run.sh net: use a private cfg directory -- a saved per-device interface=-1 silently overrides -networkprovider and no tap is ever opened

.gitignore

@@ -45,3 +45,6 @@ video/
 
 # Worker scratch
 .vt1200-scratch/
+
+# Private MAME cfg for run.sh net (holds the per-device network provider; refreshed each run)
+harness/mame/cfg-net/

harness/mame/run.sh

@@ -89,14 +89,19 @@ case "$MODE" in
         ;;
 
     net)
-        # the crash-work configuration: skip + tablet (already the default) + the
-        # LANCE attached to a host tap, so frames actually leave the machine.  The
-        # driver needs nothing -- MAME's am79c90 brings its own network interface
-        # (device_network_interface); the OSD provider is the only missing link.
-        # Requires the tap to exist and be owned by your user; see the README's
-        # "host-side network plumbing" plan for the sequence.
+        # the crash-work configuration: skip + tablet (already the default) + the LANCE
+        # attached to a host tap.
+        #
+        # A PRIVATE cfg directory is essential.  MAME stores the network provider PER
+        # DEVICE in cfg/<game>.cfg, and a saved value wins over -networkprovider -- a
+        # stale interface="-1" (i.e. "none") means no tap is ever opened, silently, with
+        # no verbose output.  Refresh it each run so a stale saved interface cannot
+        # reappear.  It needs the tap to exist and be owned by your user.
+        CFGDIR="$HERE/cfg-net"
+        rm -rf "$CFGDIR"; mkdir -p "$CFGDIR"
         exec env VT1200_SKIP_LEVEL1=1 \
-            "$MAME" vt1200 "${COMMON[@]}" -networkprovider taptun -window "$@"
+            "$MAME" vt1200 "${COMMON[@]}" -cfg_directory "$CFGDIR" \
+            -networkprovider taptun -window "$@"
         ;;
 
     mouse)