fix(ci): write browser coverage without each script's source (#432)

Every raw browser coverage file repeated the full source of each mapped
script, about 84% of its bytes, and the frontend coverage merge ran out of
Node's heap at 1,884 files. c8 reads the source from the mapped file on disk,
so the entries keep only the URL, script id and functions.

tests/vendor/browser-coverage.test.mjs

@@ -27,3 +27,23 @@ test('browser coverage maps nested JS/MJS and excludes unrelated and traversal p
     const root = fileURLToPath(new URL('../../web/js/', import.meta.url));
     assert.deepEqual(report.result.map(entry => fileURLToPath(entry.url)), [join(root, 'gallery.js'), join(root, 'shared/controls/button.mjs'), join(root, 'shared/panel.js')]);
 });
+
+// #432: every raw file repeated each script's full source (about 84% of its bytes) and the coverage merge ran out of
+// memory. c8 reads the source from the mapped file on disk, so the entries keep only the URL, id and functions.
+test('browser coverage writes no script source, only what c8 maps', async t => {
+    const directory = mkdtempSync(join(tmpdir(), 'pm-browser-coverage-'));
+    const previous = process.env.PM_JS_COVERAGE;
+    process.env.PM_JS_COVERAGE = directory;
+    t.after(() => {
+        if (previous === undefined) delete process.env.PM_JS_COVERAGE;
+        else process.env.PM_JS_COVERAGE = previous;
+        rmSync(directory, { recursive: true, force: true });
+    });
+    const functions = [{ functionName: 'f', isBlockCoverage: true, ranges: [{ startOffset: 0, endOffset: 9, count: 1 }] }];
+    await saveCoverage({ coverage: { stopJSCoverage: async () => [{ url: 'http://127.0.0.1:8765/prompt_manager/js/gallery.js',
+        scriptId: '7', source: 'x'.repeat(100_000), functions }] } }, 'chromium');
+    const report = JSON.parse(readFileSync(join(directory, readdirSync(directory)[0]), 'utf8'));
+    assert.equal(report.result.length, 1);
+    assert.deepEqual(Object.keys(report.result[0]).sort(), ['functions', 'scriptId', 'url']);
+    assert.deepEqual(report.result[0].functions, functions);
+});

tools/vendor/browser-coverage.mjs

@@ -12,7 +12,10 @@ export async function startCoverage(page, browserName) {
 export async function saveCoverage(page, browserName) {
     if (!process.env.PM_JS_COVERAGE || browserName !== 'chromium') return;
     const entries = await page.coverage.stopJSCoverage();
-    const result = mapBrowserCoverage(entries, { urlPrefix: '/prompt_manager/js/', sourceRoot: join(repositoryRoot, 'web/js') });
+    // The source is left out (#432): c8 reads it from the mapped file on disk, and repeating every script's text in every
+    // raw file made the coverage merge run out of memory.
+    const result = mapBrowserCoverage(entries, { urlPrefix: '/prompt_manager/js/', sourceRoot: join(repositoryRoot, 'web/js') })
+        .map(({ source: _source, ...entry }) => entry);
     mkdirSync(process.env.PM_JS_COVERAGE, { recursive: true });
     writeFileSync(join(process.env.PM_JS_COVERAGE, `browser-${randomUUID()}.json`), JSON.stringify({ result }));
 }