KB: step-2 closeout -- verification matrix + ledger detail (glass cockpit)

docs/GLASS_COCKPIT.md gains the 2b-2e detail + the full verification matrix
(purity build + seam audit, pod forced-walk, 2-node loopback MP via btconsole
relay on the POD build -- both nodes reach the running mission, PadRIO
authentic-path input, panel-click survival).  context/glass-cockpit.md status
updated: step 2 DONE [T2]; steps 3-4 pending.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/GLASS_COCKPIT.md

@@ -58,3 +58,51 @@ zoom-blip), so no consumer shifts.
 weapons unchanged. Regression: headless forced-walk run (`BT_FORCE_THROTTLE=1`) drives normally
 — `[mppr] thr=1 -> speedDemand=61.501`, gait cycles, position advances, 31/31 subsystems
 simulated, no faults.
+
+## 2026-07-17 — Steps 2b-2e: PadRIO, stand-downs, displays, preset — DONE + verified
+
+**2b (RIOBase + PadRIO, commit ac57a47):** `L4RIO.h` splits abstract `RIOBase` (enums, the five
+analog Scalars, pure `GetNextEvent`/`SetLamp`, no-op serial ops, NEW `IsOperational()`) out of
+serial `RIO` (`: PCSerialPacket, RIOBase` — ctor assigns as before, zero behavioral delta);
+`L4CTRL.h` `rioPointer` retyped `RIOBase*`; gated `L4CONTROLS=PAD` factory arm. NEW gated TUs
+`L4PADRIO.*` (XInput+keyboard → the surface; 3s hot-plug; focus-guarded keys; per-poll
+AnalogEvent heartbeat time-gated so the manager's drain loop terminates; `lampState[]`;
+static `SetScreenButton` — button addresses AND the keypad space 0x50-0x6F → KeyEvents) and
+`L4PADBINDINGS.*` (`content\bindings.txt`, default written on first run; deflect/slew/set axis
+model; addresses validated vs ButtonCount).
+
+**2c (stand-downs, commit 9f35a80):** engine query `BTRIODevicePresent()` (ungated —
+pod-correct); both dev bridges (`mech4.cpp` attr writes, `mechmppr.cpp` BT_KEY_BRIDGE) gate
+their WRITES: unset=auto / "0"=off / else on; forced harness always rides. **Definitive live
+test:** OS-injected LSHIFT hold slewed PadRIO throttle 0→0.33→1.0 with `pre==thr` every frame —
+the value arrives via the ENGINE push through the streamed `.CTL` binding (bridge stood down),
+`speedDemand=61.501` from authentic InterpretControls.
+
+**2d/2e (displays + preset, commits db9ac94 + 418acf0):** the on-screen panel follows **vRIO**
+(`C:\VWE\vrio` — `CockpitLayout.cs`/`PanelCanvas.cs`, per Cyd): five 4x2 MFD clusters
+(descending addresses), Throttle/Secondary/Screen/Joystick 1x8 columns, two 4x4 hex keypads
+(0x50 internal→pilot unit, 0x60 external→operator unit), physical names, red/yellow/blue
+coloration, 500/250/125ms flash, right-click latch — 104 controls. `PlasmaWindow :
+Video8BitBuffered` renders the 128x32 plasma via the SAME gauge-renderer path as serial
+(buffer is TOP-DOWN — the flip rendered it upside down, user-reported + fixed). MFD surfaces =
+the EXISTING dev-gauge modes (no new code, no L4VB16 exposure). `-platform glass` preset +
+run.cmd token. **Button-trap guard (e2c21c4 pattern):** the authentic base
+`ConfigureMappableMessageHandler` FAIL trap is `abort()` under DEBUGOFF — any aux/zoom button
+without its reconstructed L4 override KILLED the game on press (panel makes all reachable).
+Default now log+ignore; `BT_BUTTON_TRAP=1` restores the hard trap. Verified: synthetic panel
+click → 2 `[FAIL]` (press+release through panel→PadRIO→ProcessRIOEvent→streamed mapping), game
+survives. NOTE: each `[FAIL]` marks a missing L4 override — reconstruction backlog, see
+[[open-questions]].
+
+**Step-2 verification matrix (all passed 2026-07-17):**
+1. Purity: defaults `build-pod/` compiles (known mech3 /FORCE externals only); seam audit —
+   `BT_GLASS`/`BT_STEAM` mentions ONLY in CMakeLists, btl4main.cpp preset region, L4CTRL.cpp
+   (include+PAD arm), L4GREND.cpp (include+SCREEN branch), gated TUs, run.cmd docs.
+2. Pod solo forced-walk clean (§2a).
+3. **2-node loopback MP on the pod build:** A `-egg MP.EGG -net 1501` + B `-net 1601` +
+   `btconsole.py` relay — both nodes launch into the running mission (77/76 ticks, mechs at
+   their drop zones, gait/target loops live).
+4. Glass build: PadRIO drives through the authentic mapper path; panel click path live; plasma
+   window; all boot lines present.
+Deferred to the user (visual-only): panel/plasma appearance vs vRIO on screen, XInput stick
+feel, `L4PADFLIP` polarity.