Multiplayer step B: every player order is a command (dig, build, cast, hand, orders) and the simulation runs in fixed 50 ms steps, so single player and a match take the same path

docs/MULTIPLAYER.md

@@ -29,13 +29,34 @@ The server does not simulate; it relays:
 Only the commands travel over the network, so bandwidth is tiny and no game state has to be serialised
 per turn. Fog of war, particles and the camera are local and not part of the shared state.
 
+## What is there already
+
+- **Per-master state** (`game.rs`): every master has his own gold, mana, hand, research, payday, flag,
+  core... `Game::switch_to(side)` puts one master in the active fields, the simulation walks through all
+  masters step by step. A single player game has no stored masters and is unaffected.
+- **Commands** (`commands.rs`): every order a player gives is an `Act` (`Dig`, `Room`, `Tower`, `Trap`,
+  `Cast`, `Flag`, `Pickup`, `Drop`, `Slap`, `Attack`, `Guard`, `CancelOrders`, ...) wrapped in a
+  `Command { side, seq, act }`. Creature targets are *ids*, so they mean the same on every client.
+  The tools in `main.rs` only queue commands now - nothing touches the world directly.
+- **Steps**: the simulation runs in fixed steps of `STEP` = 50 ms (`Game::update` feeds real time into
+  them, `Game::apply_turn(cmds, steps)` is the lockstep entry point). Commands are applied at step
+  boundaries, so single player and a match run exactly the same path. Particles, effects and the camera
+  keep running in real time: they are local and not part of the shared state.
+- **Who speaks**: messages, hints and interface sounds belong to the master who is being processed
+  (`Game::speaking`); what another master orders never shows up on my screen.
+- Savegames, tests and the standalone file are unchanged: `cargo test --release` covers the command path
+  (including "the same actions on both paths build the same world").
+
 ## Steps
 
 | # | Step | Status |
 |---|---|---|
-| A | Simulation per master: gold, mana, research, rooms, hand, flag, traps, payday... per side; up to four masters (red, green, blue, yellow) | planned |
-| B | All player actions as commands (`Command` + `Game::apply`), single player uses the same path; fixed time step | planned |
-| C | Server: lobby and match relay over WebSocket (axum), turns, pause on disconnect, AI takeover on leave, chat | planned |
+| A | Simulation per master: gold, mana, research, rooms, hand, flag, traps, payday... per side; up to four masters (red, green, blue, yellow) | built |
+| B | All player actions as commands (`Command` + `Game::apply`), single player uses the same path; fixed time step | built |
+| C | Server: lobby and match relay over WebSocket (axum), turns, pause on disconnect, AI takeover on leave, chat | next |
 | D | Client: *Multiplayer* menu (lobby, create, join, ready, teams), WebSocket bridge in `dc_plugin.js`, chat, gold sending | planned |
 | E | Alliances and coop rules, AI masters for free and abandoned slots | planned |
 | F | Coop campaign: 20 missions with story (EN/DE) | planned |
+
+Still open on the way to C: player owners (today side 1 is the humans' and 2/3 the rivals' - four
+player sides need their own `Owner`s), the turn/turn-boundary client loop, and the state checksum.