# FlyWithLua companion — FMS two-way sync

X-Plane's Web API can't write a flight plan into the FMS. `fms-sync.lua` runs
inside X-Plane (via FlyWithLua, which has the FMS SDK) and syncs the shared
cockpit plan ↔ the in-sim FMS through two files in `Output/fms-sync/`.

## Install (sim PC only)

1. Install **FlyWithLua NG+** (free): copy its plugin folder into
   `<X-Plane>/Resources/plugins/FlyWithLua/`.
2. Start the bridge (desktop app or `node server/bridge.js`) **on the same PC**
   as X-Plane. On startup it auto-copies these three scripts into
   `<X-Plane>/Resources/plugins/FlyWithLua/Scripts/` and keeps them up to date
   on every launch (it only writes changed/missing files):
   - **`fms-sync.lua`** — flight-plan two-way sync
   - **`ui-sync.lua`** — G1000 UI state (page / range / inset)
   - **`terrain-probe.lua`** — terrain-awareness elevation grid for the MFD
3. In X-Plane: *FlyWithLua → Reload all Lua script files* (or restart).
   The log shows `[glass-cockpit] FMS sync active`.

No manual copying needed. If you install FlyWithLua *after* the bridge is
already running, trigger a re-install without restarting via
`POST /api/lua/install`. The current install state is reported under `lua` in
`GET /api/health`. The bridge must run on the **same PC** as X-Plane so both see
`<X-Plane>/Output/fms-sync/`. (The auto-install honours `LUA_SRC_DIR` — the
desktop app sets it to the bundled scripts; otherwise it finds `plugins/` itself.)

## What you get

- **App → Sim:** load/build a plan in the web cockpit → it appears in the 3-D
  G1000 and the autopilot can fly it.
- **Sim → App:** build/edit the plan in the real FMS → it shows on every tablet.
- **Terrain:** the MFD TERRAIN map colours real scenery elevation red/yellow
  relative to your altitude (probed live by `terrain-probe.lua`).

A 3-decimal lat/lon signature de-dupes the round-trip, so the two sides never
loop. Waypoints are pushed as lat/lon legs (exact route; in-sim idents are
generic — route accuracy over cosmetics).