Watch: snooze finished threads, name the files a file approval would edit, Settle on finished notifications, an instant launch from the saved feed, plain Loading states, and no more cancelled errors

Gateway: an approval push for a file change says which files it would edit

watch/WristCode/FeedCache.swift

@@ -0,0 +1,49 @@
+// The last good feed, and the last detail of each thread opened, saved as JSON in the app's caches
+// folder. Launch shows them at once while the first refresh runs. Signing out clears them, and demo
+// mode never reads or writes them.
+
+import Foundation
+
+struct FeedCache: Sendable {
+    let directory: URL
+
+    static let standard = FeedCache(directory: .cachesDirectory.appending(path: "WristCode", directoryHint: .isDirectory))
+
+    func feed() -> Feed? {
+        read(Feed.self, "feed.json")
+    }
+
+    func save(_ feed: Feed) {
+        write(feed, "feed.json")
+    }
+
+    func thread(hostId: String, threadId: String) -> ThreadDetail? {
+        read(ThreadDetail.self, Self.threadFile(hostId, threadId))
+    }
+
+    func save(_ detail: ThreadDetail) {
+        write(detail, Self.threadFile(detail.item.hostId, detail.item.threadId))
+    }
+
+    /// Deletes everything saved, as when the watch unpairs.
+    func clear() {
+        try? FileManager.default.removeItem(at: directory)
+    }
+
+    /// `thread-<hostId>-<threadId>.json`, with the ids percent-encoded so any id is a safe file name.
+    private static func threadFile(_ hostId: String, _ threadId: String) -> String {
+        let safe = { (id: String) in id.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? id }
+        return "thread-\(safe(hostId))-\(safe(threadId)).json"
+    }
+
+    private func read<Value: Decodable>(_ type: Value.Type, _ name: String) -> Value? {
+        guard let data = try? Data(contentsOf: directory.appending(path: name)) else { return nil }
+        return try? JSON.decoder().decode(type, from: data)
+    }
+
+    private func write(_ value: some Encodable, _ name: String) {
+        guard let data = try? JSON.encoder().encode(value) else { return }
+        try? FileManager.default.createDirectory(at: directory, withIntermediateDirectories: true)
+        try? data.write(to: directory.appending(path: name), options: .atomic)
+    }
+}