Summary

Fixes a Google Play crash report on Samsung Galaxy S24 Ultra running Android 16 Beta (SDK 36):

Caused by java.lang.IllegalStateException:
  at eu.darken.octi.common.navigation.NavigationController.getBackStack (NavigationController.kt:15)
  at eu.darken.octi.common.navigation.NavigationController.popTo (NavigationController.kt:61)
  at eu.darken.octi.main.ui.MainActivity.onNewIntent (MainActivity.kt:123)
  at android.app.ActivityThread.deliverNewIntents
  at android.app.ActivityThread.performResumeActivity

Root cause

NavigationController._backStack is registered via setup(backStack) from inside the setContent { } Compose lambda — asynchronous, frame-scheduled. MainActivity.onNewIntent runs synchronously and the stack trace shows it firing inside performResumeActivity → deliverNewIntents. There is a window during activity recreation (config change, dark-mode flip) or singleTask warm intent delivery where onNewIntent runs before the Compose lambda has executed. _backStack is still null, and popTo(Nav.Main.Dashboard) throws.

Fix

Move the popTo(Dashboard) step out of onNewIntent and into a Compose-level LaunchedEffect. onNewIntent becomes a pure intent-parsing entry point that emits VM events; the navigation work happens once Compose has attached, where the back stack is guaranteed initialized.

• Add MainActivityVM.deeplinkAccepted: SingleEventFlow<Unit> — fired after a successful widget or file-share-notification deeplink parse (not for system-share intents)
• MainActivity.onNewIntent now just calls vm.handleDeeplinkIntent(intent) and returns
• New LaunchedEffect inside setContent { } collects deeplinkAccepted → navCtrl.popTo(Nav.Main.Dashboard)
• incomingShareEvents collector switched to goTo(FileShareList, popUpTo = Dashboard) (single atomic call) so it does not race with the parallel popTo collector
• NavigationController is unchanged — strict error() getter stays, contract not weakened

This matches the canonical pattern already used in permission-pilot (intent → VM event → Compose-level LaunchedEffect → navCtrl.*).

Test plan

• ./gradlew :app:testFossDebugUnitTest passes (6 new VM tests covering deeplinkAccepted across widget / file-share / system-share / unrecognized / not-onboarded cases)
• ./gradlew assembleFossDebug compiles cleanly
• Manual: open Octi to Dashboard → navigate to Settings → share a file from another app via system share sheet → confirm back stack lands at [Dashboard, FileShareList]
• Manual: open Octi to Dashboard → navigate to Settings → tap a widget on the home screen → confirm back stack lands at [Dashboard] and the module detail sheet opens
• Manual: with onboarding incomplete, repeat both — confirm we stay on Welcome and no nav happens