docs: scope Windows-as-host (deferred) + update roadmap status

A 4-agent read of the host crate: a Windows host is an "add a backend" job, not a parallel
port — ~95% reuse (core/protocol/FEC/crypto/C-ABI, QUIC, GameStream, mgmt, m3/pipeline are all
platform-agnostic and already cfg-isolated). New cfg(windows) backends behind the existing
traits: DXGI Desktop Duplication (capture), Media Foundation / NVENC-SDK (encode), SendInput +
ViGEm (input), WASAPI loopback + virtual mic (audio). The blocker is the virtual-display
feature — no user-mode Windows API; it needs a signed kernel-mode IDD driver (XL).

docs/windows-host.md records the per-subsystem effort + a phased plan (Phase 0 = a "basic
Windows host" capturing an existing monitor, smallest surface). Deferred: large and unbuildable
on the Linux dev box, per the request to only take it on if manageable. roadmap.md marks
#1/#2/#4 done, #3 packaged, and adds #7 Windows.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/roadmap.md

@@ -2,9 +2,14 @@
 
 Decided 2026-06-10 (research-grounded; see commit history). Sequence:
 **KDE reliability → client compositor options → mic passthrough → Bazzite COPR RPM (then
-bootc) → touch → full UHID DualSense → iOS.**
+bootc) → touch → full UHID DualSense → iOS** (+ Windows host, scoped & deferred).
 
-## 1. Reliable headless KDE/compositor spawning *(in progress)*
+**Done (2026-06-10):** #1 KDE reliability (Phase 1 + 2), #2 compositor options (full stack incl.
+macOS client), #4 mic passthrough — all on `main`, live-validated. #3 Bazzite packaging written
+(`packaging/`); the COPR/bootc build is operator-run. Remaining: #5 touch → UHID DualSense, #6 iOS,
+and a Windows host (`docs/windows-host.md`).
+
+## 1. Reliable headless KDE/compositor spawning ✅ *(done — Phase 1 + 2)*
 
 Startup is a chain of timing-sensitive handoffs with no readiness checks — each is a blind
 `sleep`, one-shot timeout, or silent fire-and-forget that fails into a black screen.
@@ -23,17 +28,21 @@ Startup is a chain of timing-sensitive handoffs with no readiness checks — eac
 - **Phase 3 (L):** supervised systemd user session (kwin + portal + host) with the readiness
   probe as an `ExecStartPost` gate, `Restart=on-failure`.
 
-## 2. Offer available compositors in the client *(M)*
+## 2. Offer available compositors in the client ✅ *(done)*
 
 Host enumerates which backends are actually available (binary present + version OK:
 gamescope ≥3.16.22, KWin ≥6.5.6, gnome-shell, sway), advertises the list in the punktfunk/1
 Welcome + a mgmt-API field; client sends its pick in the Hello; host honors it per session.
 Picker in the Apple client + web console.
 
-## 3. Bazzite / install on other devices *(decision: COPR RPM → bootc)*
+## 3. Bazzite / install on other devices ✅ *(packaging written — `packaging/`)*
 
 Bazzite already ships gamescope + PipeWire + the NVIDIA driver (incl. `libnvidia-encode`);
 it's Fedora-atomic and the community installs Sunshine via COPR rpm-ostree — the analog.
+Written: `packaging/rpm/punktfunk.spec` (builds the host from source), `packaging/bootc/Containerfile`
+(`FROM bazzite-nvidia`), `packaging/bazzite/host.env` (gamescope default), `packaging/copr/` +
+`packaging/README.md`. The build itself is operator-run (COPR / a Fedora toolbox; not buildable on
+the Ubuntu dev box). `LICENSE-{MIT,APACHE}` added to match the declared dual license.
 
 - **M-Bazzite-1:** a **COPR RPM** (primary) — binary + `60-punktfunk.rules` (→
   `/usr/lib/udev/rules.d`) + systemd `--user` unit + `host.env.example`; `Requires` the
@@ -45,7 +54,7 @@ it's Fedora-atomic and the community installs Sunshine via COPR rpm-ostree — t
 - Flatpak only later as an explicitly-degraded convenience build (sandbox fights
   zero-copy NVENC/dmabuf/uinput).
 
-## 4. Mic passthrough — client mic → host input device *(S+M)*
+## 4. Mic passthrough — client mic → host input device ✅ *(done — host side)*
 
 The exact mirror of the host→client desktop-audio path. A PipeWire virtual source apps can
 select = a `pw_stream` with `Direction::Output` + `media.class=Audio/Source`.
@@ -75,3 +84,15 @@ select = a `pw_stream` with `Direction::Output` + `media.class=Audio/Source`.
 
 PunktfunkKit is already platform-shared; iOS needs the `UIViewRepresentable` presenter twin
 + touch capture (#5) + UI. tvOS later.
+
+## 7. Windows as a host *(scoped & deferred — `docs/windows-host.md`)*
+
+Architecturally an "add a backend" job, not a parallel port: `punktfunk-core` (protocol/FEC/
+crypto/C-ABI) + QUIC + GameStream + mgmt + the `m3`/pipeline orchestration are all platform-agnostic
+and already `cfg`-isolated (~95% reuse). New `#[cfg(windows)]` backends behind the existing traits:
+capture (DXGI Desktop Duplication), encode (Media Foundation / NVENC-SDK with a D3D11 context),
+input (SendInput + ViGEm), audio (WASAPI loopback + a virtual mic). **The blocker** is the
+virtual-display feature — no user-mode Windows API; it needs a signed kernel-mode **IDD** driver
+(XL). Recommended start: **Phase 0** — a "basic Windows host" capturing an existing monitor (no
+virtual display), proving the whole stack with the smallest surface. Deferred because it's large and
+unbuildable on the Linux dev box; the trait boundaries are already in the right places.

docs/windows-host.md

@@ -0,0 +1,68 @@
+# Windows as a host — feasibility & scoping
+
+**Status: scoped, deferred.** A Windows host is architecturally an *"add a backend"* job, not a
+parallel port — but it is a **large** implementation effort across five GPU/driver subsystems, and
+the project's headline feature (a per-client *virtual* output at the client's exact mode) has **no
+user-mode Windows API**: it needs a signed kernel-mode Indirect Display Driver (IDD). This doc
+records what it takes so the work can be picked up deliberately later.
+
+(Grounded in a 4-agent read of the host crate, 2026-06-10.)
+
+## What's already done for us
+
+punktfunk is cleanly layered. **~95% of the codebase is platform-agnostic and reuses verbatim:**
+
+| Reusable as-is | Why |
+|---|---|
+| `punktfunk-core` (protocol, FEC, crypto, session, transport, **C ABI**) | Zero platform deps — no `cfg(linux)` anywhere; the C ABI is already cross-platform |
+| QUIC control plane (`quic.rs`, pairing, mode negotiation) | quinn + tokio are portable |
+| GameStream P1.1 (mDNS, serverinfo, pairing, RTSP, ENet) — *except* `stream.rs`/`audio.rs` | pure wire logic |
+| Management REST API (`mgmt.rs`) + OpenAPI | axum/tokio, portable |
+| Pipeline + `m3.rs` orchestration | trait-generic — calls `capturer.next_frame()`, `encoder.submit/poll()`; **needs zero changes** |
+| The **trait boundaries** themselves: `Capturer`, `Encoder`, `VirtualDisplay`, `InputInjector`, `AudioCapturer`, `VirtualMic` | platform-neutral signatures; Linux deps are already isolated under `[target.'cfg(target_os="linux")'.dependencies]` |
+
+So a Windows host is **new `#[cfg(target_os = "windows")]` backend modules behind the existing
+traits** — the per-frame path, protocol, and control plane don't move. No architectural refactor is
+required; the boundaries are already in the right places.
+
+## What a Windows host needs (new code)
+
+Each row is a Linux backend that needs a Windows sibling. Effort is the *implementation* effort;
+all reuse the existing trait.
+
+| Subsystem | Linux today | Windows equivalent | Effort | Notes |
+|---|---|---|---|---|
+| **Capture** | xdg ScreenCast portal → PipeWire (dmabuf) | **DXGI Desktop Duplication** (or Windows.Graphics.Capture) → D3D11 texture | M | DXGI gives a GPU `B8G8R8A8` texture directly |
+| **Virtual display** | KWin/Mutter/Sway/gamescope protocols | **Indirect Display Driver (IDD)** — kernel UMDF mini-driver | **XL** | ⚠️ **the blocker**: no user-mode API; C++ driver + **code signing** (test-sign or WHQL). Fallback: capture an existing monitor (loses the native-resolution feature) or a borderless window |
+| **Encode** | `ffmpeg-next` NVENC, CUDA hwframes | Media Foundation H.264/HEVC/AV1, **or** NVENC SDK direct with a D3D11 device context (`AVD3D11VADeviceContext`) | M–L | `encode.rs` AU/codec logic + NVENC option strings are portable; only the hwdevice + frame-pool glue swaps |
+| **Zero-copy bridge** | dmabuf → EGL/Vulkan → CUDA | D3D11 texture → NVENC (shared texture / `cudaImportExternalMemory` + D3D12 fence) | M | **optional** — a portable CPU-copy path already exists, so v1 can skip this |
+| **Input (ptr/kbd)** | libei (RemoteDesktop portal) / wlr protocols | **SendInput** (`keybd_event`/`mouse_event`) | S | the VK→evdev table just becomes VK→`VIRTUAL_KEY` (already Win32-native) |
+| **Input (gamepads)** | uinput X-Box-360 pad + FF rumble | **ViGEm** (Virtual Gamepad Emulation) + HID reports | M | rumble back-channel maps to ViGEm notifications |
+| **Audio capture** | PipeWire sink-monitor | **WASAPI loopback** (`IAudioCaptureClient`) | S–M | also produces interleaved f32 — same `AudioCapturer` contract |
+| **Virtual mic** | PipeWire `Audio/Source` | virtual audio device (VB-Cable-style WDM driver) or WASAPI render-to-fake-device | M | needs a driver or a bundled 3rd-party cable |
+| **`sendmmsg` batching** | `gamestream/stream.rs` | already has a `cfg(not(linux))` per-packet fallback | — | nothing to do |
+
+**Rough total: ~2,000–4,000 LOC of new Rust** (+ a C++ IDD driver if the virtual-display feature is
+kept), spread over capture/encode/vdisplay/input/audio. Every reader rated the overall effort
+**large**; the input+audio layer alone is *medium*.
+
+## Recommended phasing (when picked up)
+
+1. **Phase 0 — "basic Windows host" (no virtual display).** Capture an *existing* monitor (DXGI
+   Desktop Duplication) → Media Foundation/NVENC encode → SendInput + WASAPI loopback. This proves
+   the whole stack on Windows with the smallest surface, reusing all of core/QUIC/GameStream/mgmt.
+   It loses the per-client native-resolution output but is a working Windows host quickly.
+2. **Phase 1 — input + audio parity.** ViGEm gamepads + rumble; WASAPI virtual mic; D3D11→NVENC
+   zero-copy.
+3. **Phase 2 — the virtual display (IDD).** The XL piece: a signed Indirect Display Driver that
+   surfaces a client-sized monitor, captured via DXGI. This restores punktfunk's differentiator on
+   Windows. Gated on solving driver signing/distribution.
+
+## Why it's deferred (not started now)
+
+- It's **large**, and the virtual-display blocker (IDD) is a kernel driver + signing problem
+  outside Rust — not "somewhat manageable" as a side effort.
+- None of it is **buildable or testable on the Linux dev box** — it would be unvalidated code.
+
+The architecture is ready whenever the work is scheduled; this doc + the clean trait boundaries are
+the down payment. Start at **Phase 0** for the fastest path to a working Windows host.