Add initial way to get info about execution context

express/execution-context-schema.ts

@@ -0,0 +1,11 @@
+import { z } from "zod";
+
+export const executionContextSchema = z.object({
+    diachron_root: z.string(),
+});
+
+export type ExecutionContext = z.infer<typeof executionContextSchema>;
+
+export function parseExecutionContext(env: Record<string, string | undefined>): ExecutionContext {
+    return executionContextSchema.parse(env);
+}