Default the preview multiplayer server to the bevy engine

The bevy headless server is what production multiplayer now runs, so the
preview spawned by `sdk-commands start` should exercise the same engine.
Hammurabi remains reachable via DCL_SERVER_ENGINE=hammurabi and as the
automatic fallback when bevy exits unavailable (78) — except when
DCL_SERVER_PACKAGE overrides the spec, where falling back would just
respawn the same overridden package. Rename the module accordingly and
drop the never-populated PreviewComponents.hammurabiServer field.

Author: gonpombo8

packages/@dcl/sdk-commands/src/commands/start/index.ts

@@ -29,8 +29,7 @@ import { Result } from 'arg'
 import { startValidations } from '../../logic/project-validations'
 import { runExplorerAlpha } from './explorer-alpha'
 import { getLanUrl } from './utils'
-import { spawnAuthServer } from './hammurabi-server'
-import { ChildProcess } from 'child_process'
+import { spawnAuthServer } from './multiplayer-server'
 
 interface Options {
   args: Result<typeof args>
@@ -219,18 +218,16 @@ export async function main(options: Options) {
       }
       await startComponents()
 
-      // Start Hammurabi server if needed (stored outside components to avoid lifecycle management)
-      let hammurabiServer: ChildProcess | undefined
+      // Start the multiplayer server if needed (kept outside the components object to avoid lifecycle management)
       const project = workspace.projects[0]
       if (project) {
         const realm = `http://localhost:${port}`
-        hammurabiServer = spawnAuthServer(components, project, realm)
+        const multiplayerServer = spawnAuthServer(components, project, realm)
 
-        // Register cleanup handler for hammurabi server
-        if (hammurabiServer) {
+        if (multiplayerServer) {
           const cleanup = () => {
-            if (hammurabiServer && !hammurabiServer.killed) {
-              hammurabiServer.kill('SIGTERM')
+            if (!multiplayerServer.killed) {
+              multiplayerServer.kill('SIGTERM')
             }
           }
           components.signaler.programClosed.then(cleanup).catch(() => {})

…s/src/commands/start/hammurabi-server.ts …src/commands/start/multiplayer-server.tspackages/@dcl/sdk-commands/src/commands/start/hammurabi-server.ts renamed to packages/@dcl/sdk-commands/src/commands/start/multiplayer-server.ts packages/@dcl/sdk-commands/src/commands/start/hammurabi-server.ts renamed to packages/@dcl/sdk-commands/src/commands/start/multiplayer-server.ts

@@ -18,9 +18,11 @@ const EXIT_UNAVAILABLE = 78
 
 type ServerEngine = 'bevy' | 'hammurabi'
 
+const DEFAULT_ENGINE: ServerEngine = 'bevy'
+
 function selectedEngine(): ServerEngine {
   const requested = process.env.DCL_SERVER_ENGINE
-  return requested === 'bevy' || requested === 'hammurabi' ? requested : 'hammurabi'
+  return requested === 'bevy' || requested === 'hammurabi' ? requested : DEFAULT_ENGINE
 }
 
 /**
@@ -52,11 +54,11 @@ function registerProcessCleanup(cleanup: () => void): () => void {
 /**
  * Starts the Multiplayer Server process using npx to install and run in one step
  */
-export function startHammurabiServer(
+export function startMultiplayerServer(
   components: Pick<CliComponents, 'logger'>,
   workingDir: string,
   realm: string,
-  engine: ServerEngine = 'hammurabi'
+  engine: ServerEngine = DEFAULT_ENGINE
 ): ChildProcess {
   const pkg = packageSpec(engine)
 
@@ -75,40 +77,40 @@ export function startHammurabiServer(
 
   // If npx-cli.js was found, run it directly via process.execPath (node in regular env,
   // Electron Helper with ELECTRON_RUN_AS_NODE=1 in Electron). Otherwise fall back to npx binary.
-  const hammurabiProcess = npxCliJs
+  const serverProcess = npxCliJs
     ? spawn(process.execPath, [npxCliJs, ...npxArgs], { cwd: workingDir, shell: false, stdio: 'inherit', env })
     : spawn(getNpxBin(), npxArgs, { cwd: workingDir, shell: false, stdio: 'inherit', env })
 
-  hammurabiProcess.on('error', (error) => {
+  serverProcess.on('error', (error) => {
     printWarning(components.logger, `Multiplayer Server process error: ${error.message}`)
   })
 
   // Register cleanup handlers
   const cleanup = () => {
-    if (!hammurabiProcess.killed) {
-      hammurabiProcess.kill('SIGTERM')
+    if (!serverProcess.killed) {
+      serverProcess.kill('SIGTERM')
     }
   }
 
   const removeCleanup = registerProcessCleanup(cleanup)
 
-  hammurabiProcess.on('close', (code) => {
+  serverProcess.on('close', (code) => {
     removeCleanup()
     if (code !== 0 && code !== null) {
       printWarning(components.logger, `Multiplayer Server exited with code ${code}`)
     }
   })
 
-  return hammurabiProcess
+  return serverProcess
 }
 
 /**
  * Spawns the multiplayer server for the project.
  * In the auth-server SDK, all scenes are authoritative multiplayer.
  * Uses npx to handle installation and execution in a single step (works in Electron).
  *
- * Which implementation runs is chosen by DCL_SERVER_ENGINE (bevy | hammurabi). When bevy
- * reports itself unavailable on this machine, hammurabi is started instead.
+ * Which implementation runs is chosen by DCL_SERVER_ENGINE (bevy | hammurabi), defaulting
+ * to bevy. When bevy reports itself unavailable on this machine, hammurabi is started instead.
  *
  * @param components - Preview components including logger
  * @param project - The project to start the multiplayer server for
@@ -122,12 +124,14 @@ export function spawnAuthServer(
 ): ChildProcess | undefined {
   const engine = selectedEngine()
   try {
-    const child = startHammurabiServer(components, project.workingDirectory, realm, engine)
-    if (engine === 'bevy') {
+    const child = startMultiplayerServer(components, project.workingDirectory, realm, engine)
+    // No fallback when DCL_SERVER_PACKAGE is set: packageSpec would resolve the
+    // hammurabi retry to the same overridden package that just exited 78.
+    if (engine === 'bevy' && !process.env.DCL_SERVER_PACKAGE) {
       child.on('close', (code) => {
         if (code === EXIT_UNAVAILABLE) {
           printWarning(components.logger, 'Bevy multiplayer server unavailable here — falling back to hammurabi')
-          startHammurabiServer(components, project.workingDirectory, realm, 'hammurabi')
+          startMultiplayerServer(components, project.workingDirectory, realm, 'hammurabi')
         }
       })
     }

packages/@dcl/sdk-commands/src/commands/start/types.ts

@@ -9,7 +9,6 @@ import { RoomComponent } from '@dcl/mini-comms/dist/adapters/rooms'
 import { WebSocketComponent } from './server/ws'
 import { CliComponents } from '../../components'
 import { ISignalerComponent } from '../../components/exit-signal'
-import { ChildProcess } from 'child_process'
 
 export type PreviewComponents = CliComponents & {
   logs: ILoggerComponent
@@ -20,6 +19,4 @@ export type PreviewComponents = CliComponents & {
   rooms: RoomComponent
   ws: WebSocketComponent
   signaler: ISignalerComponent
-  /** Authoritative Server process (@dcl/hammurabi-server) */
-  hammurabiServer?: ChildProcess
 }