#1 SleepPreventionManager.refreshAssertions now creates the three new
   assertions before releasing the old IDs, so the kernel always sees at
   least one of each type during a refresh (swap-then-release, not
   release-then-create). The doc comment claimed overlap but the code
   left a microsecond gap. New testRefreshCreatesNewAssertionsBeforeReleasingOld
   pins the ordering via an operationLog on the test fake.

domzilla#2 NSWorkspace session observers now use the Combine publisher API with
   AnyCancellable, so they detach automatically when the manager
   deallocates. The previous selector-based addObserver retained the
   target forever — fine for the production singleton, but every test
   that constructed a SleepPreventionManager(backend:) leaked two
   observers. testManagerDeallocatesWhenOutOfScope proves the leak is
   fixed via a weak ref.

domzilla#3 LaunchAtLoginManager.setEnabled now logs the underlying error via
   os.Logger (subsystem net.domzilla.caffeine, visible in Console.app)
   and surfaces it on a public `lastError` property so the UI layer can
   present it to the user. refresh() still snaps the published isEnabled
   back to the backend truth, so a failed register visually pops the
   Toggle back to off. Two new tests cover lastError set on throw and
   cleared on next success.

domzilla#4 scripts/integration-test.sh replaces the fixed 3 s sleep with a
   poll_for_caffeine_assertions helper that retries pmset every second
   until Caffeine-owned assertions appear (default 30 s timeout,
   overridable via ASSERTION_POLL_TIMEOUT). Avoids flakiness on slow
   runners where SwiftUI initialization takes longer than 3 s.