orchestration: sprite task lease + durable wave-completion record

The wave-3 loss was caused by sprite auto-suspend, not nohup process-group
semantics. /.sprite/llm.txt: 'When idle, sprites pause automatically. Services and
sessions keep sprites alive.' Detached processes are on neither list, so setsid is
necessary but not sufficient.

tasks/wave-guard.sh holds a /v1/tasks lease (max 3600s, renewal is DELETE+POST since
re-POST returns 409), renews every 15 min while workers run, writes logs/WAVE<N>-DONE,
then releases the lease so the sprite can suspend rather than idle hot.

Also documents hazard #6 (pgrep -f / pkill -f matching the orchestrator's own shell)
and adds the wave-3 worker prompts and shared screen contract.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tasks/_screen-contract.txt

@@ -0,0 +1,45 @@
+## SHARED SCREEN CONTRACT — fixed by the orchestrator, IDENTICAL in both wave-3
+## prompts. Do NOT change these signatures. E1 writes BookshelfNavHost against them;
+## E2 writes the screens to match. If you deviate, the other worker's code stops
+## compiling and the wave fails.
+
+Routes (string constants live in ui/nav/Routes.kt, owned by E1):
+  "setup" | "library" | "library?shelfId={shelfId}" | "detail/{bookId}" |
+  "scan" | "locations" | "settings"
+
+Screen composable signatures:
+
+  // E2 owns
+  @Composable fun LibraryScreen(
+      shelfIdFilter: String?,
+      onBookClick: (String) -> Unit,
+      onScanClick: () -> Unit,
+      onLocationsClick: () -> Unit,
+      onSettingsClick: () -> Unit,
+      container: AppContainer,
+  )
+  @Composable fun DetailScreen(
+      bookId: String,
+      onBack: () -> Unit,
+      container: AppContainer,
+  )
+  @Composable fun ScanScreen(
+      onBack: () -> Unit,
+      container: AppContainer,
+  )
+
+  // E1 owns
+  @Composable fun SetupScreen(onSetupComplete: () -> Unit, container: AppContainer)
+  @Composable fun LocationsScreen(
+      onBack: () -> Unit,
+      onShelfClick: (String) -> Unit,   // navigates to library?shelfId=...
+      container: AppContainer,
+  )
+  @Composable fun SettingsScreen(
+      onBack: () -> Unit,
+      onSignedOut: () -> Unit,          // navigates back to "setup"
+      container: AppContainer,
+  )
+
+All screens take `container: AppContainer` and construct their own ViewModel from it
+(manual DI per SPEC — NO Hilt). Package = ui.<screen>, e.g. ui.library.LibraryScreen.