fix: remove duplicate cache volumes from hook extension patch

The hook extension was redefining cache volumes that are already in the runner
template. When ARC merges the hook extension with the pod spec, duplicate volume
definitions cause Kubernetes validation to fail. Cache volumes are already defined
in the runner template and will be merged automatically, so we only need to mount
them in the job container. We only define the system volumes (sys, cgroup, proc,
dev, dev-pts, shm) that are specifically needed for the privileged job container.

Author: Test User

internal/runner/runner.go

@@ -588,15 +588,17 @@ data:
         - name: shm
           mountPath: /dev/shm`
 
-	// Add cache path volume mounts
+	// Add cache path volume mounts to job container
+	// Note: These volumes are already defined in the runner template, so we just mount them here
 	if len(installation.CachePaths) > 0 {
 		for i := range installation.CachePaths {
 			hookExtension += fmt.Sprintf("\n        - name: cache-%d\n          mountPath: %s",
 				i, installation.CachePaths[i].MountPath)
 		}
 	}
 
-	// Add volume definitions (only for host path mounts, not work which is already in runner template)
+	// Add volume definitions (only for system mounts needed by job container, NOT cache volumes)
+	// Cache volumes are already defined in the runner template and will be merged automatically
 	hookExtension += `
       volumes:
       - name: sys
@@ -624,22 +626,8 @@ data:
           path: /dev/shm
           type: Directory`
 
-	// Add cache path volumes
-	if len(installation.CachePaths) > 0 {
-		for i, path := range installation.CachePaths {
-			hostPath := path.HostPath
-			if hostPath == "" {
-				// Generate instance-specific cache path for multi-instance setups
-				if instanceNum > 0 {
-					hostPath = fmt.Sprintf("/tmp/github-runner-cache/%s-%d/cache-%d", installation.Name, instanceNum, i)
-				} else {
-					hostPath = fmt.Sprintf("/tmp/github-runner-cache/%s/cache-%d", installation.Name, i)
-				}
-			}
-			hookExtension += fmt.Sprintf("\n      - name: cache-%d\n        hostPath:\n          path: %s\n          type: DirectoryOrCreate",
-				i, hostPath)
-		}
-	}
+	// NOTE: We do NOT include cache volumes here as they are already defined in the runner template
+	// and will be merged with this patch by ARC. Including them would cause validation errors.
 
 	return hookExtension
 }