assistant",
-  )
-  const hasToolCalls = payload.messages.some(
-    (msg) => msg.tool_calls && msg.tool_calls.length > 0,
-  )
-  const hasToolMessages = payload.messages.some((msg) => msg.role === "tool")
-
-  const isFirstIteration = !hasAssistantMessage
-  const isContinuation = hasToolCalls || hasToolMessages
-
-  return isFirstIteration && !isContinuation ? "user" : "agent"
-}
-
-/**
- * Detect if this is the start of a new conversation
- */
-function isStartOfConversation(payload: ChatCompletionsPayload): boolean {
-  const hasAssistantMessage = payload.messages.some(
-    (msg) => msg.role === "assistant",
-  )
-  return !hasAssistantMessage
-}
-
-/**
- * Get session ID for compatible mode
- */
-function getSessionId(payload: ChatCompletionsPayload): string {
-  if (isStartOfConversation(payload)) {
-    return sessionManager.newSession()
-  }
-  return sessionManager.getCurrentSession()
+  const lastMessage = payload.messages.at(-1)
+  return lastMessage?.role === "user" ? "user" : "agent"
 }

src/services/copilot/create-chat-completions.ts

@@ -23,13 +23,13 @@ export const createChatCompletions = async (
   // Build headers
   const headers: Record<string, string> = {
     ...copilotHeaders(state, enableVision),
-    ...sessionHeaders, // This includes X-Initiator and optionally X-Interaction-Id
+    ...sessionHeaders, // This includes X-Initiator
   }
 
   // Optional: Add debug logging
   if (state.headerMode === "compatible") {
     consola.debug(
-      `Compatible mode headers: X-Initiator=${sessionHeaders["X-Initiator"]}, X-Interaction-Id=${sessionHeaders["X-Interaction-Id"]?.slice(0, 8)}...`,
+      `Compatible mode headers: X-Initiator=${sessionHeaders["X-Initiator"]}`,
     )
   }
 

src/start.ts

@@ -46,7 +46,7 @@ export async function runServer(options: RunServerOptions): Promise<void> {
   state.headerMode = options.headerMode as "savings" | "compatible"
 
   if (state.headerMode === "compatible") {
-    consola.info("Using compatible mode - full VS Code extension compatibility")
+    consola.info("Using compatible mode - VS Code extension compatibility")
   } else {
     consola.info("Using savings mode - optimized for premium requests savings")
   }