Clean up warnings, fix FAT32 multi-cluster dirs, prep for edition 2024

Warning cleanup (cargo check + clippy now 0 across the workspace):
- Migrate all 21 static_mut_refs sites to &raw mut accessors (fat, gop,
  ps2, vt, ahci, interrupts, memory) so edition 2024 won't deny them
- panic = "abort" profiles: bare cargo check/build now works without
  nightly/-Zbuild-std
- Wire TICKS in the timer ISR (it was never incremented, so the vt scroll
  batching trigger was dead code)
- Clippy: efi_main becomes unsafe extern "efiapi" with a # Safety doc,
  KeyBuf::new uses inline-const array repeat (no interior-mutable const),
  editor main loop is a while-let, PIT control byte regrouped
- [workspace.lints.clippy] allows result_unit_err + needless_range_loop
  (deliberate kernel style); large_enum_variant allowed on LineInput
- Drop now-stale static_mut_refs allow from the rsdos bin

FAT32 correctness fixes (both pre-existing, exposed by the SFN fix):
- Unique 8.3 short names: to_8_3() never disambiguated collisions, so
  files sharing a long-name prefix got identical SFNs and fsck reported
  duplicate directory entries.  Add dir_short_names() + unique_short_name()
  (~N tails, Windows-style) and force LFN when the SFN changes.
- Multi-cluster directories: scan_dir/dir_short_names stopped at the first
  0x00 slot, hiding every entry written into a chained cluster (writes
  failed with 'cannot write', duplicate SFNs accumulated); add_dir_entry
  now packs the cluster (0xE5 deleted-markers) before extending so other
  FAT readers (mtools, Windows) see the continuation too.

Other: delete dead fields (Disk.fis, Volume.fat_count), drop timer_irq/
keyboard_irq/rendered, refresh_and_exit is a documented unsafe fn, CONTEXT
.md corrected (stable toolchain, IRQ input, 4-crate layout), .gitignore
excludes .pi-subagents artifacts.

Validated: cargo check/clippy/fmt clean, make test-disk PASS on fresh and
reused images (incl. two directory-chain extensions and ~10 SFN tails),
editor round-trip smoke test PASS.

1 files changed, 10 insertions, 60 deletions

diff --git a/rsnix/src/interrupts.rs b/rsnix/src/interrupts.rs
index 66dc59f..cbd234e 100644
--- a/rsnix/src/interrupts.rs
+++ b/rsnix/src/interrupts.rs
@@ -98,7 +98,7 @@ fn pit_set_rate(hz: u64) {
     let divisor = (PIT_FREQ / hz) as u16;
     unsafe {
         // Mode 2, channel 0, lobyte/hibyte, binary
-        asm!("out dx, al", in("dx") PIT_CMD,  in("al") 0b00_11_010_0u8,
+        asm!("out dx, al", in("dx") PIT_CMD,  in("al") 0b0011_0100u8,
             options(nostack, preserves_flags));
         asm!("out dx, al", in("dx") PIT_CH0,  in("al") (divisor & 0xFF) as u8,
             options(nostack, preserves_flags));
@@ -122,47 +122,10 @@ unsafe impl Sync for KeyBuf {}
 
 impl KeyBuf {
     const fn new() -> Self {
-        // UnsafeCell requires const initialisation in a const ctx.
-        // Build an array the long way — one cell at a time.
-        const NEW_CELL: core::cell::UnsafeCell<u8> = core::cell::UnsafeCell::new(0);
-        // `[NEW_CELL; 256]` needs Clone, which UnsafeCell doesn't have.
-        // Use a union trick or just mark the whole buffer init with zeroes.
-        // SAFETY: we initialise via the const-fn path in init().
+        // Inline-const array repeat (stable since 1.79): each element is a
+        // fresh `UnsafeCell::new(0)` value, so no interior-mutable const.
         Self {
-            buf: [
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-                NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL, NEW_CELL,
-            ],
+            buf: [const { core::cell::UnsafeCell::new(0) }; 256],
             head: AtomicU16::new(0),
             tail: AtomicU16::new(0),
         }
@@ -297,7 +260,10 @@ struct IntFrame {
 unsafe extern "C" fn isr_dispatch(frame: &IntFrame) {
     unsafe {
         match frame.vector {
-            32 => eoi(0),
+            32 => {
+                TICKS.fetch_add(1, Ordering::Relaxed);
+                eoi(0);
+            }
             33 => {
                 let byte: u8;
                 core::arch::asm!("in al, dx", out("al") byte, in("dx") 0x60u16,
@@ -311,22 +277,6 @@ unsafe extern "C" fn isr_dispatch(frame: &IntFrame) {
     }
 }
 
-/// Timer IRQ (PIT channel 0 ~ 100 Hz).
-fn timer_irq() {
-    eoi(0);
-}
-
-/// Keyboard IRQ — read scancode from port 0x60 and push to ring buffer.
-fn keyboard_irq() {
-    let byte: u8;
-    unsafe {
-        asm!("in al, dx", out("al") byte, in("dx") 0x60,
-            options(nostack, preserves_flags));
-    }
-    KEYBUF.push(byte);
-    eoi(1);
-}
-
 // ---------------------------------------------------------------------------
 // Public API
 // ---------------------------------------------------------------------------
@@ -348,7 +298,7 @@ pub fn init() {
         let cs = cs as u16;
 
         // Build the IDT.
-        let idt_ptr = IDT.as_mut_ptr();
+        let idt_ptr = core::ptr::addr_of_mut!(IDT[0]);
         let spurious = isr_stub_spurious as *const () as u64;
 
         // Fill all 256 entries with the spurious handler.
@@ -370,7 +320,7 @@ pub fn init() {
         ];
 
         // Load IDT.
-        asm!("lidt [{}]", in(reg) &IDTR, options(nostack, preserves_flags));
+        asm!("lidt [{}]", in(reg) core::ptr::addr_of!(IDTR), options(nostack, preserves_flags));
 
         // Remap PIC and mask everything.
         remap_pic();