docs(architecture): user-data callees; drop code comment

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

core/libs/prx/libSceAgcDriver/Execution/src/Driver/Shaders/ShaderRegistry.cpp

@@ -385,8 +385,6 @@ std::vector<std::uint32_t> ReadUserDataCallee(std::uint64_t address, std::uint32
     throw std::runtime_error("its callee at " + hexText(address) + " does not return within " + std::to_string(limitWords * 4u) + " bytes");
 }
 
-// A compute shader that calls a user-data pointer gets one copy of each callee after its code, read at
-// the address the call's user data holds now; the prepared key follows the linked code.
 std::vector<std::uint32_t> LinkUserDataCallees(const ShaderRecompiler::RecompileRequest& request) {
     if (request.shader.stage != ShaderRecompiler::ShaderStage::Compute) return {};
     const auto code = request.shader.code;

docs/dev/ARCHITECTURE.md

@@ -84,6 +84,7 @@ flowchart LR
 - The shader registry maps a code address to every header registered for that code, in registration order. Static, graphics and rectangle ABI resolution pick the header at the bound address (or one equal to it, `SameHeader`); draws and dispatches pick the program by the stage's binary type (`RegisteredProgram`), and a front entry matching both type 2 and type 4 throws. Within a type the last registration wins; re-registering an identical earlier header makes its snapshot current again without preparing it again, and changed code drops the older headers.
 - The snapshot is published as pending. `SourceHandleFor`, `InvocationFor` and `ShaderPreparationTransaction::Edit` / `Read` wait for the pending job before reading `PreparedShaders`, and rethrow its failure. `APS5_SYNC_SHADER_PREPARE=1` prepares on the registering thread instead.
 - A draw or dispatch whose state matches no artifact prepared at registration (a title that builds its static ABI state itself, without `sceAgcDriverResolve*Abi`) gets one prepared at use by `SourceHandleFor` or `InvocationFor`, logged once per artifact and kept in the snapshot for the next use.
+- A compute shader whose `s_swappc_b64` calls a user-data pointer cannot be linked at registration, because the callee's address is only known at dispatch. `InvocationFor` in [`ShaderRegistry.cpp`](../../core/libs/prx/libSceAgcDriver/Execution/src/Driver/Shaders/ShaderRegistry.cpp) reads each callee from guest memory, appends one copy per call after the caller (`LinkUserDataCalls`) and prepares that linked code, so a different callee gets its own prepared entry.
 - A draw's `Graphics::Pipeline` comes from `CachedPipeline`. When the device has `VK_EXT_graphics_pipeline_library` with fast linking, `VK_EXT_extended_dynamic_state` and `VK_KHR_dynamic_rendering`, draws render with `vkCmdBeginRenderingKHR` instead of render passes and the pipeline is linked from four libraries (vertex input, pre-rasterization shaders, fragment shader, fragment output) kept per device in [`PipelineLibrary.cpp`](../../core/libs/prx/libSceAgcDriver/Graphics/src/PipelineLibrary.cpp). A library built for one pipeline is reused by the next: another blend, vertex layout or target format builds only that part (the shader libraries name no attachment format), and cull mode, front face, depth and stencil state are dynamic, so changing them only links. The fast link is what the draw waits for; a background thread then links the same libraries with link-time optimization and the pipeline binds that one from the next draw on. Push constants then use a 256-byte block with a 128-byte slot per side: the pre-rasterization stages stack from byte 0, the pixel shader always starts at byte 128 (`StagePushOffset`), so its library does not depend on how much push data its vertex shader uses. Pipelines with per-face depth bias, a separate alpha blend into an 8_8 target with the alternate component order (both draw twice), rect lists, geometry shaders or a stage without a variant id are created whole, still with dynamic rendering; devices without the extensions (or with `APS5_NO_GPL=1`) keep render passes and whole pipelines.
 
 ### Shader MODE register access