fix(bot): resolve required channel join link

backend/bot/utils/channel_subscription.py

@@ -1,4 +1,9 @@
-from typing import Optional
+import logging
+import re
+from typing import Any, Optional
+
+_TELEGRAM_LINK_RE = re.compile(r"^(?:https?://|tg://)", re.IGNORECASE)
+_TELEGRAM_USERNAME_RE = re.compile(r"^[A-Za-z0-9_]{5,64}$")
 
 
 def normalize_required_channel_id(value: object) -> Optional[int]:
@@ -28,6 +33,66 @@ def normalize_required_channel_id(value: object) -> Optional[int]:
     return -int(f"100{raw_abs}")
 
 
+def normalize_required_channel_link(value: object) -> Optional[str]:
+    if value is None:
+        return None
+
+    raw = str(value).strip()
+    if not raw:
+        return None
+
+    if _TELEGRAM_LINK_RE.match(raw):
+        return raw
+
+    raw = raw.lstrip("@").strip()
+    if not raw or re.search(r"\s", raw):
+        return None
+
+    if raw.startswith(("t.me/", "telegram.me/")):
+        return f"https://{raw}"
+
+    if raw.startswith(("+", "joinchat/", "c/")):
+        return f"https://t.me/{raw}"
+
+    if _TELEGRAM_USERNAME_RE.fullmatch(raw):
+        return f"https://t.me/{raw}"
+
+    return None
+
+
+def _required_channel_link_from_chat(chat: Any) -> Optional[str]:
+    username = str(getattr(chat, "username", "") or "").strip().lstrip("@")
+    if username:
+        return f"https://t.me/{username}"
+
+    invite_link = normalize_required_channel_link(getattr(chat, "invite_link", None))
+    if invite_link:
+        return invite_link
+
+    return None
+
+
+async def resolve_required_channel_link(
+    bot: Any,
+    required_channel_id: Optional[int],
+    configured_link: object,
+) -> Optional[str]:
+    if bot is not None and required_channel_id:
+        try:
+            chat = await bot.get_chat(required_channel_id)
+            resolved_link = _required_channel_link_from_chat(chat)
+            if resolved_link:
+                return resolved_link
+        except Exception as error:
+            logging.warning(
+                "Failed to resolve required channel link from chat %s: %s",
+                required_channel_id,
+                error,
+            )
+
+    return normalize_required_channel_link(configured_link)
+
+
 def is_required_channel_access_error(error: BaseException) -> bool:
     message = str(error).lower()
     configuration_markers = (