Merge remote-tracking branch 'origin/glass-lamp-latency'

context/decomp-reference.md

@@ -522,6 +522,7 @@ default-ON (`'0'` disables).
 | `BT_SECTOR_LOG` | SectorDisplay Make/Execute |
 | `BT_NET_TRACE` | `[net-tx]/[net-rx]/[net-upd]` MP tracing |
 | `BT_DEV_GAUGES` | render the 6 pod MFD surfaces in a separate dev window |
+| `BT_GLASS_LAMP_SWEEP` | `0` = restore authentic once-per-gauge-cycle cockpit-lamp updates; default (on) sweeps the lamps EVERY frame in the dev/glass composite path so the lit buttons track the sim even when the throttled background gauge sweep starves under MP load (`L4VB16.cpp` `BTGlassSweepLamps`; the "lighting slow/nonexistent" fix — glass-only, pod serial cadence untouched) |
 | `BT_AIM="x y"` | pin the reticle crosshair (reticle coords) — headless aim harness |
 | `BT_AIM_LOG` | `[pick]` ray/box/hit diagnostics (Mech::PickRayHit) |
 | `BT_FIRE_ARC=<deg>` | OPT-IN external-camera fire-arc clamp (unset = authentic no-arc) |

context/gauges-hud.md

@@ -111,6 +111,21 @@ viewport), and `gWindowAspect` = the view rect's on-screen aspect (`BTWorldAspec
   the work area). Green tint tunable via `BT_COCKPIT_TINT=RRGGBB` (default `0x27E8`). Labels are a
   lazy GDI-baked MANAGED atlas (survives device reset). Renders in ALL builds; only the PadRIO
   click/lamp seam is BT_GLASS-gated. Full detail: `docs/GAUGE_COMPOSITE.md`.
+- ⚠ **Cockpit-lamp LATENCY under MP load (2026-08-04, glass playtest fix) [T2 runtime-verified].**
+  The lit cockpit buttons are drawn every frame (`BTDrawCockpitPanels`, reading `PadRIO::GetLampState`),
+  but the lamp STATE sweep that fills that store — `LampManager::Update` → `AssertNewLampValue` →
+  `SetLamp` — authentically rides `GaugeRenderer::ExecuteForeground`, which fires only **once per full
+  gauge cycle** (foreground→background→copy). The cycle can't advance to the next foreground turn
+  until the THROTTLED background gauge sweep drains the ~140-instrument active list, and that
+  background task starves under load (issue #45 — "instruments freeze while fps stays healthy"). So on
+  a busy MP mission the lamp sweep ran ~1×/s: **buttons froze / flashes stalled while the 3D view (a
+  separate per-frame foreground render) stayed smooth** — the "lighting slow or nonexistent" reports
+  (all testers on glass surround). Fix: `BTGlassSweepLamps()` runs the lamp sweep EVERY frame on the
+  dev/glass composite path (`L4VB16.cpp`, in `BTDrawGaugeInset`) — cheap (deduped pushes, ~72 lamps),
+  decoupled from the gauge cycle. The pod never enters this path (real gauge hardware), so its
+  bandwidth-paced serial lamp cadence is untouched. Kill switch `BT_GLASS_LAMP_SWEEP=0`. NB the RIO
+  serial/lamp stack itself is byte-identical to pod-proven Red Planet (`L4LAMP.cpp`/`L4SERIAL.cpp`
+  diffed) — the defect was purely the glass update CADENCE, not the lamp wiring.
 
 ## MP gauge-window FREEZE = dangling bindings + permanent SEH disable (Gitea #12, 2026-07-19) [T2 log-convicted]
 The live-MP "dev-gauges window froze entirely mid-session" incident (issue #12) is NOT a