docs(architecture): describe settled watched imports of private memory on Windows

Co-Authored-By: Claude <noreply@anthropic.com>

docs/dev/ARCHITECTURE.md

@@ -106,6 +106,7 @@ flowchart LR
 - A draw whose `PA_SC_AA_CONFIG` selects 2, 4 or 8 samples renders into host-only multisampled images. [`MultisampleTarget.cpp`](../../core/libs/prx/libSceAgcDriver/Graphics/src/MultisampleTarget.cpp) keeps one image per device, surface address, format, extent and sample count (`MultisampleTargetView`); the pipeline, render pass and library keys carry `State::samples`, and a multisampled depth target is a multisampled depth surface. The guest sample planes and FMASK are never read or written, so the registry also guards the target's guest range: a CPU read (`GuestMemory::SetReadGuard`), a DMA copy, and a sampled or storage image read of it throw. A `CB_COLOR_CONTROL` resolve mode over a multisampled CB0 runs as a render pass whose resolve attachment is CB1's resident image (`ResolveMultisampleTarget`). A zero fill of the target's CMASK (`NoteColorMetadataFill`, from fill kernels and CP DMA fills) clears the image at its next use.
 - A texture over a depth surface samples the depth image itself when it views one 2D slice of the plane's own format (`DepthSurfaceTexture` in [`DepthSurface.cpp`](../../core/libs/prx/libSceAgcDriver/Graphics/src/DepthSurface.cpp)). A view of several slices (a 2D array or a cube) or an integer view of a D16 plane is served by a `DepthPlaneCopy`, an image the slices are copied into at every use: from the depth surface bound at each slice's address, else from guest memory. Such a texture is never kept in the resource templates (`RefreshedPerUse`).
 - Guest memory reaches the GPU through host imports (`VK_EXT_external_memory_host`) where the driver accepts them, and through copies otherwise ([`GuestBufferMemory.cpp`](../../core/libs/prx/libSceAgcDriver/Graphics/src/GuestBufferMemory.cpp)). A registered range larger than the import window (64 MiB) is imported per window for buffer and fill accesses and whole for an address-based build. Live imports stay under a budget, with the least recently used import retired first (see TechnicalDebt, Host import windows and budget).
+- On Windows, a host import of private `MEM_WRITE_WATCH` memory (singly mapped direct memory) stays on `GetWriteWatch` when `ProbeImportWriteProtection` shows the driver reports nothing written after the second GPU read and a GPU write, and a CPU store is collected (`decideImportWatch`). The driver marks every page of such an import written, asynchronously, until its first GPU use completes, so `settleImport` in [`GuestBufferMemory.cpp`](../../core/libs/prx/libSceAgcDriver/Graphics/src/GuestBufferMemory.cpp) copies 4 bytes out of the new import on a second queue of the graphics family (`Context::settleQueue`, own pool and mutex) inside `ImportWatched`'s window and waits for it; the main queue can't be used there because `importAllocation` holds the imports lock and `GpuMutex` comes before it in the lock order. Imports through a section alias keep tracking on the guest views, and every other Windows host import is compared. `APS5_NO_WATCHED_PRIVATE_IMPORTS=1` creates no second queue and keeps the comparisons.
 
 ### Runtime image and sampler tables