feat(plugins): add Velocity proxy and Fabric/Forge/NeoForge/Paper integration mods

Server-side integration plugins: the Velocity proxy plugin plus Fabric, Forge, NeoForge, and Paper mods with a shared module. Gradle build output is not tracked.

plugins/fabric/src/main/java/best/lolicon/felis/fabric/FelisFabricMod.java

@@ -0,0 +1,93 @@
+package best.lolicon.felis.fabric;
+
+import best.lolicon.felis.link.LinkClient;
+import best.lolicon.felis.link.LinkCode;
+import best.lolicon.felis.link.LinkConfig;
+import best.lolicon.felis.link.LinkConfigLoader;
+import best.lolicon.felis.link.LinkException;
+
+import com.mojang.brigadier.CommandDispatcher;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import com.mojang.logging.LogUtils;
+import net.fabricmc.api.DedicatedServerModInitializer;
+import net.fabricmc.fabric.api.command.v2.CommandRegistrationCallback;
+import net.fabricmc.loader.api.FabricLoader;
+import net.minecraft.commands.CommandSourceStack;
+import net.minecraft.commands.Commands;
+import net.minecraft.network.chat.Component;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.level.ServerPlayer;
+import org.slf4j.Logger;
+
+import java.io.IOException;
+import java.util.UUID;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+/**
+ * FelisFabricMod is the Fabric (dedicated-server) leg of the §10 account-link
+ * flow. A server-side {@code /link} command takes the player's already-verified
+ * UUID, asks felis-api for a one-time code, and shows it in chat; the player then
+ * redeems it on the web panel. The HTTP call is pushed onto a daemon I/O thread
+ * and the reply is hopped back onto the server thread, so a slow felis-api never
+ * stalls the tick loop. Failures collapse to a generic chat line with details
+ * confined to the server log.
+ */
+public final class FelisFabricMod implements DedicatedServerModInitializer {
+    private static final Logger LOGGER = LogUtils.getLogger();
+
+    private final ExecutorService io = Executors.newSingleThreadExecutor(r -> {
+        Thread t = new Thread(r, "felis-link-io");
+        t.setDaemon(true);
+        return t;
+    });
+    private LinkClient linkClient;
+
+    @Override
+    public void onInitializeServer() {
+        try {
+            LinkConfig config = LinkConfigLoader.load(
+                    FabricLoader.getInstance().getConfigDir().resolve("felis-link.properties"));
+            this.linkClient = new LinkClient(config);
+        } catch (IOException e) {
+            LOGGER.error("Felis link disabled: {}", e.getMessage());
+            return;
+        }
+        CommandRegistrationCallback.EVENT.register(
+                (dispatcher, registry, environment) -> register(dispatcher));
+        LOGGER.info("Felis link ready; /link is registered.");
+    }
+
+    private void register(CommandDispatcher<CommandSourceStack> dispatcher) {
+        dispatcher.register(Commands.literal("link").executes(ctx -> {
+            CommandSourceStack source = ctx.getSource();
+            ServerPlayer player;
+            try {
+                player = source.getPlayerOrException();
+            } catch (CommandSyntaxException e) {
+                source.sendFailure(Component.literal("/link can only be run by a player."));
+                return 0;
+            }
+            requestAndReply(source.getServer(), player);
+            return 1;
+        }));
+    }
+
+    private void requestAndReply(MinecraftServer server, ServerPlayer player) {
+        UUID uuid = player.getUUID();
+        player.sendSystemMessage(Component.literal("Requesting a link code…"));
+        io.submit(() -> {
+            try {
+                LinkCode code = linkClient.requestCode(uuid);
+                server.execute(() -> player.sendSystemMessage(Component.literal(
+                        "Your link code: " + code.code()
+                        + "  — enter it on the web panel → Account (valid a few minutes).")));
+            } catch (LinkException e) {
+                LOGGER.warn("link code request failed for {} (status={}, code={}): {}",
+                        uuid, e.statusCode(), e.errorCode(), e.getMessage());
+                server.execute(() -> player.sendSystemMessage(Component.literal(
+                        "Couldn't get a link code right now. Please try again in a moment.")));
+            }
+        });
+    }
+}

plugins/fabric/src/main/resources/fabric.mod.json

@@ -0,0 +1,19 @@
+{
+  "schemaVersion": 1,
+  "id": "felis-link",
+  "version": "0.1.0",
+  "name": "Felis Link",
+  "description": "In-game /link command: mints a one-time account-link code from felis-api.",
+  "authors": ["Felis"],
+  "license": "MIT",
+  "environment": "server",
+  "entrypoints": {
+    "server": ["best.lolicon.felis.fabric.FelisFabricMod"]
+  },
+  "depends": {
+    "fabricloader": ">=0.15.0",
+    "minecraft": "~1.20.1",
+    "java": ">=17",
+    "fabric-api": "*"
+  }
+}