chore: make OpenAPI export atomic and add read-only check (WealthLedger/backend#3)

scripts/generate-openapi.cjs

@@ -1,5 +1,10 @@
 const { randomBytes } = require('node:crypto');
-const { writeFile } = require('node:fs/promises');
+const { readFile, rename, rm, writeFile } = require('node:fs/promises');
+const { resolve } = require('node:path');
+
+// Relative to the working directory, as before: the contract test runs the script in a temporary directory.
+const target = resolve(process.cwd(), 'openapi.json');
+const checkOnly = process.argv.includes('--check');
 
 // Schema generation needs no deployment configuration or real credentials.
 Object.assign(process.env, {
@@ -19,23 +24,48 @@ const { NestFactory } = require('@nestjs/core');
 const { AppModule } = require('../dist/src/app.module.js');
 const { API_PREFIX, createOpenApiDocument } = require('../dist/src/openapi.js');
 
-async function generate() {
+async function render() {
   const app = await NestFactory.create(AppModule, {
     preview: true,
     logger: false,
   });
   try {
     app.setGlobalPrefix(API_PREFIX);
-    await writeFile(
-      'openapi.json',
-      JSON.stringify(createOpenApiDocument(app), null, 2) + '\n',
-    );
+    return JSON.stringify(createOpenApiDocument(app), null, 2) + '\n';
   } finally {
     await app.close();
   }
 }
 
-generate().catch((error) => {
-  console.error(error);
-  process.exitCode = 1;
-});
+// Read-only: compares the runtime document with the committed artifact and never writes.
+async function check(content) {
+  const current = await readFile(target, 'utf8').catch(() => null);
+  if (current !== content) {
+    console.error(
+      'openapi.json is out of date with the runtime schema. Run `npm run openapi:generate`.',
+    );
+    process.exitCode = 1;
+    return;
+  }
+  console.log('openapi.json matches the runtime schema.');
+}
+
+// Atomic update: write a sibling temp file, then rename over the target, so a failed run never leaves partial output.
+async function update(content) {
+  const temp = `${target}.${process.pid}.tmp`;
+  try {
+    // eslint-disable-next-line security/detect-non-literal-fs-filename -- Operator-selected working directory and fixed artifact name; no request input.
+    await writeFile(temp, content);
+    // eslint-disable-next-line security/detect-non-literal-fs-filename -- Operator-selected working directory and fixed artifact name; no request input.
+    await rename(temp, target);
+  } finally {
+    await rm(temp, { force: true });
+  }
+}
+
+render()
+  .then((content) => (checkOnly ? check(content) : update(content)))
+  .catch((error) => {
+    console.error(error);
+    process.exitCode = 1;
+  });