Module lifecycle 

App-lifecycle callbacks (docs/lifecycle.md). An app registers closures for day_spec::Lifecycle phases with on_lifecycle; each backend, at the matching moment in its native app/activity delegate, emits Event::Lifecycle(phase) (or day-core dispatches the launch phases uniformly), and the event pump routes it here to run the closures inside a reactive batch, the same rails as Event::MenuAction, so a lifecycle handler that writes signals updates the UI like any callback.

Not every platform has every phase (a desktop app doesn’t really enter the background), so a handler registered for a phase the running backend doesn’t deliver gets a one-time warning, and apps can guard with lifecycle_supported (runtime) or day::require_lifecycle! (compile time).

Functions

dispatch_lifecycle

Run every handler registered for phase, in a reactive batch. Called by the event pump on Event::Lifecycle, and directly by launch_with for the launch phases and for DidExit.

lifecycle_supported

Does the running backend deliver phase? Use this to guard registration at runtime: if day::lifecycle_supported(Lifecycle::DidEnterBackground) { on_lifecycle(...) }.

note_launch

Record the app’s name and version for the exit line, and start its clock. Called by launch_with before WillLaunch.

on_lifecycle

Register f to run whenever the app reaches phase. Handlers run in registration order, in a reactive batch (signal writes coalesce into one UI update). Register early (before launch, or at the top of the root builder) so WillLaunch/DidLaunch handlers are in place when they fire.

reset_handlers

Forget every registered handler: a re-mount (docs/settings.md “Appearance on Android”). The app’s root() is about to run again and re-register, and handlers left from the previous mount would fire a second time for every phase.

resident_memory

The process’s resident memory in bytes, from the platform’s own accounting: the task’s physical footprint on Apple platforms, the resident set from /proc on Linux and its relatives, the working set on Windows, the linear memory on wasm. None where none is readable, which the exit line reports as unknown.

warn_unsupported_registrations

Warn once for every ALREADY-registered phase the (now-known) backend doesn’t deliver. Called by launch_with right after the backend/tree is installed, covering handlers registered before launch.