fix(launch): a missing python3.12 leaves the rig up and unproven, not a held window

The gate call hardcodes python3.12 (mido is installed for 3.12 only, and a gate
that quietly ran on 3.11 would fail the MIDI probes for the wrong reason). But
propagating rc=127 from a missing interpreter would hold a terminal open over
the stage for a reason that has nothing to do with the rig — which is already
up by the time this runs. Report it, name the fix, let the launch stand.

gig-up.sh

@@ -558,6 +558,15 @@ fi
 #              worst case (120s waiting for SuperDirt + the gate) inside the
 #              300s the Bridge's RIG UP button allows before it gives up.
 echo
+# python3.12 by name, not `python3`: mido is installed for 3.12 only, and a gate
+# that silently ran on 3.11 would fail on the MIDI probes for the wrong reason.
+# If it is genuinely absent, REPORT and let the launch stand — the rig is already
+# up by this point, and a missing interpreter is not a reason to hold a window
+# over the stage.
+if ! command -v python3.12 >/dev/null 2>&1; then
+  warn "gate: python3.12 not found — rig is up but UNPROVEN. Install it, then: tools/check-gig.py"
+  GATE_RC=0
+else
 info "readiness: one gate, two layers (the set, then the machine)"
 GATE=(python3.12 "$DIR/tools/check-gig.py" --quiet --fast)
 [ -f "$SETLIST" ] && GATE+=(--setlist "$SETLIST")
@@ -571,6 +580,7 @@ case "$GATE_RC" in
        GATE_RC=0 ;;
   *)   warn "gate: NO-GO — the blocking failures and their fixes are above." ;;
 esac
+fi
 
 echo
 if [ "$HEADPHONES" = 1 ]; then