telegram: route dm sessions by sender id

src/telegram/bot/helpers.test.ts

@@ -5,6 +5,7 @@ import {
   describeReplyTarget,
   expandTextLinks,
   normalizeForwardedContext,
+  resolveTelegramDirectPeerId,
   resolveTelegramForumThreadId,
 } from "./helpers.js";
 
@@ -53,6 +54,20 @@ describe("buildTypingThreadParams", () => {
   });
 });
 
+describe("resolveTelegramDirectPeerId", () => {
+  it("prefers sender id when available", () => {
+    expect(resolveTelegramDirectPeerId({ chatId: 777777777, senderId: 123456789 })).toBe(
+      "123456789",
+    );
+  });
+
+  it("falls back to chat id when sender id is missing", () => {
+    expect(resolveTelegramDirectPeerId({ chatId: 777777777, senderId: undefined })).toBe(
+      "777777777",
+    );
+  });
+});
+
 describe("thread id normalization", () => {
   it.each([
     {

src/telegram/bot/helpers.ts

@@ -175,6 +175,24 @@ export function buildTelegramGroupPeerId(chatId: number | string, messageThreadI
   return messageThreadId != null ? `${chatId}:topic:${messageThreadId}` : String(chatId);
 }
 
+/**
+ * Resolve the direct-message peer identifier for Telegram routing/session keys.
+ *
+ * In some Telegram DM deliveries (for example certain business/chat bridge flows),
+ * `chat.id` can differ from the actual sender user id. Prefer sender id when present
+ * so per-peer DM scopes isolate users correctly.
+ */
+export function resolveTelegramDirectPeerId(params: {
+  chatId: number | string;
+  senderId?: number | string | null;
+}) {
+  const senderId = params.senderId != null ? String(params.senderId).trim() : "";
+  if (senderId) {
+    return senderId;
+  }
+  return String(params.chatId);
+}
+
 export function buildTelegramGroupFrom(chatId: number | string, messageThreadId?: number) {
   return `telegram:group:${buildTelegramGroupPeerId(chatId, messageThreadId)}`;
 }