Game build accepts a Java 1.8 target with gameengine 4.7.8, then the game only reports "Referee failed to provide output"

Feedback & Bugs
1

Hello,

While building a multiplayer contribution, I hit a crash whose message does not point to its cause. Reporting it in case it helps others.

Environment

  • CodinGame SDK, gameengine 4.7.8 (core, runner, module-entities, module-tooltip, module-endscreen, module-toggle)
  • Multiplayer contribution, uploaded with the contribution game-build upload
  • November 2026, IDE preview in Chrome

Steps to reproduce

  1. Take a game that runs fine in the local runner with gameengine 4.7.8, and set the Java target to 1.8 in pom.xml:
<properties>
  <gamengine.version>4.7.8</gamengine.version>
  <maven.compiler.source>1.8</maven.compiler.source>
  <maven.compiler.target>1.8</maven.compiler.target>
</properties>
<dependencies>
  <dependency>
    <groupId>com.codingame.gameengine</groupId>
    <artifactId>core</artifactId>
    <version>${gamengine.version}</version>
  </dependency>
  <dependency>
    <groupId>com.codingame.gameengine</groupId>
    <artifactId>module-entities</artifactId>
    <version>${gamengine.version}</version>
  </dependency>
</dependencies>
  1. Export the project and upload it as a contribution. The build succeeds with no warning.
  2. Open the preview and press Play with any starter.

What happens

  • IDE console:
    The game has crashed. Please contact the author and enclose the following error:
The Referee failed to provide output in the alloted 10000ms
  • The viewer stays black, with no frames.
  • Browser console (player iframe): TypeError: Cannot read properties of undefined (reading 'subframes') at initReplay.

Five builds in a row failed this way. Nothing in the build or the game output mentions the Java version.

Expected
One of these:

  • a build-time error or warning, for example “gameengine 4.7.8 needs Java 17”;
  • the referee’s exception or stderr shown to the author in the preview.

Workaround
Set maven.compiler.source and maven.compiler.target to 17. The next build ran normally.

Thanks for looking into it!