fix(vdisplay/windows): own the device handle, prove the ladder once, and fix two proofs that were wrong

Three of Phase 5's four items; 5.4 is held for a decision (see below).

`open_device` is a SAFE fn returning an `OwnedHandle`. It never had a caller
obligation — it takes no arguments and every precondition is internal — so the
`unsafe fn` it used to be pushed a proof burden onto four call sites with nothing to
prove, and handed back a raw `HANDLE` that two of them re-owned by hand with
`CloseHandle`. That shape has already leaked once in this file (the wrap-IMMEDIATELY
comment in `open` records it). Ownership is now a `Drop`, `probe()` is
`open_device().map(|_| ())`, `is_available()` is `open_device().is_ok()`, and
`CloseHandle` is no longer imported here at all.

`resolve_target_gdi` ran the same 60 × 50 ms poll three times verbatim, and the 2nd and
3rd copies documented themselves as "SAFETY: as the resolve loop above" — a pointer to
a proof rather than a proof, which rots silently the moment the block it points at
moves. One `poll_gdi_name`, one proof, and the three-stage ladder now reads as the
three stages its doc describes.

Two proofs were simply wrong, both discharged everything except the one obligation
that mattered:

* The SetupAPI detail buffer was a `Vec<u8>` (align 1) written through as
  `SP_DEVICE_INTERFACE_DETAIL_DATA_W` (align 4). The SAFETY comment proved bounds and
  aliasing and was silent on alignment. Now a `Vec<u64>`. Its guard also compared the
  required size against `size_of::<u32>()` while stamping
  `size_of::<SP_DEVICE_INTERFACE_DETAIL_DATA_W>()` into `cbSize` — checking a different
  number than the one it promises the OS.
* `GetMonitorInfoW` was handed `&mut info.monitorInfo`: `cbSize` promises 104 bytes but
  that pointer's provenance covers the 40-byte `MONITORINFO` prefix, so everything the
  OS writes past byte 40 — which is `szDevice`, the only field the caller reads — is out
  of bounds for it. A compiler may assume those bytes were untouched and fold the zeroed
  initializer into the reads, i.e. return an EMPTY device name. That name is what
  `panel_off_except`'s exclusion compares against, so an empty one darkens the panel it
  is meant to spare. The pointer now carries the full struct's provenance.

pf_vdisplay.rs 42 -> 34 `unsafe`, manager.rs 58 -> 56. Windows runner: clippy
--all-targets clean, 48 passed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/pf-vdisplay/src/vdisplay/ddc.rs

@@ -61,10 +61,19 @@ fn active_monitors() -> Vec<ActiveMonitor> {
         let out = unsafe { &mut *(data.0 as *mut Vec<ActiveMonitor>) };
         let mut info = MONITORINFOEXW::default();
         info.monitorInfo.cbSize = std::mem::size_of::<MONITORINFOEXW>() as u32;
-        // SAFETY: `hmon` is the live monitor handle the enumeration just handed us; `info` is a
-        // properly-sized MONITORINFOEXW local whose cbSize is set, which GetMonitorInfoW requires
-        // to safely write the extended (szDevice) variant.
-        if unsafe { GetMonitorInfoW(hmon, &mut info.monitorInfo) }.as_bool() {
+        // The pointer is derived from the WHOLE `MONITORINFOEXW`, not from its `monitorInfo` field.
+        // `cbSize` promises the OS 104 bytes, but `&mut info.monitorInfo` is a pointer to the
+        // 40-byte `MONITORINFO` prefix: everything the OS writes past byte 40 — which is `szDevice`,
+        // the only field this function reads — is then out of bounds for that pointer's provenance.
+        // A compiler is entitled to assume those bytes were untouched and fold the zeroed
+        // initializer into the reads below, i.e. hand back an EMPTY device name. That name is what
+        // `panel_off_except`'s exclusion compares against, so an empty one would darken the very
+        // panel it is meant to spare.
+        let p = (&raw mut info).cast::<windows::Win32::Graphics::Gdi::MONITORINFO>();
+        // SAFETY: `hmon` is the live monitor handle the enumeration just handed us. `p` carries the
+        // provenance of the full `MONITORINFOEXW`, so the OS may write all `cbSize` bytes it was
+        // promised; `info` is a live local that outlives this synchronous call.
+        if unsafe { GetMonitorInfoW(hmon, p) }.as_bool() {
             let len = info
                 .szDevice
                 .iter()

crates/pf-vdisplay/src/vdisplay/windows/manager.rs

@@ -183,6 +183,25 @@ enum ShrinkAction {
 /// snapshot too (from `set_virtual_primary_ccd`), so keying on the snapshot ran the EXCLUSIVE
 /// isolate on a Primary group — clearing `DISPLAYCONFIG_PATH_ACTIVE` on every non-kept path, i.e.
 /// blanking the very physical displays `Primary` exists to keep lit.
+/// One stage of [`ManagerInner::resolve_target_gdi`]'s ladder: poll for the target's GDI name until
+/// the 3 s ceiling. 50 ms sampling (latency plan P0.5) — a typical activation resolves on an early
+/// poll, so finer sampling shaves ~150 ms off every stage crossing.
+///
+/// Extracted because the ladder ran this loop three times verbatim, and the 2nd and 3rd copies
+/// documented themselves as "SAFETY: as the resolve loop above" — a pointer to a proof rather than
+/// a proof, which silently rots the moment the block it points at moves.
+fn poll_gdi_name(target_id: u32) -> Option<String> {
+    for _ in 0..60 {
+        thread::sleep(Duration::from_millis(50));
+        // SAFETY: `resolve_gdi_name` is `unsafe` for its CCD FFI; it takes a plain `Copy` `u32`
+        // target id by value and returns an owned `String`, so no caller memory is borrowed.
+        if let Some(n) = unsafe { resolve_gdi_name(target_id) } {
+            return Some(n);
+        }
+    }
+    None
+}
+
 fn shrink_action(ccd_exclusive: bool, has_saved: bool) -> ShrinkAction {
     if ccd_exclusive {
         ShrinkAction::Reisolate
@@ -1049,32 +1068,19 @@ impl VirtualDisplayManager {
         // structure encodes real failure modes (headless auto-activate, integrated-panel clone,
         // lid-closed path activation) and is untouched — but a typical activation resolves on an
         // early poll, so finer sampling shaves ~150 ms off every stage crossing.
-        for _ in 0..60 {
-            thread::sleep(Duration::from_millis(50));
-            // SAFETY: `resolve_gdi_name` is `unsafe` for its CCD FFI; it takes a plain `Copy` `u32`
-            // target id by value and returns an owned `String`, so no caller memory is borrowed.
-            if let Some(n) = unsafe { resolve_gdi_name(target_id) } {
-                return Some(n);
-            }
+        if let Some(n) = poll_gdi_name(target_id) {
+            return Some(n);
         }
         // SAFETY: `force_extend_topology` only calls `SetDisplayConfig` (CCD) with no borrowed memory.
         unsafe { force_extend_topology() };
-        for _ in 0..60 {
-            thread::sleep(Duration::from_millis(50));
-            // SAFETY: as the resolve loop above.
-            if let Some(n) = unsafe { resolve_gdi_name(target_id) } {
-                return Some(n);
-            }
+        if let Some(n) = poll_gdi_name(target_id) {
+            return Some(n);
         }
         // SAFETY: `activate_target_path` runs the CCD query/apply FFI with owned local buffers; the
         // `Copy` target id is passed by value, under the `state` lock — the sole topology mutator.
         if unsafe { pf_win_display::win_display::activate_target_path(target_id) } {
-            for _ in 0..60 {
-                thread::sleep(Duration::from_millis(50));
-                // SAFETY: as the resolve loops above.
-                if let Some(n) = unsafe { resolve_gdi_name(target_id) } {
-                    return Some(n);
-                }
+            if let Some(n) = poll_gdi_name(target_id) {
+                return Some(n);
             }
         }
         None

crates/pf-vdisplay/src/vdisplay/windows/pf_vdisplay.rs

@@ -29,7 +29,7 @@ use windows::Win32::Devices::DeviceAndDriverInstallation::{
     SetupDiGetDeviceInterfaceDetailW, DIGCF_DEVICEINTERFACE, DIGCF_PRESENT, HDEVINFO, SPINT_ACTIVE,
     SP_DEVICE_INTERFACE_DATA, SP_DEVICE_INTERFACE_DETAIL_DATA_W,
 };
-use windows::Win32::Foundation::{CloseHandle, HANDLE, LUID};
+use windows::Win32::Foundation::{HANDLE, LUID};
 use windows::Win32::Storage::FileSystem::{
     CreateFileW, FILE_FLAGS_AND_ATTRIBUTES, FILE_SHARE_READ, FILE_SHARE_WRITE, OPEN_EXISTING,
 };
@@ -325,7 +325,14 @@ impl Drop for DevInfoList {
     }
 }
 
-unsafe fn open_device() -> Result<HANDLE> {
+/// Open the pf-vdisplay control device.
+///
+/// SAFE, and owning. It has no caller obligation — it takes no arguments and every precondition is
+/// internal — so the `unsafe fn` it used to be pushed a proof burden onto four call sites that had
+/// nothing to prove; two of them then re-established ownership by hand with `CloseHandle`, a shape
+/// this file has already leaked from once (see the wrap-IMMEDIATELY comment in `open`). Returning an
+/// `OwnedHandle` makes the close a `Drop`, so there is exactly one way to get it wrong: not at all.
+fn open_device() -> Result<OwnedHandle> {
     // SAFETY: plain SetupAPI enumeration call; the returned list is solely owned by the RAII wrapper.
     let hdev = DevInfoList(
         unsafe {
@@ -369,14 +376,21 @@ unsafe fn open_device() -> Result<HANDLE> {
         let _ = unsafe {
             SetupDiGetDeviceInterfaceDetailW(hdev.0, &idata, None, 0, Some(&mut required), None)
         };
-        if (required as usize) < size_of::<u32>() {
+        // Against the struct's own size, not `u32`'s: the value stamped into `cbSize` below is
+        // `size_of::<SP_DEVICE_INTERFACE_DETAIL_DATA_W>()`, so that is what the buffer must hold.
+        if (required as usize) < size_of::<SP_DEVICE_INTERFACE_DETAIL_DATA_W>() {
             continue; // sizing failed — never stamp a cbSize through an under-sized buffer
         }
-        let mut buf = vec![0u8; required as usize];
+        // `u64`, not `u8`: this buffer is written through as `SP_DEVICE_INTERFACE_DETAIL_DATA_W`,
+        // which needs 4-byte alignment, and a `Vec<u8>` only promises 1. The old SAFETY comment
+        // proved bounds and aliasing and was silent on alignment — the one obligation the code did
+        // not actually discharge.
+        let mut buf = vec![0u64; (required as usize).div_ceil(size_of::<u64>())];
         let detail = buf.as_mut_ptr() as *mut SP_DEVICE_INTERFACE_DETAIL_DATA_W;
-        // SAFETY: `buf` is `required` bytes (>= 4, checked above), so stamping `cbSize` and letting
-        // the API fill up to `required` bytes stays in bounds; `detail` aliases `buf` only within
-        // this iteration, and the `DevicePath` pointer is read before `buf` is dropped.
+        // SAFETY: `buf` is at least `required` bytes and aligned to 8 (so also to the struct's 4),
+        // so stamping `cbSize` and letting the API fill up to `required` bytes stays in bounds;
+        // `detail` aliases `buf` only within this iteration, and the `DevicePath` pointer is read
+        // before `buf` is dropped.
         let opened = unsafe {
             (*detail).cbSize = size_of::<SP_DEVICE_INTERFACE_DETAIL_DATA_W>() as u32;
             SetupDiGetDeviceInterfaceDetailW(hdev.0, &idata, Some(detail), required, None, None)
@@ -395,7 +409,10 @@ unsafe fn open_device() -> Result<HANDLE> {
                 })
         };
         match opened {
-            Ok(h) => return Ok(h),
+            // SAFETY: `h` is the handle `CreateFileW` just returned to THIS call and nothing else
+            // holds it, so transferring it into the `OwnedHandle` gives it a single owner that
+            // closes it exactly once on drop.
+            Ok(h) => return Ok(unsafe { OwnedHandle::from_raw_handle(h.0 as _) }),
             // A raced-away or wedged device — remember the error, try the next interface.
             Err(e) => last_err = Some(e),
         }
@@ -418,10 +435,7 @@ impl VdisplayDriver for PfVdisplayDriver {
     }
 
     unsafe fn open(&self, reap_orphans: bool) -> Result<(OwnedHandle, u32, u32)> {
-        // SAFETY: `open_device` is `unsafe` only because it issues SetupAPI enumeration + `CreateFileW`
-        // FFI; it takes no arguments and returns an owned raw `HANDLE` (or `Err`). Called here on the
-        // backend-init thread, with no precondition beyond a valid thread context.
-        let device = match unsafe { open_device() } {
+        let device = match open_device() {
             Ok(d) => d,
             Err(first) => {
                 // No openable interface. If a WUDFHost crash left the devnode a hostless zombie
@@ -433,8 +447,7 @@ impl VdisplayDriver for PfVdisplayDriver {
                 let mut reopened = Err(first);
                 for _ in 0..8 {
                     std::thread::sleep(std::time::Duration::from_millis(500));
-                    // SAFETY: as above — plain SetupAPI + CreateFileW FFI, no preconditions.
-                    match unsafe { open_device() } {
+                    match open_device() {
                         Ok(d) => {
                             reopened = Ok(d);
                             break;
@@ -445,11 +458,9 @@ impl VdisplayDriver for PfVdisplayDriver {
                 reopened.context("pf-vdisplay interface still absent after an adapter cycle")?
             }
         };
-        // Wrap IMMEDIATELY: every `?` below must close the device exactly once — the old
-        // wrap-on-success-only shape leaked the raw handle whenever GET_INFO itself failed.
-        // SAFETY: `device` is the valid handle `open_device` just returned; ownership transfers into
-        // the `OwnedHandle` (single owner, `CloseHandle` on drop).
-        let device = unsafe { OwnedHandle::from_raw_handle(device.0 as _) };
+        // `open_device` hands back an `OwnedHandle`, so every `?` below closes the device exactly
+        // once by construction — the shape this used to reach by wrapping the raw handle here, and
+        // which leaked whenever GET_INFO itself failed before that wrap was moved up.
         let raw = HANDLE(device.as_raw_handle());
         // HARD protocol-version check (unlike SudoVDA's best-effort log): a mismatched host/driver pair
         // fails loudly here rather than corrupting the IOCTL stream.
@@ -828,23 +839,13 @@ impl VirtualDisplay for PfVdisplayDisplay {
 
 /// Readiness probe: can we open the pf-vdisplay control device?
 pub fn probe() -> Result<()> {
-    // SAFETY: `open_device` is `unsafe` only for its SetupAPI + `CreateFileW` FFI; no arguments, returns
-    // an owned raw `HANDLE` (or `Err`).
-    let h = unsafe { open_device()? };
-    // SAFETY: `h` is the handle just opened by `open_device` in this function, owned here and not yet
-    // handed anywhere else, so this closes it exactly once — no double-close, no use-after-close.
-    unsafe {
-        let _ = CloseHandle(h);
-    }
-    Ok(())
+    // The handle closes on drop.
+    open_device().map(|_| ())
 }
 
 /// Is the pf-vdisplay driver present (device interface enumerable)?
 pub fn is_available() -> bool {
-    // SAFETY: `open_device` returns an owned raw `HANDLE`; on `Ok(h)` the handle is moved into the
-    // closure (sole owner) and closed exactly once via `CloseHandle`, on `Err` there is nothing to
-    // close — so no double-close and no leak of an opened handle. The `unsafe` covers both FFI calls.
-    unsafe { open_device().map(|h| CloseHandle(h)).is_ok() }
+    open_device().is_ok()
 }
 
 /// [`is_available`], with self-heal: an interface-less driver whose adapter devnode EXISTS is the