Resolve unmarked channel/chat IDs passed as positive integers

[embogomolov]

What's broken

When a caller passes a bare channel ID like 1676885811 (without the -100 prefix), Telethon's get_entity(int) runs it through resolve_id(), gets PeerUser, and looks for a user with that ID. There is no such user, so it throws ValueError.

The existing fallback (get_dialogs() cache warming) doesn't help — Telethon still reads the positive int as PeerUser on retry, so the second attempt fails the same way.

This happens often with MCP callers (LLMs, automation tools) that store or copy channel IDs as plain numbers without the -100 marker.

The fix

_marked_id_candidates() generates -100{id} (PeerChannel) and -{id} (PeerChat) from a positive int.

Both resolve_entity() and resolve_input_entity() now try these variants as a last resort: original ID first, then cache warming + retry, then marked candidates. If everything fails, the error message lists what was tried.

How to test

• Call resolve_username for a channel, extract the raw channel_id from the response
• Pass that bare positive int to search_messages or get_history — should work now instead of throwing ValueError
• Negative (already marked) IDs still work as before — _marked_id_candidates returns an empty list for non-positive ints

[embogomolov]

Anyone?

[chigwell]

Hey @embogomolov, thank you for the contribution! Could I please ask you to fix the black formatting so the CI tests will pass? Thank you!