feat(kernel): add Revoke syscall for generation-based capability revocation

crates/kernel/src/syscall/capability.rs

@@ -44,4 +44,22 @@ impl<P: Platform> Kernel<P> {
             Err(e) => SyscallOutcome::Complete(SyscallResult::Error(e)),
         }
     }
+
+    pub(crate) fn handle_revoke(
+        &mut self,
+        caller_pid: types::id::ProcessId,
+        slot: types::bounded::CapSlot,
+    ) -> SyscallOutcome {
+        let resource = match self.check_cap(
+            caller_pid,
+            slot,
+            types::permission::Permission::Revoke,
+        ) {
+            Ok(cap) => cap.resource().clone(),
+            Err(e) => return SyscallOutcome::Complete(SyscallResult::Error(e)),
+        };
+
+        self.revoke_resource(&resource);
+        SyscallOutcome::Complete(SyscallResult::Ok)
+    }
 }

crates/kernel/src/syscall/mod.rs

@@ -44,6 +44,7 @@ impl<P: Platform> Kernel<P> {
             Syscall::SpawnThread { entry, stack } => self.handle_spawn_thread(pid, entry, stack),
             Syscall::CreateProcess { create_cap, image } => self.handle_create_process(pid, create_cap, image),
             Syscall::Kill { process } => self.handle_kill(pid, process),
+            Syscall::Revoke { slot } => self.handle_revoke(pid, slot),
             Syscall::Delegate { slot, to_endpoint, permissions } => {
                 self.handle_delegate(pid, slot, to_endpoint, permissions)
             }

crates/kernel/src/tests/capability.rs

@@ -143,3 +143,46 @@ fn revoke_does_not_affect_other_resources() {
     let outcome = k.handle_syscall(Syscall::Receive { endpoint: slot2 });
     assert!(matches!(outcome, SyscallOutcome::BlockCaller(_)));
 }
+
+#[test]
+fn revoke_syscall_invalidates_via_generation() {
+    let (mut k, pid) = kernel_with_process();
+    let ep_id = k.create_endpoint_for_test();
+
+    let cap_slot = k.grant_cap_for_test(
+        pid,
+        Resource::Endpoint(ep_id),
+        PermissionSet::empty()
+            .with(Permission::Read)
+            .with(Permission::Revoke),
+    );
+
+    // Revoke via syscall
+    let outcome = k.handle_syscall(Syscall::Revoke { slot: cap_slot });
+    assert!(matches!(outcome, SyscallOutcome::Complete(SyscallResult::Ok)));
+
+    // The cap itself is now revoked (generation mismatch)
+    let outcome = k.handle_syscall(Syscall::Receive { endpoint: cap_slot });
+    assert!(matches!(
+        outcome,
+        SyscallOutcome::Complete(SyscallResult::Error(domain::error::KernelError::RevokedCapability(_)))
+    ));
+}
+
+#[test]
+fn revoke_syscall_without_revoke_permission_fails() {
+    let (mut k, pid) = kernel_with_process();
+    let ep_id = k.create_endpoint_for_test();
+
+    let cap_slot = k.grant_cap_for_test(
+        pid,
+        Resource::Endpoint(ep_id),
+        PermissionSet::empty().with(Permission::Read),
+    );
+
+    let outcome = k.handle_syscall(Syscall::Revoke { slot: cap_slot });
+    assert!(matches!(
+        outcome,
+        SyscallOutcome::Complete(SyscallResult::Error(_))
+    ));
+}