wadamesh/LUA_APPS.md

Lua apps — plan + tracker

Goal: non-core apps become Lua scripts installed from a store catalog on firmware.wadamesh.com — installable, uninstallable and updatable without cutting a beta, one app artifact for every board, and writable by the community without forking the firmware. Runtime target: Lua 5.4 (vanilla, no JIT — smallest serious VM, trivial to sandbox, portable Xtensa/RISC-V).

Non-goals (v1): native dynamic loading (ELF), Lua access to LoRa TX or protocol frames, multi-file app packages, app signing (the curated catalog is the trust layer, same as firmware bins today).

Execution model — the decision that keeps this safe

Lua runs on the UI task, event-driven. No app thread, no preemption:

• The host calls the app's callbacks: on_open(w, h), on_tick(dt_ms), on_input(ev), on_close(). All LVGL work stays on the LVGL thread by construction (LVGL is not thread-safe).
• Every callback runs under a lua_sethook(LUA_MASKCOUNT) instruction budget (~100k instructions ≈ low single-digit ms). Budget exceeded → error → app closed with a toast. A buggy app can never stall the mesh loop or trip the WDT.
• Every entry is wrapped in lua_pcall. A Lua error NEVER reboots the device: toast "App error: ", close the app, free the state. Crash containment is the whole point.
• lua_newstate gets a custom allocator on PSRAM (heap_caps_malloc SPIRAM) with a hard per-app cap (256 KB to start). The V4's tight internal DRAM (#192) is never touched by app heaps.
• One app at a time (matches today's overlay model). The app root is one k_popup_registry row — red-X/Esc/status-bar close come free.

The wada.* API (v1) — deliberately small

We do NOT bind LVGL wholesale. We bind a stable, versioned surface we own (manifest.min_api gates compatibility). ~30 functions total:

• wada.ui — the app's root container + widgets: canvas(w,h) (draw_rect, draw_line, draw_text, draw_circle, fill, blit-from-table), label, chart (the Airtime/Monitor primitive), button, list. Theme colours provided (wada.ui.colors), fonts by size class only (12/14/16 → g_font_*).
• wada.input — events into on_input: touch x/y down/up, key codes, trackball dirs. (Snake's swipe steering maps here; the existing SnakeGame gesture path shows the shape.)
• wada.mesh (READ-ONLY v1) — contacts() snapshot (name/type/last_seen/ rssi), rx_log() ring (the RF Monitor feed), stats() (airtime used, duty budget, tx/rx counters, noise floor, current rssi), self() (name, lat/lon, battery_mv). No TX of any kind in v1 — mesh safety line.
• wada.net — http_get(url, cb, max_bytes) async on the existing tile-fetch worker; plain HTTP (V4 cannot TLS); response size capped (64 KB default).
• wada.store — per-app KV: get/set(key, value) under an app.<id>. prefix in the file-mode prefs. Quota 2 KB/app (respects the SdNvsPrefs blob cap).
• wada.sys — millis(), board() (id, screen w/h, caps: keyboard, trackball, gps), version(), toast(msg).
• wada.timer — every(ms) drives on_tick cadence (min 33 ms).

Sandbox env (no io, os, require, dofile, load of new chunks; whitelisted stdlib: math, string, table, pairs/ipairs/select/pcall/ tostring/tonumber). API-level bounds are the second fence, the curated catalog is the third.

App format + store

• On device: /apps/<id>.lua + /apps/<id>.json (manifest: name, version, min_api, boards allow-list, icon glyph, description) on the active storage root (SD where adopted, internal FS otherwise) — same resolution as chat history.
• Catalog: https://firmware.wadamesh.com/apps/apps.json + one .lua + .json per app in apps/<id>/<version>/. Served like firmware: VPS rsync, immutable per-version paths, mutable index. Device store page = fetch index → list → install (download 2 files) → appears in the drawer. Uninstall = delete 2 files. Update = version compare against the index.
• The Store page also lists the built-in removable apps (Snake, Airtime, RF Monitor, later more) with the same install/uninstall verbs — for built-ins that just toggles drawer visibility + services (MQTT bridge gets this too). One UX for both worlds from day one.

Budgets + board gates (measure in Phase 0, numbers are targets)

• Flash: Lua core + bindings ≤ 250 KB (-Os, no coroutines trimmed? keep coroutines, trim io/os libs at compile). Gate: CAP_LUA_APPS in device_caps.h. V4 (77.6%) and T-Deck (81.8%) are fine. The Pager is the risk board (84.3% now, 87.7% if #198 fonts land) — if Lua + fonts don't both fit, the Pager ships CAP_LUA_APPS=0 first and we revisit; measure before deciding. P4/Tanmatsu: plenty of room, plain C portability.
• RAM: state base ≤ 40 KB PSRAM, Snake running ≤ 100 KB PSRAM, ZERO new internal-DRAM allocations attributable to apps.
• Latency: worst on_tick under budget ≤ 4 ms on the V4 @ 240 MHz (measure with the STALL_SCOPE harness already in loop()).

Conversion inventory

Tier 1 — converts first (proves the API):

• Snake (SnakeGame.h — already a self-contained module): canvas + input + timer + store (high score). The reference app; native version compiled out once parity is confirmed on all boards.
• Airtime (ChannelUtil, jacobpretorius): chart + wada.mesh.stats(). Invite @jacobpretorius to do this port against the SDK — the first external Lua app author, with credit.

Tier 2 — converts once the API stabilises:

• RF Monitor: rx_log + stats + chart + recolor-safe labels.
• Telemetry charts (Sensors view): needs a wada.mesh.telemetry() read.
• LOS analyzer: http_get (SRTM), contacts picker, canvas plot.

Stays native, with reasons (do not creep):

• Spectrum — owns the raw SX1262 with ms-level timing; a Lua radio API is a different (dangerous) project.
• Discover — transmits protocol frames; revisit only if a consent-gated TX API ever exists.
• Web browser, VNC/Remote/web mirror, Terminal, Files — infrastructure, not apps.
• MQTT bridge — background service woven into the main loop; gets the catalog uninstall-toggle only.

Delivery: ALL of it ships in ONE beta — beta_59 (Kaj, 2026-08-04)

The phases below are the build order inside the beta_59 branch of work, not separate releases. Ship list for beta_59: runtime + host + wada.* v1 + the Store page + VPS catalog + Snake/Airtime/RF Monitor converted to Lua (seeded to storage at first boot so they work offline, native versions compiled out under CAP_LUA_APPS) + built-in hide/show toggles + an SDK docs page. The Pager go/no-go measurement happens mid-flight and only decides that board's CAP_LUA_APPS value, not the project.

Phases (build order within beta_59)

• Phase 0 — spike + go/no-go (behind an experimental flag, T-Deck only). Vendor Lua 5.4 under lib/lua/ (PIO) + an IDF component wrapper for P4/Tanmatsu (the ed25519/shared-src pattern). PSRAM allocator, sandbox env, instruction hook, pcall containment. A 20-line hello app drawing to a canvas. Deliverable: measured flash/RAM/latency vs the budgets above. STOP here if the Pager numbers say the whole idea needs rethinking.
• Phase 1 — API v1 + Snake. The app host (lifecycle, popup-registry row, error toasts), wada.ui/input/timer/sys/store, Snake ported + shipped as a bundled Lua app (still pre-store: file baked into the FS image or seeded). Beta-tested by the community like any feature.
• Phase 2 — the store. /apps scan, drawer integration, manifest checks, the Store page (browse/install/uninstall/update), VPS catalog + curation flow (a PR to a catalog repo dir = submission, we review = curation). Built-in-app hide/show toggles land here too.
• Phase 3 — mesh/net APIs + Tier-1/2 conversions. wada.mesh + wada.net, Airtime and RF Monitor converted, their native versions compiled out where CAP_LUA_APPS=1. Flash reclaimed is a bonus, not the goal.
• Phase 4 — SDK launch. Docs page on the site (existing docs workflow), an annotated example app, an "apps wanted" note in the release body. PixPMusic and jacobpretorius get first pings.

Parked for later: multi-file apps, app signing, TX-capable APIs with on-device consent prompts, a desktop simulator for app development (lv_port_pc + the same wada.* bindings — nice for contributors, not needed to start).

Risks, named

• Pager flash ceiling — measured in Phase 0, gated per-board; worst case the Pager waits.
• API regret — once apps exist in the wild, wada.* is an ABI. Mitigation: v1 stays tiny, everything else waits until two real apps demand it; min_api versioning from day one.
• V4 PSRAM pressure — app heaps compete with the tile pool; the 256 KB cap + tile-pool priority keeps maps working. Watch #192's findings.
• Store curation load — catalog PRs need review; that is deliberate (curation = the trust model) but it is maintainer time.

Status log

• 2026-08-04: plan written.
• 2026-08-04: Phase 0 GO — measured on the T-Deck: flash +96 KB (budget 250), state+libs 7.5 KB PSRAM / 2 ms, busy-script peak 31 KB, hostile while-true contained in 30 ms, zero leak after close. Hook cadence: 100k instructions (10k costs +111% on call-heavy code; 100k is ~free and still contains). Pager fits (+2.4%, ~87% even with #198 fonts).
• 2026-08-04: Phase 1 DONE — LuaAppHost (AppPage overlay, guarded pcall + 100k-instruction budget, deferred close from inside callbacks), wada.ui (canvas/label/button + theme colors) + input (hw swipes, trackball, touch)
  • timer + sys + store (per-app KV file, root-prefix aware), Snake ported to Lua as the embedded+seedable reference app. Verified on the T-Deck: open at 19 KB PSRAM, plays via hw-swipe steering, an early bug (pre-layout size read) was contained exactly as designed (toast + clean close, 0 leak, 4 retries, no crash). Host layer costs 13 KB on top of the VM (85.1%% T-Deck total). Next: Phase 2 store page + catalog.

2026-08-04 — Store v2: three tabs + languages-as-files. The store page is now segmented: Apps (catalog + sideloads), Built-in (show/hide switches), Languages (new). Store opens instantly — the card re-listing moved to the net worker (s_luascan_* flags) and pre-warms at boot. Card text is width-capped clear of the action button. Languages: gen-lang-files.py exports every i18n column to apps/lang/.lang + langs.json (serving on the VPS); the device downloads to /lang/, prefs v48 stores the active code, and at boot the file loads into PSRAM and overlays TR() (bsearch; file → built-in column → EN). Users can sideload/edit their own .lang files. Built-in table stays as fallback this beta; dropping its columns for the flash win is the follow-up once files are field-proven.