Report the directories a growing tree could not watch

Extending an automatically watched tree to a new directory swallowed
every error, so a reached watch limit or an unreadable directory left
part of the tree unwatched without any sign. No call of the consumer is
running at that moment, so the failures now arrive in the event stream
as InotifyEvent.watchFailed, after the event that triggered the
extension. The library watches what it can first: a reached limit ends
the attempt, an unreadable directory is skipped with its subtree, and a
directory that vanished in between is not reported.

The buffer now carries the library's own events next to the kernel's,
which keeps them in order and hides the stream's element type. The
test runner drops root's DAC capabilities so that an unreadable
directory can be tested.

Tests/InotifyIntegrationTests/Utilities/getEventsForTrigger.swift

@@ -1,4 +1,5 @@
 import Inotify
+import SystemPackage
 
 enum RecursivKind {
 	case nonrecursive
@@ -48,13 +49,7 @@ func getInotifyEventsForTrigger(
 		try await watcher.addWatchWithAutomaticSubtreeWatching(forDirectory: dir, mask: mask)
 	}
 
-	let eventTask = Task {
-		var events: [InotifyEvent] = []
-		for await event in await watcher.events {
-			events.append(event)
-		}
-		return events
-	}
+	let eventTask = Task { await collectEvents(of: watcher) }
 
 	try await Task.sleep(for: .milliseconds(100))
 	try await trigger(dir)
@@ -64,9 +59,54 @@ func getInotifyEventsForTrigger(
 	return await eventTask.value
 }
 
+/// Everything `watcher` delivers until the current task is cancelled.
+func collectEvents(of watcher: Inotify) async -> [InotifyEvent] {
+	var events: [InotifyEvent] = []
+	for await event in await watcher.events {
+		events.append(event)
+	}
+	return events
+}
+
+/// Everything `watcher` delivers up to and including the first event that
+/// satisfies `predicate`, or until `timeout` passes.
+func collectEvents(
+	of watcher: Inotify,
+	until predicate: @escaping @Sendable (InotifyEvent) -> Bool,
+	timeout: Duration
+) async -> [InotifyEvent] {
+	let eventTask = Task { () -> [InotifyEvent] in
+		var events: [InotifyEvent] = []
+		for await event in await watcher.events {
+			events.append(event)
+			if predicate(event) { break }
+		}
+		return events
+	}
+	let timeoutTask = Task {
+		try? await Task.sleep(for: timeout)
+		eventTask.cancel()
+	}
+	defer { timeoutTask.cancel() }
+	return await eventTask.value
+}
+
+/// Everything `watcher` delivers within `duration`.
+func collectEvents(of watcher: Inotify, for duration: Duration) async -> [InotifyEvent] {
+	let eventTask = Task { await collectEvents(of: watcher) }
+	try? await Task.sleep(for: duration)
+	eventTask.cancel()
+	return await eventTask.value
+}
+
 extension InotifyEvent {
 	var fileSystemEvent: FileSystemEvent? {
 		if case .fileSystem(let event) = self { return event }
 		return nil
 	}
+
+	var watchFailure: (path: FilePath, error: InotifyError)? {
+		if case .watchFailed(let path, let error) = self { return (path, error) }
+		return nil
+	}
 }