fix(plan-canvas): validate opened PDF handle

scripts/lib/plan-canvas/pdf.js

@@ -115,9 +115,9 @@ function assertLoopbackUrl(value) {
 function isCompletePdf(file, fsImpl = fs) {
   let fd;
   try {
-    const stat = fsImpl.statSync(file);
-    if (!stat.isFile() || stat.size < 12) return false;
     fd = fsImpl.openSync(file, 'r');
+    const stat = fsImpl.fstatSync(fd);
+    if (!stat.isFile() || stat.size < 12) return false;
     const head = Buffer.alloc(5);
     fsImpl.readSync(fd, head, 0, head.length, 0);
     const tailLength = Math.min(2048, stat.size);

tests/scripts/plan-canvas-pdf.test.js

@@ -102,6 +102,28 @@ async function main() {
     fs.rmSync(tmp, { recursive: true, force: true });
   });
 
+  await test('validates PDF metadata from the opened file handle', () => {
+    const content = Buffer.from('%PDF-1.4\nlocal plan\n%%EOF\n');
+    const fsImpl = {
+      openSync(file, flags) {
+        assert.strictEqual(file, '/private/export.pdf');
+        assert.strictEqual(flags, 'r');
+        return 41;
+      },
+      fstatSync(fd) {
+        assert.strictEqual(fd, 41);
+        return { isFile: () => true, size: content.length };
+      },
+      readSync(fd, target, offset, length, position) {
+        assert.strictEqual(fd, 41);
+        return content.copy(target, offset, position, position + length);
+      },
+      closeSync(fd) { assert.strictEqual(fd, 41); },
+      statSync() { throw new Error('path metadata must not be checked before opening'); }
+    };
+    assert.strictEqual(isCompletePdf('/private/export.pdf', fsImpl), true);
+  });
+
   await test('renders, terminates its private browser, and removes temporary state', async () => {
     const tempRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'plan-canvas-pdf-test-'));
     let spawned = null;