Remove the watches a failed tree call had already added

A recursive watch that hit the watch limit or an unreadable directory
threw after adding watches for part of the tree, which stayed in the
instance and kept counting against the user's limit. The call now
leaves the instance as it found it.

The test needs a second instance for the check, because a repeated
watch on the same instance only updates the existing one.

Tests/InotifyIntegrationTests/InotifyLimitTests.swift

@@ -18,6 +18,31 @@ struct InotifyLimitTests {
 		}
 	}
 
+	/// The limit counts every watch of the user, also those of other
+	/// processes, so it leaves room for the one watch of the second instance.
+	@Test func releasesTheWatchesOfATreeItCouldNotWatchCompletely() async throws {
+		try await withTempDir { dir in
+			try await withInotifyWatchLimit(of: 100, for: [.userWatches]) {
+				try createSubdirectorytree(at: dir, foldersPerLevel: 4, levels: 4)
+				let filepath = "\(dir)/new-file.txt"
+				let failedWatcher = try Inotify()
+				await #expect(throws: InotifyError.self) {
+					try await failedWatcher.addRecursiveWatch(forDirectory: dir, mask: .create)
+				}
+
+				let events = try await getEventsForTrigger(in: dir, mask: .create) { _ in
+					try createFile(at: filepath, contents: "hello")
+				}
+				// Deallocating the failed instance would free its watches too, so it
+				// must live until the second instance has added its watch.
+				withExtendedLifetime(failedWatcher) {}
+
+				let createEvent = events.first { $0.path.string == filepath }
+				#expect(createEvent != nil, "Expected a second instance to watch '\(dir)' after the failed one released its watches, got: \(events)")
+			}
+		}
+	}
+
 	@Test func watchesMassivSubtreesIfAllowed() async throws {
 		try await withTempDir { dir in
 			try await withInotifyWatchLimit(of: 1000) {