fix: preserve Telegram usernames with underscores

backend/bot/utils/text_sanitizer.py

@@ -199,10 +199,17 @@ def sanitize_display_name(value: Optional[str]) -> Optional[str]:
 def sanitize_username(value: Optional[str]) -> Optional[str]:
     if value is None:
         return None
-    clean = value.strip()
-    clean = clean.lstrip("@")
-    clean = _remove_patterns(clean)
-    return _finalize(clean)
+    clean = unicodedata.normalize("NFKC", str(value))
+    clean = clean.strip().lstrip("@").strip()
+    if not clean:
+        return None
+
+    # Telegram usernames are already a constrained identifier, not free-form display text.
+    # Do not apply display-name anti-spoofing filters here: they remove words like
+    # "service" or "support" from valid usernames such as "name_service".
+    if re.fullmatch(r"[A-Za-z0-9_-]{1,64}", clean):
+        return clean
+    return None
 
 
 def username_for_display(username: Optional[str], with_at: bool = False) -> str:

frontend/src/lib/webapp/formatters.js

@@ -47,10 +47,10 @@ export function normalizedEmail(value) {
 }
 
 export function telegramName(profile, fallback) {
+  const username = String(profile?.username || "").trim();
+  if (username) return `@${username}`;
   const first = String(profile?.first_name || "").trim();
   const last = String(profile?.last_name || "").trim();
   if (first || last) return `${first} ${last}`.trim();
-  const username = String(profile?.username || "").trim();
-  if (username) return `@${username}`;
   return fallback;
 }

tests/test_text_sanitizer.py

@@ -0,0 +1,24 @@
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "backend"))
+
+from bot.utils.text_sanitizer import sanitize_display_name, sanitize_username, username_for_display
+
+
+def test_sanitize_username_preserves_underscore_suffixes():
+    assert sanitize_username("ik_end") == "ik_end"
+    assert sanitize_username("name_service") == "name_service"
+    assert sanitize_username("@client_support") == "client_support"
+    assert sanitize_username("telegram_user") == "telegram_user"
+    assert username_for_display("ik_end", with_at=True) == "@ik_end"
+    assert username_for_display("name_service", with_at=True) == "@name_service"
+
+
+def test_sanitize_username_rejects_free_form_values_instead_of_truncating():
+    assert sanitize_username("https://t.me/name_service") is None
+    assert sanitize_username("name service") is None
+
+
+def test_display_name_filters_still_apply_to_free_form_names():
+    assert sanitize_display_name("Name service") == "Name"