The radio channel

The radio channel

Two integers, each in 1..8, from you to your partner, once a turn, delivered one turn late. The opposing team never sees them, at any delay. The game assigns them no meaning.

That is the whole specification, and it is the reason this coworld exists.

The mechanics, exactly

• Every turn, every seat sends a pair with its order. A seat that says nothing repeats its previous pair; turn 1's default is [1, 1]. A seat that fell back to the scripted layer still sends a pair — sapper's, which is a real signal, or camper's, which is [1, 1].
• The pair is delivered to the sender's partner on the following turn, as radio_from_teammate in that seat's observation. On turn 1 it is null.
• Each integer is clamped into [1, 8]. A missing, mis-shaped or non-numeric radio repeats this seat's previous pair; it is never a parse failure, because the radio is a first-class output, not a rider on the order — a reply carrying a valid radio and no order is perfectly usable.
• Both pairs are hashed into gameHash. They are inputs, and a replay that got them wrong would draw the wrong glyphs while claiming a clean chain.
• Spectator-side, both teams' pairs are drawn: over each bomber as a ≋a·b badge, and on the team's scorebug plate. The hiding is enforced in the observation builder, never in the renderer.

src/pommerman/radio.nim is deliberately paranoid about the one thing that matters: every write and every read goes through a proc that takes both a team and a seat and raises if teamOfSeat(seat) does not match. There is no code path from a seat index to a cross-team pair.

Why it is hard

You did not choose your partner and you will never learn which policy it is. In-game the four seats are RED-1, BLUE-1, RED-2 and BLUE-2 and nothing else; no real policy name reaches any observation or prompt. So the channel is not a private protocol between two copies of one prompt — it is a coordination problem between two strangers under fire, with 64 symbols a turn and 36 turns to establish anything at all.

The practical consequences, and what the shipped champion prompts do about them:

• Send something simple. A code with 64 distinct meanings is a code nobody decodes. Both champions use a two-field split: one integer for intent, one for position or contact.
• Send it consistently. A partner learns a mapping only from repetition against what it can see happening on the board.
• Read your partner's pair against the board. The position half of a pair is checkable against bombers[]; the intent half is not. pommerman-firestarter's prompt says outright: believe the position half even if the intent half looks like noise.
• One number should mean "get away from me". Both champions reserve a value for it — the single most valuable thing to be able to say in a game where your partner's bomb kills you for the same price as an opponent's.

The control

camper sends [1, 1] every single turn, on purpose. It is the silent partner: the control against which "did the radio matter?" is measured on the ladder. sapper sends [1 + ammo, 1 + enemies within four cells], which is a real, legible signal — so an all-scripted episode still exercises the channel and a champion partnered with a filler has something to decode.

What the game does NOT do

• It never interprets a pair. Nothing in the sim, the score or the viewer reads meaning into the digits; the viewer draws them and stops.
• It never widens the channel. Two integers in 1..8, once a turn, one turn late — that is 6 bits per turn per seat, and no say, notes or order text reaches the other seat.
• It never delivers across the table. Not now, not delayed, not aggregated.