diff --git a/.github/workflows/ci-web.yml b/.github/workflows/ci-web.yml
index 014723dbe78b..3d42135e2a8a 100644
--- a/.github/workflows/ci-web.yml
+++ b/.github/workflows/ci-web.yml
@@ -307,6 +307,12 @@ jobs:
     # that warm-up and ran their dev-server files two at a time: 12 shards on
     # 8 vCPU took 14.3 min (run 39347314726), barely under 2 shards' 15.5.
     # Fewer, wider shards share each warm cache across more files.
+    # On 16 vCPU a shard runs its dev-server files 4 at a time, and they are
+    # most of its wall time: 4 shards took 18-26 min of "Test webviews" each
+    # (run 41236343549), the long pole from ask to merge for a webview fix.
+    # 8 shards halve each shard's dev-server files for about 2 min more setup
+    # and Vite warm-up per added shard (Leo, 2026-10-31: a straightforward fix
+    # lands within the hour).
     timeout-minutes: 40
     name: react-apps-check (${{ matrix.shard }})
     strategy:
@@ -314,13 +320,21 @@ jobs:
       matrix:
         include:
           - shard: 1
-            shard_count: 4
+            shard_count: 8
           - shard: 2
-            shard_count: 4
+            shard_count: 8
           - shard: 3
-            shard_count: 4
+            shard_count: 8
           - shard: 4
-            shard_count: 4
+            shard_count: 8
+          - shard: 5
+            shard_count: 8
+          - shard: 6
+            shard_count: 8
+          - shard: 7
+            shard_count: 8
+          - shard: 8
+            shard_count: 8
     steps:
       - name: Checkout
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
@@ -628,6 +642,10 @@ jobs:
           - shard: 2
           - shard: 3
           - shard: 4
+          - shard: 5
+          - shard: 6
+          - shard: 7
+          - shard: 8
     steps:
       # The base is the merge commit's first parent, the commit the head shards
       # were merged onto (their prScope diff is HEAD^1 too). pull_request.base.sha
diff --git a/tests/test_web_validation.py b/tests/test_web_validation.py
index bdb807ab4312..b58eb1837703 100644
--- a/tests/test_web_validation.py
+++ b/tests/test_web_validation.py
@@ -222,18 +222,25 @@ def test_webviews_tests_shard_on_wide_runners(self):
         """Two 8 vCPU shards each ran about 65 dev-server files two at a time for 12 of
         their 14-16 minutes. Twelve 8 vCPU shards took 14.3 min: each paid a cold Vite
         warm-up. Four 32 vCPU shards run eight dev-server files at once on a shared warm
-        cache. Blacksmith is a capped paid overflow now (2026-10-30), so the four shards run at
-        16 vCPU: 14% slower at p50 than 32 for half the price."""
+        cache. Blacksmith is a capped paid overflow now (2026-10-30), so the shards run at
+        16 vCPU: 14% slower at p50 than 32 for half the price. There, four shards ran their
+        dev-server files four at a time for 18-26 min each (p50 24.4 min, 2026-10-31), the
+        long pole from ask to merge for a webview fix, so they are eight. The base replay
+        (react-apps-base-check) takes one shard per head shard's results artifact."""
         workflow = (ROOT / ".github/workflows/ci-web.yml").read_text()
         start = workflow.index("  react-apps-check-shard:")
         match = re.search(r"\n  [A-Za-z0-9_-]+:", workflow[start + 3 :])
         block = workflow[start:] if match is None else workflow[start : start + 3 + match.start()]
         shards = [int(n) for n in re.findall(r"^          - shard: (\d+)$", block, re.MULTILINE)]
         counts = set(re.findall(r"^            shard_count: (\d+)$", block, re.MULTILINE))
-        self.assertEqual(len(shards), 4)
+        self.assertEqual(len(shards), 8)
         self.assertIn("'blacksmith-16vcpu-ubuntu-2404' }}", block)
         self.assertEqual(shards, list(range(1, len(shards) + 1)))
         self.assertEqual(counts, {str(len(shards))})
+        base_start = workflow.index("  react-apps-base-check:")
+        base_match = re.search(r"\n  [A-Za-z0-9_-]+:", workflow[base_start + 3 :])
+        base = workflow[base_start:] if base_match is None else workflow[base_start : base_start + 3 + base_match.start()]
+        self.assertEqual([int(n) for n in re.findall(r"^          - shard: (\d+)$", base, re.MULTILINE)], shards)
         for step in ("Generated bundle merge driver", "Check diff viewer eager JS budget",
                      "Verify React Compiler for webviews", "Check webviews (Oxlint, Oxfmt, type check)",
                      "Check PR-scoped webview rules"):