diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 53408e48b1a..0684fd82744 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1093,12 +1093,18 @@ jobs:
           trap 'pkill -TERM -P "$SAMPLER_PID" 2>/dev/null || true; kill "$SAMPLER_PID" 2>/dev/null || true' EXIT
           corepack pnpm install --frozen-lockfile --prefer-offline --reporter=append-only
 
-      # A pool host's download usually takes under a minute but has stalled
-      # for over a quarter of an hour; bound it and try once more.
+      # Eight shards pull this same artifact at once, so the cap has to clear
+      # the slow tail rather than the median: on main four shards finished
+      # inside a minute, three needed between 2m40s and just under five
+      # minutes, and one exceeded the old five-minute cap on two consecutive
+      # runs, which skipped the unpack and failed the required check. Fifteen
+      # minutes leaves that measured tail about three times the headroom; if
+      # main still expires, the fix is fewer concurrent fetches, not a bigger
+      # cap.
       - name: 'Download the built tree'
         id: 'download_tree'
         if: "${{ needs.test_build.result == 'success' && needs.classify_pr.outputs.skip_ci != 'true' && steps.ci_profile.outputs.ci_profile == 'full' }}"
-        timeout-minutes: 5
+        timeout-minutes: 15
         continue-on-error: true
         uses: 'actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c' # v8.0.1
         with:
@@ -1107,7 +1113,7 @@ jobs:
 
       - name: 'Retry downloading the built tree'
         if: "${{ steps.download_tree.outcome == 'failure' }}"
-        timeout-minutes: 5
+        timeout-minutes: 15
         uses: 'actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c' # v8.0.1
         with:
           name: 'unit-test-tree'
diff --git a/scripts/tests/ci-platform-lanes.test.js b/scripts/tests/ci-platform-lanes.test.js
index 695f94bca37..c55741e3616 100644
--- a/scripts/tests/ci-platform-lanes.test.js
+++ b/scripts/tests/ci-platform-lanes.test.js
@@ -353,6 +353,29 @@ it('keeps every blocking test_build step under the job ceiling', () => {
   }
 });
 
+it('keeps every shard step cap under the job ceiling', () => {
+  // Same reason as the build job: the job cap cancels the job, and a cancelled
+  // job skips the failure-gated disk-pressure collector at the end. The caps
+  // are pinned one by one rather than summed — they are alternatives in
+  // practice, since a step only runs when the previous one left work to do,
+  // and install plus the test step already add up past the ceiling by design.
+  // The job cap therefore stays the outer backstop, not the sum of the parts.
+  const jobCap = Number(ci.jobs.test['timeout-minutes']);
+  const steps = new Map(
+    (ci.jobs.test.steps ?? []).map((step) => [step.name, step]),
+  );
+  for (const name of [
+    'Install dependencies',
+    'Download the built tree',
+    'Retry downloading the built tree',
+    'Run tests and generate reports',
+  ]) {
+    const minutes = steps.get(name)?.['timeout-minutes'];
+    expect(typeof minutes, `${name} has no step timeout`).toBe('number');
+    expect(minutes, `${name} cannot outlast the job`).toBeLessThan(jobCap);
+  }
+});
+
 it('reports the required Linux check only when the build and every shard pass', () => {
   const gate = ci.jobs.test_ubuntu;
   expect(gate.name).toBe('Test (ubuntu-latest, Node 22.x)');
@@ -394,6 +417,16 @@ it('pins the build-to-shard artifact handoff on both ends', () => {
   expect(name).toBeTruthy();
   expect(shard.get('Download the built tree').with.name).toBe(name);
   expect(shard.get('Retry downloading the built tree').with.name).toBe(name);
+  // Both attempts have to outlast the slow tail, not the median: eight shards
+  // fetch this same artifact at once, the slowest completed one on main took
+  // just under five minutes, and one exceeded the old five-minute cap on two
+  // runs in a row, skipping the unpack entirely.
+  for (const step of [
+    'Download the built tree',
+    'Retry downloading the built tree',
+  ]) {
+    expect(shard.get(step)?.['timeout-minutes'], step).toBe(15);
+  }
   expect(shard.get('Unpack the built tree').run).toContain(
     `\${RUNNER_TEMP}/${name}/${name}.tgz`,
   );