feat(ios): W0 scaffold + day-1 spike + WireProtocol frozen contract + TestSupport doubles

T-iOS-1: ios/ XcodeGen project (iOS 17, Swift 6 strict concurrency, ATS per PLAN §5.2), 5 SPM package shells, CI skeleton
T-iOS-2: Origin spike vs real server — URLSessionWebSocketTask custom Origin CONFIRMED (no Starscream); 16MiB replay + EMSGSIZE(40) errno correction written back to plan
T-iOS-3: WireProtocol frozen contract, 59 tests, 100% line coverage, cross-impl vectors vs src/protocol.ts via tsx
T-iOS-4: FakeTransport/FakeClock/FakeHTTPTransport doubles
Verify: independent agent re-ran all acceptance — 6/6 PASS

ios/Packages/WireProtocol/Tests/WireProtocolTests/TestHelpers.swift

@@ -0,0 +1,71 @@
+import Foundation
+import WireProtocol
+
+/// Deterministic RNG for the roundtrip property test (reproducible failures:
+/// the seed is baked into the test; change it only with a note in the test).
+struct SplitMix64: RandomNumberGenerator {
+    private var state: UInt64
+
+    init(seed: UInt64) {
+        state = seed
+    }
+
+    mutating func next() -> UInt64 {
+        state &+= 0x9E37_79B9_7F4A_7C15
+        var z = state
+        z = (z ^ (z >> 30)) &* 0xBF58_476D_1CE4_E5B9
+        z = (z ^ (z >> 27)) &* 0x94D0_49BB_1331_11EB
+        return z ^ (z >> 31)
+    }
+}
+
+enum MessageGen {
+    /// Character pool that stresses the JSON escaper: quotes, backslashes,
+    /// C0 control bytes (ESC / CR / TAB / ^C / NUL), CJK, emoji, plain ASCII.
+    private static let stressPool: [Character] = [
+        "a", "Z", "0", " ", "\"", "\\", "/", "{", "}",
+        "\u{1B}", "\r", "\n", "\t", "\u{03}", "\u{00}", "\u{7F}",
+        "中", "文", "終", "端", "🚀", "🧪", "é", "ß",
+    ]
+
+    static func randomString(using rng: inout some RandomNumberGenerator, maxLength: Int = 48) -> String {
+        let length = Int.random(in: 0...maxLength, using: &rng)
+        return String((0..<length).map { _ in stressPool.randomElement(using: &rng)! })
+    }
+
+    static func randomAbsolutePath(using rng: inout some RandomNumberGenerator) -> String {
+        "/" + randomString(using: &rng, maxLength: 24)
+    }
+
+    /// Seeded UUID v4 (version nibble 4, variant 10xx) — passes SESSION_ID_RE.
+    static func randomUUIDv4(using rng: inout some RandomNumberGenerator) -> UUID {
+        var bytes = (0..<16).map { _ in UInt8.random(in: 0...255, using: &rng) }
+        bytes[6] = (bytes[6] & 0x0F) | 0x40
+        bytes[8] = (bytes[8] & 0x3F) | 0x80
+        return UUID(uuid: (
+            bytes[0], bytes[1], bytes[2], bytes[3], bytes[4], bytes[5], bytes[6], bytes[7],
+            bytes[8], bytes[9], bytes[10], bytes[11], bytes[12], bytes[13], bytes[14], bytes[15]
+        ))
+    }
+
+    static func randomClientMessage(using rng: inout some RandomNumberGenerator) -> ClientMessage {
+        switch Int.random(in: 0...4, using: &rng) {
+        case 0:
+            let sessionId = Bool.random(using: &rng) ? randomUUIDv4(using: &rng) : nil
+            let cwd = Bool.random(using: &rng) ? randomAbsolutePath(using: &rng) : nil
+            return .attach(sessionId: sessionId, cwd: cwd)
+        case 1:
+            return .input(data: randomString(using: &rng))
+        case 2:
+            return .resize(
+                cols: Int.random(in: 1...1000, using: &rng),
+                rows: Int.random(in: 1...1000, using: &rng)
+            )
+        case 3:
+            let mode = Bool.random(using: &rng) ? ApproveMode.allCases.randomElement(using: &rng) : nil
+            return .approve(mode: mode)
+        default:
+            return .reject
+        }
+    }
+}