kernel: replace todo!(oom) with proper ENOMEM-based signal path

src/memory/mod.rs

@@ -1028,11 +1028,12 @@ pub fn page_fault_handler(
         match context::memory::try_correcting_page_tables(faulting_page, mode, &mut token) {
             Ok(()) => return Ok(()),
             Err(PfError::Oom) => {
-                log::warn!("page fault recovery failed: out of memory at {:#x}", faulting_page.start_address().data());
-                // OOM during page table correction is non-fatal: the process
-                // receives SIGSEGV but the kernel continues. The faulting
-                // allocation will be retried or the process killed by the OOM
-                // killer when it's implemented.
+                log::error!(
+                    "OOM during page fault for PID {} at {:#x}",
+                    context::current().pid,
+                    faulting_page.start_address().data()
+                );
+                return Err(Segv);
             }
             Err(PfError::Segv | PfError::RecursionLimitExceeded | PfError::NonfatalInternalError) => (),
         }