Draft: shared protocol, remote firmware, project docs

Not yet verified on hardware.

- shared/HexapodProtocol: CmdPacket (now 20 bytes, adds remote_roll /
  remote_pitch), FLAG_* bits and radio settings as the single protocol
  definition; static payload size = sizeof(CmdPacket) on both radios.
- robot: use the shared protocol; vx = forward (harness w/x <-> q/e);
  InputMapper adds remote tilt on top of the right stick when
  FLAG_REMOTE_GYRO is set, and robot.ino no longer zeroes stick
  roll/pitch when it's off.
- remote (Teensy 4.1): Sticks (calibration, EEPROM), RemoteIMU,
  RemoteState (interlocks, link-loss disarm, smoothing), PacketBuilder,
  RadioLink, NextionUI, SerialConsole.
- CLAUDE.md, README.md, remote/README.md, remote/NEXTION.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2026-current/remote/NEXTION.md

@@ -0,0 +1,75 @@
+# Nextion HMI build guide
+
+The firmware drives the display by **component name**, and the display
+talks back with small custom frames sent from each button's touch event.
+Build one page in Nextion Editor to match the tables below. Layout, fonts
+and colors are up to you. The names and event code must match exactly.
+
+The remote is authoritative. Use **plain Button** components (not
+Dual-state buttons) and don't toggle anything locally in the HMI. The
+remote repaints every label and color from its own state, including a
+full redraw every 2 s and whenever the display reboots.
+
+## Program.s / page setup
+
+In **Program.s**, before `page 0`, add:
+
+```
+bauds=115200
+```
+
+This sets the display to the `NEXTION_BAUD` in `remote/Config.h`. The
+display ships at 9600, and `bauds=` persists across power cycles.
+
+Name the page `main` (page 0). The firmware never changes pages.
+
+## Components
+
+Text components need **txt_maxl** at least as large as the longest string
+the firmware writes. Button bounds here allow some slack.
+
+| Name     | Type    | txt_maxl | Firmware writes                              |
+|----------|---------|----------|----------------------------------------------|
+| `bArm`   | Button  | 10       | `ARMED` / `DISARMED`, bco red / gray         |
+| `bKill`  | Button  | –        | nothing (static "DISARM" label, make it red) |
+| `bStand` | Button  | 6        | `STAND` / `SIT`, bco green / gray            |
+| `bGait`  | Button  | 8        | `TRIPOD` / `WAVE`                            |
+| `bMode`  | Button  | 8        | `DIRECT` / `HEADING`                         |
+| `bRs`    | Button  | 10       | `R: ROTATE` / `R: MOVE`                      |
+| `bRGyro` | Button  | –        | bco green / gray (label it "REMOTE GYRO")    |
+| `bBGyro` | Button  | –        | bco green / gray (label it "ROBOT GYRO")     |
+| `hSpeed` | Slider  | –        | `val` 0..255 (set **maxval = 255**)          |
+| `nSpeed` | Number  | –        | `val` 0..100 (speed %)                       |
+| `bCal`   | Button  | 9        | `CAL` / `SAVE CAL`, bco orange while active  |
+| `bCalX`  | Button  | –        | nothing (static "CANCEL CAL")                |
+| `bZero`  | Button  | –        | nothing (static "LEVEL")                     |
+| `tLink`  | Text    | 10       | `LINK 97%` / `NO LINK`, pco green / red      |
+| `tMsg`   | Text    | 40       | status / rejection messages                  |
+
+## Touch events
+
+Put this in each component's **Touch Release Event** (the Speed slider
+uses **Touch Move** as well so the value tracks your finger). Frame format:
+`'#'` (0x23), length, command byte, optional value byte.
+
+| Component | Event code                               | Command                        |
+|-----------|------------------------------------------|--------------------------------|
+| `bArm`    | `printh 23 01 41`                        | `A` toggle arm (needs sticks centered) |
+| `bKill`   | `printh 23 01 4B`                        | `K` disarm, always accepted    |
+| `bStand`  | `printh 23 01 53`                        | `S` toggle sit/stand           |
+| `bGait`   | `printh 23 01 47`                        | `G` tripod ↔ wave              |
+| `bMode`   | `printh 23 01 4D`                        | `M` direct ↔ heading-hold      |
+| `bRs`     | `printh 23 01 58`                        | `X` right stick rotate ↔ translate |
+| `bRGyro`  | `printh 23 01 52`                        | `R` remote-gyro tilt on/off    |
+| `bBGyro`  | `printh 23 01 42`                        | `B` robot self-stabilize on/off |
+| `hSpeed`  | `printh 23 02 56`<br>`prints hSpeed.val,1` | `V` + speed byte             |
+| `bZero`   | `printh 23 01 5A`                        | `Z` zero handset level         |
+| `bCal`    | `printh 23 01 43`                        | `C` start / save stick calibration |
+| `bCalX`   | `printh 23 01 51`                        | `Q` cancel calibration         |
+
+**Uncheck "Send Component ID"** on every component. The firmware ignores
+standard touch frames, and they only add serial traffic.
+
+Protocol details and the parser live in `NextionUI.h/.cpp`. To add a
+control, pick an unused command byte, add it to `NextionUI::decodeCustom()`
+and `UiCmd`, handle it in `RemoteState::handle()`, and add a row here.