Prune commentary and stale Rust port notes

scripts/rigs/gpu-probe/src/bin/teardown.rs

@@ -1,33 +1,3 @@
-//! Why a GPU test segfaults *after* it has passed, and what stops it.
-//!
-//! Measured here 2026-09-08, on this VM's Venus adapter. Destroying the
-//! last `VkInstance` makes the Vulkan loader `dlclose` the ICD; Mesa's
-//! ICD (`/usr/lib/libvulkan_virtio.so`) registers a `pthread_key_create`
-//! destructor pointing into its own text and is not linked `-z nodelete`,
-//! so glibc calls that destructor through unmapped memory when the thread
-//! that used Vulkan exits. libtest runs every `#[test]` on a spawned
-//! thread, which is why it looked like "wgpu crashes on drop": the drop
-//! itself completes, and the crash lands as the thread unwinds.
-//!
-//! The four modes are the experiment, and each is one variable:
-//!
-//! | mode | what it does | 2026-09-08 |
-//! |---|---|---|
-//! | `main` | wgpu instance + device on the main thread, dropped | exits 0 |
-//! | `thread` | the same on a spawned thread | **SIGSEGV** |
-//! | `keep` | the same, but the instance is never dropped | exits 0 |
-//! | `raw` | raw Vulkan (`ash`), instance + device, spawned thread | **SIGSEGV** |
-//!
-//! `raw` is the one that says whose bug it is: no wgpu is involved, so
-//! there is nothing for wgpu or a caller to fix in its drop order. `keep`
-//! is the fix -- hold one `wgpu::Instance` for the process, which is what
-//! wgpu asks for anyway. `iris/tests/mask_sdf.rs` does exactly that.
-//!
-//! `VK_LOADER_DISABLE_DYNAMIC_LIBRARY_UNLOADING=1` also makes every mode
-//! exit cleanly, which is the confirmation that the unload is the
-//! mechanism -- but it is an environment variable every caller would have
-//! to remember, so it belongs in this comment rather than in a script.
-
 use ash::vk;
 use pollster::block_on;
 use wgpu::*;
@@ -42,12 +12,9 @@ fn main() {
         other => panic!("unknown mode {other:?}: main | thread | keep | raw"),
     };
     std::thread::spawn(body).join().expect("the spawned thread");
-    // Not reached when the thread's exit takes the process with it.
     eprintln!("thread joined");
 }
 
-/// A wgpu instance and device, opened and closed. `keep_instance` is the
-/// fix under test: everything else still drops normally.
 fn wgpu_open_and_close(keep_instance: bool) {
     let instance = Instance::default();
     let adapter =
@@ -71,8 +38,6 @@ fn wgpu_open_and_close(keep_instance: bool) {
     eprintln!("wgpu closed");
 }
 
-/// The same shape with no wgpu in it at all, which is what makes this a
-/// loader/driver bug rather than a wgpu one.
 fn raw_vulkan_open_and_close() {
     unsafe {
         let entry = ash::Entry::load().expect("vulkan loader");