v0.317.0: a second copy counts only on a proven different disk; the no-drive install speaks in words (felhom.eu architecture/16, build A)

Tier-2 and the one-copy notice ask the host agent (POST /disks/same-disk, agent 0.157.0): different +
proven -> made and counted; same disk -> not made (D1); unknown (VM, hidden USB serial) -> made, not
counted, the row says why (D2); a NAS never counts and no longer hides the notice (R-1075). An older
agent keeps the st_dev rule, logged once. D4: a data-folder or media app on a box with no drive is
refused in words with a link to the drives page (R-1068's raw-error half). MinAgent 0.157.0.

Claude-Session: https://claude.ai/code/session_012qRErfCoiTkvDK9N5XHbzb

controller/cmd/controller/main.go

@@ -583,6 +583,29 @@ func main() {
 		// re-rendered or the restored shares exist on paper but are not exported. A seam rather than a
 		// direct call — the backup package must not depend on the stacks package.
 		backupMgr.SetSharesReconciler(stackMgr.ReconcileSamba)
+		// v0.317.0 (felhom.eu architecture/16-storage-physical-identity.md §4): every Tier-2 and one-copy
+		// decision asks the HOST AGENT whether two paths share a physical disk. An agent older than 0.157.0
+		// (FeatureSameDisk) or a failed call → supported=false → the backup side keeps the old st_dev rule,
+		// logged once. Pinned by TestDiskJudge_IsWiredAtStartup.
+		if cfg.LocalAPI.Endpoint != "" && cfg.LocalAPI.Token != "" {
+			if ac, err := agentapi.New(cfg.LocalAPI.Endpoint, cfg.LocalAPI.Token, cfg.LocalAPI.Fingerprint); err != nil {
+				logger.Printf("[WARN] [backup] same-disk: agent client init failed (%v) — the st_dev rule stays", err)
+			} else {
+				backupMgr.SetDiskJudge(func(a, b string) (backup.DiskVerdict, bool) {
+					jctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+					defer cancel()
+					if ac.Supports(jctx, agentapi.FeatureSameDisk) == agentapi.SupportNo {
+						return backup.DiskVerdict{}, false
+					}
+					r, err := ac.SameDisk(jctx, a, b)
+					if err != nil {
+						logger.Printf("[WARN] [backup] same-disk: agent call failed for %s / %s: %v", a, b, err)
+						return backup.DiskVerdict{}, false
+					}
+					return backup.DiskVerdict{Different: r.Different, Proven: r.Proven, Reason: r.Reason}, true
+				})
+			}
+		}
 	}
 
 	// --- Slice 4: the guarded update's backup side ---