v0.95.0: SMART coverage — union-path drives + LVM/dm root + device model

Implements SPIKE-smart-coverage-2026-07-25 fixes B+A (additive; MinAgent unchanged).
Fix B: storage.SmartReader.SMARTForBacking wired into the /disks union path (localapi
Smart seam) so registry/USB drives get a real SMART read (watchdog Known stays
enrich-free). Fix A: smartDeviceFor resolves dm/LVM to the whole disk via
/sys/block/<dm>/slaves (recursive; skips >1-disk); the builtin local dir on the LVM
root gets a SMART-only device from its containing filesystem (never touches
backing/durable_id). SmartSummary.ModelName captured from smartctl. Fix C (-d sat)
stays rejected. Tests + red-proofs (dm multi-disk skip, enrich smartHint, union
routing); Known-path-never-SMARTs asserted.

internal/localapi/disks.go

@@ -255,10 +255,17 @@ func (s *Server) handleDisks(w http.ResponseWriter, r *http.Request, vmid int) {
 				if d.UUID != "" {
 					// Resolve to the real /dev node (e.g. /dev/sdd), not the by-uuid symlink path, to match
 					// how Observe-sourced rows display the backing device.
-					if dev, err := storage.ResolveStorageDevice("uuid:" + d.UUID); err == nil {
+					if dev, err := s.resolveStorageDevice("uuid:" + d.UUID); err == nil {
 						di.BackingDevice = dev
 					}
 				}
+				// Fix B (v0.95.0): union-path drives skip Observe's enrich, so read SMART here through the
+				// same seam the dir targets use. Only set when the read actually ran (Health != "").
+				if di.BackingDevice != "" && s.smart != nil {
+					if sm := s.smart.SMARTForBacking(r.Context(), di.BackingDevice); sm.Health != "" {
+						di.Smart = &sm
+					}
+				}
 				if total, used, okc := statfsCapacity(d.MountPath); okc {
 					di.TotalBytes, di.UsedBytes = total, used
 					di.UsedFraction = float64(used) / float64(total)