fix(rpc): deep-freeze procedures in defineService, not just the map

packages/rpc/src/contract.ts

@@ -62,5 +62,16 @@ export function defineService<Procedures extends AnyProcedures>(def: {
       );
     }
   }
-  return Object.freeze({ name: def.name, procedures: Object.freeze({ ...def.procedures }) });
+  // Freeze each procedure, not just the map. AnyProcedures accepts any object
+  // of ProcedureDef shape, so a hand-built def that never went through
+  // procedure.build() would otherwise stay mutable and the "single source of
+  // truth" guarantee would rest on every call site remembering the builder.
+  const frozen: Record<string, ProcedureDef> = {};
+  for (const [name, value] of Object.entries(def.procedures)) {
+    frozen[name] = Object.freeze({ ...value });
+  }
+  return Object.freeze({
+    name: def.name,
+    procedures: Object.freeze(frozen) as Procedures,
+  });
 }