feat(ios): P1-B — W7 UI wave: deep links, timeline, quick-reply, diff, projects, session switcher, thumbnails, lock-screen push

T-iOS-22: DeepLinkRouter (full-field whitelist, cold-start stash, route(from:) for push-tap reuse), 21 tests
T-iOS-24: TimelineSheet mirroring web render() order; disabled→empty-state; reuses AwayDigest onExpand
T-iOS-25: QuickReply chips (built-ins mirror quick-reply.ts via KeyByteMap; visible iff live gate && !readOnly)
T-iOS-27: read-only DiffScreen + App-layer DiffFetcher (RO no-Origin; APIClient fold-in noted for T-iOS-38 owner)
T-iOS-26: Projects list/detail — grouping byte-identical to web group keys (prefs-shared collapse state),
prefs-clobber defenses (no blind PUT on empty base; adopt server echo), claude\r bootstrap
T-iOS-23: UnreadLedger + TitleSanitizer (SessionCore, +15 tests), lastOutputAt decode, list-boundary re-sanitize
T-iOS-29: new-in-cwd (untrusted cwd, no bootstrap re-injection) + exited-session reopen; fixes stale-controller
SwiftTerm view bug via .id(controller.id)
T-iOS-28: offscreen SwiftTerm thumbnail pipeline (LRU 32, concurrency gate 2, 256KiB cap, grid clamp)
T-iOS-21: PushRegistrar (WEBTERM_GATE category: Allow=.authenticationRequired, no .foreground) +
NotificationActionHandler (whitelisted payload, token never persisted, bg-task-wrapped POST, 403 fallback)
CRITICAL fix (verify-found boot crash): @Sendable literals on UN completion closures — MainActor-inherited
closures trapped Swift 6 executor check on UN's background queue; boot re-verified (no new crash reports,
permission prompt reached, privacy shade correctly covering during system alert)
Verified: 261 pkg + 247 app + 10 integration tests green; 7/7 semantics checks; Owns audit clean

ios/App/WebTerm/Wiring/UnreadWatermarkStore.swift

@@ -0,0 +1,44 @@
+import Foundation
+
+/// T-iOS-23 · Persistence seam for `SessionCore.UnreadLedger` watermarks.
+/// The ledger itself is persistence-agnostic (plan §7) — the App layer wires
+/// UserDefaults here. NON-SECRET UI state only (plan §5.3 split: Keychain =
+/// secrets, UserDefaults = prefs), same tier as `LastSessionStore`.
+protocol UnreadWatermarkStore: Sendable {
+    func load() -> [UUID: Int]
+    func save(_ watermarks: [UUID: Int])
+}
+
+/// UserDefaults-backed implementation with an injectable suite for tests
+/// (mirrors `UserDefaultsLastSessionStore`). `@unchecked Sendable`:
+/// `UserDefaults` is documented thread-safe and this wrapper adds no mutable
+/// state of its own.
+struct UserDefaultsUnreadWatermarkStore: UnreadWatermarkStore, @unchecked Sendable {
+    private static let key = "unreadWatermarks"
+
+    private let defaults: UserDefaults
+
+    init(defaults: UserDefaults = .standard) {
+        self.defaults = defaults
+    }
+
+    func load() -> [UUID: Int] {
+        guard let raw = defaults.dictionary(forKey: Self.key) as? [String: Int] else {
+            return [:]
+        }
+        // Stored data crosses a storage boundary — validate every key; garbage
+        // is dropped, never trusted (two case-variant spellings of one UUID
+        // collapse via max, so this can never crash on duplicates).
+        let pairs = raw.compactMap { key, value in
+            UUID(uuidString: key).map { ($0, value) }
+        }
+        return Dictionary(pairs, uniquingKeysWith: max)
+    }
+
+    func save(_ watermarks: [UUID: Int]) {
+        let plist = Dictionary(
+            uniqueKeysWithValues: watermarks.map { ($0.key.uuidString, $0.value) }
+        )
+        defaults.set(plist, forKey: Self.key)
+    }
+}