diff --git a/src/gateway/helpers.ts b/src/gateway/helpers.ts
index 1ead63a..5d6d199 100644
--- a/src/gateway/helpers.ts
+++ b/src/gateway/helpers.ts
@@ -51,21 +51,40 @@ function getChatId(thread: any, message: any): string {
 
 /**
  * Resolve the agent-facing thread ID from a chat message.
- * Private/DM → "main", group → "group:<chatId>"
+ * Private/DM → "main", group → "group:<chatId>", forum topic → "group:<chatId>:topic:<topicId>"
  */
 export function resolveAgentThreadId(thread: any, message: any): string {
   const chatType = String(message?.chat?.type ?? thread?.chat?.type ?? thread?.type ?? "").toLowerCase();
+  
+  // Extract topic ID if present (forum threads)
+  const topicId = message?.message_thread_id ?? thread?.messageThreadId ?? extractTopicFromThreadId(thread?.id);
+  
   if (["private", "dm", "direct", "im"].includes(chatType)) return "main";
-  if (["group", "supergroup", "channel"].includes(chatType)) return `group:${getChatId(thread, message)}`;
+  if (["group", "supergroup", "channel"].includes(chatType)) {
+    const base = `group:${getChatId(thread, message)}`;
+    return topicId ? `${base}:topic:${topicId}` : base;
+  }
 
   const telegramChatId = telegramChatIdFromThreadId(thread?.id);
   if (telegramChatId !== null) {
-    return telegramChatId < 0 ? `group:${telegramChatId}` : "main";
+    const base = telegramChatId < 0 ? `group:${telegramChatId}` : "main";
+    return (topicId && telegramChatId < 0) ? `${base}:topic:${topicId}` : base;
   }
 
   return String(thread?.id ?? "main");
 }
 
+/** Extract message_thread_id from thread ID string like "telegram:chatId:topicId" */
+function extractTopicFromThreadId(threadId: string | undefined): number | undefined {
+  if (!threadId) return undefined;
+  const parts = threadId.split(":");
+  if (parts.length === 3 && parts[0] === "telegram") {
+    const parsed = parseInt(parts[2], 10);
+    return Number.isFinite(parsed) ? parsed : undefined;
+  }
+  return undefined;
+}
+
 // ── System Resources ─────────────────────────────────
 
 export interface SystemResources {
diff --git a/test/gateway-helpers.test.ts b/test/gateway-helpers.test.ts
index 699bb1c..97fc652 100644
--- a/test/gateway-helpers.test.ts
+++ b/test/gateway-helpers.test.ts
@@ -61,6 +61,24 @@ describe("gateway/helpers", () => {
       expect(resolveAgentThreadId(thread, message)).toBe("group:-456");
     });
 
+    it("routes forum topic to separate session", () => {
+      const thread = { id: "telegram:-100123:42" };
+      const message = { chat: { type: "supergroup", id: -100123 } };
+      expect(resolveAgentThreadId(thread, message)).toBe("group:-100123:topic:42");
+    });
+
+    it("routes forum topic via message_thread_id", () => {
+      const thread = { id: "telegram:-100123" };
+      const message = { chat: { type: "supergroup", id: -100123 }, message_thread_id: 99 };
+      expect(resolveAgentThreadId(thread, message)).toBe("group:-100123:topic:99");
+    });
+
+    it("group without topic stays flat", () => {
+      const thread = { id: "telegram:-100123" };
+      const message = { chat: { type: "supergroup", id: -100123 } };
+      expect(resolveAgentThreadId(thread, message)).toBe("group:-100123");
+    });
+
     it("routes telegram positive IDs to main", () => {
       const thread = { id: "telegram:789" };
       const message = {};