Tactility/.claude/rules/app-framework.md

Architecture: App Framework

Apps are event-driven, C API (app-module, <app/*.h>), not a C++ class. Each app has an AppManifest (id, name, category, location, flags) and a main(argc, argv) entry point (AppMainFn), modelled on a C program's main(). Every app instance gets its own dedicated task for its whole lifetime, and blocks in that task until it returns. Use app_scheduler_current_app_id() (app/scheduler.h) to identify the running instance - it's not passed as a parameter.

Lifecycle and inter-app communication go through app_manager_*() (app/manager.h) and app_event_*() (app/event.h):

• app_manager_start()/app_manager_start_with_parameters() launch a plain instance; app_manager_start_for_result() launches a modal child that reports back to a parent instance.
• An app subscribes with app_event_subscribe() (registers for its own instance's events, no id argument needed), blocks via task_event_group_wait()/task_event_group_wait_any(), and drains with app_event_poll(), reacting to APP_EVENT_CLOSE (terminate now) and APP_EVENT_RESULT (a child it started reported back).
• An app closes itself by calling app_manager_finish() right before returning from main(); another instance is closed via app_manager_stop().

Apps are registered at startup via app_manager_add(). External apps can be loaded from SD card via manifest.properties files, or side-loaded as ELF binaries on ESP32 (see app/loader.h's AppLoaderApi).

Apps can be loaded from:

• memory (APP_LOCATION_MEMORY)
• a path pointing to an install folder where an .app file was installed (APP_LOCATION_PATH)
• a path pointing to an .elf file (APP_LOCATION_PATH)

An app can build an optional UI via the LVGL window-manager module (see lvgl.md).