From 285a1d06be6084cb719c83c0096a2f7119cdea39 Mon Sep 17 00:00:00 2001
From: Scott Werner <stwerner@vt.edu>
Date: Tue, 27 Oct 2026 13:59:56 -0400
Subject: [PATCH] Name the failed branch of a fan-out as the stop step

The stop step was the latest step to start, and only if it failed, so a
sibling branch starting a few milliseconds after the failed one hid it.
Name the latest failed step that no later step went on from, where a
concurrent sibling branch or the step's own branches don't count as
going on.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../app/routes/run-detail/failure.test.ts     | 14 +++++++++
 .../app/routes/run-detail/failure.ts          | 30 ++++++++++++++-----
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/apps/fabro-web/app/routes/run-detail/failure.test.ts b/apps/fabro-web/app/routes/run-detail/failure.test.ts
index e3421feb7..7476e598a 100644
--- a/apps/fabro-web/app/routes/run-detail/failure.test.ts
+++ b/apps/fabro-web/app/routes/run-detail/failure.test.ts
@@ -135,6 +135,20 @@ describe("buildRunFailureView", () => {
     expect(failure?.headline).toBe("The steps finished, but publishing the result failed");
   });
 
+  test("names the failed branch of a fan-out, though a sibling started after it", () => {
+    const runStages = stages(
+      ["checks@1", "failed", "2026-10-10T15:20:00.000Z"],
+      ["lint@1", "failed", "2026-10-10T15:20:00.010Z"],
+      ["test@1", "cancelled", "2026-10-10T15:20:00.013Z"],
+    );
+    runStages["lint@1"]!.parallel_branch_id = "checks@1:0";
+    runStages["test@1"]!.parallel_branch_id = "checks@1:1";
+    expect(view(failedRun({ message: "script exited with status 1" }, { runStages }))?.stage).toBe("lint");
+
+    runStages["report@1"] = { state: "succeeded", started_at: "2026-10-10T15:21:00Z" } as State["stages"][string];
+    expect(view(failedRun({ message: "push rejected" }, { reason: "publish_failed", runStages }))?.stage).toBeNull();
+  });
+
   test("shows nothing for a cancelled run, and says what happened for other endings", () => {
     expect(view(failedRun({ message: "Run cancelled before worker launch completed" }, { reason: "cancelled" }))).toBeNull();
     expect(view(failedRun({ message: "denied at review" }, { reason: "approval_denied" }))?.headline).toBe("Approval was denied");
diff --git a/apps/fabro-web/app/routes/run-detail/failure.ts b/apps/fabro-web/app/routes/run-detail/failure.ts
index 3788db2a2..7e06c09a4 100644
--- a/apps/fabro-web/app/routes/run-detail/failure.ts
+++ b/apps/fabro-web/app/routes/run-detail/failure.ts
@@ -207,17 +207,31 @@ function stepAdvice(message: string, category: FailureCategory, output: string |
 }
 
 /**
- * The key of the last step to start, if it failed. An earlier failure that a
- * later step recovered from isn't where the run stopped, so it isn't named.
+ * The key of the failed step the run stopped at: the latest failed step that
+ * no later step went on from. A step that started later in a sibling branch
+ * of the same fan-out ran beside it, not after it, so it doesn't count; an
+ * earlier failure that a later step recovered from isn't named.
  */
 function stoppedAt(stages: FailureState["stages"]): string | null {
-  let last: [string, number] | null = null;
-  for (const [key, stage] of Object.entries(stages)) {
-    const started = stage.started_at ? Date.parse(stage.started_at) : NaN;
-    if (!Number.isNaN(started) && (!last || started > last[1])) last = [key, started];
+  const started = Object.entries(stages).flatMap(([key, stage]) => {
+    const at = stage.started_at ? Date.parse(stage.started_at) : NaN;
+    if (Number.isNaN(at)) return [];
+    const branch = stage.parallel_branch_id ?? null;
+    const group = branch && branch.includes(":") ? branch.slice(0, branch.lastIndexOf(":")) : null;
+    return [{ key, at, branch, group, failed: stage.state === "failed" }];
+  });
+  let stop: (typeof started)[number] | null = null;
+  for (const step of started) {
+    if (!step.failed) continue;
+    const wentOn = started.some(
+      (later) =>
+        later.at > step.at &&
+        later.group !== step.key &&
+        !(step.group !== null && later.group === step.group && later.branch !== step.branch),
+    );
+    if (!wentOn && (!stop || step.at > stop.at)) stop = step;
   }
-  if (!last || stages[last[0]]?.state !== "failed") return null;
-  return last[0];
+  return stop?.key ?? null;
 }
 
 function outputTail(tail: ExecOutputTail | null | undefined): string | null {