feat: migrate from Cedar to SpiceDB authorization system

This is a major architectural change that replaces the Cedar policy-based
authorization system with SpiceDB's relation-based authorization.

Key changes:

- Migrate from Rust to Go implementation
- Replace Cedar policies with SpiceDB schema and relationships
- Switch from envoy `ext_authz` with Cedar to SpiceDB permission checks
- Update build system and dependencies for Go ecosystem
- Maintain Envoy integration for external authorization

This change enables more flexible permission modeling through SpiceDB's
Google Zanzibar inspired relation-based system, supporting complex
hierarchical permissions that were difficult to express in Cedar.

Breaking change: Existing Cedar policies and Rust-based configuration
will no longer work and need to be migrated to SpiceDB schema.

11 files changed, 0 insertions, 572 deletions

diff --git a/vendor/stacker/src/alloc_stack_restore_guard.rs b/vendor/stacker/src/alloc_stack_restore_guard.rs
deleted file mode 100644
index ef2babb7..00000000
--- a/vendor/stacker/src/alloc_stack_restore_guard.rs
+++ /dev/null
@@ -1,47 +0,0 @@
-use crate::{get_stack_limit, set_stack_limit};
-
-pub struct StackRestoreGuard {
-    new_stack: *mut u8,
-    stack_bytes: usize,
-    old_stack_limit: Option<usize>,
-}
-
-const ALIGNMENT: usize = 16;
-
-impl StackRestoreGuard {
-    pub fn new(stack_bytes: usize) -> StackRestoreGuard {
-        // On these platforms we do not use stack guards. this is very unfortunate,
-        // but there is not much we can do about it without OS support.
-        // We simply allocate the requested size from the global allocator with a suitable
-        // alignment.
-        let stack_bytes = stack_bytes
-            .checked_add(ALIGNMENT - 1)
-            .expect("unreasonably large stack requested")
-            / ALIGNMENT
-            * ALIGNMENT;
-        let layout = std::alloc::Layout::from_size_align(stack_bytes, ALIGNMENT).unwrap();
-        let ptr = unsafe { std::alloc::alloc(layout) };
-        assert!(!ptr.is_null(), "unable to allocate stack");
-        StackRestoreGuard {
-            new_stack: ptr,
-            stack_bytes,
-            old_stack_limit: get_stack_limit(),
-        }
-    }
-
-    pub fn stack_area(&self) -> (*mut u8, usize) {
-        (self.new_stack, self.stack_bytes)
-    }
-}
-
-impl Drop for StackRestoreGuard {
-    fn drop(&mut self) {
-        unsafe {
-            std::alloc::dealloc(
-                self.new_stack,
-                std::alloc::Layout::from_size_align_unchecked(self.stack_bytes, ALIGNMENT),
-            );
-        }
-        set_stack_limit(self.old_stack_limit);
-    }
-}
diff --git a/vendor/stacker/src/arch/asm.h b/vendor/stacker/src/arch/asm.h
deleted file mode 100644
index 56c9d289..00000000
--- a/vendor/stacker/src/arch/asm.h
+++ /dev/null
@@ -1,5 +0,0 @@
-#if defined(APPLE) || (defined(WINDOWS) && defined(X86))
-#define GLOBAL(name) .globl _ ## name; _ ## name
-#else
-#define GLOBAL(name) .globl name; name
-#endif
diff --git a/vendor/stacker/src/arch/windows.c b/vendor/stacker/src/arch/windows.c
deleted file mode 100644
index 89485a0c..00000000
--- a/vendor/stacker/src/arch/windows.c
+++ /dev/null
@@ -1,5 +0,0 @@
-#include <windows.h>

-

-PVOID __stacker_get_current_fiber() {

-    return GetCurrentFiber();

-}

diff --git a/vendor/stacker/src/backends/fallback.rs b/vendor/stacker/src/backends/fallback.rs
deleted file mode 100644
index a812cbc9..00000000
--- a/vendor/stacker/src/backends/fallback.rs
+++ /dev/null
@@ -1,4 +0,0 @@
-#[inline(always)]
-pub unsafe fn guess_os_stack_limit() -> Option<usize> {
-    None
-}
diff --git a/vendor/stacker/src/backends/macos.rs b/vendor/stacker/src/backends/macos.rs
deleted file mode 100644
index 42b28516..00000000
--- a/vendor/stacker/src/backends/macos.rs
+++ /dev/null
@@ -1,6 +0,0 @@
-pub unsafe fn guess_os_stack_limit() -> Option<usize> {
-    Some(
-        libc::pthread_get_stackaddr_np(libc::pthread_self()) as usize
-            - libc::pthread_get_stacksize_np(libc::pthread_self()) as usize,
-    )
-}
diff --git a/vendor/stacker/src/backends/mod.rs b/vendor/stacker/src/backends/mod.rs
deleted file mode 100644
index 8da895d6..00000000
--- a/vendor/stacker/src/backends/mod.rs
+++ /dev/null
@@ -1,28 +0,0 @@
-cfg_if! {
-    if #[cfg(miri)] {
-        mod fallback;
-        pub use fallback::guess_os_stack_limit;
-    } else if #[cfg(windows)] {
-        pub(crate) mod windows;
-        pub use windows::guess_os_stack_limit;
-    } else if #[cfg(any(
-        target_os = "linux",
-        target_os = "solaris",
-        target_os = "netbsd",
-        target_os = "freebsd",
-        target_os = "dragonfly",
-        target_os = "illumos"
-    ))] {
-        mod unix;
-        pub use unix::guess_os_stack_limit;
-    } else if #[cfg(target_os = "openbsd")] {
-        mod openbsd;
-        pub use openbsd::guess_os_stack_limit;
-    } else if #[cfg(target_os = "macos")] {
-        mod macos;
-        pub use macos::guess_os_stack_limit;
-    } else {
-        mod fallback;
-        pub use fallback::guess_os_stack_limit;
-    }
-}
diff --git a/vendor/stacker/src/backends/openbsd.rs b/vendor/stacker/src/backends/openbsd.rs
deleted file mode 100644
index ee582d84..00000000
--- a/vendor/stacker/src/backends/openbsd.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-pub unsafe fn guess_os_stack_limit() -> Option<usize> {
-    let mut stackinfo = std::mem::MaybeUninit::<libc::stack_t>::uninit();
-    let res = libc::pthread_stackseg_np(libc::pthread_self(), stackinfo.as_mut_ptr());
-    if res != 0 {
-        return None;
-    }
-    let stackinfo = stackinfo.assume_init();
-    Some(stackinfo.ss_sp as usize - stackinfo.ss_size)
-}
diff --git a/vendor/stacker/src/backends/unix.rs b/vendor/stacker/src/backends/unix.rs
deleted file mode 100644
index 97ef209f..00000000
--- a/vendor/stacker/src/backends/unix.rs
+++ /dev/null
@@ -1,40 +0,0 @@
-#[cfg(any(target_os = "freebsd", target_os = "dragonfly", target_os = "illumos"))]
-use libc::pthread_attr_get_np as get_attr;
-#[cfg(any(target_os = "linux", target_os = "solaris", target_os = "netbsd"))]
-use libc::pthread_getattr_np as get_attr;
-
-pub unsafe fn guess_os_stack_limit() -> Option<usize> {
-    let mut attr = PthreadAttr::new()?;
-    (get_attr(libc::pthread_self(), &mut attr.0) == 0).then_some(())?;
-    let mut stackaddr = std::ptr::null_mut();
-    let mut stacksize = 0;
-    (libc::pthread_attr_getstack(&attr.0, &mut stackaddr, &mut stacksize) == 0).then_some(())?;
-    Some(stackaddr as usize)
-}
-
-struct PthreadAttr(libc::pthread_attr_t);
-
-impl Drop for PthreadAttr {
-    fn drop(&mut self) {
-        unsafe {
-            let ret = libc::pthread_attr_destroy(&mut self.0);
-            if ret != 0 {
-                let err = std::io::Error::last_os_error();
-                panic!(
-                    "pthread_attr_destroy failed with error code {}: {}",
-                    ret, err
-                );
-            }
-        }
-    }
-}
-
-impl PthreadAttr {
-    unsafe fn new() -> Option<Self> {
-        let mut attr = std::mem::MaybeUninit::<libc::pthread_attr_t>::uninit();
-        if libc::pthread_attr_init(attr.as_mut_ptr()) != 0 {
-            return None;
-        }
-        Some(PthreadAttr(attr.assume_init()))
-    }
-}
diff --git a/vendor/stacker/src/backends/windows.rs b/vendor/stacker/src/backends/windows.rs
deleted file mode 100644
index 69c76133..00000000
--- a/vendor/stacker/src/backends/windows.rs
+++ /dev/null
@@ -1,142 +0,0 @@
-use libc::c_void;
-use std::io;
-use std::ptr;
-use windows_sys::Win32::Foundation::BOOL;
-use windows_sys::Win32::System::Memory::VirtualQuery;
-use windows_sys::Win32::System::Threading::{
-    ConvertFiberToThread, ConvertThreadToFiber, CreateFiber, DeleteFiber, IsThreadAFiber,
-    SetThreadStackGuarantee, SwitchToFiber,
-};
-
-// Make sure the libstacker.a (implemented in C) is linked.
-// See https://github.com/rust-lang/rust/issues/65610
-#[link(name = "stacker")]
-extern "C" {
-    fn __stacker_get_current_fiber() -> *mut c_void;
-}
-
-struct FiberInfo<F> {
-    callback: std::mem::MaybeUninit<F>,
-    panic: Option<Box<dyn std::any::Any + Send + 'static>>,
-    parent_fiber: *mut c_void,
-}
-
-unsafe extern "system" fn fiber_proc<F: FnOnce()>(data: *mut c_void) {
-    // This function is the entry point to our inner fiber, and as argument we get an
-    // instance of `FiberInfo`. We will set-up the "runtime" for the callback and execute
-    // it.
-    let data = &mut *(data as *mut FiberInfo<F>);
-    let old_stack_limit = crate::get_stack_limit();
-    crate::set_stack_limit(guess_os_stack_limit());
-    let callback = data.callback.as_ptr();
-    data.panic = std::panic::catch_unwind(std::panic::AssertUnwindSafe(callback.read())).err();
-
-    // Restore to the previous Fiber
-    crate::set_stack_limit(old_stack_limit);
-    SwitchToFiber(data.parent_fiber);
-}
-
-pub fn _grow(stack_size: usize, callback: &mut dyn FnMut()) {
-    // Fibers (or stackful coroutines) is the only official way to create new stacks on the
-    // same thread on Windows. So in order to extend the stack we create fiber and switch
-    // to it so we can use it's stack. After running `callback` within our fiber, we switch
-    // back to the current stack and destroy the fiber and its associated stack.
-    unsafe {
-        let was_fiber = IsThreadAFiber() == 1 as BOOL;
-        let mut data = FiberInfo {
-            callback: std::mem::MaybeUninit::new(callback),
-            panic: None,
-            parent_fiber: {
-                if was_fiber {
-                    // Get a handle to the current fiber. We need to use a C implementation
-                    // for this as GetCurrentFiber is an header only function.
-                    __stacker_get_current_fiber()
-                } else {
-                    // Convert the current thread to a fiber, so we are able to switch back
-                    // to the current stack. Threads coverted to fibers still act like
-                    // regular threads, but they have associated fiber data. We later
-                    // convert it back to a regular thread and free the fiber data.
-                    ConvertThreadToFiber(ptr::null_mut())
-                }
-            },
-        };
-
-        if data.parent_fiber.is_null() {
-            panic!(
-                "unable to convert thread to fiber: {}",
-                io::Error::last_os_error()
-            );
-        }
-
-        let fiber = CreateFiber(
-            stack_size as usize,
-            Some(fiber_proc::<&mut dyn FnMut()>),
-            &mut data as *mut FiberInfo<&mut dyn FnMut()> as *mut _,
-        );
-        if fiber.is_null() {
-            panic!("unable to allocate fiber: {}", io::Error::last_os_error());
-        }
-
-        // Switch to the fiber we created. This changes stacks and starts executing
-        // fiber_proc on it. fiber_proc will run `callback` and then switch back to run the
-        // next statement.
-        SwitchToFiber(fiber);
-        DeleteFiber(fiber);
-
-        // Clean-up.
-        if !was_fiber && ConvertFiberToThread() == 0 {
-            // FIXME: Perhaps should not panic here?
-            panic!(
-                "unable to convert back to thread: {}",
-                io::Error::last_os_error()
-            );
-        }
-
-        if let Some(p) = data.panic {
-            std::panic::resume_unwind(p);
-        }
-    }
-}
-
-#[inline(always)]
-fn get_thread_stack_guarantee() -> Option<usize> {
-    let min_guarantee = if cfg!(target_pointer_width = "32") {
-        0x1000
-    } else {
-        0x2000
-    };
-    let mut stack_guarantee = 0;
-    unsafe {
-        // Read the current thread stack guarantee
-        // This is the stack reserved for stack overflow
-        // exception handling.
-        // This doesn't return the true value so we need
-        // some further logic to calculate the real stack
-        // guarantee. This logic is what is used on x86-32 and
-        // x86-64 Windows 10. Other versions and platforms may differ
-        let ret = SetThreadStackGuarantee(&mut stack_guarantee);
-        if ret == 0 {
-            return None;
-        }
-    };
-    Some(std::cmp::max(stack_guarantee, min_guarantee) as usize + 0x1000)
-}
-
-#[inline(always)]
-pub unsafe fn guess_os_stack_limit() -> Option<usize> {
-    // Query the allocation which contains our stack pointer in order
-    // to discover the size of the stack
-    //
-    // FIXME: we could read stack base from the TIB, specifically the 3rd element of it.
-    type QueryT = windows_sys::Win32::System::Memory::MEMORY_BASIC_INFORMATION;
-    let mut mi = std::mem::MaybeUninit::<QueryT>::uninit();
-    let res = VirtualQuery(
-        psm::stack_pointer() as *const _,
-        mi.as_mut_ptr(),
-        std::mem::size_of::<QueryT>() as usize,
-    );
-    if res == 0 {
-        return None;
-    }
-    Some(mi.assume_init().AllocationBase as usize + get_thread_stack_guarantee()? + 0x1000)
-}
diff --git a/vendor/stacker/src/lib.rs b/vendor/stacker/src/lib.rs
deleted file mode 100644
index ee5803c3..00000000
--- a/vendor/stacker/src/lib.rs
+++ /dev/null
@@ -1,181 +0,0 @@
-//! A library to help grow the stack when it runs out of space.
-//!
-//! This is an implementation of manually instrumented segmented stacks where points in a program's
-//! control flow are annotated with "maybe grow the stack here". Each point of annotation indicates
-//! how far away from the end of the stack it's allowed to be, plus the amount of stack to allocate
-//! if it does reach the end.
-//!
-//! Once a program has reached the end of its stack, a temporary stack on the heap is allocated and
-//! is switched to for the duration of a closure.
-//!
-//! For a set of lower-level primitives, consider the `psm` crate.
-//!
-//! # Examples
-//!
-//! ```
-//! // Grow the stack if we are within the "red zone" of 32K, and if we allocate
-//! // a new stack allocate 1MB of stack space.
-//! //
-//! // If we're already in bounds, just run the provided closure on current stack.
-//! stacker::maybe_grow(32 * 1024, 1024 * 1024, || {
-//!     // guaranteed to have at least 32K of stack
-//! });
-//! ```
-
-#![allow(improper_ctypes)]
-
-#[macro_use]
-extern crate cfg_if;
-extern crate libc;
-#[cfg(windows)]
-extern crate windows_sys;
-#[macro_use]
-extern crate psm;
-
-mod backends;
-
-use std::cell::Cell;
-
-/// Grows the call stack if necessary.
-///
-/// This function is intended to be called at manually instrumented points in a program where
-/// recursion is known to happen quite a bit. This function will check to see if we're within
-/// `red_zone` bytes of the end of the stack, and if so it will allocate a new stack of at least
-/// `stack_size` bytes.
-///
-/// The closure `f` is guaranteed to run on a stack with at least `red_zone` bytes, and it will be
-/// run on the current stack if there's space available.
-#[inline(always)]
-pub fn maybe_grow<R, F: FnOnce() -> R>(red_zone: usize, stack_size: usize, callback: F) -> R {
-    // if we can't guess the remaining stack (unsupported on some platforms) we immediately grow
-    // the stack and then cache the new stack size (which we do know now because we allocated it.
-    let enough_space = match remaining_stack() {
-        Some(remaining) => remaining >= red_zone,
-        None => false,
-    };
-    if enough_space {
-        callback()
-    } else {
-        grow(stack_size, callback)
-    }
-}
-
-/// Always creates a new stack for the passed closure to run on.
-/// The closure will still be on the same thread as the caller of `grow`.
-/// This will allocate a new stack with at least `stack_size` bytes.
-pub fn grow<R, F: FnOnce() -> R>(stack_size: usize, callback: F) -> R {
-    // To avoid monomorphizing `_grow()` and everything it calls,
-    // we convert the generic callback to a dynamic one.
-    let mut opt_callback = Some(callback);
-    let mut ret = None;
-    let ret_ref = &mut ret;
-
-    // This wrapper around `callback` achieves two things:
-    // * It converts the `impl FnOnce` to a `dyn FnMut`.
-    //   `dyn` because we want it to not be generic, and
-    //   `FnMut` because we can't pass a `dyn FnOnce` around without boxing it.
-    // * It eliminates the generic return value, by writing it to the stack of this function.
-    //   Otherwise the closure would have to return an unsized value, which isn't possible.
-    let dyn_callback: &mut dyn FnMut() = &mut || {
-        let taken_callback = opt_callback.take().unwrap();
-        *ret_ref = Some(taken_callback());
-    };
-
-    _grow(stack_size, dyn_callback);
-    ret.unwrap()
-}
-
-/// Queries the amount of remaining stack as interpreted by this library.
-///
-/// This function will return the amount of stack space left which will be used
-/// to determine whether a stack switch should be made or not.
-pub fn remaining_stack() -> Option<usize> {
-    let current_ptr = current_stack_ptr();
-    get_stack_limit().map(|limit| current_ptr.saturating_sub(limit))
-}
-
-psm_stack_information!(
-    yes {
-        fn current_stack_ptr() -> usize {
-            psm::stack_pointer() as usize
-        }
-    }
-    no {
-        #[inline(always)]
-        fn current_stack_ptr() -> usize {
-            unsafe {
-                let mut x = std::mem::MaybeUninit::<u8>::uninit();
-                // Unlikely to be ever exercised. As a fallback we execute a volatile read to a
-                // local (to hopefully defeat the optimisations that would make this local a static
-                // global) and take its address. This way we get a very approximate address of the
-                // current frame.
-                x.as_mut_ptr().write_volatile(42);
-                x.as_ptr() as usize
-            }
-        }
-    }
-);
-
-thread_local! {
-    static STACK_LIMIT: Cell<Option<usize>> = Cell::new(unsafe {
-        backends::guess_os_stack_limit()
-    })
-}
-
-#[inline(always)]
-fn get_stack_limit() -> Option<usize> {
-    STACK_LIMIT.with(|s| s.get())
-}
-
-#[inline(always)]
-#[allow(unused)]
-fn set_stack_limit(l: Option<usize>) {
-    STACK_LIMIT.with(|s| s.set(l))
-}
-
-psm_stack_manipulation! {
-    yes {
-        #[cfg(not(any(target_arch = "wasm32",target_os = "hermit")))]
-        #[path = "mmap_stack_restore_guard.rs"]
-        mod stack_restore_guard;
-
-        #[cfg(any(target_arch = "wasm32",target_os = "hermit"))]
-        #[path = "alloc_stack_restore_guard.rs"]
-        mod stack_restore_guard;
-
-        use stack_restore_guard::StackRestoreGuard;
-
-        fn _grow(requested_stack_size: usize, callback: &mut dyn FnMut()) {
-            // Other than that this code has no meaningful gotchas.
-            unsafe {
-                // We use a guard pattern to ensure we deallocate the allocated stack when we leave
-                // this function and also try to uphold various safety invariants required by `psm`
-                // (such as not unwinding from the callback we pass to it).
-                // `StackRestoreGuard` allocates a memory area with suitable size and alignment.
-                // It also sets up stack guards if supported on target.
-                let guard = StackRestoreGuard::new(requested_stack_size);
-                let (stack_base, allocated_stack_size) = guard.stack_area();
-                debug_assert!(allocated_stack_size >= requested_stack_size);
-                set_stack_limit(Some(stack_base as usize));
-                // TODO should we not pass `allocated_stack_size` here?
-                let panic = psm::on_stack(stack_base, requested_stack_size, move || {
-                    std::panic::catch_unwind(std::panic::AssertUnwindSafe(callback)).err()
-                });
-                drop(guard);
-                if let Some(p) = panic {
-                    std::panic::resume_unwind(p);
-                }
-            }
-        }
-    }
-
-    no {
-        #[cfg(not(windows))]
-        fn _grow(stack_size: usize, callback: &mut dyn FnMut()) {
-            let _ = stack_size;
-            callback();
-        }
-        #[cfg(windows)]
-        use backends::windows::_grow;
-    }
-}
diff --git a/vendor/stacker/src/mmap_stack_restore_guard.rs b/vendor/stacker/src/mmap_stack_restore_guard.rs
deleted file mode 100644
index 1e021c2d..00000000
--- a/vendor/stacker/src/mmap_stack_restore_guard.rs
+++ /dev/null
@@ -1,105 +0,0 @@
-use crate::{get_stack_limit, set_stack_limit};
-
-pub struct StackRestoreGuard {
-    mapping: *mut u8,
-    size_with_guard: usize,
-    page_size: usize,
-    old_stack_limit: Option<usize>,
-}
-
-impl StackRestoreGuard {
-    pub fn new(requested_size: usize) -> StackRestoreGuard {
-        // For maximum portability we want to produce a stack that is aligned to a page and has
-        // a size that’s a multiple of page size. It is natural to use mmap to allocate
-        // these pages. Furthermore, we want to allocate two extras pages for the stack guard.
-        // To achieve that we do our calculations in number of pages and convert to bytes last.
-        let page_size = page_size();
-        let requested_pages = requested_size
-            .checked_add(page_size - 1)
-            .expect("unreasonably large stack requested")
-            / page_size;
-        let page_count_with_guard = std::cmp::max(1, requested_pages) + 2;
-        let size_with_guard = page_count_with_guard
-            .checked_mul(page_size)
-            .expect("unreasonably large stack requested");
-
-        unsafe {
-            let new_stack = libc::mmap(
-                std::ptr::null_mut(),
-                size_with_guard,
-                libc::PROT_NONE,
-                libc::MAP_PRIVATE | libc::MAP_ANON,
-                -1, // Some implementations assert fd = -1 if MAP_ANON is specified
-                0,
-            );
-            assert_ne!(
-                new_stack,
-                libc::MAP_FAILED,
-                "mmap failed to allocate stack: {}",
-                std::io::Error::last_os_error()
-            );
-            let guard = StackRestoreGuard {
-                mapping: new_stack as *mut u8,
-                page_size,
-                size_with_guard,
-                old_stack_limit: get_stack_limit(),
-            };
-            // We leave two guard pages without read/write access in our allocation.
-            // There is one guard page below the stack and another above it.
-            let above_guard_page = new_stack.add(page_size);
-            #[cfg(not(target_os = "openbsd"))]
-            let result = libc::mprotect(
-                above_guard_page,
-                size_with_guard - 2 * page_size,
-                libc::PROT_READ | libc::PROT_WRITE,
-            );
-            #[cfg(target_os = "openbsd")]
-            let result = if libc::mmap(
-                above_guard_page,
-                size_with_guard - 2 * page_size,
-                libc::PROT_READ | libc::PROT_WRITE,
-                libc::MAP_FIXED | libc::MAP_PRIVATE | libc::MAP_ANON | libc::MAP_STACK,
-                -1,
-                0,
-            ) == above_guard_page
-            {
-                0
-            } else {
-                -1
-            };
-            assert_ne!(
-                result,
-                -1,
-                "mprotect/mmap failed: {}",
-                std::io::Error::last_os_error()
-            );
-            guard
-        }
-    }
-
-    // TODO this should return a *mut [u8], but pointer slices only got proper support with Rust 1.79.
-    pub fn stack_area(&self) -> (*mut u8, usize) {
-        unsafe {
-            (
-                self.mapping.add(self.page_size),
-                self.size_with_guard - self.page_size,
-            )
-        }
-    }
-}
-
-impl Drop for StackRestoreGuard {
-    fn drop(&mut self) {
-        unsafe {
-            // FIXME: check the error code and decide what to do with it.
-            // Perhaps a debug_assertion?
-            libc::munmap(self.mapping as *mut std::ffi::c_void, self.size_with_guard);
-        }
-        set_stack_limit(self.old_stack_limit);
-    }
-}
-
-fn page_size() -> usize {
-    // FIXME: consider caching the page size.
-    unsafe { libc::sysconf(libc::_SC_PAGE_SIZE) as usize }
-}