Cure53 test coverage

config/rollup.coverage.config.mjs

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+/**
+ * Coverage build: the ESM module instrumented with Istanbul, written to a separate file the node
+ * test suite imports when DOMFORTIFY_COV is set. Mirrors DOMPurify's instrument-then-nyc approach;
+ * Istanbul's per-file counters accumulate correctly across the suite's fresh-module-per-test imports,
+ * where V8 coverage would fragment on the cache-busting query.
+ */
+import { createRequire } from 'node:module';
+import typescript from '@rollup/plugin-typescript';
+import replace from '@rollup/plugin-replace';
+import istanbul from 'rollup-plugin-istanbul';
+
+const require = createRequire(import.meta.url);
+const pkg = require('../package.json');
+
+export default {
+  input: 'src/index.ts',
+  output: { file: 'dist/fortify.cov.es.mjs', format: 'es', sourcemap: true },
+  plugins: [
+    replace({ preventAssignment: true, values: { __VERSION__: pkg.version } }),
+    typescript({ tsconfig: './config/tsconfig.build.json' }),
+    istanbul({ include: ['src/**/*.ts'] }),
+  ],
+};

scripts/coverage.mjs

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+/**
+ * Runs the node QUnit suite against the Istanbul-instrumented build and writes the collected counters
+ * to .nyc_output so `nyc report` can render them. DOMFORTIFY_COV is set before the suite is imported
+ * (dynamic import, so it is read in time) to select the instrumented module.
+ */
+process.env.DOMFORTIFY_COV = '1';
+
+const QUnit = (await import('qunit')).default;
+const { mkdirSync, writeFileSync } = await import('node:fs');
+await import('../test/test-suite.mjs');
+
+QUnit.on('runEnd', (data) => {
+  if (globalThis.__coverage__) {
+    mkdirSync('.nyc_output', { recursive: true });
+    writeFileSync('.nyc_output/out.json', JSON.stringify(globalThis.__coverage__));
+  }
+  if (data.testCounts.failed > 0) process.exitCode = 1;
+});
+
+QUnit.start();