Extract instance-owned civil-flight components

src/testSupport/readLayerSource.mjs

@@ -0,0 +1,12 @@
+import { readFileSync, readdirSync } from 'node:fs';
+import { dirname, join, basename } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+/** Read actual component owners for structural regression assertions. */
+export function readLayerSource(file) {
+  const path = file instanceof URL ? fileURLToPath(file) : file;
+  if (basename(path) !== 'flights.js') return readFileSync(path, 'utf8');
+  const directory = join(dirname(path), '../layers/flights');
+  return readdirSync(directory).filter((name) => name.endsWith('.js'))
+    .sort().map((name) => readFileSync(join(directory, name), 'utf8')).join('\n');
+}