Shared-mailbox reality: module firmware is its own handler client (internal GET_CURRENT_TEMP ~3.5s, proven idle-watch), handler writes wedge the uC in busy windows; quiet-window writes, bare GETs double-read with CMD-readback tripwire, SNR floor, SETs verified externally; sentinel handshake and wire-probe jumbo check removed

main.go

@@ -750,9 +750,13 @@ func run(aName, bName string) (err error) {
 			if diag.kick(&done) {
 				fmt.Println(stats.rule("measuring cable"))
 			}
-		case <-diag.completed:
-			info, _ := diag.snapshot()
-			fmt.Println(stats.rule("cable diag: " + cableLine(info)))
+		case err := <-diag.completed:
+			if err != nil {
+				fmt.Println(stats.rule("cable diag failed: " + err.Error()))
+			} else {
+				info, _ := diag.snapshot()
+				fmt.Println(stats.rule("cable diag: " + cableLine(info)))
+			}
 			start = resetAll(dirs, modules, stats)
 		case <-disp.fb.flips:
 			now := time.Now()