fix(interrupts): use transmute to satisfy IDT type requirements

The x86-interrupt ABI doesn't support return types, but the IDT
expects a diverging handler for double faults. Using transmute to
convert our handler to the expected type signature. The panic\!
ensures the function never returns in practice.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: ryanbreen

kernel/src/interrupts.rs

@@ -66,7 +66,11 @@ pub fn init_idt() {
         idt.invalid_opcode.set_handler_fn(invalid_opcode_handler);
         idt.general_protection_fault.set_handler_fn(general_protection_fault_handler);
         unsafe {
-            idt.double_fault.set_handler_fn(double_fault_handler)
+            // The x86-interrupt ABI doesn't support return types, but the IDT expects
+            // a diverging handler. The panic! ensures it never returns.
+            let handler: extern "x86-interrupt" fn(InterruptStackFrame, u64) -> ! = 
+                core::mem::transmute(double_fault_handler as extern "x86-interrupt" fn(InterruptStackFrame, u64));
+            idt.double_fault.set_handler_fn(handler)
                 .set_stack_index(gdt::DOUBLE_FAULT_IST_INDEX);
         }
         idt.page_fault.set_handler_fn(page_fault_handler);
@@ -148,7 +152,7 @@ extern "x86-interrupt" fn breakpoint_handler(stack_frame: InterruptStackFrame) {
 extern "x86-interrupt" fn double_fault_handler(
     stack_frame: InterruptStackFrame,
     _error_code: u64,
-) -> ! {
+) {
     // Log additional debug info before panicking
     log::error!("DOUBLE FAULT - Error Code: {:#x}", _error_code);
     log::error!("Instruction Pointer: {:#x}", stack_frame.instruction_pointer.as_u64());
@@ -162,11 +166,6 @@ extern "x86-interrupt" fn double_fault_handler(
     log::error!("Current page table frame: {:?}", frame);
 
     panic!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
-    // This is unreachable but needed to satisfy the type checker
-    #[allow(unreachable_code)]
-    loop {
-        x86_64::instructions::hlt();
-    }
 }