Own small widget kit on M5GFX, not LVGL

The UI is drawn with M5GFX into an off-screen buffer, using a small widget kit we own: list, text view, line editor, dialog, Status Bar and Toast. We chose this over LVGL.

LVGL would give us ready-made widgets, but it costs roughly 40–60 KB of RAM on a device with no PSRAM. It would also need to coexist with the Mesh Service, the Wi-Fi stack and TLS, and it brings a large learning surface. Most of our Apps are lists and text on a 240×135 screen, and full control of the UX is a primary goal.

Consequences

• We write and maintain our own widgets.
• Switching to LVGL later would mean rewriting every App's view layer.