feat(kernel): console cap gates DebugPutchar, no uart fast path; spawn start arg in a0; delegate returns slot

crates/domain/src/resource.rs

@@ -10,4 +10,6 @@ pub enum Resource {
     ProcessCreate,
     /// Machine-wide controls such as halting; given only to init at boot.
     SystemControl,
+    /// The debug console (UART); held by the log server.
+    Console,
 }

crates/domain/src/syscall.rs

@@ -93,9 +93,11 @@ pub enum Syscall {
     DropCap {
         slot: CapSlot,
     },
+    /// `arg` arrives in the new thread's `a0`.
     SpawnThread {
         entry: EntryPoint,
         stack: StackPointer,
+        arg: usize,
     },
     ExitThread,
     RequestPages {
@@ -114,7 +116,9 @@ pub enum Syscall {
         control: CapSlot,
     },
     CreateEndpoint,
+    /// Writes one byte to the console; needs a Console capability.
     DebugPutchar {
+        console: CapSlot,
         byte: u8,
     },
     MapPage {
@@ -127,5 +131,6 @@ pub enum Syscall {
         process: CapSlot,
         entry: EntryPoint,
         stack: StackPointer,
+        arg: usize,
     },
 }