Writing and persistence behavior

Writes are throttled so rapidly changing local state does not hammer the external representation:

URL mirror default: 50 ms
KV mirror default:  250 ms

A newer slice supersedes a pending write through Foldkit's dependency restart behavior.

A key-value mirror stores one versioned JSON document under its configured key. It may also be scoped to a user or tenant:

Mirror.kv(App, {
  key: 'todo/prefs',
  scope: principal.userId,
  fields: ...,
})

A document with another version/scope, or a malformed document, is discarded and removed. This is safe because Mirror represents disposable state, not unsent user operations. Discarding is not migrating: a port that wants another application's saved state writes an importer for that shape, or stores under a new key and version, rather than letting the old document fail to decode and calling the clean start a migration.

Store failures are absorbed and logged rather than failing the application. A slice back at all defaults removes the stored document.

Contracts and Module#

Every mirror exposes a contract of kind mirror.

Conceptually:

field owner:   local application Model
mirror:        observer / representation

So Module.manifest still reports the field as local with the mirror beside it. A mirror never becomes a second owner.

A key-value mirror declares MirrorRestored among its Messages. If the application union forgot to spread Mirror.messages, Module.validate can report that as an unknown Message dependency.

A URL key belongs to one URL mirror per application. Constructing another mirror that claims the same key fails and names the original owner of that URL key.