diff --git a/docs/roadmaps/entries/PMAT-4715.yaml b/docs/roadmaps/entries/PMAT-4715.yaml
new file mode 100644
index 0000000000..398c99140b
--- /dev/null
+++ b/docs/roadmaps/entries/PMAT-4715.yaml
@@ -0,0 +1,19 @@
+- id: PMAT-4715
+  github_issue: 4715
+  item_type: task
+  title: 'B2: root-cause fixes for red nightlies on main'
+  status: inprogress
+  priority: critical
+  assigned_to: aprender-wmainred
+  created: 2026-10-04T00:00:00Z
+  updated: 2026-10-04T00:00:00Z
+  acceptance_criteria:
+  - Each red or cancelled scheduled workflow on main has a root cause named in its fix PR, one PR per defect, listed on issue #4715
+  - Each fix PR changes no gate's acceptance; a threshold or acceptance change goes to the train lead's sign-off batch instead
+  - After each fix merges, the next scheduled or dispatched run of that workflow on main gets past the step that failed
+  phases: []
+  subtasks: []
+  estimated_effort: null
+  labels:
+  - kind:ci
+  notes: 'Parent #4678 (0.70.2), bar B2: no check red on main for more than 24 h. Proposed by aprender-a7, minted by cop aprender-14.'
diff --git a/docs/roadmaps/roadmap.yaml b/docs/roadmaps/roadmap.yaml
index f65016f6ce..6d12cec68b 100644
--- a/docs/roadmaps/roadmap.yaml
+++ b/docs/roadmaps/roadmap.yaml
@@ -24060,3 +24060,22 @@ Not done, pending the ruling: moving the 31 fixture files to an obviously synthe
   labels:
   - kind:docs
   notes: 'Operator C197, 2026-10-01 12:40Z: re-date via the spec''s own procedure; check unchanged; not a waiver.'
+- id: PMAT-4715
+  github_issue: 4715
+  item_type: task
+  title: 'B2: root-cause fixes for red nightlies on main'
+  status: inprogress
+  priority: critical
+  assigned_to: aprender-wmainred
+  created: 2026-10-04T00:00:00Z
+  updated: 2026-10-04T00:00:00Z
+  acceptance_criteria:
+  - Each red or cancelled scheduled workflow on main has a root cause named in its fix PR, one PR per defect, listed on issue #4715
+  - Each fix PR changes no gate's acceptance; a threshold or acceptance change goes to the train lead's sign-off batch instead
+  - After each fix merges, the next scheduled or dispatched run of that workflow on main gets past the step that failed
+  phases: []
+  subtasks: []
+  estimated_effort: null
+  labels:
+  - kind:ci
+  notes: 'Parent #4678 (0.70.2), bar B2: no check red on main for more than 24 h. Proposed by aprender-a7, minted by cop aprender-14.'
diff --git a/scripts/nightly_manifest.py b/scripts/nightly_manifest.py
index 206b97fce7..05c06cd215 100755
--- a/scripts/nightly_manifest.py
+++ b/scripts/nightly_manifest.py
@@ -327,6 +327,19 @@ def publish_plan(manifest, sha, dist_files):
     return names + [MANIFEST_ASSET]
 
 
+def release_assets(A, rel_id, token, get=api):
+    """{name: id} for EVERY asset on the release, all pages. GitHub caps a page at 100;
+    page one alone missed 134 of 234 assets, so the staged leftovers past it were never
+    deleted and the next upload of the same name died 422 already_exists (run 37171118510)."""
+    out, page = {}, 1
+    while True:
+        batch = get("GET", f"{A}/releases/{rel_id}/assets?per_page=100&page={page}", token)
+        out.update({a["name"]: a["id"] for a in batch})
+        if len(batch) < 100:
+            return out
+        page += 1
+
+
 def publish(manifest_path, dist, sha, repo, token):
     with open(manifest_path) as f:
         man = json.load(f)
@@ -349,7 +362,7 @@ def publish(manifest_path, dist, sha, repo, token):
         rel = api("POST", f"{A}/releases", token, json.dumps({
             "tag_name": "nightly", "target_commitish": sha, "name": "Nightly Build",
             "prerelease": True, "make_latest": "false"}).encode())
-    existing = {a["name"]: a["id"] for a in api("GET", f"{A}/releases/{rel['id']}/assets?per_page=100", token)}
+    existing = release_assets(A, rel["id"], token)
     for n, i in existing.items():  # a staged upload an earlier run died holding
         if n.startswith(STAGED):
             api("DELETE", f"{A}/releases/assets/{i}", token)
@@ -379,6 +392,18 @@ def publish(manifest_path, dist, sha, repo, token):
 
 # ---------------------------------------------------------------- self-test
 
+def _self_test_release_assets(check):
+    print("release assets:")
+    rows = [{"name": f"staged.a{i}" if i % 2 else f"a{i}", "id": i} for i in range(234)]
+
+    def pages(of):
+        return lambda m, url, tok: of[(int(url.rsplit("page=", 1)[1]) - 1) * 100:][:100]
+    got = release_assets("A", 1, None, pages(rows))
+    check("every page is read: 234 assets over 3 pages, all 117 staged leftovers seen",
+          (len(got), sum(n.startswith(STAGED) for n in got)), (234, 117))
+    check("an exact multiple of 100 ends on the empty page", len(release_assets("A", 1, None, pages(rows[:200]))), 200)
+
+
 def self_test():
     fails = []
 
@@ -608,6 +633,7 @@ def pkg(name, bins, root=False, feats=None):
     except ValueError:
         got = "error"
     check("a manifest naming an absent asset refuses to publish", got, "error")
+    _self_test_release_assets(check)
 
     print(f"\n{'PASS' if not fails else 'FAIL'}: {len(fails)} failing row(s)")
     return 1 if fails else 0