fix(telegram): strip own @mention from inbound content

Agents previously saw their own Telegram handle (e.g. "@viet_super_bot")
in user messages and mistook it for a different bot, replying NO_REPLY.
The username was only used for the mention gate, never removed from the
content passed to the LLM.

Slack and Feishu already strip their own bot mentions (handlers_mention.go
stripBotMention, bot_parse.go resolveMentions); Telegram was the odd one out.

Implementation:
- Add stripBotMention helper with leading/trailing word-boundary anchors so
  inline matches inside words (e.g. contact@viet_super_bot.com) are not
  falsely stripped.
- Apply in handleMessage right after the mention gate, before pairing/media
  processing, so history recording for unmentioned messages keeps raw text.
- Restore "[empty message]" placeholder when a message consisting only of
  "@botname" becomes empty after stripping.

internal/channels/telegram/handlers.go

@@ -361,6 +361,15 @@ func (c *Channel) handleMessage(ctx context.Context, update telego.Update) {
 		}
 	}
 
+	// Strip bot's own @mention so the LLM sees clean content and does not
+	// mistake itself for another bot (cross-channel parity with Slack/Feishu).
+	// Re-check empty state: a message containing only "@botname" becomes empty
+	// after stripping, so we restore the placeholder used for originally-empty inbounds.
+	content = stripBotMention(content, c.bot.Username())
+	if content == "" {
+		content = "[empty message]"
+	}
+
 	// --- Group pairing gate (only reached when bot is mentioned) ---
 	if isGroup && topicCfg.groupPolicy == "pairing" && c.PairingService() != nil {
 		if !c.IsGroupApproved(chatIDStr) {

internal/channels/telegram/handlers_utils.go

@@ -1,11 +1,30 @@
 package telegram
 
 import (
+	"regexp"
 	"strings"
 
 	"github.com/mymmrac/telego"
 )
 
+// stripBotMention removes @botUsername tokens from text (case-insensitive).
+// Applied after the mention gate passes so the LLM does not see its own Telegram handle
+// and mistake itself for another bot (e.g. persona "Tiểu Hổ" receiving "@viet_super_bot vẽ...").
+//
+// Boundary rules match valid Telegram mentions:
+//   - Leading: start-of-string OR a non-word char (whitespace/punct). Prevents false strips
+//     inside words like "contact@viet_super_bot.com".
+//   - Trailing: \b (word-boundary). Prevents matching "@bot" inside "@bot_2".
+//
+// The leading non-word char is preserved via capture group $1.
+func stripBotMention(text, botUsername string) string {
+	if botUsername == "" || text == "" {
+		return text
+	}
+	pattern := `(?i)(^|[^\w])@` + regexp.QuoteMeta(botUsername) + `\b`
+	return strings.TrimSpace(regexp.MustCompile(pattern).ReplaceAllString(text, "$1"))
+}
+
 // detectMention checks if a Telegram message mentions the bot.
 // Checks both msg.Text/Entities (text messages) and msg.Caption/CaptionEntities (photo/media messages).
 func (c *Channel) detectMention(msg *telego.Message, botUsername string) bool {

internal/channels/telegram/handlers_utils_test.go

@@ -208,6 +208,70 @@ func TestHasOtherMention_CaptionWithOtherMention(t *testing.T) {
 	}
 }
 
+// --- stripBotMention ---
+
+func TestStripBotMention_RemovesMention(t *testing.T) {
+	got := stripBotMention("@viet_super_bot vẽ ảnh minh họa", "viet_super_bot")
+	want := "vẽ ảnh minh họa"
+	if got != want {
+		t.Errorf("stripBotMention = %q, want %q", got, want)
+	}
+}
+
+func TestStripBotMention_CaseInsensitive(t *testing.T) {
+	got := stripBotMention("@Viet_Super_Bot hello", "viet_super_bot")
+	if got != "hello" {
+		t.Errorf("stripBotMention case-insensitive = %q, want %q", got, "hello")
+	}
+}
+
+func TestStripBotMention_PreservesOtherMentions(t *testing.T) {
+	got := stripBotMention("@viet_super_bot hỏi @alice về X", "viet_super_bot")
+	want := "hỏi @alice về X"
+	if got != want {
+		t.Errorf("stripBotMention = %q, want %q", got, want)
+	}
+}
+
+func TestStripBotMention_WordBoundary(t *testing.T) {
+	// @viet_super_bot2 must NOT match @viet_super_bot (different bot with similar prefix).
+	got := stripBotMention("@viet_super_bot2 hello", "viet_super_bot")
+	if got != "@viet_super_bot2 hello" {
+		t.Errorf("stripBotMention should not match prefix; got %q", got)
+	}
+}
+
+func TestStripBotMention_EmptyUsername(t *testing.T) {
+	text := "@anything else"
+	if got := stripBotMention(text, ""); got != text {
+		t.Errorf("stripBotMention with empty botUsername should return text unchanged; got %q", got)
+	}
+}
+
+func TestStripBotMention_MultipleOccurrences(t *testing.T) {
+	got := stripBotMention("hey @viet_super_bot, @viet_super_bot help!", "viet_super_bot")
+	// Both removed; internal spacing/punctuation preserved.
+	want := "hey ,  help!"
+	if got != want {
+		t.Errorf("stripBotMention multi = %q, want %q", got, want)
+	}
+}
+
+func TestStripBotMention_PreservesEmailLike(t *testing.T) {
+	// "@viet_super_bot" embedded inside a word (e.g. email/URL) must NOT be stripped.
+	// Telegram mentions require a leading word-boundary, so inline matches are false positives.
+	in := "contact@viet_super_bot.com please"
+	if got := stripBotMention(in, "viet_super_bot"); got != in {
+		t.Errorf("stripBotMention should not strip mention embedded in word; got %q, want %q", got, in)
+	}
+}
+
+func TestStripBotMention_OnlyMentionBecomesEmpty(t *testing.T) {
+	if got := stripBotMention("@viet_super_bot", "viet_super_bot"); got != "" {
+		t.Errorf("mention-only input should become empty; got %q", got)
+	}
+}
+
 // --- isServiceMessage ---
 
 func TestIsServiceMessage_WithText(t *testing.T) {