fix: normalize required channel checks

backend/bot/utils/channel_subscription.py

@@ -0,0 +1,40 @@
+from typing import Optional
+
+
+def normalize_required_channel_id(value: object) -> Optional[int]:
+    if value is None:
+        return None
+
+    raw = str(value).strip()
+    if not raw:
+        return None
+
+    try:
+        channel_id = int(raw)
+    except (TypeError, ValueError):
+        return None
+
+    if channel_id == 0:
+        return None
+
+    if channel_id > 0:
+        return int(f"-100{channel_id}")
+
+    raw_abs = str(abs(channel_id))
+    if raw.startswith("-100"):
+        return channel_id
+    if abs(channel_id) < 1_000_000_000:
+        return channel_id
+    return -int(f"100{raw_abs}")
+
+
+def is_required_channel_access_error(error: BaseException) -> bool:
+    message = str(error).lower()
+    configuration_markers = (
+        "chat not found",
+        "bot is not a member",
+        "not enough rights",
+        "have no rights",
+        "kicked",
+    )
+    return any(marker in message for marker in configuration_markers)