punktfunk/docs/windows-host-rewrite.md

# Windows Host Rewrite — Design & Plan

Status: **proposed** (2026-06-24). This plan takes the current, hard-won Windows host (pf-vdisplay
all-Rust IddCx driver + IDD-push zero-copy capture, live-validated 5120×1440@240 HDR on the RTX box)
as a *knowledge base* and re-derives a clean, stable, well-layered architecture from it. It drops all
SudoVDA back-compat (we own both ends now) and drives `unsafe` to a contained minimum.

It supersedes the stale conclusion in `docs/windows-virtual-display-rust-port.md` ("IDD-push not
viable") — that verdict was written in the *same commit* (`e2c9bfd`) that shipped the working
922-line consumer + 424-line producer. **IDD-push works and is the architecture.** The breakthrough the
prose never recorded: once the CCD topology makes the virtual display the sole composited desktop in the
console session, DWM composites to it and the IddCx swap-chain *is* assigned
(`run_core: FIRST FRAME acquired — DWM IS compositing the virtual display!`). Per the owner, **IDD-push
also captures the secure desktop (Winlogon / UAC / lock)** — so it is the universal primary path, not
just the normal-desktop path.

### Decisions resolved (2026-06-24)

| # | Decision | Chosen |
|---|----------|--------|
| A. Execution | greenfield vs staged | **Greenfield rewrite** — rebuild the Windows host fresh against the clean architecture, salvaging the validated "jewels" (§1) verbatim. (Risk acknowledged: no CI for the Windows paths — mitigated by the §1 preservation checklist + on-glass gates, §10.) |
| B. Capture surface | IDD-only / IDD+secure-DDA / keep fallbacks | **IDD-push primary for everything (incl. the secure desktop); keep WGC + DDA as fallbacks.** |
| C. Driver binding stack | wdf-umdf vs windows-drivers-rs | **Extend `microsoft/windows-drivers-rs`** with an `iddcx` subset; unify all three drivers on it; **solve `/INTEGRITYCHECK` properly** (§6). |
| D. GameStream on Windows | keep / keep-secure-default / drop | **Keep Moonlight compat; flip the installer/service default to secure `serve`** (GameStream an explicit opt-in). |

---

## 0. Goals (from the brief)

1. **Clean, stable, well-layered architecture.** Decompose the god-files, give every subsystem one
   owner, and replace the ~40-knob `PUNKTFUNK_*` env soup with a typed config resolved once per session.
2. **Drop every trace of SudoVDA back-compat.** We own the driver (`pf-vdisplay`) and the host. The
   byte-identical IOCTL ABI, the reused `{e5bcc234}` GUID, the `sudovda` module name, the "SudoVDA
   ignores this" conditionals — all pure liability now.
3. **Minimize `unsafe`.** ~480 `unsafe` occurrences across the Windows surface; the large majority are
   FFI-mechanical (windows-rs/NVENC/WDK already return `Result`). Target: host ~144→~35, drivers
   ~227→~60, with the irreducible floor *contained* in 3–4 named modules under
   `deny(unsafe_op_in_unsafe_fn)`.

### Non-goals / invariants (do not regress)

- **Linux host behavior is out of scope and must not change.** The host crate is shared; Linux is
  validated across KWin/gamescope/Mutter/Sway. Touch only the seams.
- **`punktfunk-core` stays the one linked core.** Protocol/FEC/crypto/QUIC live there behind the C
  ABI; the host is a leaf binary. No protocol changes here.
- **No async on the per-frame path.** Native threads only (the existing discipline).

---

## 1. What we KEEP (validated, load-bearing — port, don't rewrite)

These are expensive empirical wins. The rewrite relocates/wraps them but must preserve behavior
byte-for-byte:

- **The IDD-push frame transport shape**: host-creates / driver-opens shared keyed-mutex texture ring
  with the permissive `D:(A;;GA;;;WD)` SDDL (forced by the restricted WUDFHost token, mirrors the
  gamepad drivers); the generation-tagged `latest = gen<<40 | seq<<8 | slot` stale-ring reject (kills
  the HDR-flip garbage frame); 0 ms try-acquire / drop-on-full publish (never block the swap-chain
  thread); the host output ring `OUT_RING` + `pipeline_depth=2` overlap of convert/copy vs NVENC.
- **The IddCx driver internals that earned their keep**: `edid.rs` in full (128-byte EDID + CTA-861.3
  HDR block, serial-as-index round-trip, dual checksums); the HDR enablement recipe (`CAN_PROCESS_FP16`
  + the `*2` mode DDIs + `set_gamma_ramp`/`set_default_hdr_metadata` accept-stubs + `HIGH_COLOR_SPACE` +
  8|10 bpc); `DEVICE_POOL` one-device-per-render-LUID (the NVIDIA UMD-thread/VRAM leak fix); stamping
  the OS target id onto the monitor context (the recreated-monitor `target_id=0` fix); the swap-chain
  processor's two real leak fixes (borrow `IDXGIDevice` across `SetDevice` retries; check `terminate`
  at the loop top during a frame burst).
- **The monitor-lifecycle concurrency correctness**: serialized ADD/REMOVE/teardown, the documented
  lock order, the watchdog CAS + re-check-under-lock, the creation grace window, the
  generation-stamped lease (a stale lease can't tear down a fresh monitor). *Structure* can change;
  these properties must survive.
- **The CCD topology fixes**: `isolate_displays_ccd` (the iGPU-attached-monitor hybrid-box correctness;
  the `SDC_FORCE_MODE_ENUMERATION` re-commit that drives `COMMIT_MODES → ASSIGN_SWAPCHAIN`); restore
  topology *before* REMOVE.
- **The HDR color math**: `hdr.rs` verbatim (pure, unit-tested, ST.2086 G/B/R + big-endian SEI);
  `HdrConverter`/`HdrP010Converter` + the f64 `p010_reference` + `hdr_p010_selftest`; `VideoConverter`
  (RGB→NV12/P010 on the video engine — a measured latency win); the cursor decomposition
  (`convert_pointer_shape` color/masked/monochrome edge cases).
- **NVENC tuning**: caps-probe-before-configure (disambiguate unsupported-config vs too-high-bitrate;
  10-bit→8-bit graceful downgrade); the bitrate-clamp binary search (finds each GPU's real ceiling);
  true RFI over the DPB; the low-latency configs (CBR, infinite GOP, P-only, ~1-frame VBV).
- **The gamepad driver wins**: the SwDeviceCreate identity recipe (enumerator with no `_`; mandatory
  completion callback; synthesized `USB\VID_054C&PID_0CE6` compat-ids for native-DS5 detection; the
  non-null per-pad `ContainerId` dodging the xinput1_4 slot-skip); one `pf_dualsense` serving
  DualSense+DS4 via a `device_type` byte; XUSB declining `WAIT_*` to force synchronous `GET_STATE`;
  the static HID descriptors/feature blobs; per-pad index via `pszDeviceLocation`.
- **The session-glue patterns**: the `Capturer`/`VirtualDisplay`/`Encoder` trait seam + RAII keepalive
  teardown; host-lifetime shared services (`InjectorService`/`MicService`/`AudioCapSlot`) with
  per-session gamepads; the encode|send thread split + microburst pacing; `build_pipeline_with_retry`
  + permanent-vs-transient classification; the control-task `select!` + adaptive-FEC; the GameStream
  `VideoPacketizer` (GF8 Cauchy, Moonlight byte-exact); the pairing/trust handshake.
- **The SCM supervisor model**: Session-0 LocalSystem supervisor → token-retarget →
  `CreateProcessAsUserW` `serve` into the console session, relaunch-on-session-change, kill-on-close
  Job Object; the file-append log-mask; the two-tier logging init.
- **Build/CI wins**: the `wdf-umdf-sys` build.rs SDK-version resolution (picks the SDK version that
  actually contains `iddcx`, not the max base SDK); the ARM64 cross-compile off the x64 runner; the
  thin-.iss / fat-binary installer delegating to `service install`.

---

## 2. Target architecture

### 2.1 Crate & workspace strategy

**Keep ONE shared `crates/punktfunk-host` crate** (do *not* split `punktfunk-host-windows`). The host is
a leaf binary consumed by nobody; the "one core, linked everywhere" invariant is already satisfied by
`punktfunk-core`. A split would only fork the genuinely-shared session glue, traits, and `hdr.rs`. The
cfg-sprawl win comes instead from confining all Windows code under one `src/windows/` subtree behind a
single `#[cfg(windows)] mod windows;` seam, with backend impls next to their trait's dispatch point.

**Pull the three drivers into ONE in-tree driver workspace** (`packaging/windows/drivers/`) on a single
binding stack, one `rust-toolchain.toml`, one signing recipe, one CI build. Today they are 2–3 disjoint
cargo packages on two incompatible WDK stacks (see §6).

**Add ONE shared `no_std` ABI crate** (`crates/pf-vdisplay-proto`, name TBD) consumed by both the host
crate and the driver workspace. It owns *every* cross-process binary contract that is currently
hand-duplicated with "must match" comments. This is the single highest-value correctness change (§4.1).

### 2.2 Target file tree (host crate)

```
crates/punktfunk-host/src/
  main.rs                  clap-derive subcommand dispatch only (kills parse_serve/parse_spike/hand --help)
  config.rs                HostConfig (typed; parsed ONCE from host.env/env/flags) + config_dir
  session/
    mod.rs                 SessionFactory, SessionPlan, SessionContext, Session (the ONLY teardown path)
    server.rs              QUIC accept loop, handshake, shared-service wiring
    serve_session.rs       resolve_* → Welcome/Start → spawn → RAII teardown
    control.rs             mid-stream renegotiation select! loop
    pipeline.rs            REAL shared encode|send split, send_loop, FrameMsg, pacing (used by native AND GameStream)
  capture.rs               Capturer trait + CapturedFrame/PixelFormat/FramePayload (platform-neutral)
  capture/linux.rs
  capture/windows/         mod.rs (dispatch), idd_push.rs, dda.rs, wgc.rs, secure_desktop.rs*
  vdisplay.rs              VirtualDisplay/VirtualOutput trait + open() dispatch (neutral)
  vdisplay/{kwin,gamescope,mutter,wlroots}.rs
  vdisplay/windows.rs      was sudovda.rs → PfVirtualDisplay + VirtualDisplayManager
  encode.rs                Encoder trait, EncodedFrame, validate_dimensions, open_encoder dispatch
  encode/{linux,vaapi,sw}.rs
  encode/windows/          mod.rs (dispatch), nvenc.rs, nvenc_sys.rs, ffmpeg_win/{mod,system,zerocopy,d3d11va_ffi}.rs
  hdr.rs                   PRESERVE VERBATIM
  inject.rs / inject/linux/* / inject/windows/{mod,sendinput,pad_manager,xusb,dualsense,dualshock4,swdevice,section}.rs
  inject/proto/{dualsense,dualshock4}.rs   shared pure codecs (PRESERVE)
  audio.rs / audio/linux.rs / audio/windows/{mod,wasapi_cap,wasapi_mic}.rs
  windows/                 mod.rs, d3d/{mod,texture,ring,convert}.rs, color/{hdr,p010,video_proc}.rs,
                           cursor.rs, display_ccd.rs, adapter.rs, process.rs (Token/Event/Job/Child/spawn_as_user),
                           service.rs (SCM; uses process.rs), win32u_hook.rs*, gpu_priority.rs
  session_tuning.rs (PRESERVE) / pwinit.rs / discovery.rs / mgmt.rs / native_pairing.rs / library.rs
  gamestream/              unchanged module set; stream.rs slims by reusing session/pipeline.rs
```
`*` = survives only per the secure-desktop / WGC product decisions (§5, §11).

### 2.3 The seam traits (keep the shape; tighten 3 things)

```rust
trait VirtualDisplay: Send {
    fn name(&self) -> &str;
    fn create(&self, mode: Mode) -> Result<VirtualOutput>;
    fn set_launch_command(&self, cmd: Option<String>);   // per-instance, not a global env var
}
struct VirtualOutput {
    node_id: u32,
    preferred_mode: Mode,
    #[cfg(windows)] win_capture: WinCaptureTarget,        // target_id + adapter_luid + monitor_gen (carried, not ambient)
    keepalive: Box<dyn VirtualLease>,
}
trait VirtualLease: Send {                                // Drop = release; replaces the sudovda free-fns + CURRENT_MON_GEN reach-in
    fn set_hdr(&self, on: bool) -> Result<()>;
    fn hdr_enabled(&self) -> bool;
    fn await_released(&self, timeout: Duration) -> bool;
}

trait Capturer: Send {
    fn next_frame(&mut self) -> Result<CapturedFrame>;
    fn try_latest(&mut self) -> Option<CapturedFrame>;
    fn set_active(&mut self, a: bool);
    fn hdr_meta(&self) -> Option<HdrMeta>;
    fn pipeline_depth(&self) -> usize;
}
fn open_capturer(vout: VirtualOutput, want: OutputFormat) -> Result<Box<dyn Capturer>>;  // format+HDR passed IN

trait Encoder: Send {
    fn submit(&mut self, f: &CapturedFrame) -> Result<()>;
    fn poll(&mut self) -> Option<EncodedFrame>;
    fn flush(&mut self);
    fn request_keyframe(&mut self);
    fn caps(&self) -> EncoderCaps;                        // query, don't rely on default no-ops
    fn set_hdr_meta(&mut self, m: Option<HdrMeta>);
    fn invalidate_ref_frames(&mut self, lo: u64, hi: u64) -> bool;
}
fn open_encoder(plan: &EncodePlan) -> Result<Box<dyn Encoder>>;

trait AudioCapturer: Send { fn next_chunk(&mut self) -> Result<Vec<f32>>; fn channels(&self) -> u16; fn drain(&mut self); }
trait VirtualMic:    Send { fn push(&mut self, pcm: &[f32]); fn channels(&self) -> u16; }
trait InputInjector: Send { fn inject(&mut self, e: &InputEvent); }
trait PadManager:    Send { /* handle/apply_rich/pump/heartbeat — Box<dyn PadManager> via select(GamepadPref), replaces the PadBackend enum */ }
```

The three tightenings: (1) `Capturer` takes the desired `OutputFormat` IN — kills the
`capture → encode::windows_resolved_backend()` back-reference that's recomputed in `dxgi.rs`; (2) HDR
control + monitor-release become `VirtualLease` methods so the session glue never names a concrete
backend and contains zero `unsafe`; (3) optional encoder capabilities are queried via `EncoderCaps`.

### 2.4 SessionFactory + typed plan (the single biggest clarity lever)

Today the Windows capture/topology/encoder decision is made by ~40 scattered env reads, recomputed in
THREE places (`capture_virtual_output`, `should_use_helper`, `virtual_stream`) with no single owner and
a latent mirrored-dispatch bug (capture and encode can disagree on the backend). Replace with:

```rust
struct SessionPlan {
    display:  DisplayBackend,
    capture:  CaptureBackend,        // IddPush | Dda | Wgc
    topology: SessionTopology,       // SingleProcess | TwoProcessRelay
    encoder:  EncoderBackend,        // Nvenc | Amf | Qsv | Software
    input_format: OutputFormat,
    bit_depth: u8, hdr: bool, pipeline_depth: usize,
}
struct SessionFactory { cfg: Arc<HostConfig>, vdm: Arc<VirtualDisplayManager>, injector, mic, audio }
impl SessionFactory {
    fn plan(&self, welcome: &Welcome) -> SessionPlan;          // resolves ONCE from HostConfig; no env reads downstream
    fn build(&self, plan: &SessionPlan, ctx: SessionContext) -> Result<Session>;  // owns the RAII chain
}
```

`build()` owns the chain `vdm.lease(mode) → open_capturer(vout, fmt) → open_encoder(plan) → spawn
pipeline`, and `Session::drop` is the only teardown path. This kills the env soup, makes the deployed
path readable, and removes the capture/encode backend-disagreement bug class. It also lets us drop the
12–13-arg `#[allow(too_many_arguments)]` signatures (a `SessionContext` struct) and the dead
`Compositor` ceremony threaded through the Windows path.

### 2.5 Ownership model — delete the global statics

Today the lifecycle is smeared across `IDD_PERSIST` + `open_or_reuse` (dead code), `CURRENT_MON_GEN`
(read per-frame), `IDD_SETUP_LOCK`/`IDD_SESSION_STOP` (the preempt dance), `MGR: Mutex<Mgr>`, and on
the driver side `ADAPTER`/`MONITOR_MODES`/`NEXT_ID`/`WATCHDOG_*`/`DEVICE_POOL`. Replace with:

- A host-lifetime **`VirtualDisplayManager`** owning a *typed* `OwnedHandle` device handle (not a raw
  `isize` smuggled across threads) and the refcounted Idle/Active/Lingering state machine (preserve the
  machine — it's earned).
- A per-session **`MonitorLease`** whose `Drop` releases the refcount; the monitor **generation carried
  through `WinCaptureTarget`** instead of the ambient `CURRENT_MON_GEN`.
- On the driver: **wire `EvtCleanupCallback` for `MonitorContext`** (only `DeviceContext` has it today)
  so the `SwapChainProcessor` + D3D resources drop via WDF RAII — deleting `free_swap_chain_processor`
  and the manual-free-before-departure dance that is the **documented dominant reconnect leak**. Move
  the process-global driver state into the `DeviceContext`; collapse the 3-way monitor identity
  (`MONITOR_MODES` / EDID serial / context stamp) to one `Monitor` owned by the context.

---

## 3. The host↔driver contract (own it; define once)

### 3.1 `pf-vdisplay-proto` (no_std, bytemuck/zerocopy)

One crate, both build graphs (path dep). Owns:

- **Control plane**: a fresh interface GUID; a contiguous, versioned op enum; `#[repr(C)]` request/reply
  structs carrying only used fields.
- **Frame plane**: `SharedHeader`, the `FrameToken { generation, seq, slot }` with `pack`/`unpack`
  (replacing the hand-twiddled `gen<<40|seq<<8|slot` on both sides), the `Global\pfvd-*` name helpers.
- **Gamepad sections**: `XusbShm` (64 B) and `PadShm` (256 B, incl. `device_type`) layouts.
- Derive `FromBytes`/`IntoBytes`/`Pod`; `const` size+offset asserts; round-trip tests. **ABI drift
  becomes a compile error, not a runtime corruption.** (bytemuck is already a dep in the driver +
  wdf-umdf-sys.) This deletes every `OFF_*` constant + `read/write_unaligned` on both sides of every
  boundary — the largest single block of shared-memory `unsafe`, and the top drift hazard.

### 3.2 Control plane — keep DeviceIoControl, redesign the ABI

`DeviceIoControl` is the correct WDF idiom for a driver with no control device and is low-frequency
(ADD/REMOVE per session + a keepalive); the shared-memory pattern buys nothing here. Keep it; redesign
the surface:

- Ops actually needed: `Add(mode, identity) → {luid, target_id}`, `Remove`, `SetRenderAdapter`
  (now **unconditional** — pf-vdisplay honors it for hybrid-GPU IDD-push; drop the SudoVDA-parity
  default-off branch), `ClearAll` (first-class startup orphan reap, not an "ignored by SudoVDA" hack),
  `GetInfo` (a real version handshake), and keepalive (see §3.4).
- Drop the SudoVDA-isms: `AddParams.device_name[14]`/`serial[14]` (ignored), the 16-byte GUID → a
  monotonic `u64` session id (the refcount manager owns collision safety; retires `next_monitor_guid`'s
  pid-mangling), the 4-byte `{major,minor,incr,test}` version tuple → one `u32`, the gappy
  `0x800/0x888/0x8FF` func numbering → contiguous.
- One typed IOCTL dispatch helper retrieves+validates+aligns the buffers and hands the body a safe
  `&Req` / `&mut MaybeUninit<Reply>` — collapses ~20 of `control.rs`'s 29 `unsafe` blocks.

### 3.3 Frame plane — keep the inversion, retire the scaffolding

Keep the host-creates / driver-opens ring exactly. **Remove the bring-up scaffolding** that diagnosed
the now-solved `run_core=0` mystery: the `DebugBlock` channel + `DBG_MAGIC`, `spawn_observer` /
`PUNKTFUNK_IDD_PUSH_OBSERVE`, the `error!`-as-`info!` logging, the intentional handle leak, and the
20 s blind no-frame deadline (replace with the `DRV_STATUS_OPENED` handshake as a bounded liveness
signal).

### 3.4 Driver swap-chain reuse — the one open root cause

Today a *reused* IddCx monitor's swap-chain dies after ~2 sessions (target id resolves to 0, `SetDevice`
fails `0x80070057`, then an access violation), forcing fresh-monitor-per-session + the host-side
preempt/`wait_for_monitor_released` dance + the `IDD_PERSIST` "create once, never recreate" workaround.
The fix is in the **driver**: with `EvtCleanupCallback` wired + state owned by `DeviceContext` + the
identity collapsed to one `Monitor` (the recreate-path bugs are exactly the 3-way identity desync), the
clean recreate should become stable. **If** that holds, delete `IDD_SETUP_LOCK`/`IDD_SESSION_STOP` +
the preempt dance and unblock `max_concurrent>1` on Windows. **If** it can't be fixed cheaply, isolate
the residual serialization inside `VirtualDisplayManager` (not smeared back into the session loop).
Separately, evaluate replacing the polling watchdog (PING/countdown/grace/linger constellation) with a
**WDF file-object `EvtFileClose`** (host holds the control handle open; close = host gone) — feasibility
TBD on UMDF/IddCx.

---

## 4. Capture strategy

**IDD-push is the universal primary path — normal AND secure desktop (Decision B).** It composes
in-process (cross-session via `Global\` shared textures: driver in WUDFHost/Session 0, `serve` in the
console session), needs no DXGI Desktop Duplication and no `win32u` reparenting hook, is live-validated
at 5K@240 HDR, and (per the owner) also captures the secure desktop (Winlogon/UAC/lock). So there is no
separate "secure capturer" in the primary path: the same `IddPushCapturer` spans the lock screen and
UAC. Capture selection moves into a typed `CaptureBackend` in the `SessionPlan` — replacing the 3-way
env branch with `IddPush` (default) → `Dda`/`Wgc` (explicit fallbacks).

**WGC + DDA are kept as fallbacks, not deleted (Decision B).** They cover non-IddCx / pre-pf-vdisplay
hardware and act as a safety net if IDD-push fails to attach. But they are **demoted**: they are no
longer the default, no longer entangled with the secure-desktop mux, and selected only via the explicit
`CaptureBackend` fallback in the plan. This lets the DDA module shed the parts that existed *only* to
make virtual-display-over-DDA survive on a hybrid box, while the genuinely-useful capture/recovery core
stays:
- **Scope the `win32u` self-modifying-code hook + the GPU-pref hook to the DDA fallback leg** (one
  `win32u_hook::install()`), so the primary IDD-push path never touches them. Re-confirm whether DDA
  even needs the `win32u` hook against pf-vdisplay (it may not — open verification item).
- **The two-process WGC relay's secure-desktop mux is retired** — IDD-push handles the secure desktop
  directly, so `desktop_watch.rs` + `composed_flip.rs` + the `virtual_stream_relay` monolith are no
  longer needed for their original purpose. Keep a **minimal** WGC fallback capturer if the WGC backend
  is retained; do not port the 400-line relay state machine. (The cross-session input concern below is
  handled by the `InputInjector`/topology abstraction, not the AU video relay.)

**Shared D3D primitives** move out of `dxgi.rs` (today the de-facto dumping ground that `wgc.rs` and
`idd_push.rs` import from) into `windows/d3d/` (typed `Texture2d`/`Ring`/`CopyResource`/`Map`-as-bytes),
`windows/color/` (the converters + `hdr_p010_selftest` verbatim), and `windows/cursor.rs`. All three
capturers consume them — deletes the duplicated `tex_desc`, cursor, HDR-poll, repeat-last logic.

**The texture-ownership contract becomes type-level.** NVENC encodes the capturer's texture *in place*
(no copy), sound today only because the IDD-push capturer rotates `OUT_RING` and the loop honors
`pipeline_depth()` — an undocumented cross-module coupling that is *already* a latent corruption risk.
Fix: either the encoder always `CopySubresourceRegion`s (as `ffmpeg_win` does), or the capturer hands an
explicitly-leased ring texture with a documented lifetime. No more relying on the synchronous-loop
assumption.

**The IDD-push input question** (must confirm on-glass): capture+encode run in `serve`; input must reach
the *streamed* (console-session) desktop. If `serve` runs in the console session, `SendInput` works
directly. A code comment flags "SendInput from Session 0 can't reach Session 1" — so the architecture
must make `InputInjector` satisfiable either by in-session `SendInput` *or* by a tiny **input-only
Session-1 agent** (re-scope the old WGC helper to input only). The `SessionPlan.topology` expresses
this.

---

## 5. Encode layer

- Resolve backend + input format + pipeline depth **once** into `EncodePlan` and hand it to both the
  capturer and the encoder factory — kill the duplicated `windows_resolved_backend()` call in `dxgi.rs`
  (the highest-severity coupling). Trim `open_video`'s 8-arg grab-bag (`cuda` is always false on
  Windows; `bit_depth` is overridden by the capture format anyway).
- **`nvenc_sys.rs`**: a thin safe wrapper — RAII `NvSession`/`NvBitstream`/`NvRegistration`/
  `NvMappedInput` (Drop = destroy/unregister/unmap) + an `NV_ENC_CONFIG` builder. The public encoder
  then has near-zero `unsafe` and no hand-written teardown loops. (The SDK table already returns
  `Result` via `result_without_string()`.) This is the single biggest encode-side `unsafe` reduction.
- **`ffmpeg_win`**: RAII `AvFrame`/`SwsCtx`/`HwDeviceCtx`/`HwFramesCtx` delete every manual `av_*_free`
  and the error-path cleanup ladders (also the biggest leak-risk reduction); a checked `MappedSurface`
  for the staging readback; a `const` size-assert on the hand-mirrored `AVD3D11VA*` structs in a
  dedicated `d3d11va_ffi` submodule (silent FFmpeg ABI drift is currently undetectable). Keep
  system-readback the default; zero-copy stays opt-in/experimental (no AMD/Intel lab box).
- **HDR symmetry**: make in-band ST.2086/CLL SEI a shared post-encode step so AMF/QSV get the same
  mastering metadata as NVENC (today only NVENC attaches it; AMF/QSV rely solely on the 0xCE datagram).
  Centralize "when does the client learn HDR metadata" in one owner.
- Keep `hdr.rs`, the `Encoder` trait, `EncodedFrame`, `validate_dimensions`, the caps-probe + RFI logic
  verbatim. Delete the `pipeline.rs` `pump_once` doc stub (the real loop is `session/pipeline.rs`).

---

## 6. Drivers — one binding stack (`windows-drivers-rs`), one workspace, one signing recipe

Today: `pf-vdisplay` on the vendored **`wdf-umdf`** stack; `pf_dualsense` + `pf_xusb` on
**`microsoft/windows-drivers-rs`** (`wdk`/`wdk-sys`/`wdk-build`). Two bindgen passes, two SDK
resolutions, two `NTSTATUS`, two build systems, two signing recipes.

**Decision C: unify all three on `microsoft/windows-drivers-rs`** (the official Microsoft stack), in one
in-tree `packaging/windows/drivers/` workspace, edition 2024, one `rust-toolchain.toml`, one CI build.
The gamepad drivers already ship on it; the work is to **migrate `pf-vdisplay` onto it** and **add the
IddCx surface** it lacks today.

**Required pieces of this migration (each a Phase-0/early task):**

1. **Add an `iddcx` subset to `wdk-sys`.** IddCx DDIs are *not* WDF-table functions — they are direct
   `IddCxStub` exports — so the extension is bounded: an `ApiSubset::Iddcx` + `iddcx` feature →
   bindgen `IddCx.h` + link `IddCxStub`, then ~15 thin `extern`/wrapper fns. Use the current
   `wdf-umdf/src/iddcx.rs` (~345 LOC, validated) as a **line-by-line oracle**, including the IddCx 1.10
   `*2` HDR DDIs (`IddCxSwapChainReleaseAndAcquireBuffer2`, `IDARG_*2`, `_METADATA2`).
2. **Solve `/INTEGRITYCHECK` for self-signed loading — properly.** `wdk-build` links the driver with
   `/INTEGRITYCHECK`, which a self-signed cert can't satisfy (CodeIntegrity 3004/3089). Today the
   gamepad drivers hand-patch the FORCE_INTEGRITY PE bit post-link. Replace that hack with a robust
   solution, in order of preference: (a) **override the linker flag** — drop `/INTEGRITYCHECK` via
   `wdk-build` config / `RUSTFLAGS`/`link-args` if it can be suppressed cleanly; else (b) a
   **deterministic, tested CI post-link tool** (a small Rust/PowerShell step that clears bit `0x80` at
   `e_lfanew+0x5e` and re-signs, run in CI, not by hand) so it's reproducible and not a footgun; (c) for
   a public build, real **attestation signing** (Partner Center) satisfies `/INTEGRITYCHECK`
   legitimately. Pick (a) if feasible; (b) as the fleet-self-signed fallback. This is the headline cost
   of choosing this stack and must be nailed in Phase 0.
3. **Backport the `wdf-umdf-sys` build.rs SDK-resolution fix** into `wdk-build` (or a local override):
   resolve `IddCx.h`/`IddCxStub` by the SDK version that *actually contains* `um\x64\iddcx`, not the max
   base SDK (the real failure where a newer base SDK shadows the WDK SDK). windows-drivers-rs's default
   resolution doesn't exercise IddCx today, so this likely needs porting.
4. **Port `pf-vdisplay`'s typed safety wins** onto the new stack: re-create the
   `WDF_DECLARE_CONTEXT_TYPE!` `Arc<RwLock<T>>` context abstraction (the gold-standard contained
   `unsafe`); the version-gate protocol (`IddCxIsFunctionAvailable!` / `IDD_STRUCTURE_SIZE!`); and a
   thin safe wrapper layer so the gamepad drivers stop emitting raw `call_unsafe_wdf_function_binding!`
   everywhere (the biggest driver-`unsafe` lever).

While unifying, also: adopt WDF device contexts for per-pad state (drop the
`UmdfHostProcessSharing=ProcessSharingDisabled`-dependent statics → true multi-pad-per-host); replace
`mem::zeroed()` configs with the `WDF_*_CONFIG_INIT` initializers (kills the recurring zeroed-default
bug class that already caused 3 driver bugs); cache the shm view (RAII `ShmView`) instead of
re-mapping ~125×/s; **delete the world-writable `C:\Users\Public\*.log` driver logging** and the "M0
spike" naming; collapse `is_nt_error()`/`dyn-Any`/`From<()>`-as-error into a typed `IntoDriverResult`;
collapse the per-call dispatch `unsafe` into one generic `dispatch()` helper.

**Provenance note:** confirm where `wdk`/`wdk-sys`/`wdk-build` come from (the gamepad drivers' Cargo.toml
path-deps `../../crates/wdk*` don't exist in this checkout — they resolve inside a windows-drivers-rs
checkout on the dev box). Pin them as crates.io deps or a vendored, version-pinned copy so the driver
workspace builds reproducibly in CI.

---

## 7. Input, audio, service, packaging

- **Input**: consolidate the host-side device plumbing (`create_swdevice`/`create_shm_section`/
  `SwDeviceProfile`) into one `inject/windows/swdevice.rs` used by all three managers (XUSB included,
  which currently re-implements its own). The shm layouts come from `pf-vdisplay-proto`. Re-scope the
  cross-session helper (if any) to input-only.
- **Audio**: small, already fairly clean. Replace the lone `newdev.dll` `LoadLibrary`+`transmute`
  (`wasapi_mic.rs`, the audio runtime's *only* `unsafe`) with the windows-rs `DiInstallDriverW` binding
  (or move provisioning to the installer) → zero `unsafe` in the audio runtime.
- **Service / process**: one `windows/process.rs` owning RAII `Token`/`Event`/`Job`/`Child` + a single
  `spawn_as_user()` used by BOTH the SCM supervisor and any helper — deletes the duplicated
  token-dup/`merged_env_block`/`CreateProcessAsUserW` machinery and ~12 manual `CloseHandle` sites. Add
  a **cooperative stop**: a named stop event the supervisor sets and `serve` waits on, so Stop runs RAII
  teardown (today `TerminateProcess` skips Drop → the virtual monitor lingers, the documented
  stale-monitor gotcha); `TerminateProcess` only as a bounded fallback.
- **Packaging/CI**: keep the thin-.iss / fat-binary model; add a `punktfunk-host web install/uninstall`
  subcommand to absorb the web-setup PowerShell. **Build + sign the unified driver workspace in CI from
  source** (or a CI guard that fails on stale-vendored-DLL / un-bumped DriverVer) so the driver can't
  silently drift from its source. Mint the **fresh pf-vdisplay GUID** coordinated across host + driver +
  INF. Single source of truth for version → build + ISCC AppVersion + INF DriverVer. Investigate
  retiring `nefconc` by creating the ROOT devnode via SwDevice/CM in Rust. Keep the
  devgen-never / nefconc-only and DriverVer-bump gotchas codified.

---

## 8. Unsafe-reduction program (run at port time, not as a separate pass)

- **P0 lints first** (a few lines, before new code): `#![deny(unsafe_op_in_unsafe_fn)]` (host crate has
  none today; the driver workspace already has it), `#![warn(clippy::undocumented_unsafe_blocks)]`,
  `#![warn(clippy::multiple_unsafe_ops_per_block)]`. Generated bindings keep their opt-out.
- **P0 std handle ownership**: `std::os::windows::io::OwnedHandle` / `std::fs::File::from_raw_handle`
  everywhere a raw `HANDLE`/`isize` is held (events/jobs/tokens/sections/pipes). Used in **zero** host
  files today — the single biggest cheap win. Deletes the bespoke `unsafe impl Read/Write/Drop`
  (`HandleReader`), the never-closed sudovda control handle, the `AtomicIsize` HANDLE globals, ~6 manual
  `CloseHandle` sites — and fixes real leaks.
- **P0 the proto crate** (§3.1) — kills the shared-memory pointer-cast `unsafe`.
- **P1 typed wrappers**: `windows/d3d/` (most COM calls already return `Result`; per-frame loop bodies
  become `unsafe`-free, the irreducible keyed-mutex/`from_raw_parts` lands in one `frame_xfer` fn);
  `nvenc_sys` + RAII ffmpeg (§5); one `windows/process.rs` (§7); collapse the 21 `unsafe impl Send`
  onto one audited `SendPtr<T>`/`ThreadBound<T>` (directly de-risks the NVENC in-place coupling).
- **P2 contain the irreducible**: `win32u_hook.rs` (one `install()`; scope to secure-DDA or drop),
  `gpu_priority.rs` (the D3DKMT transmute), the WDF context-blob macro, the IddCx swap-chain DDI +
  `from_raw_borrowed` (wrap in a typed `SwapChain` guard returning a borrowed `AcquiredSurface<'_>`).
  Document a `// SAFETY:` per residual site.
- **P2 delete `unsafe` by deleting code**: the `present_trigger` dead diagnostic, the `DebugBlock`
  channel, `spawn_observer`, `IDD_PERSIST`/`open_or_reuse`, `helpers.rs Sendable<T>`, the WGC-open
  thread-watchdog hack (gone with WGC), the driver file-logging.

Estimated: host ~144→~35, drivers ~227→~60, residual concentrated and auditable. (`#![forbid(unsafe)]`
is impossible for the drivers and the per-frame D3D path — the realistic target is *containment*.)

---

## 9. SudoVDA decoupling (mechanical rename + scrub)

`vdisplay/sudovda.rs` → `vdisplay/windows.rs`; `SudoVdaDisplay` → `PfVirtualDisplay`; scrub "SudoVDA"
from all log/error/doc strings across `capture.rs`/`dxgi.rs`/`wgc*.rs`/`idd_push.rs`/`punktfunk1.rs`/
`main.rs`/`sendinput.rs` (141 refs / 15 files). **Split the reach-in helpers out** of the vdisplay
backend (they're display-utility, not virtual-display creation): `set_advanced_color`,
`advanced_color_enabled`, `resolve_gdi_name`, `isolate/restore_displays_ccd`, `set_active_mode` →
`windows/display_ccd.rs` (collapsing the 4× copy-pasted `QueryDisplayConfig` preamble into one safe
`query_active_config()`); `resolve_render_adapter_luid` → `windows/adapter.rs`. Both vdisplay and
capture then depend on these as peers, breaking the circular reach-in. `WinCaptureTarget` moves to a
neutral location (defined in `dxgi.rs`, constructed in `sudovda.rs` today). Drop the dual-driver
fallback conditionals. Expose HDR/monitor-release as `VirtualLease` methods (zero `unsafe` in the
session glue).

---

## 10. Build plan (greenfield — Decision A)

A from-scratch rebuild of the Windows host against the clean architecture, **salvaging the §1 jewels
verbatim** (the already-clean, already-tested modules: `hdr.rs`, `edid.rs`, the `inject/proto` codecs,
the HDR/cursor converters + their self-tests, the GF8 packetizer, the pairing handshake). The old
Windows code stays in-tree, untouched, as the *reference implementation* until the new path reaches
parity on glass, then is deleted.

**Greenfield-risk mitigation (the survey's strong caveat stands):** almost none of this is
CI-validatable — the Windows backends + drivers need the RTX box (192.168.1.173) + the build VM, and
**AMF/QSV have no lab hardware at all**. A greenfield rewrite therefore carries real risk of silently
dropping a layered bug-fix. Two guardrails are mandatory:
1. **The §1 preservation checklist is a test/assert contract**, not prose: each rebuilt module ports its
   hard-won invariants as unit tests or runtime asserts — RAII teardown order (restore displays *before*
   REMOVE), keyed-mutex held only across convert/copy, `terminate` checked at the swap-chain loop top,
   magic stamped last, `OUT_RING` texture rotation under `pipeline_depth>1`, the NVENC caps-probe
   downgrade, the SwDeviceCreate identity recipe. A rebuild that drops one fails its own test.
2. **On-glass A/B gates** at each milestone below, on the RTX box, against the current shipping build:
   1080p60, 5K@240 HDR, reconnect-storm, secure desktop (lock/UAC), multi-pad. Nothing replaces the old
   path until its A/B passes.

### Build order

- **M0 — Foundations + the `/INTEGRITYCHECK` answer.** Stand up `crates/pf-vdisplay-proto` (the clean,
  owned ABI: fresh GUID, the redesigned IOCTL op enum + `#[repr(C)]` structs, `SharedHeader`,
  `FrameToken`, the gamepad shm layouts, `const` size-asserts, round-trip tests). Stand up the in-tree
  `packaging/windows/drivers/` workspace on `windows-drivers-rs` and **prove the two hard unknowns**:
  (a) the `iddcx` `wdk-sys` subset bindgen+links and a trivial IddCx adapter loads; (b) `/INTEGRITYCHECK`
  is solved (§6.2) so a self-signed driver loads under Secure Boot with no hand-patching. Add the P0
  lints to the host crate. *No host behavior yet.*
- **M1 — pf-vdisplay on the new stack, first light.** Rebuild the IddCx driver against
  `windows-drivers-rs`+`iddcx`, clean from the start: `DeviceContext`-owned state (no process-globals),
  one `Monitor` identity, `EvtCleanupCallback` on `MonitorContext`, the ported `Arc<RwLock<T>>` context,
  the EDID + HDR recipe verbatim, the redesigned control plane from the proto crate. *(On-glass: ADD →
  monitor arrives → IDD-push ring attaches → frames flow at 1080p; REMOVE clean.)*
- **M2 — IDD-push capture + NVENC, glass-to-glass.** New `src/windows/` tree: `windows/d3d/` typed
  wrappers, `windows/color/` (converters + self-tests), `windows/cursor.rs`, `capture/windows/idd_push.rs`
  consuming the proto ring with a **type-level texture-ownership contract** (no in-place-encode
  assumption), `encode/windows/{nvenc.rs,nvenc_sys.rs}`, `vdisplay/windows.rs` + `windows/display_ccd.rs`
  + `windows/adapter.rs`. Wire the `SessionFactory`/`SessionPlan` (M2 only needs the IDD-push+NVENC
  plan). *(On-glass A/B: 1080p60 + 5K@240 HDR, latency parity with the current build.)*
- **M3 — Service, input, audio, secure desktop.** `windows/process.rs` (RAII Token/Event/Job/Child +
  `spawn_as_user` + cooperative stop) + `windows/service.rs`; `inject/windows/*` on the proto shm +
  consolidated `swdevice.rs`; `audio/windows/*` (zero-`unsafe` runtime). Confirm IDD-push captures the
  secure desktop (lock/UAC) and input reaches the streamed session (in-session `SendInput`, or the
  input-only agent if needed). *(On-glass: full session incl. lock screen + UAC + a real pad.)*
- **M4 — Gamepad drivers onto the unified stack.** Rebuild `pf_dualsense` + `pf_xusb` on
  `windows-drivers-rs` in the same workspace, WDF device contexts (true multi-pad), proto shm,
  `WDF_*_CONFIG_INIT`, no file logging, no "M0 spike" naming. *(On-glass: 2 XInput + 2 DualSense pads,
  rumble/lightbar/adaptive-trigger round-trip.)*
- **M5 — Fallbacks + GameStream + AMF/QSV.** Port the demoted WGC + DDA fallback capturers (minimal,
  `win32u` hook scoped to the DDA leg); `encode/windows/ffmpeg_win/*` with RAII FFmpeg + the
  `d3d11va_ffi` size-assert (system-readback default; zero-copy experimental); GameStream planes reusing
  `session/pipeline.rs`, installer default flipped to secure `serve`. *(On-glass: Moonlight client on
  the DDA fallback; AMF/QSV stays CI-only.)*
- **M6 — Cut over + delete.** Flip the default to the new path, run the full A/B matrix, then delete the
  old `dxgi.rs`/`wgc*`/`sudovda.rs`/`punktfunk1.rs` Windows monoliths + the bring-up scaffolding
  (`DebugBlock`/`spawn_observer`/observe gate) + the old gamepad driver crates. Single source of truth
  for version; CI builds+signs all drivers from source.

Milestones are roughly dependency-ordered; M0 is the long pole (the `/INTEGRITYCHECK` + `iddcx` proof
gates everything else). M5's AMF/QSV cannot be validated without hardware — keep it system-readback-only
and clearly experimental.

---

## 11. Decisions (resolved 2026-06-24) + open verification items

The five product forks are decided (see the table in §0): **A** greenfield; **B** IDD-push primary for
everything incl. secure desktop, WGC+DDA kept as demoted fallbacks; **C** extend `windows-drivers-rs` +
solve `/INTEGRITYCHECK`; **D** keep GameStream, default secure. On **E (concurrent sessions)**: fix the
driver swap-chain lifecycle regardless (it removes the leak + the preempt dance); treat true
`max_concurrent>1` on Windows as a follow-on once clean reuse is proven on glass.

What remains are **technical unknowns to confirm on the RTX box** (not user decisions):

- **`/INTEGRITYCHECK` resolution path (M0 long pole).** Can `wdk-build` suppress `/INTEGRITYCHECK` via
  config/link-args (preferred), or must we keep a deterministic CI post-link bit-clear? Decides the
  signing story for all three drivers.
- **`iddcx` subset on `wdk-sys`.** Does the bindgen+`IddCxStub` link cleanly, and does the SDK-resolution
  fix need backporting? (windows-drivers-rs doesn't exercise IddCx today.)
- **Driver swap-chain reuse.** Does the clean ownership model (`EvtCleanupCallback` + DeviceContext state
  + single `Monitor` identity) actually fix the "reused swap-chain dies after ~2 sessions" root cause? If
  not, the residual serialization stays inside `VirtualDisplayManager`.
- **IDD-push input + secure desktop.** Confirm `serve` runs in the console session so `SendInput` reaches
  the streamed desktop (a code comment warns about Session 0→1); confirm IDD-push frames flow through the
  lock screen / UAC (owner reports yes — verify and lock it in as the primary, demoting the DDA secure
  leg to fallback).
- **Does the demoted DDA fallback still need the `win32u` hook** against pf-vdisplay, or was that purely
  a SudoVDA/hybrid pathology? If unneeded, the self-modifying-code hook can be deleted entirely.
- **AMF/QSV** stays CI-only (no hardware) — system-readback default, zero-copy experimental.

---

## 12. Risks

- **Greenfield with no CI (the dominant risk).** The build VM is headless/WARP; the WinUI/hardware/driver
  paths need the RTX box, and AMF/QSV have no hardware. A from-scratch rebuild can silently drop a
  layered bug-fix. Mitigation: the §1 preservation checklist is a *test/assert contract* per rebuilt
  module; on-glass A/B gates the new path before the old one is deleted (M6); keep the old code in-tree
  as the reference until parity.
- **`/INTEGRITYCHECK` (M0 long pole).** Choosing `windows-drivers-rs` means self-signed loading depends
  on solving it cleanly (§6.2). If neither linker-flag suppression nor a deterministic CI post-link step
  works, drivers can't load self-signed — prove this first, it gates everything.
- **`iddcx` on `wdk-sys`** is new surface (windows-drivers-rs doesn't bind IddCx). Bounded
  (`IddCxStub` exports + ~15 wrappers, with the validated `wdf-umdf/iddcx.rs` as oracle) but unproven on
  this stack — M0 must light it.
- **`pf-vdisplay-proto` spans two cargo build graphs** (host workspace + the driver workspace). Validate
  the path-dep resolves on the Windows build env in M0; pin `wdk*` provenance so the driver workspace
  builds reproducibly in CI.
- **Driver swap-chain-reuse root cause still undiagnosed.** The clean ownership model *should* fix it;
  if not, residual serialization stays inside `VirtualDisplayManager` and `max_concurrent>1` stays
  blocked. Keep `await_released` on the trait until reuse is proven on glass.
- **NVENC in-place encode + `pipeline_depth>1`** is a latent corruption risk; the M2 texture-ownership
  contract must be type-level (not the synchronous-loop assumption). Verify the ring on glass.
- **Host/driver version drift in the field.** New host + new driver are always built together (greenfield),
  but the installer bundles both — enforce a startup version handshake (proto version in both binaries)
  and a CI guarantee they're built from the same revision.
- **Big-bang cutover (M6).** Flipping the default and deleting the old monoliths is the riskiest moment;
  it is gated on the full A/B matrix passing, and the old code is recoverable from git if a regression
  surfaces post-cutover.

---

## 13. Progress log + M1 IddCx-binding recipe (2026-06-24)

**M0 COMPLETE** (commits through `f896f70`, on `main`, CI-green + validated on the RTX box):
- `crates/pf-vdisplay-proto` — owned host↔driver ABI (fresh GUID, typed IOCTLs + frame transport, const
  size-asserts). Green Linux + MSVC.
- Runner **and** RTX box provisioned: WDK 26100 (WDF 2.31, IddCx 1.10), LLVM **21.1.2** (the runner's
  default was a ToT/22-dev build → wdk-sys bindgen `E0080` layout-test overflow; 21.1.2 builds clean —
  windows-drivers-rs discussion #591). cargo-wdk on the runner.
- `packaging/windows/drivers/` — unified driver workspace on windows-drivers-rs; `wdk-probe` (minimal
  UMDF) builds clean end-to-end (bindgen + WDF link + static-CRT `.cargo/config` + `pf-vdisplay-proto`
  path-dep). Build layers solved: in-tree target dir (wdk-build walks OUT_DIR ancestors for `Cargo.lock`);
  `[workspace.metadata.wdk.driver-model]` = UMDF 2.31; `target-feature=+crt-static` w/ explicit target;
  `Version_Number=10.0.26100.0`; `LIBCLANG_PATH` → LLVM 21.1.2.
- **`/INTEGRITYCHECK` resolved**: wdk-build sets it unconditionally (no opt-out) → `packaging/windows/
  clear-force-integrity.ps1` clears the PE `FORCE_INTEGRITY` bit (0x0080 @ e_lfanew+0x5e) post-link,
  before signing. Proven `0x01E0→0x0160` on CI and in PS 5.1 on the box. Self-signed UMDF load itself is
  already proven on the box (the gamepad drivers).

**RTX box** (`ssh "Enrico Bühler"@192.168.1.173`, ENRICOS-DESKTOP, RTX 4090 driver 610.62, PS 5.1 shell):
**ephemeral** — boots to Proxmox on reboot, so unreachable after a reboot. Treat as opportunistic on-glass
(driver load + IDD-push streaming) only; **CI on the windows-amd64 runner is the persistent validator**.
A build clone is at `C:\Users\Public\pf-rewrite`; builds the driver in ~29 s with the box's LLVM 21.1.2.

### M1 — IddCx binding on windows-drivers-rs (the recipe)

IddCx DDIs are **function-table dispatched** (`IddFunctions[]` indexed by `IDDFUNCENUM::<Name>TableIndex`,
`IddDriverGlobals` implicit first arg) — *exactly* the model wdk-sys already implements for WDF (not direct
`IddCxStub` exports as first assumed).

**Approach (Option 1, recommended):** vendor windows-drivers-rs **0.5.1** in-tree (pinned; source staged at
`scratchpad/wdr`, commit `0e3499d`), patched via `[patch.crates-io]` for just `wdk-build` + `wdk-sys`, and
add a first-class **`ApiSubset::Iddcx`** that bindgens `iddcx/1.10/IddCx.h` in an extra pass **reusing the
identical `bindgen::Builder::wdk_default(config)` baseline** (so its WDF/DXGI types *resolve to*, not
redefine, wdk-sys's — type identity by construction). This mirrors wdk-sys's existing gpio/hid/spb/usb
versioned-subpath subsets exactly.
- wdk-build: add `ApiSubset::Iddcx`, a `headers` match arm, `iddcx_headers() -> ["iddcx/1.10/IddCx.h"]`
  (UMDF-only).
- wdk-sys build.rs: `generate_iddcx` as a copy of `generate_gpio` — `bindgen_header_contents([Base, Wdf,
  Iddcx])`, `(TYPES|VARS).complement()`, `.allowlist_file("(?i).*iddcx.*")`; behind an `iddcx` feature;
  add to `ENABLED_API_SUBSETS`; `pub mod iddcx` in lib.rs.
- A `wdk-iddcx` wrapper crate (port of `wdf-umdf/src/iddcx.rs`): table dispatch via
  `wdk_sys::iddcx::_IDDFUNCENUM::<Name>TableIndex as usize` (ModuleConsts const, **not** the oracle's
  NewType `.0`); NTSTATUS is plain `i32` in wdk-sys (use `wdk_sys::NT_SUCCESS`, drop the oracle's newtype).
- Driver build.rs: add `link-search` to `Lib/<sdk>/um/<arch>/iddcx/1.10` (the SDK version that *contains*
  iddcx — glob, don't trust max) + `static=IddCxStub`; hand-declare `#[no_mangle] pub static
  IddMinimumVersionRequired: ULONG = 4;`; keep the FORCE_INTEGRITY clear.

**Make-or-break (the spike to run FIRST):** can `IddCx.h` bindgen in wdk-sys's config without a header
conflict? (upstream #514/#516; clean-fix PR #654 is **unmerged**.) Validate by adding the subset + an
`iddcx-probe` that calls `IddCxDeviceInitConfig`/`IddCxDeviceInitialize`/`IddCxAdapterInitAsync` →
**CI gate**: cdylib compiles + links IddCxStub. **On-glass gate (RTX box)**: self-signed driver loads +
the IddCx adapter initializes (runtime table/struct-index correctness only surfaces here). Possible gotcha:
IddCx.h may need an `IDD_STUB` preprocessor define to emit the table model (the oracle's wrapper.h set it).

**Fallback** if the bindgen header-conflict can't be resolved: keep the proven vendored unified
`wdf-umdf-sys` as a second `-sys` crate for `pf-vdisplay` only (a second stack, contra Decision C, but
already green + on-glass-proven) and track upstream #654. **Reject** Option 2 (standalone `iddcx-sys` +
`use wdk_sys::*` + giant WDF/DXGI blocklist) — version-fragile, structs embed WDF/DXGI by value.

Only after the spike passes: port the full ~30-DDI / ~40-struct surface (incl. the HDR `*2` DDIs) + the
swap-chain processor + frame transport, with the clean ownership model (DeviceContext-owned state,
`EvtCleanupCallback` on `MonitorContext`, single `Monitor` identity, the owned `pf-vdisplay-proto` plane).