run.sh: replace the now-redundant tablet mode with a faithful mouse mode (tablet is the default)

harness/mame/run.sh

@@ -8,8 +8,8 @@
 #   ./run.sh headless [N]    no window; dump frame N (default 600) into this directory
 #   ./run.sh stub            faithful, plus an opt-in stand-in for the level-0
 #                            keyboard-port test fixture -> reaches level 1
-#   ./run.sh tablet          skip + VSXXX-AB tablet: interactive GUI with ABSOLUTE
-#                            pointing (the cursor follows the host pointer)
+#   ./run.sh mouse           skip + VSXXX-AA mouse: the *faithful* pointing device.
+#                            The tablet is the default; this sets VT1200_MOUSE=1
 #   ./run.sh <mode> -- <extra MAME options>
 #
 # Reboot the running machine with Shift+F3 (MAME's UI_RESET_MACHINE; plain F3 is a
@@ -30,11 +30,12 @@
 #         It is NOT a keyboard model: that test checks only the byte *count* and never
 #         compares the content, so the bytes are arbitrary.  It stands in for an
 #         unknown test fixture, and it is opt-in so the default stays honest.
-#   tablet selects the VSXXX-AB tablet instead of the mouse (VT1200_TABLET=1).  It is
-#         ABSOLUTE: the host pointer position maps directly to where the cursor is,
-#         rather than being integrated from deltas, and it does not grab the pointer.
-#         The mouse stays the default device.  Compose it with any mode by setting the
-#         variable yourself, e.g.  VT1200_TABLET=1 ./run.sh skip
+#   mouse forces the VSXXX-AA mouse (VT1200_MOUSE=1) -- the *faithful* pointing device,
+#         since the real terminal almost certainly has a mouse.  The DEFAULT is the
+#         VSXXX-AB tablet: it is ABSOLUTE, so the host pointer position maps directly
+#         to where the cursor is rather than being integrated from deltas, and it does
+#         not grab the pointer.  That default is a deliberate divergence -- see the
+#         divergences table in harness/mame/README.md.
 #
 # Modes other than 'headless' open a window at real speed, so you can watch.
 
@@ -85,13 +86,11 @@ case "$MODE" in
             "$MAME" vt1200 "${COMMON[@]}" -window "$@"
         ;;
 
-    tablet)
-        # the useful combination: the OS is only reachable through the skip gate, and
-        # the tablet gives absolute pointing, so the cursor follows the host pointer
-        # positionally instead of through relative deltas.  The OS distinguishes tablet
-        # from mouse by the device-code nibble in its "T" self-test reply, and then
-        # frames 5-byte absolute reports (3-byte relative for the mouse).
-        exec env VT1200_SKIP_LEVEL1=1 VT1200_TABLET=1 \
+    mouse)
+        # force the faithful VSXXX-AA mouse.  The tablet is the default (absolute
+        # pointing), so this is the opt-out.  Both need the lightgun options in COMMON
+        # for the host pointer to reach them.
+        exec env VT1200_SKIP_LEVEL1=1 VT1200_MOUSE=1 \
             "$MAME" vt1200 "${COMMON[@]}" -window "$@"
         ;;