feat(nescapture): open the capture layer

A Vulkan implicit layer that captures frames from inside the workload's own
process and encodes them on the GPU they were drawn on. Fourth and last of this
batch, imported as a tree from `nestrilabs/nescapture` on the same terms.

Filed under `apps/` rather than `crates/` despite building a cdylib. The rule
here is what a thing *is*, not what it compiles to: this is a finished artefact
that gets installed into an image beside its layer manifest, not a library
another crate in this tree depends on. `crates/` is for the latter, and putting
this there would make the distinction useless the first time someone looked.

Wired to the workspace, `nesprotocol` by path. Its description named the
transport component; that reads better as what it actually is — where the frames
go — so it says that instead.

Whole workspace builds and tests: 21 across four members.

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

apps/nescapture/src/instance.rs

@@ -0,0 +1,80 @@
+// ─────────────────────────────────────────────────────────────────────────────
+//  instance.rs — vkCreateInstance and vkDestroyInstance
+// ─────────────────────────────────────────────────────────────────────────────
+
+use crate::dispatch::NextInstanceFn;
+use crate::state::INSTANCE_STATE;
+use crate::{VkLayerInstanceCreateInfo, dispatch_key, find_layer_link, load_instance_fn};
+use ash::vk::{self, Handle};
+use std::os::raw::c_void;
+use std::sync::Arc;
+
+use crate::dispatch::PFN_vkCreateInstance;
+
+const VK_LAYER_LINK_INFO: u32 = 0;
+
+#[unsafe(no_mangle)]
+pub unsafe extern "system" fn vkCreateInstance(
+    p_create_info: *const vk::InstanceCreateInfo,
+    p_allocator: *const vk::AllocationCallbacks,
+    p_instance: *mut vk::Instance,
+) -> vk::Result {
+    crate::init_logger();
+
+    // ── Walk the pNext chain to find the loader's layer link ─────────────────
+    let layer_info: *mut VkLayerInstanceCreateInfo = match unsafe {
+        find_layer_link((*p_create_info).p_next as *const c_void, VK_LAYER_LINK_INFO)
+    } {
+        Some(p) => p,
+        None => return vk::Result::ERROR_INITIALIZATION_FAILED,
+    };
+
+    let layer_link = unsafe { (*layer_info).u.pLayerInfo };
+    let next_gipa = match unsafe { (*layer_link).pfnNextGetInstanceProcAddr } {
+        Some(f) => f,
+        None => return vk::Result::ERROR_INITIALIZATION_FAILED,
+    };
+    // Advance the chain before calling through so the next layer gets its link.
+    unsafe { (*layer_info).u.pLayerInfo = (*layer_link).pNext };
+
+    // ── Call the next layer / loader's vkCreateInstance ──────────────────────
+    let next_create: PFN_vkCreateInstance =
+        unsafe { load_instance_fn(next_gipa, vk::Instance::null(), b"vkCreateInstance\0") };
+
+    let result = unsafe { next_create(p_create_info, p_allocator, p_instance) };
+    if result != vk::Result::SUCCESS {
+        return result;
+    }
+
+    let instance = unsafe { *p_instance };
+    let key = unsafe { dispatch_key(instance.as_raw() as *const c_void) };
+
+    // ── Build and store per-instance dispatch table ───────────────────────────
+    let istate = Arc::new(NextInstanceFn {
+        get_instance_proc_addr: next_gipa,
+        destroy_instance: unsafe { load_instance_fn(next_gipa, instance, b"vkDestroyInstance\0") },
+        get_physical_device_memory_properties: unsafe {
+            load_instance_fn(
+                next_gipa,
+                instance,
+                b"vkGetPhysicalDeviceMemoryProperties\0",
+            )
+        },
+        create_device: unsafe { load_instance_fn(next_gipa, instance, b"vkCreateDevice\0") },
+    });
+
+    INSTANCE_STATE.insert(key, istate);
+    log::debug!("vkCreateInstance OK (enabled={})", crate::enabled());
+    vk::Result::SUCCESS
+}
+
+#[unsafe(no_mangle)]
+pub unsafe extern "system" fn vkDestroyInstance(
+    instance: vk::Instance,
+    p_allocator: *const vk::AllocationCallbacks,
+) {
+    let key = unsafe { dispatch_key(instance.as_raw() as *const c_void) };
+    if let Some((_, state)) = INSTANCE_STATE.remove(&key) {
+        unsafe { (state.destroy_instance)(instance, p_allocator) };
+    }
+}