fix(ci): read the suite file of Flutter widget tests in flake check

The Flutter flake-check lane marked every iteration FAILED on PR #8601
even though `flutter test` passed all 65 selected tests. The Dart JSON
reporter gives a test declared through a helper, which includes every
`testWidgets`, the helper's `package:flutter_test/...` url and puts the
suite file in `root_url`. parseDartReport passed that `package:` url to
fileURLToPath, which throws ERR_INVALID_URL_SCHEME. repeatDart's catch
then turned the throw into an empty status map, so any selection that
contained a widget test could never pass.

parseDartReport now prefers `root_url` and falls back to `url`. Parsing
the CI run's iter-1.json report now gives 65 passed and 1 skipped, which
matches flutter's own summary. The parser table gains a widget-test
event, and that row fails with ERR_INVALID_URL_SCHEME without the fix.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Matt Toohey <contact@matttoohey.com>

scripts/flake-check.mjs

@@ -1115,6 +1115,8 @@ function repeatNode(files, iterations) {
 
 // Per-test statuses of a `dart test` JSON report (one event per line), keyed
 // `<file> › <name>`. Hidden entries are the runner's own file-loading steps.
+// A test declared through a helper (every `testWidgets`) has the helper's
+// `package:` url; `root_url` then names the suite file.
 export function parseDartReport(text, mobileRoot = `${root}mobile/`) {
   const started = new Map();
   const statuses = new Map();
@@ -1129,7 +1131,10 @@ export function parseDartReport(text, mobileRoot = `${root}mobile/`) {
     if (event.type !== "testDone" || event.hidden) continue;
     const test = started.get(event.testID);
     if (!test) continue;
-    const file = fileURLToPath(test.url ?? "file:///").replace(mobileRoot, "");
+    const file = fileURLToPath(test.root_url ?? test.url ?? "file:///").replace(
+      mobileRoot,
+      "",
+    );
     statuses.set(
       `${file} › ${test.name}`,
       event.skipped

scripts/flake-check.test.mjs

@@ -951,6 +951,15 @@ test("reports give per-test statuses per iteration", () => {
           type: "testStart",
           test: { id: 4, name: "later", url: "file:///m/test/b_test.dart" },
         }),
+        event({
+          type: "testStart",
+          test: {
+            id: 5,
+            name: "widget",
+            url: "package:flutter_test/src/widget_tester.dart",
+            root_url: "file:///m/test/b_test.dart",
+          },
+        }),
         "not json",
         event({
           type: "testDone",
@@ -973,6 +982,13 @@ test("reports give per-test statuses per iteration", () => {
           hidden: false,
           skipped: true,
         }),
+        event({
+          type: "testDone",
+          testID: 5,
+          result: "success",
+          hidden: false,
+          skipped: false,
+        }),
         event({ type: "done", success: false }),
       ].join("\n"),
       "/m/",
@@ -981,6 +997,7 @@ test("reports give per-test statuses per iteration", () => {
       ["test/a_test.dart › group renders", "passed"],
       ["test/a_test.dart › group fails", "failed"],
       ["test/b_test.dart › later", "skipped"],
+      ["test/b_test.dart › widget", "passed"],
     ]),
   );
   // Playwright lists a --repeat-each journey once per repetition, in order.