midiviz: a fader at zero silences that orbit's HL

PLN: 'dont HL when d1-d12 controls are at zero volume (so D1 at 0 kills
d1 HLs, A1 at 0 kills d9, etc)'. A trigger the mix cannot hear is not a
picture the lens should paint. Only a KNOWN zero gates — a fader never
touched is unknown, not silent. Existing glow decays naturally instead of
vanishing mid-note.

tools/bridge/midiviz.py

@@ -1185,6 +1185,10 @@ def build_widget(port_label: str, reader: "Reader | None", scale: float = 1.0,
             self.hl = hl
             self.hl_t: dict[int, float] = {}
             self._hl_cells_cache: dict[int, list[int]] = {}
+            # orbit -> its level fader's CC (D1-D8 for d1-d8, A1-A4 for
+            # d9-d12), for the zero-volume HL gate above.
+            self._level_cc = {o: grid.orbit_home(o).get("level")
+                              for o in range(1, 15)}
             self.wave = False                 # the ParVagues wave, behind all
             self.word = False                 # …and the PARVAGUES lettering
             self._wave_pm: QtGui.QPixmap | None = None
@@ -1664,6 +1668,16 @@ def build_widget(port_label: str, reader: "Reader | None", scale: float = 1.0,
             self._bucket_n += len(evs)
             for ev in evs:
                 o = ev["orbit"]
+                # PLN, 2026-09-24: "dont HL when d1-d12 controls are at zero
+                # volume (so D1 at 0 kills d1 HLs, A1 at 0 kills d9, etc)".
+                # A trigger the mix cannot hear is not a picture the lens
+                # should paint. Only a KNOWN zero suppresses — a fader never
+                # touched on the surface is unknown, not silent, and stays lit.
+                lvl = self._level_cc.get(o)
+                if lvl is not None:
+                    st = self.cc.get(lvl)
+                    if st is not None and st[0] == 0:
+                        continue
                 if 1 <= o <= 8:
                     self.col_t[o] = now
                 for cc in self._hl_cells(o):