perf(ci): switch sccache from S3 to local block storage PVC

- Create 20Gi sccache-pvc (scw-bssd) for fast local cache hits
- Mount at /mnt/sccache in CI build pods via runner helm values
- Use SCCACHE_DIR instead of SCCACHE_BUCKET for check/test jobs
- Kaniko builds keep S3 sccache (can't mount PVCs in Kaniko)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitlab-ci.yml

@@ -19,12 +19,12 @@ variables:
   JWT_SECRET: "CiTestSecret_Kx7mP9nR2sW5vY8bC3fG6jH1kL4pQ7tZ0uN9dM5eV8xS2wT6yA4zB_64chars_min"
   # Training data on block storage PVC (mounted at /mnt/training-data by runner)
   FOXHUNT_DATA_DIR: "/mnt/training-data/futures-baseline"
-  SCCACHE_BUCKET: $SCCACHE_BUCKET
-  SCCACHE_ENDPOINT: $SCCACHE_ENDPOINT
-  SCCACHE_S3_USE_SSL: "true"
+  # sccache on local block storage PVC (mounted at /mnt/sccache by runner)
+  SCCACHE_DIR: "/mnt/sccache"
+  RUSTC_WRAPPER: /usr/local/bin/sccache
+  # S3 credentials still needed for Kaniko (Dockerfile) sccache
   AWS_ACCESS_KEY_ID: $SCW_ACCESS_KEY
   AWS_SECRET_ACCESS_KEY: $SCW_SECRET_KEY
-  RUSTC_WRAPPER: /usr/local/bin/sccache
   # CI builder image on Scaleway Container Registry (reachable by Kapsule nodes)
   CI_BUILDER_IMAGE: rg.fr-par.scw.cloud/foxhunt-ci/ci-builder:latest
   # Scaleway Container Registry for service images

infra/k8s/gitlab/runner-values.yaml

@@ -52,6 +52,11 @@ runners:
         name = "training-data-pvc"
         mount_path = "/mnt/training-data"
         read_only = true
+      # sccache on local block storage — faster than S3 for cache hits
+      [[runners.kubernetes.volumes.pvc]]
+        name = "sccache-pvc"
+        mount_path = "/mnt/sccache"
+        read_only = false
 
   # Runner tags for job matching
   tags: "kapsule,rust,docker,gpu"

infra/k8s/storage/sccache-pvc.yaml

@@ -0,0 +1,16 @@
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: sccache-pvc
+  namespace: foxhunt
+  labels:
+    app.kubernetes.io/name: sccache
+    app.kubernetes.io/part-of: foxhunt
+    app.kubernetes.io/component: ci
+spec:
+  storageClassName: scw-bssd
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 20Gi