This is the Java module runtime. New Java modules reference it as their runtime (github.com/dagger/java-sdk/runtime); the root Dang module (main.dang) sets it via targetRuntime.

It is written in Dang (main.dang), so the engine runs its dispatch (moduleRuntime / codegen) natively in-process — there is no runtime container for the dispatcher itself. The actual Java build still runs in a Maven container.

It only fetches dependencies, builds, and packages a Java module from its committed sources — it does not generate code.

moduleRuntime mounts the module, runs mvn package -DskipTests, and returns a JRE container that runs the resulting jar. New-style modules are self-contained: the Java SDK is vendored as source under <module>/sdk/ and the entrypoint is committed under <module>/src/generated/java, so a plain mvn package (the module pom defaults dagger.proc=none) compiles them together and only downloads third-party dependencies.

Before packaging, moduleRuntime checks that the committed entrypoint (src/generated/java/io/dagger/gen/entrypoint/Entrypoint.java) exists and is non-empty, failing early with an actionable error if dagger generate was never run or its output was not committed.

Code generation lives in this repository's root Dang module (main.dang / mod.dang) and runs at dagger generate time. New-style modules commit the generated files, so the engine skips codegen at module load — this runtime never regenerates them.

codegen here is an intentional no-op (returns the module source unchanged): the SDK runtime contract still includes it, but generation is owned by generate.