feat: add Halt syscall, fault notification to fault handler, supervisor with back-off, shutdown with timeout

- Halt syscall: only pid 0 (init) can halt, adapter uses SBI SRST
- Fault notification: kernel delivers fault info to process fault handler endpoint before killing
- Supervisor: tracks restart counts, back-off up to 5 restarts
- Shutdown: notifies servers, waits with timeout, calls halt
- Trap handler: faults now call kernel.handle_fault instead of halting

crates/adapter-riscv/src/platform.rs

@@ -126,4 +126,17 @@ impl Platform for RiscVPlatform {
             ),
         });
     }
+
+    fn halt(&self) -> ! {
+        unsafe {
+            core::arch::asm!(
+                "ecall",
+                in("a0") 0usize,
+                in("a1") 0usize,
+                in("a7") 0x53525354usize,
+                in("a6") 0usize,
+            );
+        }
+        loop { unsafe { core::arch::asm!("wfi") }; }
+    }
 }

crates/adapter-riscv/src/trap/mod.rs

@@ -161,6 +161,7 @@ fn decode_syscall(frame: &TrapFrame) -> Option<domain::syscall::Syscall> {
 
     match nr {
         SYS_EXIT => Some(Syscall::Exit),
+        SYS_HALT => Some(Syscall::Halt),
         SYS_EXIT_THREAD => Some(Syscall::ExitThread),
         SYS_YIELD => Some(Syscall::Yield),
         SYS_GET_TIME => Some(Syscall::GetTime),
@@ -408,7 +409,21 @@ fn handle_exception(frame: &mut TrapFrame, scause: usize) {
             uart.write_str(" sepc=");
             uart.write_hex(frame.sepc);
             uart.put_char(b'\n');
-            loop { unsafe { core::arch::asm!("wfi") }; }
+
+            let kern = crate::kernel_ref();
+            if let Some(current_tid) = kern.current_thread() {
+                let fault = match scause {
+                    2 => domain::fault::Fault::IllegalInstruction,
+                    5 | 7 | 13 | 15 => domain::fault::Fault::MemoryFault {
+                        address: types::address::VirtualAddress::from_raw(stval),
+                    },
+                    _ => domain::fault::Fault::InvalidSyscall,
+                };
+                kern.handle_fault(current_tid, fault, frame.sepc);
+                switch_to_next(frame, current_tid);
+            } else {
+                loop { unsafe { core::arch::asm!("wfi") }; }
+            }
         }
     }
 }