feat(windows-drivers): pf-vdisplay STEP 2 — IddCx device skeleton

DriverEntry -> driver_add builds the full IDD_CX_CLIENT_CONFIG (14 IddCx callbacks +
PnP EvtDeviceD0Entry, all stubs with correct PFN signatures) sized via the ported
IDD_STRUCTURE_SIZE! (size.rs), runs IddCxDeviceInitConfig -> WdfDeviceCreate ->
WdfDeviceCreateDeviceInterface(the owned pf-vdisplay GUID, not SudoVDA) ->
IddCxDeviceInitialize. callbacks.rs has all 14 + device_d0_entry; query_target_info
implements HIGH_COLOR_SPACE. edid.rs salvaged verbatim from the oracle. proto gains
interface_guid_fields() (u128 -> Windows GUID fields). Links IddCxStub (the CI gate);
adapter/monitor/swapchain/IDD-push fill the stubs in STEP 3-6.

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

packaging/windows/drivers/pf-vdisplay/src/size.rs

@@ -0,0 +1,30 @@
+//! Versioned IddCx struct sizing — the oracle's `IDD_STRUCTURE_SIZE!` ported to wdk-sys.
+//!
+//! IddCx structs are versioned: if the running framework is OLDER than the (1.10) headers we built
+//! against, our locally-compiled struct may be LARGER than the framework understands, so `.Size` must
+//! come from the framework's own size table (`IddStructures[INDEX_<struct>]`), not `size_of`. `None`
+//! means the struct is unusable on this framework. When the framework is at least our version,
+//! `size_of` is correct. (wdk-sys uses ModuleConsts: `_IDDSTRUCTENUM::INDEX_*`, not the oracle's
+//! NewType `.0`.)
+
+use wdk_sys::iddcx;
+
+/// Correct `.Size` for `IDD_CX_CLIENT_CONFIG`, or `None` if it can't be used on this framework.
+#[must_use]
+pub fn idd_cx_client_config_size() -> Option<u32> {
+    // SAFETY: read-only access to the stub-provided framework globals.
+    let higher = unsafe { (&raw const iddcx::IddClientVersionHigherThanFramework).read() } != 0;
+    if !higher {
+        return u32::try_from(core::mem::size_of::<iddcx::IDD_CX_CLIENT_CONFIG>()).ok();
+    }
+    // SAFETY: read-only.
+    let count = unsafe { (&raw const iddcx::IddStructureCount).read() };
+    let index = iddcx::_IDDSTRUCTENUM::INDEX_IDD_CX_CLIENT_CONFIG as u32;
+    if index >= count {
+        return None; // struct cannot be used on this (older) framework
+    }
+    // SAFETY: `IddStructures` is the framework's size table; `index` is validated `< count`.
+    let table = unsafe { (&raw const iddcx::IddStructures).read() };
+    let size = unsafe { table.add(index as usize).read() };
+    u32::try_from(size).ok()
+}