feat: add TextInserter with clipboard restore and PassthroughCleaner

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Sources/SstCore/TextInserter.swift

@@ -0,0 +1,39 @@
+import Foundation
+
+public typealias PasteboardItem = [String: Data]
+
+public protocol PasteboardProviding {
+    func readItems() -> [PasteboardItem]
+    func writeString(_ text: String)
+    func writeItems(_ items: [PasteboardItem])
+}
+
+public protocol KeystrokePosting {
+    func postPaste() throws
+}
+
+public struct TextInserter: TextInserting {
+    private let pasteboard: PasteboardProviding
+    private let paster: KeystrokePosting
+    private let restoreDelay: Duration
+
+    public init(
+        pasteboard: PasteboardProviding,
+        paster: KeystrokePosting,
+        restoreDelay: Duration = .milliseconds(150)
+    ) {
+        self.pasteboard = pasteboard
+        self.paster = paster
+        self.restoreDelay = restoreDelay
+    }
+
+    public func insert(_ text: String) async throws {
+        let saved = pasteboard.readItems()
+        pasteboard.writeString(text)
+        // On failure the text deliberately stays on the clipboard.
+        try paster.postPaste()
+        // Give the target app time to read the clipboard before restoring it.
+        try await Task.sleep(for: restoreDelay)
+        pasteboard.writeItems(saved)
+    }
+}