feat(runtime): allow Python interactors in interact

CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to WASM-OJ are recorded here. Releases follow
 [Semantic Versioning](https://semver.org/) and the contract/package versioning policy in
 [the versioning policy](docs/versioning.md).
 
+## Unreleased
+
+- Accept runtime-bundle interactors (for example CPython) in `Runner.interact` on the server
+  and in the browser runner Worker. Either side of an interactive session may now be a
+  standalone Wasm module or a runtime bundle that provides streaming fd 0.
+
 ## 0.2.3 - 2026-10-05
 
 - Download pinned browser toolchain assets before the compiler timeout starts, so slow

docs/library-contract.md

@@ -241,7 +241,8 @@ set/multiset, output-file sets, and standalone sandboxed Wasm checkers.
 
 Interactive cases start contestant and interactor concurrently with full-duplex pipes, independent
 resource policies, process-local deterministic clocks, and secret inputs mounted only on the
-interactor side. Runtime bundles that cannot provide streaming fd 0 are rejected for interaction.
+interactor side. Either side may be a standalone Wasm module or a runtime bundle such as CPython;
+runtime bundles that cannot provide streaming fd 0 are rejected for interaction.
 
 Each case executes under the broad hard policy once. Correct output and the same normalized metrics
 are evaluated against ordered cumulative `baseline`, `efficient`, and `optimal` policies. The

src/runtime/runner.worker.ts

@@ -412,9 +412,6 @@ async function interactArtifacts(
 ): Promise<InteractiveRunResult> {
   const started = performance.now();
   if (!runtimeDrivers) throw new Error("The WASM-OJ runtime-driver registry is not initialized.");
-  if (request.interactor.kind !== "wasm") {
-    throw new Error("Interactive judge artifacts must be standalone Wasm modules.");
-  }
   progress(request.requestId, "loading-toolchain", "Resolving contestant and interactor runtimes", 0.1);
   const [contestant, interactor] = await Promise.all([
     prepareArtifactInteraction(

src/server/judge.integration.test.ts

@@ -130,6 +130,46 @@ describe.skipIf(!enabled)("real server judge contracts", () => {
     });
   });
 
+  it("runs a CPython interactor against a compiled contestant", { timeout: 300_000 }, async () => {
+    const contestant = await compileC("bundle-contestant", [
+        "#include <stdio.h>",
+        "int main(void) {",
+        "  int challenge = 0;",
+        "  if (scanf(\"%d\", &challenge) != 1) return 2;",
+        "  printf(\"%d\\n\", challenge + 1);",
+        "  fflush(stdout);",
+        "  return 0;",
+        "}",
+      ].join("\n"));
+    const built = await engine.compile({
+      projectId: "judge-integration:python-interactor",
+      name: "python-interactor",
+      language: "python",
+      entry: "main.py",
+      files: {
+        "main.py": [
+          "import sys",
+          "target = int(open(sys.argv[1]).read())",
+          "print(target - 1, flush=True)",
+          "sys.exit(0 if int(input()) == target else 1)",
+        ].join("\n") + "\n",
+      },
+    }, { cache: false });
+    expect(built.success).toBe(true);
+    expect(built.artifact?.kind).toBe("runtime-bundle");
+
+    const result = await engine.interact(contestant, built.artifact!, {
+      interactor: { args: ["/judge/input.txt"], files: { "/judge/input.txt": "42\n" } },
+    });
+
+    expect(result).toMatchObject({
+      contestantToInteractor: "42\n",
+      interactorToContestant: "41\n",
+      contestant: { code: 0, termination: "exited" },
+      interactor: { code: 0, termination: "exited" },
+    });
+  });
+
   async function compileC(name: string, source: string): Promise<BuildArtifact> {
     const entry = `src/${name}.c`;
     const input: CompileInput = {

src/server/server-runner.ts

@@ -303,9 +303,6 @@ export class ServerRunner implements Runner {
     if (this.activeOperation || this.cacheClearActive) {
       throw new Error("ServerRunner accepts one active operation at a time.");
     }
-    if (interactorArtifact.kind !== "wasm") {
-      throw new Error("Interactive judge artifacts must be standalone Wasm modules.");
-    }
     const operation = createServerRunOperation(this.generation);
     this.activeOperation = operation;
     this.inFlightRuns.add(operation);