feat(ios): a sideloadable iOS client over the shared Rust engine

A SwiftUI app that drives the same UniFFI engine as Android: Rust owns the
Proton sessions, SQLite and every decrypted byte, and Swift asks it questions
off the main thread. Playback goes through MPVKit's libmpv, with the pstr://
stream protocol ported from the Android JNI half, and secrets live in the
Keychain.

scripts/build-ios.sh builds the static library for aarch64-apple-ios, writes
the Swift bindings (module PstrBridge), generates the Xcode project with
XcodeGen and packages an unsigned .ipa for SideStore or AltStore, which
re-sign it with the viewer's own Apple ID. The generated project, Info.plist
and build output are ignored.

ios/ProtonStream/Player/MpvPlayer.swift

@@ -0,0 +1,298 @@
+import Foundation
+import Libmpv
+import Observation
+import UIKit
+
+/// MoltenVK can set the drawable to 1x1 to force a presentation through, which
+/// flickers and can stick. MPVKit's demo carries the same guard
+/// (mpv-player/mpv#13651).
+final class MpvMetalLayer: CAMetalLayer {
+    override var drawableSize: CGSize {
+        get { super.drawableSize }
+        set {
+            if Int(newValue.width) > 1, Int(newValue.height) > 1 {
+                super.drawableSize = newValue
+            }
+        }
+    }
+}
+
+struct MpvTrack: Identifiable, Hashable {
+    let id: Int64
+    let type: String
+    let language: String
+    let title: String
+    let selected: Bool
+
+    var label: String {
+        let parts = [title, language.uppercased()].filter { !$0.isEmpty }
+        return parts.isEmpty ? "Track \(id)" : parts.joined(separator: " · ")
+    }
+}
+
+/// One libmpv core rendering into a Metal layer. Every public method runs on
+/// the main thread; mpv's events are read on a thread of their own and applied
+/// back on the main thread.
+@MainActor
+@Observable
+final class MpvPlayer {
+    enum EndReason { case eof, stopped, failed }
+
+    private(set) var position: Double = 0
+    private(set) var duration: Double = 0
+    private(set) var paused = false
+    private(set) var buffering = false
+    private(set) var tracks: [MpvTrack] = []
+    private(set) var chapters: [ChapterRecord] = []
+    private(set) var failure: String?
+    /// Between `loadfile` and mpv's `FILE_LOADED`. Everything mpv reports in
+    /// that window still describes the *outgoing* file, including the
+    /// `END_FILE(stop)` stopping it emits.
+    private(set) var loading = false
+
+    /// Called once per file that ends, never for the one a load replaced.
+    @ObservationIgnored var onEnded: ((EndReason) -> Void)?
+
+    @ObservationIgnored let layer = MpvMetalLayer()
+    @ObservationIgnored private var mpv: OpaquePointer?
+
+    init() {
+        layer.framebufferOnly = true
+        layer.backgroundColor = UIColor.black.cgColor
+        guard let mpv = mpv_create() else {
+            failure = "libmpv did not start"
+            return
+        }
+        var wid = layer
+        mpv_set_option(mpv, "wid", MPV_FORMAT_INT64, &wid)
+        for (name, value) in [
+            ("config", "no"),
+            ("vo", "gpu-next"),
+            ("gpu-api", "vulkan"),
+            ("gpu-context", "moltenvk"),
+            ("hwdec", "videotoolbox"),
+            ("video-rotate", "no"),
+            ("keep-open", "no"),
+            ("cache", "yes"),
+            ("cache-secs", "30"),
+            ("demuxer-readahead-secs", "30"),
+            ("demuxer-max-bytes", "50331648"),
+            ("subs-fallback", "yes"),
+        ] {
+            mpv_set_option_string(mpv, name, value)
+        }
+        guard registerStreamProtocol(mpv), mpv_initialize(mpv) >= 0 else {
+            mpv_terminate_destroy(mpv)
+            failure = "libmpv did not initialize"
+            return
+        }
+        mpv_observe_property(mpv, 1, "time-pos", MPV_FORMAT_DOUBLE)
+        mpv_observe_property(mpv, 2, "duration", MPV_FORMAT_DOUBLE)
+        mpv_observe_property(mpv, 3, "pause", MPV_FORMAT_FLAG)
+        mpv_observe_property(mpv, 4, "paused-for-cache", MPV_FORMAT_FLAG)
+        mpv_observe_property(mpv, 5, "track-list/count", MPV_FORMAT_INT64)
+        mpv_observe_property(mpv, 6, "chapter-list/count", MPV_FORMAT_INT64)
+        mpv_request_log_messages(mpv, "error")
+        self.mpv = mpv
+
+        let thread = Thread { [weak self] in Self.eventLoop(mpv) { event in self?.apply(event) } }
+        thread.name = "mpv-events"
+        thread.start()
+    }
+
+    // MARK: Commands
+
+    /// Load `pstr://<handle>`. On `false` nothing was issued, and the caller
+    /// still owns the handle's release.
+    func load(handle: UInt64, start: Double, audio: String?, subtitle: String?, subtitles: Bool) -> Bool {
+        guard mpv != nil else { return false }
+        setString("start", start > 0 ? String(format: "%.3f", start) : "none")
+        setString("alang", audio ?? "")
+        setString("slang", subtitle ?? "")
+        setString("sid", subtitles ? "auto" : "no")
+        position = 0
+        duration = 0
+        tracks = []
+        chapters = []
+        failure = nil
+        loading = true
+        if command(["loadfile", "pstr://\(handle)", "replace"]) < 0 {
+            loading = false
+            return false
+        }
+        return true
+    }
+
+    func setPaused(_ value: Bool) { setFlag("pause", value) }
+    func seek(to seconds: Double) { setDouble("time-pos", max(0, seconds)) }
+    func seek(by seconds: Double) { _ = command(["seek", String(seconds), "relative"]) }
+    func setSpeed(_ value: Double) { setDouble("speed", min(max(value, 0.25), 4)) }
+    func setVolume(_ value: Double) { setDouble("volume", min(max(value, 0), 100)) }
+    func setMuted(_ value: Bool) { setFlag("mute", value) }
+
+    func select(audio: Bool, track: MpvTrack?) {
+        let property = audio ? "aid" : "sid"
+        if let track { setString(property, String(track.id)) } else { setString(property, "no") }
+        refreshTracks()
+    }
+
+    /// Showing no picture while backgrounded keeps the audio playing and avoids
+    /// the black frame MoltenVK otherwise leaves on return.
+    func setVideoEnabled(_ enabled: Bool) { setString("vid", enabled ? "auto" : "no") }
+
+    /// Stop and tear the core down. `cancel_fn` interrupts a read parked in a
+    /// block fetch, and the event thread destroys the core once it is down.
+    func shutdown() {
+        guard let mpv else { return }
+        self.mpv = nil
+        mpv_command_string(mpv, "quit")
+    }
+
+    // MARK: Events
+
+    private enum Event {
+        case double(UInt64, Double)
+        case flag(UInt64, Bool)
+        case count(UInt64)
+        case loaded
+        case ended(Int32)
+        case log(String)
+    }
+
+    /// Runs until the core shuts down, then destroys it. Nothing else calls
+    /// `mpv_terminate_destroy`, so no main-thread call can race it.
+    private nonisolated static func eventLoop(_ mpv: OpaquePointer, _ deliver: @escaping @MainActor (Event) -> Void) {
+        while true {
+            guard let event = mpv_wait_event(mpv, -1)?.pointee else { continue }
+            var decoded: Event?
+            switch event.event_id {
+            case MPV_EVENT_SHUTDOWN:
+                mpv_terminate_destroy(mpv)
+                return
+            case MPV_EVENT_PROPERTY_CHANGE:
+                guard let property = event.data?.assumingMemoryBound(to: mpv_event_property.self).pointee,
+                      let data = property.data else { break }
+                switch property.format {
+                case MPV_FORMAT_DOUBLE: decoded = .double(event.reply_userdata, data.load(as: Double.self))
+                case MPV_FORMAT_FLAG: decoded = .flag(event.reply_userdata, data.load(as: Int32.self) != 0)
+                case MPV_FORMAT_INT64: decoded = .count(event.reply_userdata)
+                default: break
+                }
+            case MPV_EVENT_FILE_LOADED:
+                decoded = .loaded
+            case MPV_EVENT_END_FILE:
+                if let end = event.data?.assumingMemoryBound(to: mpv_event_end_file.self).pointee {
+                    decoded = .ended(end.reason.rawValue)
+                }
+            case MPV_EVENT_LOG_MESSAGE:
+                if let message = event.data?.assumingMemoryBound(to: mpv_event_log_message.self).pointee,
+                   let text = message.text {
+                    decoded = .log(String(cString: text).trimmingCharacters(in: .whitespacesAndNewlines))
+                }
+            default:
+                break
+            }
+            if let decoded {
+                DispatchQueue.main.async { deliver(decoded) }
+            }
+        }
+    }
+
+    private func apply(_ event: Event) {
+        switch event {
+        case let .double(id, value):
+            if loading { return }
+            if id == 1 { position = value } else if id == 2 { duration = value }
+        case let .flag(id, value):
+            if id == 3 { paused = value } else if id == 4 { buffering = value }
+        case let .count(id):
+            if loading { return }
+            if id == 5 { refreshTracks() } else if id == 6 { refreshChapters() }
+        case .loaded:
+            loading = false
+            refreshTracks()
+            refreshChapters()
+        case let .ended(reason):
+            // The outgoing file's END_FILE arrives after the next load began.
+            if loading { return }
+            switch reason {
+            case MPV_END_FILE_REASON_EOF.rawValue: onEnded?(.eof)
+            case MPV_END_FILE_REASON_ERROR.rawValue:
+                failure = failure ?? "The file could not be played"
+                onEnded?(.failed)
+            default: onEnded?(.stopped)
+            }
+        case let .log(text):
+            if !text.isEmpty { failure = text }
+        }
+    }
+
+    private func refreshTracks() {
+        let count = getInt("track-list/count")
+        tracks = (0 ..< max(0, count)).map { index in
+            let base = "track-list/\(index)/"
+            return MpvTrack(
+                id: getInt(base + "id"),
+                type: getString(base + "type") ?? "",
+                language: getString(base + "lang") ?? "",
+                title: getString(base + "title") ?? "",
+                selected: getString(base + "selected") == "yes"
+            )
+        }
+    }
+
+    private func refreshChapters() {
+        let count = getInt("chapter-list/count")
+        chapters = (0 ..< max(0, count)).map { index in
+            let base = "chapter-list/\(index)/"
+            return ChapterRecord(index: index, title: getString(base + "title"), start: getDouble(base + "time"))
+        }
+    }
+
+    // MARK: Property plumbing
+
+    private func command(_ args: [String]) -> Int32 {
+        guard let mpv else { return -1 }
+        var pointers = args.map { UnsafePointer<CChar>(strdup($0)) }
+        pointers.append(nil)
+        defer { pointers.forEach { free(UnsafeMutablePointer(mutating: $0)) } }
+        return mpv_command(mpv, &pointers)
+    }
+
+    private func setString(_ name: String, _ value: String) {
+        guard let mpv else { return }
+        mpv_set_property_string(mpv, name, value)
+    }
+
+    private func setDouble(_ name: String, _ value: Double) {
+        guard let mpv else { return }
+        var value = value
+        mpv_set_property(mpv, name, MPV_FORMAT_DOUBLE, &value)
+    }
+
+    private func setFlag(_ name: String, _ value: Bool) {
+        guard let mpv else { return }
+        var flag: Int32 = value ? 1 : 0
+        mpv_set_property(mpv, name, MPV_FORMAT_FLAG, &flag)
+    }
+
+    private func getInt(_ name: String) -> Int64 {
+        guard let mpv else { return 0 }
+        var value: Int64 = 0
+        mpv_get_property(mpv, name, MPV_FORMAT_INT64, &value)
+        return value
+    }
+
+    private func getDouble(_ name: String) -> Double {
+        guard let mpv else { return 0 }
+        var value = 0.0
+        mpv_get_property(mpv, name, MPV_FORMAT_DOUBLE, &value)
+        return value
+    }
+
+    private func getString(_ name: String) -> String? {
+        guard let mpv, let raw = mpv_get_property_string(mpv, name) else { return nil }
+        defer { mpv_free(raw) }
+        return String(cString: raw)
+    }
+}