Add managed UIKit iOS client

docs/tech-stack.md

@@ -37,16 +37,16 @@ explicit resampling (speexdsp/libsamplerate) is only needed when a device can't
 
 ## 2. Clients
 
-### macOS / iOS — Swift
+### Apple clients — .NET native UI with a Swift ReplayKit exception
 
 | Concern | Choice | Notes |
 |---------|--------|-------|
 | Language | **Swift 5.9+** | Direct **Swift↔C interop** — the C ABI (`voicecat.h`) is imported as a Clang module (`import VoiceCatC`) via a module map in the XCFramework headers; no manual struct/function redeclaration (unlike the C# P/Invoke layer). A Swift wrapper (`VoiceCatCore` package) provides Swift-idiomatic types on top. |
 | UI — macOS | **AppKit** | Chosen over SwiftUI for the most mature, granular **VoiceOver** accessibility story (per-control `accessibilityLabel`/`accessibilityHelp`/`accessibilityRole`, `NSAccessibility.post(.announcement)` for live announcements) — the same rationale that drove the Windows client to WinForms over WinUI 3 for screen-reader (NVDA/JAWS/Narrator) UIA support (resolved decision in `docs/roadmap.md`). macOS 14 (Sonoma) deployment target. |
-| UI — iOS | **SwiftUI** | iOS has a narrower control surface (no channel-tree moderation, etc.) and SwiftUI's VoiceOver support is sufficient; revisit if gaps emerge. iOS 18.0 deployment target (unlocks newest AVAudioSession APIs: stereo capture, polar patterns, data sources). |
+| UI — iOS | **C# / UIKit (`net10.0-ios`)** | Native UIKit keeps direct lifecycle/audio control and predictable VoiceOver semantics. MAUI was rejected because a cross-platform abstraction provides no benefit for this platform-specific client. iOS 18.0 deployment target. |
 | Shared core | **VoiceCatCore** Swift Package | One Swift library wrapping the C ABI, consumed by both the macOS AppKit app and the iOS SwiftUI app. Mirrors the C# `VoiceCat.Interop` layer. Events delivered on `@MainActor` via a coalesced `DispatchQueue.main` drain (the Swift analog of C#'s `Channel<VoiceCatEvent>` + 30ms WinForms Timer pump). |
-| Audio session (iOS) | **AVAudioSession** + **IOSAudioRouter** | App owns category `.playAndRecord`, mic permission, interruption/route-change handling; calls `vc_audio_suspend`/`vc_audio_resume`/`vc_audio_restart` (implemented) on the core. All iOS audio routing (input port selection, mic orientation/polar patterns, HFP vs A2DP, measurement/raw mode, stereo capture via `.stereo` polar pattern + `setPreferredInput` + `setInputDataSource`) is driven from Swift via `AVAudioSession` *before* the core (miniaudio) opens its device — miniaudio does NOT touch `AVAudioSession` on iOS. The `IOSAudioRouter` singleton owns this; the core is told the channel count via `vc_set_capture_channels`. When settings change mid-session, devices are suspended (`vc_audio_suspend`), the session is reconfigured, and devices are restarted (`vc_audio_restart`) to pick up the new route. macOS uses CoreAudio via the core directly. |
-| Packaging | Swift Package + Xcode project | Core shipped as an **XCFramework** binary target — a fat static library (`libvoicecat-fat.a`) bundling `libvoicecat.a` + all vcpkg static deps (protobuf/mbedtls/sodium/opus/sqlite3/spdlog/asio), so the Swift Package links a single self-contained `.a` per slice. macOS slice validated; iOS device + sim slices are scaffolding. |
+| Audio session (iOS) | **AVAudioSession + AVAudioEngine from C#** | The UIKit host owns category, permission, interruptions, routes, VPIO capture and planar playback. Converted PCM crosses bounded managed rings; callbacks allocate no managed objects, lock, or block. |
+| Packaging | .NET Apple workloads + Xcode appex | The managed iOS host statically links merged Opus/RNNoise archives. MSBuild invokes Xcode to build/embed the small Swift ReplayKit extension, which communicates through the versioned App Group PCM ring. |
 | Future | CallKit / PushKit | For background VoIP + incoming-call UX on iOS. Post-v1. |
 
 ### Windows — C# (shipped in M4, 2026-06-17)