diff --git a/.github/workflows/conleche-nightly.yml b/.github/workflows/conleche-nightly.yml
index 63285936a7..767e167d96 100644
--- a/.github/workflows/conleche-nightly.yml
+++ b/.github/workflows/conleche-nightly.yml
@@ -42,7 +42,6 @@ jobs:
     # 2.6 min) -> T = max(15, 68, 65) = 68, rounded up for a shared host. The first three runs replace this basis.
     timeout-minutes: 90
     env:
-      CI_CACHE: /mnt/nvme-raid0/ci-cache/pvl-conleche
       ELAN_VERSION: v4.2.4
       ELAN_SHA256: 42b94d4244e8353142c456ec0e4ca6528fd898a6c604d4059f494e706e431f63
       LEAN_NUM_THREADS: '8'
@@ -55,6 +54,11 @@ jobs:
       - name: Pinned elan in the job's own directory (sha256-checked, never a host install)
         run: |
           set -euo pipefail
+          # The cache lives beside the runner's _work dir, as nightly.yml's cache-nightly does. The old
+          # /mnt/nvme-raid0/ci-cache path exists only on lambda; on the clean-room hosts /mnt/nvme-raid0 is
+          # root-owned, so mkdir failed and the job never ran (runs 37082537768, 37163229207).
+          CI_CACHE="$(cd "$GITHUB_WORKSPACE/../.." && pwd)/cache-conleche"
+          echo "CI_CACHE=$CI_CACHE" >> "$GITHUB_ENV"
           export ELAN_HOME="$CI_CACHE/elan"
           mkdir -p "$CI_CACHE"
           if [ ! -x "$ELAN_HOME/bin/elan" ] || ! "$ELAN_HOME/bin/elan" --version | grep -q "${ELAN_VERSION#v}"; then
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.'