feat(multiplayer): add Steam transport foundation

2026-09-13 17:42:09 +00:00 · 2026-08-21 18:52:07 +01:00
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+# Steam development setup
+
+Steam support is optional. The default Godot build and every Phase 6 Docker
+check use ENet; they do not need a Steam client, SDK, or App ID. Selecting
+`transport="steam"` never falls back to ENet: a missing custom build or failed
+Steam initialization returns an error with the missing prerequisite.
+
+## Pinned inputs
+
+The exact expected build inputs live in
+[`steam-dependencies.lock.json`](steam-dependencies.lock.json). They are not
+committed to this repository because the Steamworks SDK is governed by Valve's
+partner access and the engine binaries are platform-specific. Use the matching
+GodotSteam client build, server build, and `SteamMultiplayerPeer` extension
+from that lock file; do not mix release families.
+
+Place the resulting custom executables/templates outside this checkout and set:
+
+```bash
+export COSMIC_CLASH_STEAM_CLIENT_GODOT=/absolute/path/to/godotsteam
+export COSMIC_CLASH_STEAM_SERVER_GODOT=/absolute/path/to/godotsteam-server
+make verify-steam-templates
+```
+
+The command imports the project with each custom build, checks the `steam`
+feature plus the `Steam`/`SteamServer` singleton and `SteamMultiplayerPeer`,
+then exports `Linux Steam Client` and `Linux Steam Dedicated Server`. It
+refuses to use a normal Godot binary, so a green result proves the expected
+native pieces are in the supplied builds. It writes only ignored `steam/build/`
+artifacts.
+
+## App IDs and scope
+
+The local-development default is Valve's Spacewar App ID **480**. To use a
+different development App ID, set `COSMIC_CLASH_STEAM_APP_ID` to a positive
+integer and place `steam_appid.txt` beside the executable (never commit that
+file). Spacewar is only for local bootstrap/transport tests: it must not be
+used to advertise servers, validate ownership/VAC, or ship.
+
+A project-owned Steamworks App ID and its server credentials are required
+before Phase 7 server browser, `BeginAuthSession`, identity-backed slot
+reclaim, bans, or public hosting. Until then, Phase 6's external test is
+controlled-only because display-name slot reclaim is insecure.
+
+## Transport contract
+
+`NetworkManager.host()` and `NetworkManager.join()` default to `"enet"`.
+Passing `"steam"` explicitly creates a `SteamMultiplayerPeer` over SDR; for
+this foundation the join address is the server's numeric Steam ID and the
+virtual port is zero. Discovery and server advertisement intentionally remain
+unimplemented until the project-owned App ID exists.