diff --git a/examples/contract/scripts/check-repo-materialization.ts b/examples/contract/scripts/check-repo-materialization.ts
index be2f69e52..f6fc573e8 100644
--- a/examples/contract/scripts/check-repo-materialization.ts
+++ b/examples/contract/scripts/check-repo-materialization.ts
@@ -27,7 +27,7 @@ interface Assertion {
   readonly evidence?: string;
 }
 
-const payloadText = readFileSync('/dev/stdin', 'utf8');
+const payloadText = readFileSync(0, 'utf8');
 const payload = JSON.parse(payloadText) as GraderPayload;
 const workspacePath = payload.workspace_path ?? process.env.AGENTV_WORKSPACE_PATH;
 const assertions: Assertion[] = [];
diff --git a/examples/contract/scripts/check-script-grader-payload.ts b/examples/contract/scripts/check-script-grader-payload.ts
index 7860c064e..af30ef0b4 100644
--- a/examples/contract/scripts/check-script-grader-payload.ts
+++ b/examples/contract/scripts/check-script-grader-payload.ts
@@ -46,7 +46,7 @@ function collectStrings(value: unknown, strings: string[]): void {
 let payload: Record<string, unknown>;
 
 try {
-  const parsed = JSON.parse(readFileSync('/dev/stdin', 'utf8')) as unknown;
+  const parsed = JSON.parse(readFileSync(0, 'utf8')) as unknown;
   if (!isRecord(parsed)) {
     push('stdin payload is a JSON object', false, `Received ${typeof parsed}`);
     console.log(JSON.stringify({ assertions }));
diff --git a/examples/contract/scripts/check-workspace.ts b/examples/contract/scripts/check-workspace.ts
index ad113b6c2..09769d3ba 100644
--- a/examples/contract/scripts/check-workspace.ts
+++ b/examples/contract/scripts/check-workspace.ts
@@ -20,7 +20,7 @@ interface Assertion {
   readonly evidence?: string;
 }
 
-const payload = JSON.parse(readFileSync('/dev/stdin', 'utf8')) as GraderPayload;
+const payload = JSON.parse(readFileSync(0, 'utf8')) as GraderPayload;
 const workspacePath = payload.workspace_path ?? process.env.AGENTV_WORKSPACE_PATH;
 const assertions: Assertion[] = [];