fix(telegram): exclude forum topic system messages from implicitMention

When a Telegram Forum topic is created by the bot, Telegram generates a
system message with from.id=botId and empty text.  Every subsequent user
message in that topic has reply_to_message pointing to this system
message, causing the implicitMention check to fire and bypassing
requireMention for every single message.

Add a guard that recognises system messages (is_bot=true with no text)
and excludes them from implicit mention detection, so that only genuine
replies to bot messages trigger the bypass.

Closes #32256

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/telegram/bot-message-context.implicit-mention.test.ts

@@ -0,0 +1,98 @@
+import { describe, expect, it } from "vitest";
+import { buildTelegramMessageContextForTest } from "./bot-message-context.test-harness.js";
+
+describe("buildTelegramMessageContext implicitMention forum system messages", () => {
+  /**
+   * Build a group message context where the user sends a message inside a
+   * forum topic that has `reply_to_message` pointing to a message from the
+   * bot.  Callers control whether the reply target looks like a system
+   * message (empty text) or a real bot reply (non-empty text).
+   */
+  async function buildGroupReplyCtx(params: {
+    replyToMessageText?: string;
+    replyFromIsBot?: boolean;
+    replyFromId?: number;
+  }) {
+    const BOT_ID = 7; // matches test harness primaryCtx.me.id
+    return await buildTelegramMessageContextForTest({
+      message: {
+        message_id: 100,
+        chat: { id: -1001234567890, type: "supergroup", title: "Forum Group" },
+        date: 1700000000,
+        text: "hello everyone",
+        from: { id: 42, first_name: "Alice" },
+        reply_to_message: {
+          message_id: 1,
+          text: params.replyToMessageText ?? undefined,
+          from: {
+            id: params.replyFromId ?? BOT_ID,
+            first_name: "OpenClaw",
+            is_bot: params.replyFromIsBot ?? true,
+          },
+        },
+      },
+      resolveGroupActivation: () => true,
+      resolveGroupRequireMention: () => true,
+      resolveTelegramGroupConfig: () => ({
+        groupConfig: { requireMention: true },
+        topicConfig: undefined,
+      }),
+    });
+  }
+
+  it("does NOT trigger implicitMention for forum topic system messages (empty-text bot message)", async () => {
+    // System message: bot created the topic → text is empty, from.is_bot = true
+    const ctx = await buildGroupReplyCtx({
+      replyToMessageText: undefined,
+      replyFromIsBot: true,
+    });
+
+    // With requireMention and no explicit @mention, the message should be
+    // skipped (null) because implicitMention should NOT fire.
+    expect(ctx).toBeNull();
+  });
+
+  it("does NOT trigger implicitMention for empty-string text system messages", async () => {
+    const ctx = await buildGroupReplyCtx({
+      replyToMessageText: "",
+      replyFromIsBot: true,
+    });
+
+    expect(ctx).toBeNull();
+  });
+
+  it("DOES trigger implicitMention for real bot replies (non-empty text)", async () => {
+    const ctx = await buildGroupReplyCtx({
+      replyToMessageText: "Here is my answer",
+      replyFromIsBot: true,
+    });
+
+    // Real bot reply → implicitMention fires → message is NOT skipped.
+    expect(ctx).not.toBeNull();
+    expect(ctx?.ctxPayload?.WasMentioned).toBe(true);
+  });
+
+  it("DOES trigger implicitMention for bot reply with whitespace-only text", async () => {
+    // A bot message that has actual whitespace text is NOT a system message,
+    // so it should still count as an implicit mention.  (Telegram's forum
+    // system messages have undefined / empty text, not whitespace.)
+    const ctx = await buildGroupReplyCtx({
+      replyToMessageText: " ",
+      replyFromIsBot: true,
+    });
+
+    expect(ctx).not.toBeNull();
+    expect(ctx?.ctxPayload?.WasMentioned).toBe(true);
+  });
+
+  it("does NOT trigger implicitMention when reply is from a different user", async () => {
+    const ctx = await buildGroupReplyCtx({
+      replyToMessageText: "some message",
+      replyFromIsBot: false,
+      replyFromId: 999,
+    });
+
+    // Different user's message → not an implicit mention → skipped.
+    expect(ctx).toBeNull();
+  });
+});

src/telegram/bot-message-context.ts

@@ -471,9 +471,15 @@ export const buildTelegramMessageContext = async ({
     return null;
   }
   // Reply-chain detection: replying to a bot message acts like an implicit mention.
+  // Exclude forum-topic system messages (auto-generated "Topic created" messages by the
+  // bot that have empty text) so that every message inside a bot-created topic does not
+  // incorrectly bypass requireMention (#32256).
   const botId = primaryCtx.me?.id;
   const replyFromId = msg.reply_to_message?.from?.id;
-  const implicitMention = botId != null && replyFromId === botId;
+  const replyToBotMessage = botId != null && replyFromId === botId;
+  const isReplyToSystemMessage =
+    replyToBotMessage && msg.reply_to_message?.from?.is_bot === true && !msg.reply_to_message?.text;
+  const implicitMention = replyToBotMessage && !isReplyToSystemMessage;
   const canDetectMention = Boolean(botUsername) || mentionRegexes.length > 0;
   const mentionGate = resolveMentionGatingWithBypass({
     isGroup,