feat: implement new IPC layer

kernel/src/Api/Common.hpp

@@ -1,37 +1,115 @@
 #pragma once
+
 #include <Sched/Scheduler.hpp>
+#include <Ipc/Ipc.hpp>
 
 namespace Montauk {
-    // Find the process that owns the I/O ring buffers for a redirected process.
+
-    // If proc owns buffers itself (spawned via spawn_redir), returns proc.
-    // If proc inherited redirection (spawned via spawn from a redirected parent),
-    // follows parentPid to find the buffer owner.
     static Sched::Process* GetRedirTarget(Sched::Process* proc) {
         if (!proc || !proc->redirected) return nullptr;
-        if (proc->outBuf) return proc;  // owns buffers
+        if (proc->ioOutHandle >= 0 || proc->ioInHandle >= 0 || proc->ioKeyHandle >= 0) {
-        return Sched::GetProcessByPid(proc->parentPid);
+            return proc;
-    }
-
-    // SPSC ring buffer helpers. On x86 TSO, atomic-width aligned
-    // loads/stores are naturally atomic. The compiler barrier ensures
-    // the data write is visible before the head update.
-    static void RingWrite(uint8_t* buf, volatile uint32_t& head, uint32_t /*tail*/, uint32_t size, uint8_t byte) {
-        uint32_t h = head;
-        buf[h] = byte;
-        asm volatile("" ::: "memory");  // compiler barrier
-        head = (h + 1) % size;
-    }
-
-    static int RingRead(uint8_t* buf, volatile uint32_t& head, volatile uint32_t& tail, uint32_t size, uint8_t* out, int maxLen) {
-        int count = 0;
-        uint32_t t = tail;
-        uint32_t h = head;
-        while (t != h && count < maxLen) {
-            out[count++] = buf[t];
-            t = (t + 1) % size;
         }
-        asm volatile("" ::: "memory");  // compiler barrier
+        return (proc->parentPid >= 0) ? Sched::GetProcessByPid(proc->parentPid) : nullptr;
-        tail = t;
+    }
-        return count;
+
+    static bool ResolveProcessHandle(Sched::Process* proc, int handle, Ipc::HandleType expectedType,
+                                     Ipc::Object*& outObject, uint32_t* outRights = nullptr) {
+        if (proc == nullptr || handle < 0) return false;
+
+        int slot = Ipc::SlotForPid(proc->pid);
+        if (slot < 0) return false;
+
+        Ipc::HandleType type = Ipc::HandleType::None;
+        Ipc::Object* object = nullptr;
+        uint32_t rights = 0;
+        if (!Ipc::SnapshotHandleForSlot(slot, handle, type, object, rights)) return false;
+        if (type != expectedType || object == nullptr) return false;
+
+        outObject = object;
+        if (outRights != nullptr) *outRights = rights;
+        return true;
+    }
+
+    static Ipc::Stream* GetRedirOutStream(Sched::Process* proc) {
+        proc = GetRedirTarget(proc);
+        if (proc == nullptr) return nullptr;
+
+        Ipc::Object* object = nullptr;
+        if (!ResolveProcessHandle(proc, proc->ioOutHandle, Ipc::HandleType::Stream, object)) return nullptr;
+        return (Ipc::Stream*)object;
+    }
+
+    static Ipc::Stream* GetRedirInStream(Sched::Process* proc) {
+        proc = GetRedirTarget(proc);
+        if (proc == nullptr) return nullptr;
+
+        Ipc::Object* object = nullptr;
+        if (!ResolveProcessHandle(proc, proc->ioInHandle, Ipc::HandleType::Stream, object)) return nullptr;
+        return (Ipc::Stream*)object;
+    }
+
+    static Ipc::Mailbox* GetRedirKeyMailbox(Sched::Process* proc) {
+        proc = GetRedirTarget(proc);
+        if (proc == nullptr) return nullptr;
+
+        Ipc::Object* object = nullptr;
+        if (!ResolveProcessHandle(proc, proc->ioKeyHandle, Ipc::HandleType::Mailbox, object)) return nullptr;
+        return (Ipc::Mailbox*)object;
+    }
+
+    static int DuplicateHandleBetweenSlots(int srcSlot, int handle, int dstSlot) {
+        if (srcSlot < 0 || dstSlot < 0 || handle < 0) return -1;
+
+        Ipc::HandleType type = Ipc::HandleType::None;
+        Ipc::Object* object = nullptr;
+        uint32_t rights = 0;
+        if (!Ipc::SnapshotHandleForSlot(srcSlot, handle, type, object, rights)) return -1;
+        if ((rights & Ipc::RightDup) == 0) return -1;
+        return Ipc::InstallHandleForSlot(dstSlot, object, type, rights);
+    }
+
+    static bool ConfigureRedirWaitsetForSlot(int slot, Sched::Process* proc) {
+        if (slot < 0 || proc == nullptr) return false;
+
+        int waitset = Ipc::CreateWaitsetHandleForSlot(slot);
+        if (waitset < 0) return false;
+
+        if (proc->ioInHandle >= 0) {
+            if (Ipc::WaitsetAddHandleForSlot(slot, waitset, proc->ioInHandle,
+                                             Ipc::SignalReadable | Ipc::SignalPeerClosed) < 0) {
+                Ipc::CloseHandleForSlot(slot, waitset);
+                return false;
+            }
+        }
+
+        if (proc->ioKeyHandle >= 0) {
+            if (Ipc::WaitsetAddHandleForSlot(slot, waitset, proc->ioKeyHandle,
+                                             Ipc::SignalReadable | Ipc::SignalPeerClosed) < 0) {
+                Ipc::CloseHandleForSlot(slot, waitset);
+                return false;
+            }
+        }
+
+        proc->ioWaitsetHandle = waitset;
+        return true;
+    }
+
+    static int WriteAllToStream(Ipc::Stream* stream, const uint8_t* data, int len) {
+        if (stream == nullptr || data == nullptr || len <= 0) return -1;
+
+        int total = 0;
+        while (total < len) {
+            int written = Ipc::StreamWrite(stream, data + total, len - total, false);
+            if (written < 0) {
+                return (total > 0) ? total : -1;
+            }
+            if (written == 0) {
+                Sched::BlockOnObject(stream, 0);
+                continue;
+            }
+            total += written;
+        }
+        return total;
     }
 }

kernel/src/Api/Filesystem.hpp

@@ -12,25 +12,26 @@
 #include <Memory/HHDM.hpp>
 #include <Memory/Paging.hpp>
 #include <Libraries/Memory.hpp>
+#include <Ipc/Ipc.hpp>
 #include "Path.hpp"
 
 namespace Montauk {
     static int Sys_Open(const char* path) {
         char resolved[256];
         if (!ResolveProcessPath(path, resolved, sizeof(resolved))) return -1;
-        return Fs::Vfs::VfsOpen(resolved);
+        return Ipc::OpenFileHandle(resolved);
     }
 
     static int Sys_Read(int handle, uint8_t* buffer, uint64_t offset, uint64_t size) {
-        return Fs::Vfs::VfsRead(handle, buffer, offset, size);
+        return Ipc::FileReadHandle(handle, buffer, offset, size);
     }
 
     static uint64_t Sys_GetSize(int handle) {
-        return Fs::Vfs::VfsGetSize(handle);
+        return Ipc::FileGetSizeHandle(handle);
     }
 
     static void Sys_Close(int handle) {
-        Fs::Vfs::VfsClose(handle);
+        Ipc::CloseHandle(handle);
     }
 
     static int Sys_ReadDir(const char* path, const char** outNames, int maxEntries) {
@@ -89,13 +90,13 @@ namespace Montauk {
     }
 
     static int Sys_FWrite(int handle, const uint8_t* data, uint64_t offset, uint64_t size) {
-        return Fs::Vfs::VfsWrite(handle, data, offset, size);
+        return Ipc::FileWriteHandle(handle, data, offset, size);
     }
 
     static int Sys_FCreate(const char* path) {
         char resolved[256];
         if (!ResolveProcessPath(path, resolved, sizeof(resolved))) return -1;
-        return Fs::Vfs::VfsCreate(resolved);
+        return Ipc::CreateFileHandle(resolved);
     }
 
     static int Sys_FDelete(const char* path) {

kernel/src/Api/Graphics.hpp

@@ -66,6 +66,9 @@ namespace Montauk {
         // If the process is redirected to a GUI terminal, return those dimensions
         auto* proc = Sched::GetCurrentProcessPtr();
         if (proc && proc->redirected) {
+            if (proc->termCols > 0 && proc->termRows > 0) {
+                return ((uint64_t)proc->termRows << 32) | ((uint64_t)proc->termCols & 0xFFFFFFFF);
+            }
             auto* target = GetRedirTarget(proc);
             if (target && target->termCols > 0 && target->termRows > 0) {
                 return ((uint64_t)target->termRows << 32) | ((uint64_t)target->termCols & 0xFFFFFFFF);

kernel/src/Api/IoRedir.hpp

@@ -7,8 +7,6 @@
 
 #pragma once
 #include <Sched/Scheduler.hpp>
-#include <Memory/PageFrameAllocator.hpp>
-
 #include "Syscall.hpp"
 #include "Common.hpp"
 #include "Path.hpp"
@@ -19,53 +17,92 @@ namespace Montauk {
         char resolved[256];
         if (!ResolveProcessPath(path, resolved, sizeof(resolved))) return -1;
 
+        int parentSlot = Ipc::CurrentSlot();
         int childPid = Sched::Spawn(resolved, args);
         if (childPid < 0) return -1;
 
         auto* child = Sched::GetProcessByPid(childPid);
-        if (child == nullptr) return -1;
+        int childSlot = Ipc::SlotForPid(childPid);
+        if (child == nullptr || childSlot < 0 || parentSlot < 0) return -1;
 
-        // Allocate ring buffers
+        Ipc::Stream* outStream = Ipc::CreateStream();
-        void* outPage = Memory::g_pfa->AllocateZeroed();
+        Ipc::Stream* inStream = Ipc::CreateStream();
-        void* inPage = Memory::g_pfa->AllocateZeroed();
+        Ipc::Mailbox* keyMailbox = Ipc::CreateMailbox();
-        if (!outPage || !inPage) return -1;
+        if (outStream == nullptr || inStream == nullptr || keyMailbox == nullptr) {
+            if (outStream != nullptr) Ipc::ReleaseStream(outStream, false, false);
+            if (inStream != nullptr) Ipc::ReleaseStream(inStream, false, false);
+            if (keyMailbox != nullptr) Ipc::ReleaseMailbox(keyMailbox, false, false);
+            Sched::KillProcess(childPid);
+            return -1;
+        }
+
+        int parentOutHandle = Ipc::InstallHandleForSlot(
+            parentSlot, (Ipc::Object*)outStream, Ipc::HandleType::Stream, Ipc::RightRead);
+        int parentInHandle = Ipc::InstallHandleForSlot(
+            parentSlot, (Ipc::Object*)inStream, Ipc::HandleType::Stream, Ipc::RightWrite);
+        int parentKeyHandle = Ipc::InstallHandleForSlot(
+            parentSlot, (Ipc::Object*)keyMailbox, Ipc::HandleType::Mailbox, Ipc::RightSend);
+
+        child->ioOutHandle = Ipc::InstallHandleForSlot(
+            childSlot, (Ipc::Object*)outStream, Ipc::HandleType::Stream,
+            Ipc::RightWrite | Ipc::RightWait | Ipc::RightDup);
+        child->ioInHandle = Ipc::InstallHandleForSlot(
+            childSlot, (Ipc::Object*)inStream, Ipc::HandleType::Stream,
+            Ipc::RightRead | Ipc::RightWait | Ipc::RightDup);
+        child->ioKeyHandle = Ipc::InstallHandleForSlot(
+            childSlot, (Ipc::Object*)keyMailbox, Ipc::HandleType::Mailbox,
+            Ipc::RightRecv | Ipc::RightWait | Ipc::RightDup);
+
+        if (parentOutHandle < 0 || parentInHandle < 0 || parentKeyHandle < 0 ||
+            child->ioOutHandle < 0 || child->ioInHandle < 0 || child->ioKeyHandle < 0 ||
+            !ConfigureRedirWaitsetForSlot(childSlot, child)) {
+            if (parentOutHandle >= 0) Ipc::CloseHandleForSlot(parentSlot, parentOutHandle);
+            if (parentInHandle >= 0) Ipc::CloseHandleForSlot(parentSlot, parentInHandle);
+            if (parentKeyHandle >= 0) Ipc::CloseHandleForSlot(parentSlot, parentKeyHandle);
+            if (child->ioOutHandle < 0) Ipc::ReleaseStream(outStream, false, false);
+            if (child->ioInHandle < 0) Ipc::ReleaseStream(inStream, false, false);
+            if (child->ioKeyHandle < 0) Ipc::ReleaseMailbox(keyMailbox, false, false);
+            Sched::KillProcess(childPid);
+            return -1;
+        }
 
-        child->outBuf = (uint8_t*)outPage;
-        child->inBuf = (uint8_t*)inPage;
-        child->outHead = 0;
-        child->outTail = 0;
-        child->inHead = 0;
-        child->inTail = 0;
-        child->keyHead = 0;
-        child->keyTail = 0;
         child->redirected = true;
         child->parentPid = Sched::GetCurrentPid();
+        child->termCols = 0;
+        child->termRows = 0;
 
         return childPid;
     }
 
     static int Sys_ChildIoRead(int childPid, char* buf, int maxLen) {
         auto* child = Sched::GetProcessByPid(childPid);
-        if (child == nullptr || !child->redirected || !child->outBuf) return -1;
+        Ipc::Stream* stream = GetRedirOutStream(child);
-        return RingRead(child->outBuf, child->outHead, child->outTail, Sched::Process::IoBufSize, (uint8_t*)buf, maxLen);
+        if (child == nullptr || !child->redirected || stream == nullptr) return -1;
+        return Ipc::StreamRead(stream, (uint8_t*)buf, maxLen, true);
     }
 
     static int Sys_ChildIoWrite(int childPid, const char* data, int len) {
         auto* child = Sched::GetProcessByPid(childPid);
-        if (child == nullptr || !child->redirected || !child->inBuf) return -1;
+        Ipc::Stream* stream = GetRedirInStream(child);
-        for (int i = 0; i < len; i++) {
+        if (child == nullptr || !child->redirected || stream == nullptr) return -1;
-            RingWrite(child->inBuf, child->inHead, child->inTail, Sched::Process::IoBufSize, (uint8_t)data[i]);
+        return WriteAllToStream(stream, (const uint8_t*)data, len);
-        }
-        return len;
     }
 
     static int Sys_ChildIoWriteKey(int childPid, const KeyEvent* key) {
         if (key == nullptr) return -1;
         auto* child = Sched::GetProcessByPid(childPid);
-        if (child == nullptr || !child->redirected) return -1;
+        Ipc::Mailbox* mailbox = GetRedirKeyMailbox(child);
-        child->keyBuf[child->keyHead] = *key;
+        if (child == nullptr || !child->redirected || mailbox == nullptr) return -1;
-        child->keyHead = (child->keyHead + 1) % 64;
+
-        return 0;
+        for (;;) {
+            int rc = Ipc::MailboxSend(mailbox, 0, key, sizeof(KeyEvent));
+            if (rc < 0) return -1;
+            if (rc == 0) {
+                Sched::BlockOnObject(mailbox, 0);
+                continue;
+            }
+            return 0;
+        }
     }
 
     static int Sys_ChildIoSetTermsz(int childPid, int cols, int rows) {

kernel/src/Api/IpcSyscall.hpp

@@ -0,0 +1,101 @@
+/*
+    * IpcSyscall.hpp
+    * Generic IPC handle, stream, mailbox, waitset, process, and surface syscalls
+    * Copyright (c) 2026 Daniel Hammer
+*/
+
+#pragma once
+#include <Ipc/Ipc.hpp>
+#include <Sched/Scheduler.hpp>
+#include "Syscall.hpp"
+
+namespace Montauk {
+
+    static int Sys_DupHandle(int handle) {
+        return Ipc::DupHandle(handle);
+    }
+
+    static uint32_t Sys_WaitHandle(int handle, uint32_t wantedSignals, uint64_t timeoutMs) {
+        return Ipc::WaitOnHandle(handle, wantedSignals, timeoutMs);
+    }
+
+    static int Sys_StreamCreate(int* outReadHandle, int* outWriteHandle, uint32_t capacity) {
+        if (outReadHandle == nullptr || outWriteHandle == nullptr) return -1;
+
+        int readHandle = -1;
+        int writeHandle = -1;
+        if (Ipc::CreateStreamHandlePair(capacity, readHandle, writeHandle) < 0) return -1;
+
+        *outReadHandle = readHandle;
+        *outWriteHandle = writeHandle;
+        return 0;
+    }
+
+    static int Sys_StreamRead(int handle, uint8_t* buffer, int maxLen) {
+        return Ipc::StreamReadHandle(handle, buffer, maxLen);
+    }
+
+    static int Sys_StreamWrite(int handle, const uint8_t* data, int len) {
+        return Ipc::StreamWriteHandle(handle, data, len);
+    }
+
+    static int Sys_MailboxCreate(int* outSendHandle, int* outRecvHandle) {
+        if (outSendHandle == nullptr || outRecvHandle == nullptr) return -1;
+
+        int sendHandle = -1;
+        int recvHandle = -1;
+        if (Ipc::CreateMailboxHandlePair(sendHandle, recvHandle) < 0) return -1;
+
+        *outSendHandle = sendHandle;
+        *outRecvHandle = recvHandle;
+        return 0;
+    }
+
+    static int Sys_MailboxSend(int handle, uint32_t msgType, const void* data, uint16_t len, int attachHandle) {
+        return Ipc::MailboxSendHandle(handle, msgType, data, len, attachHandle);
+    }
+
+    static int Sys_MailboxRecv(int handle, uint32_t* outMsgType, void* data,
+                               uint16_t* inOutLen, int* outAttachHandle) {
+        return Ipc::MailboxRecvHandle(handle, outMsgType, data, inOutLen, outAttachHandle);
+    }
+
+    static int Sys_WaitsetCreate() {
+        return Ipc::CreateWaitsetHandleForCurrent();
+    }
+
+    static int Sys_WaitsetAdd(int waitsetHandle, int targetHandle, uint32_t signals) {
+        return Ipc::WaitsetAddHandle(waitsetHandle, targetHandle, signals);
+    }
+
+    static int Sys_WaitsetRemove(int waitsetHandle, int index) {
+        return Ipc::WaitsetRemoveIndex(waitsetHandle, index);
+    }
+
+    static int Sys_WaitsetWait(int waitsetHandle, IpcWaitResult* outReady, uint64_t timeoutMs) {
+        Ipc::WaitsetReady ready = {-1, 0};
+        int result = Ipc::WaitsetWaitHandle(waitsetHandle, outReady ? &ready : nullptr, timeoutMs);
+        if (result > 0 && outReady != nullptr) {
+            outReady->index = ready.index;
+            outReady->signals = ready.signals;
+        }
+        return result;
+    }
+
+    static int Sys_ProcOpen(int pid) {
+        return Ipc::OpenProcessHandle(pid);
+    }
+
+    static int Sys_SurfaceCreate(uint64_t byteSize) {
+        return Ipc::CreateSurfaceHandle(byteSize);
+    }
+
+    static uint64_t Sys_SurfaceMap(int handle) {
+        return Ipc::MapSurfaceHandle(handle);
+    }
+
+    static int Sys_SurfaceResize(int handle, uint64_t newSize) {
+        return Ipc::ResizeSurfaceHandle(handle, newSize);
+    }
+
+}

kernel/src/Api/Keyboard.hpp

@@ -7,6 +7,7 @@
 #pragma once
 #include <Sched/Scheduler.hpp>
 #include <Drivers/PS2/Keyboard.hpp>
+#include <Libraries/Memory.hpp>
 
 #include "Common.hpp"
 
@@ -14,8 +15,8 @@ namespace Montauk {
     static bool Sys_IsKeyAvailable() {
         auto* proc = Sched::GetCurrentProcessPtr();
         if (proc && proc->redirected) {
-            auto* target = GetRedirTarget(proc);
+            Ipc::Mailbox* mailbox = GetRedirKeyMailbox(proc);
-            if (target) return target->keyHead != target->keyTail;
+            if (mailbox != nullptr) return Ipc::MailboxHasMessage(mailbox);
         }
         return Drivers::PS2::Keyboard::IsKeyAvailable();
     }
@@ -24,15 +25,18 @@ namespace Montauk {
         if (outEvent == nullptr) return;
         auto* proc = Sched::GetCurrentProcessPtr();
         if (proc && proc->redirected) {
-            auto* target = GetRedirTarget(proc);
+            Ipc::Mailbox* mailbox = GetRedirKeyMailbox(proc);
-            if (target) {
+            if (mailbox != nullptr) {
-                // Wait for key in target's keyBuf ring
+                for (;;) {
-                while (target->keyHead == target->keyTail) {
+                    uint16_t len = sizeof(KeyEvent);
-                    Sched::Schedule();
+                    int rc = Ipc::MailboxRecv(mailbox, nullptr, outEvent, &len, true);
+                    if (rc > 0) return;
+                    if (rc < 0) {
+                        memset(outEvent, 0, sizeof(KeyEvent));
+                        return;
+                    }
+                    Sched::BlockOnObject(mailbox, 0);
                 }
-                *outEvent = target->keyBuf[target->keyTail];
-                target->keyTail = (target->keyTail + 1) % 64;
-                return;
             }
         }
         auto k = Drivers::PS2::Keyboard::GetKey();
@@ -47,24 +51,40 @@ namespace Montauk {
     static char Sys_GetChar() {
         auto* proc = Sched::GetCurrentProcessPtr();
         if (proc && proc->redirected) {
-            auto* target = GetRedirTarget(proc);
+            Ipc::Stream* input = GetRedirInStream(proc);
-            if (target) {
+            Ipc::Mailbox* mailbox = GetRedirKeyMailbox(proc);
-                while (true) {
+            if (input != nullptr || mailbox != nullptr) {
-                    if (target->inBuf && target->inTail != target->inHead) {
+                for (;;) {
-                        uint8_t c = target->inBuf[target->inTail];
+                    if (input != nullptr) {
-                        target->inTail = (target->inTail + 1) % Sched::Process::IoBufSize;
+                        uint8_t c = 0;
-                        return (char)c;
+                        int rc = Ipc::StreamRead(input, &c, 1, true);
+                        if (rc > 0) return (char)c;
+                        if (rc < 0 && mailbox == nullptr) return 0;
                     }
 
-                    if (target->keyTail != target->keyHead) {
+                    if (mailbox != nullptr) {
-                        auto ev = target->keyBuf[target->keyTail];
+                        KeyEvent ev{};
-                        target->keyTail = (target->keyTail + 1) % 64;
+                        uint16_t len = sizeof(ev);
-                        if (ev.pressed && ev.ascii != 0) {
+                        int rc = Ipc::MailboxRecv(mailbox, nullptr, &ev, &len, true);
-                            return ev.ascii;
+                        if (rc > 0) {
+                            if (ev.pressed && ev.ascii != 0) return ev.ascii;
+                            continue;
                         }
+                        if (rc < 0 && input == nullptr) return 0;
                     }
 
-                    Sched::Schedule();
+                    if (proc->ioWaitsetHandle >= 0) {
+                        Ipc::WaitsetReady ready{};
+                        if (Ipc::WaitsetWaitHandle(proc->ioWaitsetHandle, &ready, ~0ULL) < 0) {
+                            return 0;
+                        }
+                    } else if (input != nullptr) {
+                        Sched::BlockOnObject(input, 0);
+                    } else if (mailbox != nullptr) {
+                        Sched::BlockOnObject(mailbox, 0);
+                    } else {
+                        return 0;
+                    }
                 }
             }
         }

kernel/src/Api/Process.hpp

@@ -14,6 +14,7 @@
 #include <Fs/Vfs.hpp>
 
 #include "Syscall.hpp"
+#include "Common.hpp"
 #include "WinServer.hpp"
 #include "Path.hpp"
 
@@ -44,22 +45,32 @@ namespace Montauk {
         if (!ResolveProcessPath(path, resolved, sizeof(resolved))) return -1;
 
         auto* parent = Sched::GetCurrentProcessPtr();
+        int parentSlot = Ipc::CurrentSlot();
         int childPid = Sched::Spawn(resolved, args);
         if (childPid < 0) return childPid;
 
-            // Inherit I/O redirection: if the parent is redirected, the child
-            // is marked redirected too. It stores a parentPid pointing to the
-            // process that owns the actual ring buffers (the one spawned via
-            // spawn_redir). The child does NOT get its own buffers — Sys_Print
-            // et al. look up the buffer owner at write time.
         if (parent && parent->redirected) {
             auto* child = Sched::GetProcessByPid(childPid);
-            if (child) {
+            int childSlot = Ipc::SlotForPid(childPid);
-                child->redirected = true;
+            if (child == nullptr || childSlot < 0 || parentSlot < 0) {
-                // Point to the buffer owner: if parent owns buffers, target parent;
+                Sched::KillProcess(childPid);
-                // if parent itself inherited, follow the chain.
+                return -1;
-                child->parentPid = parent->outBuf ? parent->pid : parent->parentPid;
             }
+
+            child->ioOutHandle = DuplicateHandleBetweenSlots(parentSlot, parent->ioOutHandle, childSlot);
+            child->ioInHandle = DuplicateHandleBetweenSlots(parentSlot, parent->ioInHandle, childSlot);
+            child->ioKeyHandle = DuplicateHandleBetweenSlots(parentSlot, parent->ioKeyHandle, childSlot);
+
+            if (child->ioOutHandle < 0 || child->ioInHandle < 0 || child->ioKeyHandle < 0 ||
+                !ConfigureRedirWaitsetForSlot(childSlot, child)) {
+                Sched::KillProcess(childPid);
+                return -1;
+            }
+
+            child->redirected = true;
+            child->parentPid = parent->pid;
+            child->termCols = parent->termCols;
+            child->termRows = parent->termRows;
         }
 
         return childPid;
@@ -157,9 +168,9 @@ namespace Montauk {
             const char* entries[1];
             if (Fs::Vfs::VfsReadDir(resolved, entries, 1) < 0) return -1;
         } else {
-            int handle = Fs::Vfs::VfsOpen(resolved);
+            Fs::Vfs::BackendFile file = {-1, -1};
-            if (handle < 0) return -1;
+            if (Fs::Vfs::OpenBackendFile(resolved, file) < 0) return -1;
-            Fs::Vfs::VfsClose(handle);
+            Fs::Vfs::CloseBackendFile(file);
         }
 
         int i = 0;

kernel/src/Api/Syscall.cpp

@@ -32,6 +32,7 @@
 #include "Window.hpp"     // SYS_WINCREATE, SYS_WINDESTROY, SYS_WINPRESENT, SYS_WINPOLL, SYS_WINENUM, SYS_WINMAP, SYS_WINSENDEVENT, SYS_WINRESIZE, SYS_WINSETSCALE, SYS_WINGETSCALE
 #include "Audio.hpp"      // SYS_AUDIOOPEN, SYS_AUDIOCLOSE, SYS_AUDIOWRITE, SYS_AUDIOCTL
 #include "BluetoothSyscall.hpp" // SYS_BTSCAN, SYS_BTCONNECT, SYS_BTDISCONNECT, SYS_BTLIST, SYS_BTINFO
+#include "IpcSyscall.hpp" // SYS_DUPHANDLE, SYS_WAIT_HANDLE, SYS_STREAM_CREATE, SYS_STREAM_READ, SYS_STREAM_WRITE, SYS_MAILBOX_CREATE, SYS_MAILBOX_SEND, SYS_MAILBOX_RECV, SYS_WAITSET_CREATE, SYS_WAITSET_ADD, SYS_WAITSET_REMOVE, SYS_WAITSET_WAIT, SYS_PROC_OPEN, SYS_SURFACE_CREATE, SYS_SURFACE_MAP, SYS_SURFACE_RESIZE
 
 // Assembly entry point
 extern "C" void SyscallEntry();
@@ -256,6 +257,8 @@ namespace Montauk {
                 return (int64_t)Sys_WinEnum((WinInfo*)frame->arg1, (int)frame->arg2);
             case SYS_WINMAP:
                 return (int64_t)Sys_WinMap((int)frame->arg1);
+            case SYS_WINUNMAP:
+                return (int64_t)Sys_WinUnmap((int)frame->arg1);
             case SYS_WINSENDEVENT:
                 if (!ValidUserPtr(frame->arg2)) return -1;
                 return (int64_t)Sys_WinSendEvent((int)frame->arg1, (const WinEvent*)frame->arg2);
@@ -353,6 +356,56 @@ namespace Montauk {
             case SYS_CHDIR:
                 if (!ValidUserPtr(frame->arg1)) return -1;
                 return Sys_Chdir((const char*)frame->arg1);
+            case SYS_DUPHANDLE:
+                return Sys_DupHandle((int)frame->arg1);
+            case SYS_WAIT_HANDLE:
+                return (int64_t)Sys_WaitHandle((int)frame->arg1, (uint32_t)frame->arg2, frame->arg3);
+            case SYS_STREAM_CREATE:
+                if (!ValidUserPtr(frame->arg1) || !ValidUserPtr(frame->arg2)) return -1;
+                return Sys_StreamCreate((int*)frame->arg1, (int*)frame->arg2, (uint32_t)frame->arg3);
+            case SYS_STREAM_READ:
+                if (!ValidUserPtr(frame->arg2)) return -1;
+                return Sys_StreamRead((int)frame->arg1, (uint8_t*)frame->arg2, (int)frame->arg3);
+            case SYS_STREAM_WRITE:
+                if (!ValidUserPtr(frame->arg2)) return -1;
+                return Sys_StreamWrite((int)frame->arg1, (const uint8_t*)frame->arg2, (int)frame->arg3);
+            case SYS_MAILBOX_CREATE:
+                if (!ValidUserPtr(frame->arg1) || !ValidUserPtr(frame->arg2)) return -1;
+                return Sys_MailboxCreate((int*)frame->arg1, (int*)frame->arg2);
+            case SYS_MAILBOX_SEND:
+                if (frame->arg3 != 0 && !ValidUserPtr(frame->arg3)) return -1;
+                return Sys_MailboxSend((int)frame->arg1, (uint32_t)frame->arg2,
+                                       (const void*)frame->arg3, (uint16_t)frame->arg4,
+                                       (int)frame->arg5);
+            case SYS_MAILBOX_RECV:
+                if (frame->arg2 != 0 && !IsUserPtr(frame->arg2)) return -1;
+                if (frame->arg3 != 0 && !IsUserPtr(frame->arg3)) return -1;
+                if (!ValidUserPtr(frame->arg4)) return -1;
+                if (frame->arg5 != 0 && !IsUserPtr(frame->arg5)) return -1;
+                return Sys_MailboxRecv((int)frame->arg1,
+                                       IsUserPtr(frame->arg2) ? (uint32_t*)frame->arg2 : nullptr,
+                                       IsUserPtr(frame->arg3) ? (void*)frame->arg3 : nullptr,
+                                       (uint16_t*)frame->arg4,
+                                       IsUserPtr(frame->arg5) ? (int*)frame->arg5 : nullptr);
+            case SYS_WAITSET_CREATE:
+                return Sys_WaitsetCreate();
+            case SYS_WAITSET_ADD:
+                return Sys_WaitsetAdd((int)frame->arg1, (int)frame->arg2, (uint32_t)frame->arg3);
+            case SYS_WAITSET_REMOVE:
+                return Sys_WaitsetRemove((int)frame->arg1, (int)frame->arg2);
+            case SYS_WAITSET_WAIT:
+                if (frame->arg2 != 0 && !ValidUserPtr(frame->arg2)) return -1;
+                return Sys_WaitsetWait((int)frame->arg1,
+                                       IsUserPtr(frame->arg2) ? (IpcWaitResult*)frame->arg2 : nullptr,
+                                       frame->arg3);
+            case SYS_PROC_OPEN:
+                return Sys_ProcOpen((int)frame->arg1);
+            case SYS_SURFACE_CREATE:
+                return Sys_SurfaceCreate(frame->arg1);
+            case SYS_SURFACE_MAP:
+                return (int64_t)Sys_SurfaceMap((int)frame->arg1);
+            case SYS_SURFACE_RESIZE:
+                return Sys_SurfaceResize((int)frame->arg1, frame->arg2);
             default:
                 return -1;
         }

kernel/src/Api/Syscall.hpp

@@ -123,6 +123,7 @@ namespace Montauk {
     static constexpr uint64_t SYS_WINPOLL      = 57;
     static constexpr uint64_t SYS_WINENUM      = 58;
     static constexpr uint64_t SYS_WINMAP       = 59;
+    static constexpr uint64_t SYS_WINUNMAP     = 97;
     static constexpr uint64_t SYS_WINSENDEVENT = 60;
     static constexpr uint64_t SYS_WINRESIZE    = 64;
     static constexpr uint64_t SYS_WINSETSCALE  = 65;
@@ -187,6 +188,30 @@ namespace Montauk {
     static constexpr uint64_t SYS_GETCWD        = 95;
     static constexpr uint64_t SYS_CHDIR         = 96;
 
+    /* IpcSyscall.hpp */
+    static constexpr uint64_t SYS_DUPHANDLE     = 98;
+    static constexpr uint64_t SYS_WAIT_HANDLE   = 99;
+    static constexpr uint64_t SYS_STREAM_CREATE = 100;
+    static constexpr uint64_t SYS_STREAM_READ   = 101;
+    static constexpr uint64_t SYS_STREAM_WRITE  = 102;
+    static constexpr uint64_t SYS_MAILBOX_CREATE = 103;
+    static constexpr uint64_t SYS_MAILBOX_SEND   = 104;
+    static constexpr uint64_t SYS_MAILBOX_RECV   = 105;
+    static constexpr uint64_t SYS_WAITSET_CREATE = 106;
+    static constexpr uint64_t SYS_WAITSET_ADD    = 107;
+    static constexpr uint64_t SYS_WAITSET_REMOVE = 108;
+    static constexpr uint64_t SYS_WAITSET_WAIT   = 109;
+    static constexpr uint64_t SYS_PROC_OPEN      = 110;
+    static constexpr uint64_t SYS_SURFACE_CREATE = 111;
+    static constexpr uint64_t SYS_SURFACE_MAP    = 112;
+    static constexpr uint64_t SYS_SURFACE_RESIZE = 113;
+
+    static constexpr uint32_t IPC_SIGNAL_READABLE   = 1u << 0;
+    static constexpr uint32_t IPC_SIGNAL_WRITABLE   = 1u << 1;
+    static constexpr uint32_t IPC_SIGNAL_PEER_CLOSED = 1u << 2;
+    static constexpr uint32_t IPC_SIGNAL_EXITED     = 1u << 3;
+    static constexpr uint32_t IPC_SIGNAL_READY      = 1u << 4;
+
     static constexpr int SOCK_TCP = 1;
     static constexpr int SOCK_UDP = 2;
 
@@ -239,6 +264,11 @@ namespace Montauk {
         uint8_t  buttons;
     };
 
+    struct IpcWaitResult {
+        int32_t index;
+        uint32_t signals;
+    };
+
     // Window server shared types
     struct WinEvent {
         uint8_t type;     // 0=key, 1=mouse, 2=resize, 3=close, 4=scale

kernel/src/Api/Terminal.hpp

@@ -15,10 +15,12 @@ namespace Montauk {
     static void Sys_Print(const char* text) {
         auto* proc = Sched::GetCurrentProcessPtr();
         if (proc && proc->redirected) {
-            auto* target = GetRedirTarget(proc);
+            Ipc::Stream* stream = GetRedirOutStream(proc);
-            if (target && target->outBuf) {
+            if (stream != nullptr) {
-                for (int i = 0; text[i]; i++) {
+                int len = 0;
-                    RingWrite(target->outBuf, target->outHead, target->outTail, Sched::Process::IoBufSize, (uint8_t)text[i]);
+                while (text[len]) len++;
+                if (len > 0) {
+                    WriteAllToStream(stream, (const uint8_t*)text, len);
                 }
                 return;
             }
@@ -31,9 +33,10 @@ namespace Montauk {
     static void Sys_Putchar(char c) {
         auto* proc = Sched::GetCurrentProcessPtr();
         if (proc && proc->redirected) {
-            auto* target = GetRedirTarget(proc);
+            Ipc::Stream* stream = GetRedirOutStream(proc);
-            if (target && target->outBuf) {
+            if (stream != nullptr) {
-                RingWrite(target->outBuf, target->outHead, target->outTail, Sched::Process::IoBufSize, (uint8_t)c);
+                uint8_t byte = (uint8_t)c;
+                WriteAllToStream(stream, &byte, 1);
                 return;
             }
         }

kernel/src/Api/WinServer.cpp

@@ -5,118 +5,104 @@
 */
 
 #include "WinServer.hpp"
-#include <Memory/PageFrameAllocator.hpp>
-#include <Memory/Paging.hpp>
-#include <Memory/HHDM.hpp>
 #include <Libraries/Memory.hpp>
 #include <Terminal/Terminal.hpp>
 #include <CppLib/Spinlock.hpp>
 #include <Sched/Scheduler.hpp>
-#include <Timekeeping/ApicTimer.hpp>
 
 namespace WinServer {
 
     static WindowSlot g_slots[MaxWindows];
     static int g_uiScale = 1;
     static kcp::Mutex wsLock;
-    static constexpr uint64_t RetireGraceMs = 2000;
+    static constexpr int MaxRetiredSnapshots = MaxWindows * 4;
-    static constexpr int MaxRetiredBatches = MaxWindows * 4;
 
-    struct RetiredBatch {
+    struct RetiredSnapshot {
         bool used;
-        int numPages;
+        int windowId;
-        uint64_t freeAfterMs;
+        Ipc::Surface* surface;
-        uint64_t physPages[MaxPixelPages];
     };
 
-    static RetiredBatch g_retired[MaxRetiredBatches];
+    static RetiredSnapshot g_retiredSnapshots[MaxRetiredSnapshots];
 
-    // RAII lock guard for WinServer operations
     struct WsGuard {
         WsGuard()  { wsLock.Acquire(); }
         ~WsGuard() { wsLock.Release(); }
     };
 
-    static void FreePageBatchLocked(uint64_t* physPages, int numPages) {
+    static void ResetSlotLocked(WindowSlot& slot) {
-        for (int i = 0; i < numPages; i++) {
+        memset(&slot, 0, sizeof(WindowSlot));
-            if (physPages[i] != 0) {
-                Memory::g_pfa->Free((void*)Memory::HHDM(physPages[i]));
-                physPages[i] = 0;
-            }
-        }
     }
 
-    static void ProcessRetiredLocked() {
+    static void RetireSnapshotLocked(int windowId, Ipc::Surface* surface) {
-        uint64_t now = Timekeeping::GetMilliseconds();
+        if (surface == nullptr) return;
-        for (int i = 0; i < MaxRetiredBatches; i++) {
-            if (!g_retired[i].used) continue;
-            if (now < g_retired[i].freeAfterMs) continue;
-            FreePageBatchLocked(g_retired[i].physPages, g_retired[i].numPages);
-            g_retired[i].used = false;
-            g_retired[i].numPages = 0;
-            g_retired[i].freeAfterMs = 0;
-        }
-    }
 
-    static void RetirePageBatchLocked(uint64_t* physPages, int numPages) {
+        for (int i = 0; i < MaxRetiredSnapshots; i++) {
-        if (numPages <= 0) return;
+            if (g_retiredSnapshots[i].used) continue;
-
+            g_retiredSnapshots[i].used = true;
-        int retireIdx = -1;
+            g_retiredSnapshots[i].windowId = windowId;
-        for (int i = 0; i < MaxRetiredBatches; i++) {
+            g_retiredSnapshots[i].surface = surface;
-            if (!g_retired[i].used) {
-                retireIdx = i;
-                break;
-            }
-        }
-
-        if (retireIdx < 0) {
-            ProcessRetiredLocked();
-            for (int i = 0; i < MaxRetiredBatches; i++) {
-                if (!g_retired[i].used) {
-                    retireIdx = i;
-                    break;
-                }
-            }
-        }
-
-        if (retireIdx < 0) {
-            uint64_t oldest = ~0ULL;
-            for (int i = 0; i < MaxRetiredBatches; i++) {
-                if (g_retired[i].freeAfterMs < oldest) {
-                    oldest = g_retired[i].freeAfterMs;
-                    retireIdx = i;
-                }
-            }
-            if (retireIdx >= 0) {
-                Kt::KernelLogStream(Kt::ERROR, "WinServer")
-                    << "Retire queue full, forcing early free of stale window pages";
-                FreePageBatchLocked(g_retired[retireIdx].physPages, g_retired[retireIdx].numPages);
-                g_retired[retireIdx].used = false;
-                g_retired[retireIdx].numPages = 0;
-                g_retired[retireIdx].freeAfterMs = 0;
-            }
-        }
-
-        if (retireIdx < 0) {
-            FreePageBatchLocked(physPages, numPages);
             return;
         }
 
-        RetiredBatch& batch = g_retired[retireIdx];
+        Ipc::ReleaseSurface(surface);
-        batch.used = true;
+    }
-        batch.numPages = numPages;
+
-        batch.freeAfterMs = Timekeeping::GetMilliseconds() + RetireGraceMs;
+    static int UnmapRetiredSnapshotsLocked(int windowId, int callerPid, uint64_t callerPml4) {
-        for (int i = 0; i < numPages; i++) {
+        int result = -1;
-            batch.physPages[i] = physPages[i];
+        for (int i = 0; i < MaxRetiredSnapshots; i++) {
-            physPages[i] = 0;
+            if (!g_retiredSnapshots[i].used || g_retiredSnapshots[i].windowId != windowId) continue;
+
+            if (g_retiredSnapshots[i].surface != nullptr) {
+                if (Ipc::UnmapSurfaceForPid(g_retiredSnapshots[i].surface, callerPid, callerPml4) == 0) {
+                    result = 0;
+                }
+                Ipc::ReleaseSurface(g_retiredSnapshots[i].surface);
+            }
+
+            g_retiredSnapshots[i].used = false;
+            g_retiredSnapshots[i].windowId = -1;
+            g_retiredSnapshots[i].surface = nullptr;
         }
+        return result;
+    }
+
+    static void ReleaseSlotResourcesLocked(WindowSlot& slot, bool unmapOwner) {
+        if (unmapOwner && slot.liveSurface != nullptr) {
+            auto* owner = Sched::GetProcessByPid(slot.ownerPid);
+            if (owner != nullptr) {
+                Ipc::UnmapSurfaceForPid(slot.liveSurface, slot.ownerPid, owner->pml4Phys);
+            }
+        }
+
+        if (slot.eventMailbox != nullptr) {
+            Ipc::ReleaseMailbox(slot.eventMailbox, true, true);
+        }
+        if (slot.liveSurface != nullptr) {
+            Ipc::ReleaseSurface(slot.liveSurface);
+        }
+        if (slot.snapshotSurface != nullptr) {
+            RetireSnapshotLocked((int)(&slot - g_slots), slot.snapshotSurface);
+        }
+
+        ResetSlotLocked(slot);
+    }
+
+    static int SendEventLocked(int windowId, const Montauk::WinEvent* event) {
+        if (windowId < 0 || windowId >= MaxWindows || event == nullptr) return -1;
+        WindowSlot& slot = g_slots[windowId];
+        if (!slot.used || slot.eventMailbox == nullptr) return -1;
+
+        int rc = Ipc::MailboxSend(slot.eventMailbox, 0, event, sizeof(*event));
+        return rc > 0 ? 0 : -1;
     }
 
     int Create(int ownerPid, uint64_t ownerPml4, const char* title, int w, int h,
                uint64_t& heapNext, uint64_t& outVa) {
         WsGuard guard;
-        ProcessRetiredLocked();
+
-        // Find a free slot
+        if (w <= 0 || h <= 0 || w > 16384 || h > 16384) return -1;
+
         int slotIdx = -1;
         for (int i = 0; i < MaxWindows; i++) {
             if (!g_slots[i].used) {
@@ -126,26 +112,42 @@ namespace WinServer {
         }
         if (slotIdx < 0) return -1;
 
-        // Validate dimensions (cap at 16384 to prevent integer overflow in w*h*4)
+        uint64_t bufSize = (uint64_t)w * (uint64_t)h * 4ULL;
-        if (w <= 0 || h <= 0 || w > 16384 || h > 16384) return -1;
+        Ipc::Surface* live = Ipc::CreateSurface(bufSize);
-        uint64_t bufSize = (uint64_t)w * h * 4;
+        Ipc::Surface* snapshot = Ipc::CreateSurface(bufSize);
-        int numPages = (int)((bufSize + 0xFFF) / 0x1000);
+        Ipc::Mailbox* mailbox = Ipc::CreateMailbox();
-        if (numPages > MaxPixelPages) return -1;
+        if (live == nullptr || snapshot == nullptr || mailbox == nullptr) {
+            if (live != nullptr) Ipc::ReleaseSurface(live);
+            if (snapshot != nullptr) Ipc::ReleaseSurface(snapshot);
+            if (mailbox != nullptr) Ipc::ReleaseMailbox(mailbox, false, false);
+            return -1;
+        }
+
+        Ipc::RetainSurface(live);
+        Ipc::RetainSurface(snapshot);
+        Ipc::RetainMailbox(mailbox, true, true);
+
+        uint64_t userVa = 0;
+        if (Ipc::MapSurfaceForPid(live, ownerPid, ownerPml4, heapNext, userVa) != 0) {
+            Ipc::ReleaseMailbox(mailbox, true, true);
+            Ipc::ReleaseSurface(snapshot);
+            Ipc::ReleaseSurface(live);
+            return -1;
+        }
 
         WindowSlot& slot = g_slots[slotIdx];
-        memset(&slot, 0, sizeof(WindowSlot));
+        ResetSlotLocked(slot);
         slot.used = true;
         slot.ownerPid = ownerPid;
         slot.width = w;
         slot.height = h;
-        slot.pixelNumPages = numPages;
+        slot.liveSurface = live;
-        slot.eventHead = 0;
+        slot.snapshotSurface = snapshot;
-        slot.eventTail = 0;
+        slot.eventMailbox = mailbox;
+        slot.ownerVa = userVa;
         slot.dirty = false;
-        slot.desktopVa = 0;
+        slot.cursor = 0;
-        slot.desktopPid = 0;
 
-        // Copy title
         int tlen = 0;
         while (title[tlen] && tlen < 63) {
             slot.title[tlen] = title[tlen];
@@ -153,127 +155,55 @@ namespace WinServer {
         }
         slot.title[tlen] = '\0';
 
-        // Allocate live pixel pages (app renders here) and snapshot pages
-        // (compositor reads here). Present copies live -> snapshot.
-        uint64_t userVa = heapNext;
-        for (int i = 0; i < numPages; i++) {
-            void* page = Memory::g_pfa->AllocateZeroed();
-            if (page == nullptr) {
-                slot.used = false;
-                return -1;
-            }
-            uint64_t physAddr = Memory::SubHHDM((uint64_t)page);
-            slot.pixelPhysPages[i] = physAddr;
-            if (!Memory::VMM::Paging::MapUserIn(ownerPml4, physAddr, userVa + (uint64_t)i * 0x1000)) {
-                slot.used = false;
-                return -1;
-            }
-
-            // Allocate corresponding snapshot page
-            void* snapPage = Memory::g_pfa->AllocateZeroed();
-            if (snapPage == nullptr) {
-                slot.used = false;
-                return -1;
-            }
-            slot.snapshotPhysPages[i] = Memory::SubHHDM((uint64_t)snapPage);
-        }
-
-        slot.ownerVa = userVa;
-        heapNext += (uint64_t)numPages * 0x1000;
         outVa = userVa;
-
-        Kt::KernelLogStream(Kt::OK, "WinServer") << "Created window " << slotIdx
-            << " (" << w << "x" << h << ") for PID " << ownerPid;
-
         return slotIdx;
     }
 
     int Destroy(int windowId, int callerPid) {
         WsGuard guard;
-        ProcessRetiredLocked();
         if (windowId < 0 || windowId >= MaxWindows) return -1;
+
         WindowSlot& slot = g_slots[windowId];
         if (!slot.used || slot.ownerPid != callerPid) return -1;
 
-        // Unmap LIVE pixel pages from the owner's address space so that
+        ReleaseSlotResourcesLocked(slot, true);
-        // FreeUserHalf() won't double-free them when the process exits.
-        // Physical page reclamation is deferred below to avoid stale-TLB
-        // consumers reading freed memory.
-        {
-            auto* ownerProc = Sched::GetProcessByPid(slot.ownerPid);
-            if (ownerProc) {
-                for (int p = 0; p < slot.pixelNumPages; p++) {
-                    Memory::VMM::Paging::UnmapUserIn(
-                        ownerProc->pml4Phys,
-                        slot.ownerVa + (uint64_t)p * 0x1000);
-                }
-            }
-        }
-
-        // Retire both the owner-facing live pages and the compositor-facing
-        // snapshot pages. The desktop can still hold stale mappings to the
-        // snapshot pages for a short time after Enumerate notices the window
-        // is gone, so freeing them immediately turns that stale mapping into
-        // a use-after-free.
-        RetirePageBatchLocked(slot.pixelPhysPages, slot.pixelNumPages);
-        RetirePageBatchLocked(slot.snapshotPhysPages, slot.pixelNumPages);
-
-        slot.used = false;
-        slot.pixelNumPages = 0;
-        slot.ownerVa = 0;
-        slot.desktopVa = 0;
-        slot.desktopPid = 0;
         return 0;
     }
 
     int Present(int windowId, int callerPid) {
-        // Validate ownership under the lock (brief)
+        WsGuard guard;
-        wsLock.Acquire();
+        if (windowId < 0 || windowId >= MaxWindows) return -1;
-        ProcessRetiredLocked();
-        if (windowId < 0 || windowId >= MaxWindows) { wsLock.Release(); return -1; }
-        WindowSlot& slot = g_slots[windowId];
-        if (!slot.used || slot.ownerPid != callerPid) { wsLock.Release(); return -1; }
-        int numPages = slot.pixelNumPages;
-        wsLock.Release();
 
-        // Snapshot memcpy OUTSIDE the lock. This is safe because only the
+        WindowSlot& slot = g_slots[windowId];
-        // owning process calls Present/Resize, and a process runs on one
+        if (!slot.used || slot.ownerPid != callerPid ||
-        // CPU at a time. Holding wsLock during an 8MB copy would block
+            slot.liveSurface == nullptr || slot.snapshotSurface == nullptr) {
-        // ALL other WinServer operations (Poll, Enumerate, SendEvent)
+            return -1;
-        // across all CPUs, causing convoy stalls and lockups.
-        for (int i = 0; i < numPages; i++) {
-            void* src = (void*)Memory::HHDM(slot.pixelPhysPages[i]);
-            void* dst = (void*)Memory::HHDM(slot.snapshotPhysPages[i]);
-            memcpy(dst, src, 0x1000);
         }
 
-        // Set dirty under lock
+        if (Ipc::CopySurface(slot.snapshotSurface, slot.liveSurface) != 0) return -1;
-        wsLock.Acquire();
         slot.dirty = true;
-        wsLock.Release();
         return 0;
     }
 
     int Poll(int windowId, int callerPid, Montauk::WinEvent* outEvent) {
         WsGuard guard;
-        ProcessRetiredLocked();
+        if (windowId < 0 || windowId >= MaxWindows || outEvent == nullptr) return -1;
-        if (windowId < 0 || windowId >= MaxWindows) return -1;
+
         WindowSlot& slot = g_slots[windowId];
-        if (!slot.used || slot.ownerPid != callerPid) return -1;
+        if (!slot.used || slot.ownerPid != callerPid || slot.eventMailbox == nullptr) return -1;
 
-        if (slot.eventHead == slot.eventTail) return 0; // no events
+        uint16_t len = sizeof(*outEvent);
-
+        int rc = Ipc::MailboxRecv(slot.eventMailbox, nullptr, outEvent, &len, true);
-        *outEvent = slot.events[slot.eventTail];
+        if (rc < 0) return -1;
-        slot.eventTail = (slot.eventTail + 1) % MaxEvents;
+        return rc > 0 ? 1 : 0;
-        return 1;
     }
 
     int Enumerate(Montauk::WinInfo* outArray, int maxCount) {
         WsGuard guard;
-        ProcessRetiredLocked();
         int count = 0;
         for (int i = 0; i < MaxWindows && count < maxCount; i++) {
             if (!g_slots[i].used) continue;
+
             Montauk::WinInfo& info = outArray[count];
             info.id = i;
             info.ownerPid = g_slots[i].ownerPid;
@@ -282,7 +212,7 @@ namespace WinServer {
             info.height = g_slots[i].height;
             info.dirty = g_slots[i].dirty ? 1 : 0;
             info.cursor = g_slots[i].cursor;
-            g_slots[i].dirty = false; // clear dirty after read
+            g_slots[i].dirty = false;
             count++;
         }
         return count;
@@ -290,59 +220,43 @@ namespace WinServer {
 
     uint64_t Map(int windowId, int callerPid, uint64_t callerPml4, uint64_t& heapNext) {
         WsGuard guard;
-        ProcessRetiredLocked();
         if (windowId < 0 || windowId >= MaxWindows) return 0;
+
         WindowSlot& slot = g_slots[windowId];
-        if (!slot.used) return 0;
+        if (!slot.used || slot.snapshotSurface == nullptr) return 0;
 
-        // If already mapped into this process, return existing VA
+        uint64_t outVa = 0;
-        if (slot.desktopPid == callerPid && slot.desktopVa != 0) {
+        if (Ipc::MapSurfaceForPid(slot.snapshotSurface, callerPid, callerPml4, heapNext, outVa) != 0) {
-            return slot.desktopVa;
+            return 0;
         }
-
+        return outVa;
-        uint64_t userVa = heapNext;
-
-        // Map the SNAPSHOT pages (not live pages) so the compositor
-        // always reads a complete frame captured at Present time.
-        for (int i = 0; i < slot.pixelNumPages; i++) {
-            if (!Memory::VMM::Paging::MapUserIn(callerPml4, slot.snapshotPhysPages[i],
-                                           userVa + (uint64_t)i * 0x1000)) {
-                return 0;
-            }
-        }
-
-        slot.desktopVa = userVa;
-        slot.desktopPid = callerPid;
-        heapNext += (uint64_t)slot.pixelNumPages * 0x1000;
-
-        return userVa;
     }
 
-    // Internal: send event without acquiring lock (caller must hold wsLock)
+    int Unmap(int windowId, int callerPid, uint64_t callerPml4) {
-    static int SendEventLocked(int windowId, const Montauk::WinEvent* event) {
+        WsGuard guard;
-        if (windowId < 0 || windowId >= MaxWindows) return -1;
+        if (windowId < 0 || windowId >= MaxWindows) {
+            return UnmapRetiredSnapshotsLocked(windowId, callerPid, callerPml4);
+        }
+
+        int result = UnmapRetiredSnapshotsLocked(windowId, callerPid, callerPml4);
         WindowSlot& slot = g_slots[windowId];
-        if (!slot.used) return -1;
+        if (!slot.used || slot.snapshotSurface == nullptr) return result;
 
-        int nextHead = (slot.eventHead + 1) % MaxEvents;
+        int current = Ipc::UnmapSurfaceForPid(slot.snapshotSurface, callerPid, callerPml4);
-        if (nextHead == slot.eventTail) return -1; // queue full, drop event
+        if (current == 0) return 0;
-
+        return result;
-        slot.events[slot.eventHead] = *event;
-        slot.eventHead = nextHead;
-        return 0;
     }
 
     int SendEvent(int windowId, const Montauk::WinEvent* event) {
         WsGuard guard;
-        ProcessRetiredLocked();
         return SendEventLocked(windowId, event);
     }
 
     int Resize(int windowId, int callerPid, uint64_t ownerPml4, int newW, int newH,
                uint64_t& heapNext, uint64_t& outVa) {
         WsGuard guard;
-        ProcessRetiredLocked();
         if (windowId < 0 || windowId >= MaxWindows) return -1;
+
         WindowSlot& slot = g_slots[windowId];
         if (!slot.used || slot.ownerPid != callerPid) return -1;
         if (newW <= 0 || newH <= 0 || newW > 16384 || newH > 16384) return -1;
@@ -351,56 +265,48 @@ namespace WinServer {
             return 0;
         }
 
-        uint64_t bufSize = (uint64_t)newW * newH * 4;
+        uint64_t bufSize = (uint64_t)newW * (uint64_t)newH * 4ULL;
-        int numPages = (int)((bufSize + 0xFFF) / 0x1000);
+        Ipc::Surface* newLive = Ipc::CreateSurface(bufSize);
-        if (numPages > MaxPixelPages) return -1;
+        Ipc::Surface* newSnapshot = Ipc::CreateSurface(bufSize);
-
+        if (newLive == nullptr || newSnapshot == nullptr) {
-        // Unmap old LIVE pixel pages from the owner's address space. Actual
+            if (newLive != nullptr) Ipc::ReleaseSurface(newLive);
-        // physical page reclamation is deferred below for both live and
+            if (newSnapshot != nullptr) Ipc::ReleaseSurface(newSnapshot);
-        // snapshot pages so stale desktop mappings cannot turn into
+            return -1;
-        // use-after-free reads during remap.
-        int oldNumPages = slot.pixelNumPages;
-        for (int i = 0; i < oldNumPages; i++) {
-            Memory::VMM::Paging::UnmapUserIn(
-                ownerPml4, slot.ownerVa + (uint64_t)i * 0x1000);
-        }
-        RetirePageBatchLocked(slot.pixelPhysPages, oldNumPages);
-        RetirePageBatchLocked(slot.snapshotPhysPages, oldNumPages);
-
-        // Allocate new live + snapshot pages and map live into owner's address space
-        uint64_t userVa = heapNext;
-        for (int i = 0; i < numPages; i++) {
-            void* page = Memory::g_pfa->AllocateZeroed();
-            if (page == nullptr) return -1;
-            uint64_t physAddr = Memory::SubHHDM((uint64_t)page);
-            slot.pixelPhysPages[i] = physAddr;
-            if (!Memory::VMM::Paging::MapUserIn(ownerPml4, physAddr, userVa + (uint64_t)i * 0x1000)) {
-                return -1;
-            }
-
-            void* snapPage = Memory::g_pfa->AllocateZeroed();
-            if (snapPage == nullptr) return -1;
-            slot.snapshotPhysPages[i] = Memory::SubHHDM((uint64_t)snapPage);
         }
 
+        Ipc::RetainSurface(newLive);
+        Ipc::RetainSurface(newSnapshot);
+
+        uint64_t newOwnerVa = 0;
+        if (Ipc::MapSurfaceForPid(newLive, callerPid, ownerPml4, heapNext, newOwnerVa) != 0) {
+            Ipc::ReleaseSurface(newSnapshot);
+            Ipc::ReleaseSurface(newLive);
+            return -1;
+        }
+
+        if (slot.liveSurface != nullptr) {
+            Ipc::UnmapSurfaceForPid(slot.liveSurface, callerPid, ownerPml4);
+            Ipc::ReleaseSurface(slot.liveSurface);
+        }
+        if (slot.snapshotSurface != nullptr) {
+            RetireSnapshotLocked(windowId, slot.snapshotSurface);
+        }
+
+        slot.liveSurface = newLive;
+        slot.snapshotSurface = newSnapshot;
         slot.width = newW;
         slot.height = newH;
-        slot.pixelNumPages = numPages;
+        slot.ownerVa = newOwnerVa;
-        slot.ownerVa = userVa;
+        slot.dirty = true;
-        heapNext += (uint64_t)numPages * 0x1000;
 
-        // Invalidate desktop mapping so it re-maps on next enumerate
+        outVa = newOwnerVa;
-        slot.desktopVa = 0;
-        slot.desktopPid = 0;
-
-        outVa = userVa;
         return 0;
     }
 
     int SetCursor(int windowId, int callerPid, int cursor) {
         WsGuard guard;
-        ProcessRetiredLocked();
         if (windowId < 0 || windowId >= MaxWindows) return -1;
+
         WindowSlot& slot = g_slots[windowId];
         if (!slot.used || slot.ownerPid != callerPid) return -1;
         slot.cursor = (uint8_t)cursor;
@@ -409,14 +315,11 @@ namespace WinServer {
 
     int SetScale(int scale) {
         WsGuard guard;
-        ProcessRetiredLocked();
         if (scale < 0) scale = 0;
         if (scale > 2) scale = 2;
         g_uiScale = scale;
 
-        // Broadcast scale event to all active windows
+        Montauk::WinEvent ev{};
-        Montauk::WinEvent ev;
-        memset(&ev, 0, sizeof(ev));
         ev.type = 4;
         ev.scale.scale = scale;
         for (int i = 0; i < MaxWindows; i++) {
@@ -433,42 +336,9 @@ namespace WinServer {
 
     void CleanupProcess(int pid) {
         WsGuard guard;
-        ProcessRetiredLocked();
         for (int i = 0; i < MaxWindows; i++) {
-            if (g_slots[i].used && g_slots[i].ownerPid == pid) {
+            if (!g_slots[i].used || g_slots[i].ownerPid != pid) continue;
-                Kt::KernelLogStream(Kt::INFO, "WinServer") << "Cleaning up window "
+            ReleaseSlotResourcesLocked(g_slots[i], false);
-                    << i << " for exited PID " << pid;
-
-                // Do NOT free live pixel pages here -- they are still mapped
-                // in the owner's page tables and FreeUserHalf() (called right
-                // after CleanupProcess) will free them.
-
-                // Snapshot pages can still be mapped into the desktop, so
-                // retire them instead of freeing them immediately.
-                RetirePageBatchLocked(g_slots[i].snapshotPhysPages, g_slots[i].pixelNumPages);
-
-                g_slots[i].used = false;
-                g_slots[i].pixelNumPages = 0;
-                g_slots[i].ownerVa = 0;
-                g_slots[i].desktopVa = 0;
-                g_slots[i].desktopPid = 0;
-            }
-
-            // If this process had windows mapped INTO it (was the desktop viewer),
-            // unmap those pixel pages so FreeUserHalf() won't free pages owned
-            // by other processes.
-            if (g_slots[i].used && g_slots[i].desktopPid == pid) {
-                auto* proc = Sched::GetProcessByPid(pid);
-                if (proc) {
-                    for (int p = 0; p < g_slots[i].pixelNumPages; p++) {
-                        Memory::VMM::Paging::UnmapUserIn(
-                            proc->pml4Phys,
-                            g_slots[i].desktopVa + (uint64_t)p * 0x1000);
-                    }
-                }
-                g_slots[i].desktopVa = 0;
-                g_slots[i].desktopPid = 0;
-            }
         }
     }
 

kernel/src/Api/WinServer.hpp

@@ -7,28 +7,23 @@
 #pragma once
 #include "Syscall.hpp"
 #include <cstdint>
+#include <Ipc/Ipc.hpp>
 
 namespace WinServer {
 
     static constexpr int MaxWindows = 8;
-    static constexpr int MaxEvents = 64;
-    static constexpr int MaxPixelPages = 8192; // up to 3840x2160 @ 32bpp = 32MB
 
     struct WindowSlot {
         bool used;
         int ownerPid;
         char title[64];
         int width, height;
-        uint64_t pixelPhysPages[MaxPixelPages];     // live buffer (app writes here)
+        Ipc::Surface* liveSurface;      // app writes here
-        uint64_t snapshotPhysPages[MaxPixelPages];   // snapshot (compositor reads here)
+        Ipc::Surface* snapshotSurface;  // compositor/viewers read here
-        int pixelNumPages;
+        Ipc::Mailbox* eventMailbox;     // input/control events for the app
-        uint64_t ownerVa;      // VA in owner's address space
+        uint64_t ownerVa;               // mapped VA of liveSurface in owner
-        uint64_t desktopVa;    // VA in desktop's address space (0 = not yet mapped)
-        int desktopPid;        // PID of the process that mapped it
-        Montauk::WinEvent events[MaxEvents];
-        int eventHead, eventTail;
         bool dirty;
-        uint8_t cursor;     // cursor style requested by app (0=arrow, 1=resize_h, 2=resize_v)
+        uint8_t cursor;                 // 0=arrow, 1=resize_h, 2=resize_v
     };
 
     int Create(int ownerPid, uint64_t ownerPml4, const char* title, int w, int h,
@@ -38,6 +33,7 @@ namespace WinServer {
     int Poll(int windowId, int callerPid, Montauk::WinEvent* outEvent);
     int Enumerate(Montauk::WinInfo* outArray, int maxCount);
     uint64_t Map(int windowId, int callerPid, uint64_t callerPml4, uint64_t& heapNext);
+    int Unmap(int windowId, int callerPid, uint64_t callerPml4);
     int SendEvent(int windowId, const Montauk::WinEvent* event);
     int Resize(int windowId, int callerPid, uint64_t ownerPml4, int newW, int newH,
                uint64_t& heapNext, uint64_t& outVa);

kernel/src/Api/Window.hpp

@@ -51,6 +51,12 @@ namespace Montauk {
         return WinServer::Map(windowId, proc->pid, proc->pml4Phys, proc->heapNext);
     }
 
+    static int Sys_WinUnmap(int windowId) {
+        auto* proc = Sched::GetCurrentProcessPtr();
+        if (proc == nullptr) return -1;
+        return WinServer::Unmap(windowId, proc->pid, proc->pml4Phys);
+    }
+
     static int Sys_WinSendEvent(int windowId, const WinEvent* event) {
         if (event == nullptr) return -1;
         return WinServer::SendEvent(windowId, event);

kernel/src/Fs/Vfs.cpp

@@ -10,14 +10,7 @@
 
 namespace Fs::Vfs {
 
-    struct HandleEntry {
-        bool inUse;
-        int driveNumber;
-        int localHandle;
-    };
-
     static FsDriver* driveTable[MaxDrives];
-    static HandleEntry handleTable[MaxHandles];
 
     // Protects handle table and driver dispatch from concurrent CPU access.
     // Uses Mutex (not Spinlock) so interrupts stay enabled while held --
@@ -49,22 +42,12 @@ namespace Fs::Vfs {
         return true;
     }
 
-    static int AllocHandle() {
-        for (int i = 0; i < MaxHandles; i++) {
-            if (!handleTable[i].inUse) return i;
-        }
-        return -1;
-    }
-
     void Initialize() {
         for (int i = 0; i < MaxDrives; i++) {
             driveTable[i] = nullptr;
         }
-        for (int i = 0; i < MaxHandles; i++) {
-            handleTable[i].inUse = false;
-        }
 
-        Kt::KernelLogStream(Kt::OK, "VFS") << "Initialized (" << MaxDrives << " drives, " << MaxHandles << " handles)";
+        Kt::KernelLogStream(Kt::OK, "VFS") << "Initialized (" << MaxDrives << " drives)";
     }
 
     int RegisterDrive(int driveNumber, FsDriver* driver) {
@@ -76,7 +59,10 @@ namespace Fs::Vfs {
         return 0;
     }
 
-    int VfsOpen(const char* path) {
+    int OpenBackendFile(const char* path, BackendFile& outFile) {
+        outFile.driveNumber = -1;
+        outFile.localHandle = -1;
+
         int drive;
         const char* localPath;
 
@@ -84,67 +70,86 @@ namespace Fs::Vfs {
         if (drive < 0 || drive >= MaxDrives || driveTable[drive] == nullptr) return -1;
 
         vfsLock.Acquire();
-
         int localHandle = driveTable[drive]->Open(localPath);
-        if (localHandle < 0) { vfsLock.Release(); return -1; }
+        vfsLock.Release();
+        if (localHandle < 0) return -1;
 
-        int globalHandle = AllocHandle();
+        outFile.driveNumber = drive;
-        if (globalHandle < 0) {
+        outFile.localHandle = localHandle;
-            driveTable[drive]->Close(localHandle);
+        return 0;
+    }
+
+    int ReadBackendFile(const BackendFile& file, uint8_t* buffer, uint64_t offset, uint64_t size) {
+        vfsLock.Acquire();
+        if (file.driveNumber < 0 || file.driveNumber >= MaxDrives || driveTable[file.driveNumber] == nullptr ||
+            file.localHandle < 0) {
             vfsLock.Release();
             return -1;
         }
 
-        handleTable[globalHandle].inUse = true;
+        int result = driveTable[file.driveNumber]->Read(file.localHandle, buffer, offset, size);
-        handleTable[globalHandle].driveNumber = drive;
-        handleTable[globalHandle].localHandle = localHandle;
-
-        vfsLock.Release();
-        return globalHandle;
-    }
-
-    int VfsRead(int handle, uint8_t* buffer, uint64_t offset, uint64_t size) {
-        vfsLock.Acquire();
-        if (handle < 0 || handle >= MaxHandles || !handleTable[handle].inUse) { vfsLock.Release(); return -1; }
-
-        HandleEntry& entry = handleTable[handle];
-        int result = driveTable[entry.driveNumber]->Read(entry.localHandle, buffer, offset, size);
         vfsLock.Release();
         return result;
     }
 
-    uint64_t VfsGetSize(int handle) {
+    uint64_t GetBackendFileSize(const BackendFile& file) {
         vfsLock.Acquire();
-        if (handle < 0 || handle >= MaxHandles || !handleTable[handle].inUse) { vfsLock.Release(); return 0; }
+        if (file.driveNumber < 0 || file.driveNumber >= MaxDrives || driveTable[file.driveNumber] == nullptr ||
+            file.localHandle < 0) {
+            vfsLock.Release();
+            return 0;
+        }
 
-        HandleEntry& entry = handleTable[handle];
+        uint64_t result = driveTable[file.driveNumber]->GetSize(file.localHandle);
-        uint64_t result = driveTable[entry.driveNumber]->GetSize(entry.localHandle);
         vfsLock.Release();
         return result;
     }
 
-    void VfsClose(int handle) {
+    bool BackendFileCanWrite(const BackendFile& file) {
         vfsLock.Acquire();
-        if (handle < 0 || handle >= MaxHandles || !handleTable[handle].inUse) { vfsLock.Release(); return; }
+        bool canWrite = file.driveNumber >= 0 && file.driveNumber < MaxDrives &&
-
+            driveTable[file.driveNumber] != nullptr &&
-        HandleEntry& entry = handleTable[handle];
+            file.localHandle >= 0 &&
-        driveTable[entry.driveNumber]->Close(entry.localHandle);
+            driveTable[file.driveNumber]->Write != nullptr;
-        entry.inUse = false;
         vfsLock.Release();
+        return canWrite;
     }
 
-    int VfsWrite(int handle, const uint8_t* buffer, uint64_t offset, uint64_t size) {
+    void CloseBackendFile(BackendFile& file) {
         vfsLock.Acquire();
-        if (handle < 0 || handle >= MaxHandles || !handleTable[handle].inUse) { vfsLock.Release(); return -1; }
+        if (file.driveNumber < 0 || file.driveNumber >= MaxDrives || driveTable[file.driveNumber] == nullptr ||
+            file.localHandle < 0) {
+            vfsLock.Release();
+            file.driveNumber = -1;
+            file.localHandle = -1;
+            return;
+        }
 
-        HandleEntry& entry = handleTable[handle];
+        driveTable[file.driveNumber]->Close(file.localHandle);
-        if (driveTable[entry.driveNumber]->Write == nullptr) { vfsLock.Release(); return -1; }
+        vfsLock.Release();
-        int result = driveTable[entry.driveNumber]->Write(entry.localHandle, buffer, offset, size);
+
+        file.driveNumber = -1;
+        file.localHandle = -1;
+    }
+
+    int WriteBackendFile(const BackendFile& file, const uint8_t* buffer, uint64_t offset, uint64_t size) {
+        vfsLock.Acquire();
+        if (file.driveNumber < 0 || file.driveNumber >= MaxDrives || driveTable[file.driveNumber] == nullptr ||
+            file.localHandle < 0) {
+            vfsLock.Release();
+            return -1;
+        }
+
+        if (driveTable[file.driveNumber]->Write == nullptr) { vfsLock.Release(); return -1; }
+        int result = driveTable[file.driveNumber]->Write(file.localHandle, buffer, offset, size);
         vfsLock.Release();
         return result;
     }
 
-    int VfsCreate(const char* path) {
+    int CreateBackendFile(const char* path, BackendFile& outFile) {
+        outFile.driveNumber = -1;
+        outFile.localHandle = -1;
+
         int drive;
         const char* localPath;
 
@@ -155,20 +160,12 @@ namespace Fs::Vfs {
         vfsLock.Acquire();
 
         int localHandle = driveTable[drive]->Create(localPath);
-        if (localHandle < 0) { vfsLock.Release(); return -1; }
-
-        int globalHandle = AllocHandle();
-        if (globalHandle < 0) {
-            vfsLock.Release();
-            return -1;
-        }
-
-        handleTable[globalHandle].inUse = true;
-        handleTable[globalHandle].driveNumber = drive;
-        handleTable[globalHandle].localHandle = localHandle;
-
         vfsLock.Release();
-        return globalHandle;
+        if (localHandle < 0) return -1;
+
+        outFile.driveNumber = drive;
+        outFile.localHandle = localHandle;
+        return 0;
     }
 
     int VfsDelete(const char* path) {

kernel/src/Fs/Vfs.hpp

@@ -11,7 +11,11 @@
 namespace Fs::Vfs {
 
     static constexpr int MaxDrives = 16;
-    static constexpr int MaxHandles = 64;
+
+    struct BackendFile {
+        int driveNumber;
+        int localHandle;
+    };
 
     struct FsDriver {
         int (*Open)(const char* path);
@@ -29,13 +33,15 @@ namespace Fs::Vfs {
     void Initialize();
     int RegisterDrive(int driveNumber, FsDriver* driver);
 
-    int VfsOpen(const char* path);
+    int OpenBackendFile(const char* path, BackendFile& outFile);
-    int VfsRead(int handle, uint8_t* buffer, uint64_t offset, uint64_t size);
+    int CreateBackendFile(const char* path, BackendFile& outFile);
-    int VfsWrite(int handle, const uint8_t* buffer, uint64_t offset, uint64_t size);
+    int ReadBackendFile(const BackendFile& file, uint8_t* buffer, uint64_t offset, uint64_t size);
-    int VfsCreate(const char* path);
+    int WriteBackendFile(const BackendFile& file, const uint8_t* buffer, uint64_t offset, uint64_t size);
+    uint64_t GetBackendFileSize(const BackendFile& file);
+    bool BackendFileCanWrite(const BackendFile& file);
+    void CloseBackendFile(BackendFile& file);
+
     int VfsDelete(const char* path);
-    uint64_t VfsGetSize(int handle);
-    void VfsClose(int handle);
     int VfsReadDir(const char* path, const char** outNames, int maxEntries);
     int VfsMkdir(const char* path);
     int VfsRename(const char* oldPath, const char* newPath);

kernel/src/Ipc/Ipc.hpp

@@ -0,0 +1,150 @@
+#pragma once
+
+#include <cstdint>
+
+namespace Net::Tcp { struct Connection; }
+
+namespace Ipc {
+
+    static constexpr int MaxHandlesPerProcess = 128;
+    static constexpr int MaxSurfaceMapsPerProcess = 64;
+    static constexpr uint32_t DefaultStreamCapacity = 4096;
+
+    enum class HandleType : uint8_t {
+        None = 0,
+        Stream,
+        Mailbox,
+        File,
+        Socket,
+        Surface,
+        Process,
+        Waitset
+    };
+
+    enum Rights : uint32_t {
+        RightWait   = 1u << 0,
+        RightRead   = 1u << 1,
+        RightWrite  = 1u << 2,
+        RightSend   = 1u << 3,
+        RightRecv   = 1u << 4,
+        RightMap    = 1u << 5,
+        RightManage = 1u << 6,
+        RightDup    = 1u << 7
+    };
+
+    enum Signals : uint32_t {
+        SignalNone       = 0,
+        SignalReadable   = 1u << 0,
+        SignalWritable   = 1u << 1,
+        SignalPeerClosed = 1u << 2,
+        SignalExited     = 1u << 3,
+        SignalReady      = 1u << 4
+    };
+
+    struct Object;
+    struct Stream;
+    struct Mailbox;
+    struct File;
+    struct Socket;
+    struct Surface;
+    struct ProcessObject;
+    struct Waitset;
+
+    struct HandleEntry {
+        bool used;
+        uint32_t rights;
+        HandleType type;
+        Object* object;
+    };
+
+    struct WaitsetReady {
+        int32_t index;
+        uint32_t signals;
+    };
+
+    void Initialize();
+
+    int CurrentSlot();
+    int SlotForPid(int pid);
+
+    int InstallHandleForSlot(int slot, Object* object, HandleType type, uint32_t rights);
+    int CloseHandleForSlot(int slot, int handle);
+    int CloseHandle(int handle);
+    int DupHandle(int handle);
+
+    bool SnapshotHandleForSlot(int slot, int handle, HandleType& type, Object*& object, uint32_t& rights);
+    uint32_t GetHandleSignalsForSlot(int slot, int handle);
+
+    Stream* CreateStream(uint32_t capacity = DefaultStreamCapacity);
+    int CreateStreamHandlePairForSlot(int slot, uint32_t capacity, int& outReadHandle, int& outWriteHandle);
+    int CreateStreamHandlePair(uint32_t capacity, int& outReadHandle, int& outWriteHandle);
+    void RetainStream(Stream* stream, bool readSide, bool writeSide);
+    void ReleaseStream(Stream* stream, bool readSide, bool writeSide);
+    int StreamRead(Stream* stream, uint8_t* out, int maxLen, bool nonBlocking);
+    int StreamWrite(Stream* stream, const uint8_t* data, int len, bool nonBlocking);
+    int StreamReadHandle(int handle, uint8_t* out, int maxLen);
+    int StreamWriteHandle(int handle, const uint8_t* data, int len);
+    bool StreamHasData(Stream* stream);
+
+    Mailbox* CreateMailbox();
+    int CreateMailboxHandlePairForSlot(int slot, int& outSendHandle, int& outRecvHandle);
+    int CreateMailboxHandlePair(int& outSendHandle, int& outRecvHandle);
+    void RetainMailbox(Mailbox* mailbox, bool sender, bool receiver);
+    void ReleaseMailbox(Mailbox* mailbox, bool sender, bool receiver);
+    int MailboxSend(Mailbox* mailbox, uint32_t msgType, const void* data, uint16_t len);
+    int MailboxRecv(Mailbox* mailbox, uint32_t* msgType, void* data, uint16_t* inOutLen, bool nonBlocking);
+    int MailboxSendHandle(int handle, uint32_t msgType, const void* data, uint16_t len, int attachHandle);
+    int MailboxRecvHandle(int handle, uint32_t* msgType, void* data, uint16_t* inOutLen, int* outAttachHandle);
+    bool MailboxHasMessage(Mailbox* mailbox);
+
+    int OpenFileHandleForSlot(int slot, const char* path, bool create);
+    int OpenFileHandle(const char* path);
+    int CreateFileHandle(const char* path);
+    int FileReadHandle(int handle, uint8_t* buffer, uint64_t offset, uint64_t size);
+    int FileWriteHandle(int handle, const uint8_t* buffer, uint64_t offset, uint64_t size);
+    uint64_t FileGetSizeHandle(int handle);
+
+    int CreateSocketHandleForSlot(int slot, int type);
+    int CreateSocketHandle(int type);
+    int SocketConnectHandle(int handle, uint32_t ip, uint16_t port);
+    int SocketBindHandle(int handle, uint16_t port);
+    int SocketListenHandle(int handle);
+    int SocketAcceptHandle(int handle);
+    int SocketSendHandle(int handle, const uint8_t* data, uint32_t len);
+    int SocketRecvHandle(int handle, uint8_t* buffer, uint32_t maxLen);
+    int SocketSendToHandle(int handle, const uint8_t* data, uint32_t len, uint32_t destIp, uint16_t destPort);
+    int SocketRecvFromHandle(int handle, uint8_t* buffer, uint32_t maxLen, uint32_t* srcIp, uint16_t* srcPort);
+    void NotifyTcpConnectionChanged(Net::Tcp::Connection* connection);
+
+    Surface* CreateSurface(uint64_t byteSize);
+    int CreateSurfaceHandle(uint64_t byteSize);
+    void RetainSurface(Surface* surface);
+    void ReleaseSurface(Surface* surface);
+    uint64_t GetSurfaceSize(const Surface* surface);
+    int ResizeSurface(Surface* surface, uint64_t newSize);
+    int CopySurface(Surface* dst, Surface* src);
+    uint64_t MapSurfaceHandle(int handle);
+    int ResizeSurfaceHandle(int handle, uint64_t newSize);
+    int MapSurfaceForPid(Surface* surface, int pid, uint64_t pml4Phys, uint64_t& heapNext, uint64_t& outVa);
+    int UnmapSurfaceForPid(Surface* surface, int pid, uint64_t pml4Phys);
+
+    ProcessObject* GetProcessObject(int pid);
+    int OpenProcessHandle(int pid);
+    void ProcessStartedInSlot(int slot, int pid);
+    void ProcessExitedInSlot(int slot, int pid);
+    bool ProcessHasExited(ProcessObject* process);
+
+    uint32_t WaitOnHandle(int handle, uint32_t wantedSignals, uint64_t timeoutMs);
+
+    int CreateWaitsetHandleForSlot(int slot);
+    int CreateWaitsetHandleForCurrent();
+    int WaitsetAddHandleForSlot(int slot, int waitsetHandle, int targetHandle, uint32_t signals);
+    int WaitsetAddHandle(int waitsetHandle, int targetHandle, uint32_t signals);
+    int WaitsetRemoveIndexForSlot(int slot, int waitsetHandle, int index);
+    int WaitsetRemoveIndex(int waitsetHandle, int index);
+    int WaitsetWaitHandle(int waitsetHandle, WaitsetReady* outReady, uint64_t timeoutMs);
+
+    void NotifyObjectChanged(Object* object);
+    void CleanupProcessSlot(int slot, int pid, uint64_t pml4Phys);
+
+}

kernel/src/Main.cpp

@@ -38,6 +38,7 @@
 #include <Fs/Ext2.hpp>
 #include <Fs/FsProbe.hpp>
 #include <Sched/Scheduler.hpp>
+#include <Ipc/Ipc.hpp>
 #include <Api/Syscall.hpp>
 #include <Hal/SmpBoot.hpp>
 using namespace Kt;
@@ -227,6 +228,7 @@ extern "C" void kmain() {
     Montauk::InitializeSyscalls();
 
     Sched::Initialize();
+    Ipc::Initialize();
 
     // Boot Application Processors (all subsystems ready, APs can schedule)
     Smp::BootAPs();

kernel/src/Net/Socket.cpp

@@ -5,324 +5,60 @@
 */
 
 #include "Socket.hpp"
-#include <Net/Tcp.hpp>
+#include <Ipc/Ipc.hpp>
-#include <Net/Udp.hpp>
-#include <Net/NetConfig.hpp>
 #include <Terminal/Terminal.hpp>
-#include <CppLib/Stream.hpp>
-#include <Libraries/Memory.hpp>
 
 using namespace Kt;
 
 namespace Net::Socket {
 
-    // ---- UDP socket state ----
-
-    static constexpr uint32_t UDP_RING_SIZE = 4096;
-    static constexpr int MAX_UDP_SOCKETS = 16;
-
-    struct UdpDgramHeader {
-        uint32_t SrcIp;
-        uint16_t SrcPort;
-        uint16_t DataLen;
-    };
-
-    struct UdpSocketState {
-        uint8_t  Ring[UDP_RING_SIZE];
-        uint32_t Head;
-        uint32_t Tail;
-        uint32_t Count;
-        uint16_t LocalPort;
-        bool     Active;
-    };
-
-    static UdpSocketState g_udpSockets[MAX_UDP_SOCKETS] = {};
-    static SocketEntry g_sockets[MAX_SOCKETS] = {};
-    static uint16_t g_nextEphemeralPort = 49152;
-
-    static uint16_t AllocEphemeralPort() {
-        uint16_t port = g_nextEphemeralPort++;
-        if (g_nextEphemeralPort == 0) g_nextEphemeralPort = 49152;
-        return port;
-    }
-
-    static bool ValidFd(int fd, int pid) {
-        if (fd < 0 || fd >= MAX_SOCKETS) return false;
-        if (!g_sockets[fd].Active) return false;
-        if (g_sockets[fd].OwnerPid != pid) return false;
-        return true;
-    }
-
-    static UdpSocketState* AllocUdpState() {
-        for (int i = 0; i < MAX_UDP_SOCKETS; i++) {
-            if (!g_udpSockets[i].Active) {
-                g_udpSockets[i].Active = true;
-                g_udpSockets[i].Head = 0;
-                g_udpSockets[i].Tail = 0;
-                g_udpSockets[i].Count = 0;
-                g_udpSockets[i].LocalPort = 0;
-                return &g_udpSockets[i];
-            }
-        }
-        return nullptr;
-    }
-
-    static void FreeUdpState(UdpSocketState* state) {
-        if (state) {
-            if (state->LocalPort != 0) {
-                Udp::Unbind(state->LocalPort);
-            }
-            state->Active = false;
-        }
-    }
-
-    static void UdpSocketDispatcher(uint32_t srcIp, uint16_t srcPort,
-                                     uint16_t dstPort,
-                                     const uint8_t* data, uint16_t length) {
-        for (int i = 0; i < MAX_UDP_SOCKETS; i++) {
-            if (g_udpSockets[i].Active && g_udpSockets[i].LocalPort == dstPort) {
-                UdpSocketState* st = &g_udpSockets[i];
-                uint32_t needed = sizeof(UdpDgramHeader) + length;
-                if (st->Count + needed > UDP_RING_SIZE) {
-                    return; // drop if buffer full
-                }
-
-                // Enqueue header
-                UdpDgramHeader hdr;
-                hdr.SrcIp = srcIp;
-                hdr.SrcPort = srcPort;
-                hdr.DataLen = length;
-
-                const uint8_t* hdrBytes = (const uint8_t*)&hdr;
-                for (uint32_t j = 0; j < sizeof(UdpDgramHeader); j++) {
-                    st->Ring[st->Tail] = hdrBytes[j];
-                    st->Tail = (st->Tail + 1) % UDP_RING_SIZE;
-                }
-
-                // Enqueue payload
-                for (uint16_t j = 0; j < length; j++) {
-                    st->Ring[st->Tail] = data[j];
-                    st->Tail = (st->Tail + 1) % UDP_RING_SIZE;
-                }
-
-                st->Count += needed;
-                return;
-            }
-        }
-    }
-
-    // ---- Public API ----
-
     void Initialize() {
-        for (int i = 0; i < MAX_SOCKETS; i++) {
+        KernelLogStream(OK, "Net") << "Socket handles initialized";
-            g_sockets[i].Active = false;
-        }
-        for (int i = 0; i < MAX_UDP_SOCKETS; i++) {
-            g_udpSockets[i].Active = false;
-        }
-        KernelLogStream(OK, "Net") << "Socket table initialized";
     }
 
     int Create(int type, int pid) {
-        if (type != SOCK_TCP && type != SOCK_UDP) return -1;
+        return Ipc::CreateSocketHandleForSlot(Ipc::SlotForPid(pid), type);
-
-        for (int i = 0; i < MAX_SOCKETS; i++) {
-            if (!g_sockets[i].Active) {
-                g_sockets[i].Active = true;
-                g_sockets[i].Type = type;
-                g_sockets[i].OwnerPid = pid;
-                g_sockets[i].TcpConn = nullptr;
-                g_sockets[i].UdpState = nullptr;
-                g_sockets[i].LocalPort = 0;
-
-                if (type == SOCK_UDP) {
-                    UdpSocketState* us = AllocUdpState();
-                    if (!us) {
-                        g_sockets[i].Active = false;
-                        return -1;
-                    }
-                    g_sockets[i].UdpState = us;
-                }
-
-                return i;
-            }
-        }
-        return -1;
     }
 
-    int Connect(int fd, uint32_t ip, uint16_t port, int pid) {
+    int Connect(int fd, uint32_t ip, uint16_t port, int /*pid*/) {
-        if (!ValidFd(fd, pid)) return -1;
+        return Ipc::SocketConnectHandle(fd, ip, port);
-        if (g_sockets[fd].Type != SOCK_TCP) return -1;
-        if (g_sockets[fd].TcpConn != nullptr) return -1;
-
-        uint16_t srcPort = AllocEphemeralPort();
-        g_sockets[fd].LocalPort = srcPort;
-
-        Tcp::Connection* conn = Tcp::Connect(ip, port, srcPort);
-        if (conn == nullptr) return -1;
-
-        g_sockets[fd].TcpConn = conn;
-        return 0;
     }
 
-    int Bind(int fd, uint16_t port, int pid) {
+    int Bind(int fd, uint16_t port, int /*pid*/) {
-        if (!ValidFd(fd, pid)) return -1;
+        return Ipc::SocketBindHandle(fd, port);
-        g_sockets[fd].LocalPort = port;
-
-        if (g_sockets[fd].Type == SOCK_UDP) {
-            UdpSocketState* us = g_sockets[fd].UdpState;
-            if (!us) return -1;
-            us->LocalPort = port;
-            if (!Udp::Bind(port, UdpSocketDispatcher)) return -1;
-        }
-
-        return 0;
     }
 
-    int Listen(int fd, int pid) {
+    int Listen(int fd, int /*pid*/) {
-        if (!ValidFd(fd, pid)) return -1;
+        return Ipc::SocketListenHandle(fd);
-        if (g_sockets[fd].Type != SOCK_TCP) return -1;
-        if (g_sockets[fd].LocalPort == 0) return -1;
-        if (g_sockets[fd].TcpConn != nullptr) return -1;
-
-        Tcp::Connection* conn = Tcp::Listen(g_sockets[fd].LocalPort);
-        if (conn == nullptr) return -1;
-
-        g_sockets[fd].TcpConn = conn;
-        return 0;
     }
 
-    int Accept(int fd, int pid) {
+    int Accept(int fd, int /*pid*/) {
-        if (!ValidFd(fd, pid)) return -1;
+        return Ipc::SocketAcceptHandle(fd);
-        if (g_sockets[fd].Type != SOCK_TCP) return -1;
-        if (g_sockets[fd].TcpConn == nullptr) return -1;
-
-        Tcp::Connection* clientConn = Tcp::Accept(g_sockets[fd].TcpConn);
-        if (clientConn == nullptr) return -1;
-
-        // Allocate a new socket entry for the accepted connection
-        for (int i = 0; i < MAX_SOCKETS; i++) {
-            if (!g_sockets[i].Active) {
-                g_sockets[i].Active = true;
-                g_sockets[i].Type = SOCK_TCP;
-                g_sockets[i].OwnerPid = pid;
-                g_sockets[i].TcpConn = clientConn;
-                g_sockets[i].UdpState = nullptr;
-                g_sockets[i].LocalPort = g_sockets[fd].LocalPort;
-                return i;
-            }
-        }
-
-        // No free socket slot — close the accepted connection
-        Tcp::Close(clientConn);
-        return -1;
     }
 
-    int Send(int fd, const uint8_t* data, uint32_t len, int pid) {
+    int Send(int fd, const uint8_t* data, uint32_t len, int /*pid*/) {
-        if (!ValidFd(fd, pid)) return -1;
+        return Ipc::SocketSendHandle(fd, data, len);
-        if (g_sockets[fd].Type != SOCK_TCP) return -1;
-        if (g_sockets[fd].TcpConn == nullptr) return -1;
-        return Tcp::Send(g_sockets[fd].TcpConn, data, (uint16_t)len);
     }
 
-    int Recv(int fd, uint8_t* buf, uint32_t maxLen, int pid) {
+    int Recv(int fd, uint8_t* buf, uint32_t maxLen, int /*pid*/) {
-        if (!ValidFd(fd, pid)) return -1;
+        return Ipc::SocketRecvHandle(fd, buf, maxLen);
-        if (g_sockets[fd].Type != SOCK_TCP) return -1;
-        if (g_sockets[fd].TcpConn == nullptr) return -1;
-        return Tcp::ReceiveNonBlocking(g_sockets[fd].TcpConn, buf, (uint16_t)maxLen);
     }
 
     int SendTo(int fd, const uint8_t* data, uint32_t len,
-               uint32_t destIp, uint16_t destPort, int pid) {
+               uint32_t destIp, uint16_t destPort, int /*pid*/) {
-        if (!ValidFd(fd, pid)) return -1;
+        return Ipc::SocketSendToHandle(fd, data, len, destIp, destPort);
-        if (g_sockets[fd].Type != SOCK_UDP) return -1;
-
-        UdpSocketState* us = g_sockets[fd].UdpState;
-        if (!us) return -1;
-
-        // Auto-bind ephemeral port if not already bound
-        if (us->LocalPort == 0) {
-            uint16_t ep = AllocEphemeralPort();
-            us->LocalPort = ep;
-            g_sockets[fd].LocalPort = ep;
-            if (!Udp::Bind(ep, UdpSocketDispatcher)) return -1;
-        }
-
-        if (!Udp::Send(destIp, us->LocalPort, destPort, data, (uint16_t)len)) {
-            return -1;
-        }
-        return (int)len;
     }
 
     int RecvFrom(int fd, uint8_t* buf, uint32_t maxLen,
-                 uint32_t* srcIp, uint16_t* srcPort, int pid) {
+                 uint32_t* srcIp, uint16_t* srcPort, int /*pid*/) {
-        if (!ValidFd(fd, pid)) return -1;
+        return Ipc::SocketRecvFromHandle(fd, buf, maxLen, srcIp, srcPort);
-        if (g_sockets[fd].Type != SOCK_UDP) return -1;
-
-        UdpSocketState* us = g_sockets[fd].UdpState;
-        if (!us) return -1;
-
-        if (us->Count < sizeof(UdpDgramHeader)) {
-            return -1; // no data available
-        }
-
-        // Dequeue header
-        UdpDgramHeader hdr;
-        uint8_t* hdrBytes = (uint8_t*)&hdr;
-        for (uint32_t j = 0; j < sizeof(UdpDgramHeader); j++) {
-            hdrBytes[j] = us->Ring[us->Head];
-            us->Head = (us->Head + 1) % UDP_RING_SIZE;
-        }
-        us->Count -= sizeof(UdpDgramHeader);
-
-        // Dequeue payload
-        uint16_t copyLen = hdr.DataLen;
-        if (copyLen > maxLen) copyLen = (uint16_t)maxLen;
-
-        for (uint16_t j = 0; j < copyLen; j++) {
-            buf[j] = us->Ring[us->Head];
-            us->Head = (us->Head + 1) % UDP_RING_SIZE;
-        }
-
-        // Skip remaining data if buffer was too small
-        for (uint16_t j = copyLen; j < hdr.DataLen; j++) {
-            us->Head = (us->Head + 1) % UDP_RING_SIZE;
-        }
-        us->Count -= hdr.DataLen;
-
-        if (srcIp) *srcIp = hdr.SrcIp;
-        if (srcPort) *srcPort = hdr.SrcPort;
-
-        return (int)copyLen;
     }
 
-    void Close(int fd, int pid) {
+    void Close(int fd, int /*pid*/) {
-        if (!ValidFd(fd, pid)) return;
+        Ipc::CloseHandle(fd);
-        if (g_sockets[fd].TcpConn != nullptr) {
-            Tcp::Close(g_sockets[fd].TcpConn);
-            g_sockets[fd].TcpConn = nullptr;
-        }
-        if (g_sockets[fd].UdpState != nullptr) {
-            FreeUdpState(g_sockets[fd].UdpState);
-            g_sockets[fd].UdpState = nullptr;
-        }
-        g_sockets[fd].Active = false;
     }
 
-    void CleanupProcess(int pid) {
+    void CleanupProcess(int /*pid*/) {
-        for (int i = 0; i < MAX_SOCKETS; i++) {
-            if (g_sockets[i].Active && g_sockets[i].OwnerPid == pid) {
-                if (g_sockets[i].TcpConn != nullptr) {
-                    Tcp::Close(g_sockets[i].TcpConn);
-                    g_sockets[i].TcpConn = nullptr;
-                }
-                if (g_sockets[i].UdpState != nullptr) {
-                    FreeUdpState(g_sockets[i].UdpState);
-                    g_sockets[i].UdpState = nullptr;
-                }
-                g_sockets[i].Active = false;
-            }
-        }
     }
 
 }

kernel/src/Net/Socket.hpp

@@ -6,40 +6,27 @@
 
 #pragma once
 #include <cstdint>
-#include <Net/Tcp.hpp>
 
 namespace Net::Socket {
 
     static constexpr int SOCK_TCP = 1;
     static constexpr int SOCK_UDP = 2;
-    static constexpr int MAX_SOCKETS = 64;
-
-    struct UdpSocketState;
-
-    struct SocketEntry {
-        bool     Active;
-        int      Type;
-        int      OwnerPid;
-        Tcp::Connection* TcpConn;
-        UdpSocketState*  UdpState;
-        uint16_t LocalPort;
-    };
 
     void Initialize();
 
-    // Create a socket of the given type. Returns fd or -1.
+    // Create a socket of the given type. Returns an IPC handle or -1.
     int Create(int type, int pid);
 
-    // Connect socket fd to remote ip:port. Returns 0 or -1.
+    // Connect socket handle to remote ip:port. Returns 0 or -1.
     int Connect(int fd, uint32_t ip, uint16_t port, int pid);
 
-    // Bind socket fd to a local port. Returns 0 or -1.
+    // Bind socket handle to a local port. Returns 0 or -1.
     int Bind(int fd, uint16_t port, int pid);
 
     // Start listening on a bound socket. Returns 0 or -1.
     int Listen(int fd, int pid);
 
-    // Accept an incoming connection. Returns new fd or -1.
+    // Accept an incoming connection. Returns a new IPC handle or -1.
     int Accept(int fd, int pid);
 
     // Send data on a connected socket. Returns bytes sent or -1.
@@ -59,7 +46,7 @@ namespace Net::Socket {
     // Close a socket.
     void Close(int fd, int pid);
 
-    // Close all sockets owned by a process (called on process exit).
+    // Per-process cleanup is handled by IPC handle teardown.
     void CleanupProcess(int pid);
 
 }

kernel/src/Net/Tcp.cpp

@@ -8,11 +8,13 @@
 #include <Net/Ipv4.hpp>
 #include <Net/ByteOrder.hpp>
 #include <Net/NetConfig.hpp>
+#include <Ipc/Ipc.hpp>
 #include <Libraries/Memory.hpp>
 #include <Terminal/Terminal.hpp>
 #include <CppLib/Stream.hpp>
 #include <CppLib/Spinlock.hpp>
 #include <Timekeeping/ApicTimer.hpp>
+#include <Sched/Scheduler.hpp>
 
 using namespace Kt;
 
@@ -216,6 +218,8 @@ namespace Net::Tcp {
                     listener->PendingRemotePort = srcPort;
                     listener->PendingSeq = seqNum;
                     listener->Lock.Release();
+                    Sched::WakeObjectWaiters(listener);
+                    Ipc::NotifyTcpConnectionChanged(listener);
                     return;
                 }
             }
@@ -235,12 +239,15 @@ namespace Net::Tcp {
         }
 
         conn->Lock.Acquire();
+        bool notify = false;
 
         // RST handling
         if (flags & FLAG_RST) {
             conn->CurrentState = State::Closed;
             conn->Active = false;
             conn->Lock.Release();
+            Sched::WakeObjectWaiters(conn);
+            Ipc::NotifyTcpConnectionChanged(conn);
             return;
         }
 
@@ -255,6 +262,7 @@ namespace Net::Tcp {
 
                         // Send ACK
                         SendSegment(conn, FLAG_ACK, nullptr, 0);
+                        notify = true;
                     }
                 }
                 break;
@@ -266,6 +274,7 @@ namespace Net::Tcp {
                     if (ackNum == conn->SendNext) {
                         conn->SendUnack = ackNum;
                         conn->CurrentState = State::Established;
+                        notify = true;
                     }
                 }
                 break;
@@ -275,6 +284,7 @@ namespace Net::Tcp {
                 // Handle incoming data
                 if (flags & FLAG_ACK) {
                     conn->SendUnack = ackNum;
+                    notify = true;
                 }
 
                 if (payloadLen > 0 && seqNum == conn->RecvNext) {
@@ -283,6 +293,7 @@ namespace Net::Tcp {
 
                     // Send ACK
                     SendSegment(conn, FLAG_ACK, nullptr, 0);
+                    notify = true;
                 }
 
                 if (flags & FLAG_FIN) {
@@ -291,6 +302,7 @@ namespace Net::Tcp {
 
                     // Send ACK for the FIN
                     SendSegment(conn, FLAG_ACK, nullptr, 0);
+                    notify = true;
                 }
                 break;
             }
@@ -302,13 +314,16 @@ namespace Net::Tcp {
                         conn->RecvNext = seqNum + 1;
                         conn->CurrentState = State::TimeWait;
                         SendSegment(conn, FLAG_ACK, nullptr, 0);
+                        notify = true;
                     } else {
                         conn->CurrentState = State::FinWait2;
+                        notify = true;
                     }
                 } else if (flags & FLAG_FIN) {
                     conn->RecvNext = seqNum + 1;
                     conn->CurrentState = State::TimeWait;
                     SendSegment(conn, FLAG_ACK, nullptr, 0);
+                    notify = true;
                 }
                 break;
             }
@@ -318,6 +333,7 @@ namespace Net::Tcp {
                     conn->RecvNext = seqNum + 1;
                     conn->CurrentState = State::TimeWait;
                     SendSegment(conn, FLAG_ACK, nullptr, 0);
+                    notify = true;
                 }
                 break;
             }
@@ -326,6 +342,7 @@ namespace Net::Tcp {
                 if (flags & FLAG_ACK) {
                     conn->CurrentState = State::Closed;
                     conn->Active = false;
+                    notify = true;
                 }
                 break;
             }
@@ -340,6 +357,10 @@ namespace Net::Tcp {
         }
 
         conn->Lock.Release();
+        if (notify) {
+            Sched::WakeObjectWaiters(conn);
+            Ipc::NotifyTcpConnectionChanged(conn);
+        }
     }
 
     Connection* Listen(uint16_t port) {
@@ -421,19 +442,25 @@ namespace Net::Tcp {
                 }
 
                 // Wait for ACK to complete the handshake
-                for (int i = 0; i < 100; i++) {
+                uint64_t deadline = Timekeeping::GetMilliseconds() + 5000;
+                while (Timekeeping::GetMilliseconds() < deadline) {
                     if (conn->CurrentState == State::Established) {
                         return conn;
                     }
-                    Timekeeping::Sleep(50);
+                    uint64_t now = Timekeeping::GetMilliseconds();
+                    uint64_t waitMs = (deadline > now) ? (deadline - now) : 0;
+                    if (waitMs == 0) break;
+                    Sched::BlockOnObject(conn, waitMs);
                 }
 
                 // Timed out waiting for ACK
                 conn->Active = false;
+                Sched::WakeObjectWaiters(conn);
+                Ipc::NotifyTcpConnectionChanged(conn);
                 return nullptr;
             }
             listener->Lock.Release();
-            Timekeeping::Sleep(10);
+            Sched::BlockOnObject(listener, 0);
         }
     }
 
@@ -480,11 +507,15 @@ namespace Net::Tcp {
 
         // Wait for SYN-ACK
         for (int attempt = 0; attempt < MAX_RETRANSMITS; attempt++) {
-            for (int i = 0; i < 20; i++) {
+            uint64_t deadline = Timekeeping::GetMilliseconds() + 1000;
+            while (Timekeeping::GetMilliseconds() < deadline) {
                 if (conn->CurrentState == State::Established) {
                     return conn;
                 }
-                Timekeeping::Sleep(50);
+                uint64_t now = Timekeeping::GetMilliseconds();
+                uint64_t waitMs = (deadline > now) ? (deadline - now) : 0;
+                if (waitMs == 0) break;
+                Sched::BlockOnObject(conn, waitMs);
             }
 
             if (conn->CurrentState == State::SynSent) {
@@ -512,6 +543,8 @@ namespace Net::Tcp {
 
         // Failed to connect
         conn->Active = false;
+        Sched::WakeObjectWaiters(conn);
+        Ipc::NotifyTcpConnectionChanged(conn);
         return nullptr;
     }
 
@@ -580,8 +613,15 @@ namespace Net::Tcp {
                 conn->RetransmitTime = Timekeeping::GetMilliseconds();
                 conn->Lock.Release();
                 asm volatile("push %0; popfq" :: "r"(flags) : "memory");
+                continue;
             }
-            Timekeeping::Sleep(10);
+
+            uint64_t waitMs = 10;
+            if (conn->RetransmitLen > 0 && now <= conn->RetransmitTime + RETRANSMIT_TIMEOUT_MS) {
+                waitMs = (conn->RetransmitTime + RETRANSMIT_TIMEOUT_MS) - now;
+                if (waitMs == 0) waitMs = 1;
+            }
+            Sched::BlockOnObject(conn, waitMs);
         }
 
         return sent;
@@ -625,7 +665,7 @@ namespace Net::Tcp {
 
             conn->Lock.Release();
             asm volatile("push %0; popfq" :: "r"(flags) : "memory");
-            Timekeeping::Sleep(10);
+            Sched::BlockOnObject(conn, 0);
         }
     }
 
@@ -691,9 +731,11 @@ namespace Net::Tcp {
                         conn->CurrentState == State::Closed) {
                         break;
                     }
-                    Timekeeping::Sleep(50);
+                    Sched::BlockOnObject(conn, 50);
                 }
                 conn->Active = false;
+                Sched::WakeObjectWaiters(conn);
+                Ipc::NotifyTcpConnectionChanged(conn);
                 return;
             }
 
@@ -709,9 +751,11 @@ namespace Net::Tcp {
                     if (conn->CurrentState == State::Closed) {
                         break;
                     }
-                    Timekeeping::Sleep(50);
+                    Sched::BlockOnObject(conn, 50);
                 }
                 conn->Active = false;
+                Sched::WakeObjectWaiters(conn);
+                Ipc::NotifyTcpConnectionChanged(conn);
                 return;
             }
 
@@ -721,6 +765,8 @@ namespace Net::Tcp {
                 conn->Active = false;
                 conn->Lock.Release();
                 asm volatile("push %0; popfq" :: "r"(flags) : "memory");
+                Sched::WakeObjectWaiters(conn);
+                Ipc::NotifyTcpConnectionChanged(conn);
                 return;
             }
 
@@ -728,6 +774,8 @@ namespace Net::Tcp {
                 conn->Lock.Release();
                 asm volatile("push %0; popfq" :: "r"(flags) : "memory");
                 conn->Active = false;
+                Sched::WakeObjectWaiters(conn);
+                Ipc::NotifyTcpConnectionChanged(conn);
                 return;
         }
     }
@@ -736,7 +784,44 @@ namespace Net::Tcp {
         if (conn == nullptr) {
             return State::Closed;
         }
-        return conn->CurrentState;
+        conn->Lock.Acquire();
+        State state = conn->CurrentState;
+        conn->Lock.Release();
+        return state;
+    }
+
+    bool HasPendingAccept(Connection* conn) {
+        if (conn == nullptr) return false;
+        conn->Lock.Acquire();
+        bool pending = conn->PendingAccept;
+        conn->Lock.Release();
+        return pending;
+    }
+
+    bool HasReceiveData(Connection* conn) {
+        if (conn == nullptr) return false;
+        conn->Lock.Acquire();
+        bool hasData = conn->RecvCount > 0;
+        conn->Lock.Release();
+        return hasData;
+    }
+
+    bool CanSend(Connection* conn) {
+        if (conn == nullptr) return false;
+        conn->Lock.Acquire();
+        bool writable = conn->CurrentState == State::Established;
+        conn->Lock.Release();
+        return writable;
+    }
+
+    bool IsClosedForIo(Connection* conn) {
+        if (conn == nullptr) return true;
+        conn->Lock.Acquire();
+        bool closed = conn->CurrentState == State::CloseWait ||
+                      conn->CurrentState == State::Closed ||
+                      conn->CurrentState == State::TimeWait;
+        conn->Lock.Release();
+        return closed;
     }
 
 }

kernel/src/Net/Tcp.hpp

@@ -80,4 +80,10 @@ namespace Net::Tcp {
     // Get the state of a connection
     State GetState(Connection* conn);
 
+    // Readiness helpers used by the IPC layer.
+    bool HasPendingAccept(Connection* conn);
+    bool HasReceiveData(Connection* conn);
+    bool CanSend(Connection* conn);
+    bool IsClosedForIo(Connection* conn);
+
 }

kernel/src/Sched/ElfLoader.cpp

@@ -52,15 +52,15 @@ namespace Sched {
     }
 
     uint64_t ElfLoad(const char* vfsPath, uint64_t pml4Phys) {
-        int handle = Fs::Vfs::VfsOpen(vfsPath);
+        Fs::Vfs::BackendFile file = {-1, -1};
-        if (handle < 0) {
+        if (Fs::Vfs::OpenBackendFile(vfsPath, file) < 0) {
             return 0;
         }
 
-        uint64_t fileSize = Fs::Vfs::VfsGetSize(handle);
+        uint64_t fileSize = Fs::Vfs::GetBackendFileSize(file);
         if (fileSize < sizeof(Elf64Header)) {
             Kt::KernelLogStream(Kt::ERROR, "ELF") << "File too small (" << fileSize << " bytes)";
-            Fs::Vfs::VfsClose(handle);
+            Fs::Vfs::CloseBackendFile(file);
             return 0;
         }
 
@@ -68,12 +68,12 @@ namespace Sched {
         uint8_t* fileData = (uint8_t*)Memory::g_heap->Request(fileSize);
         if (fileData == nullptr) {
             Kt::KernelLogStream(Kt::ERROR, "ELF") << "Failed to allocate " << fileSize << " bytes for file";
-            Fs::Vfs::VfsClose(handle);
+            Fs::Vfs::CloseBackendFile(file);
             return 0;
         }
 
-        Fs::Vfs::VfsRead(handle, fileData, 0, fileSize);
+        Fs::Vfs::ReadBackendFile(file, fileData, 0, fileSize);
-        Fs::Vfs::VfsClose(handle);
+        Fs::Vfs::CloseBackendFile(file);
 
         // Prevent the optimizer from reordering the VfsRead store past the
         // header validation reads that follow.

kernel/src/Sched/Scheduler.cpp

@@ -18,6 +18,7 @@
 #include <Hal/SmpBoot.hpp>
 #include <Timekeeping/ApicTimer.hpp>
 #include <Api/WinServer.hpp>
+#include <Ipc/Ipc.hpp>
 
 // Assembly: context switch with CR3 and FPU state parameters
 extern "C" void SchedContextSwitch(uint64_t* oldRsp, uint64_t newRsp, uint64_t newCR3,
@@ -47,6 +48,45 @@ namespace Sched {
         return (uint64_t)Memory::VMM::g_paging->PML4;
     }
 
+    static void SwitchAwayFromBlockedCurrentLocked() {
+        auto* cpu = Smp::GetCurrentCpuData();
+        int slot = cpu->currentSlot;
+        if (slot < 0) {
+            schedLock.Release();
+            return;
+        }
+
+        int next = -1;
+        for (int i = 0; i < MaxProcesses; i++) {
+            if (processTable[i].state == ProcessState::Ready) {
+                next = i;
+                break;
+            }
+        }
+
+        if (next >= 0) {
+            cpu->currentSlot = next;
+            processTable[next].state = ProcessState::Running;
+            readyCount--;
+            processTable[next].runningOnCpu = cpu->cpuIndex;
+            processTable[next].sliceRemaining = TimeSliceMs;
+
+            cpu->kernelRsp = processTable[next].kernelStackTop;
+            cpu->tss->rsp0 = processTable[next].kernelStackTop;
+
+            SchedContextSwitch(&processTable[slot].savedRsp, processTable[next].savedRsp,
+                              processTable[next].pml4Phys,
+                              processTable[slot].fpuState, processTable[next].fpuState);
+            schedLock.Release();
+            return;
+        }
+
+        cpu->currentSlot = -1;
+        SchedContextSwitch(&processTable[slot].savedRsp, cpu->idleSavedRsp,
+                          GetKernelCR3(), processTable[slot].fpuState, nullptr);
+        schedLock.Release();
+    }
+
     // Startup function for newly spawned processes.
     // SchedContextSwitch "returns" here on first schedule.
     // The schedLock is held (acquired by the switching-from CPU's Schedule).
@@ -97,6 +137,7 @@ namespace Sched {
             processTable[i].killPending = false;
             processTable[i].waitingForPid = -1;
             processTable[i].sleepUntilTick = 0;
+            processTable[i].waitingOnObject = nullptr;
             processTable[i].redirected = false;
             processTable[i].parentPid = -1;
             processTable[i].outBuf = nullptr;
@@ -109,6 +150,10 @@ namespace Sched {
             processTable[i].keyTail = 0;
             processTable[i].termCols = 0;
             processTable[i].termRows = 0;
+            processTable[i].ioOutHandle = -1;
+            processTable[i].ioInHandle = -1;
+            processTable[i].ioKeyHandle = -1;
+            processTable[i].ioWaitsetHandle = -1;
         }
 
         nextPid = 0;
@@ -276,6 +321,7 @@ namespace Sched {
         proc.killPending = false;
         proc.waitingForPid = -1;
         proc.sleepUntilTick = 0;
+        proc.waitingOnObject = nullptr;
 
         // Copy arguments string into process
         proc.args[0] = '\0';
@@ -333,12 +379,18 @@ namespace Sched {
         proc.keyTail = 0;
         proc.termCols = 0;
         proc.termRows = 0;
+        proc.ioOutHandle = -1;
+        proc.ioInHandle = -1;
+        proc.ioKeyHandle = -1;
+        proc.ioWaitsetHandle = -1;
 
         // Initialize FPU state: zero out, then set default FCW and MXCSR
         memset(proc.fpuState, 0, 512);
         *(uint16_t*)&proc.fpuState[0] = 0x037F;   // FCW: default x87 control word
         *(uint32_t*)&proc.fpuState[24] = 0x1F80;   // MXCSR: default SSE control/status
 
+        Ipc::ProcessStartedInSlot(slot, proc.pid);
+
         int resultPid = proc.pid;
         schedLock.Release();
 
@@ -486,6 +538,8 @@ namespace Sched {
                     processTable[i].sleepUntilTick != 0 &&
                     now >= processTable[i].sleepUntilTick) {
                     processTable[i].sleepUntilTick = 0;
+                    processTable[i].waitingForPid = -1;
+                    processTable[i].waitingOnObject = nullptr;
                     processTable[i].state = ProcessState::Ready;
                     readyCount++;
                 }
@@ -554,15 +608,30 @@ namespace Sched {
         // Clean up any windows owned by this process
         WinServer::CleanupProcess(exitingPid);
 
-        // Free I/O redirect buffers
+        // Release process-scoped IPC handles/mappings before tearing down the address space.
-        if (proc.outBuf) {
+        Ipc::CleanupProcessSlot(slot, exitingPid, proc.pml4Phys);
-            Memory::g_pfa->Free(proc.outBuf);
+
-            proc.outBuf = nullptr;
+        proc.waitingForPid = -1;
-        }
+        proc.sleepUntilTick = 0;
-        if (proc.inBuf) {
+        proc.waitingOnObject = nullptr;
-            Memory::g_pfa->Free(proc.inBuf);
+        proc.redirected = false;
-            proc.inBuf = nullptr;
+        proc.parentPid = -1;
-        }
+        proc.outBuf = nullptr;
+        proc.outHead = 0;
+        proc.outTail = 0;
+        proc.inBuf = nullptr;
+        proc.inHead = 0;
+        proc.inTail = 0;
+        proc.keyHead = 0;
+        proc.keyTail = 0;
+        proc.termCols = 0;
+        proc.termRows = 0;
+        proc.ioOutHandle = -1;
+        proc.ioInHandle = -1;
+        proc.ioKeyHandle = -1;
+        proc.ioWaitsetHandle = -1;
+
+        Ipc::ProcessExitedInSlot(slot, exitingPid);
 
         // Free all user-space physical pages and page table structures
         Memory::VMM::Paging::FreeUserHalf(proc.pml4Phys);
@@ -579,6 +648,8 @@ namespace Sched {
                 processTable[i].state = ProcessState::Ready;
                 readyCount++;
                 processTable[i].waitingForPid = -1;
+                processTable[i].waitingOnObject = nullptr;
+                processTable[i].sleepUntilTick = 0;
             }
         }
 
@@ -664,6 +735,9 @@ namespace Sched {
             readyCount--;
         proc.state = ProcessState::Terminated;
         proc.killPending = false;
+        proc.waitingForPid = -1;
+        proc.sleepUntilTick = 0;
+        proc.waitingOnObject = nullptr;
 
         // Wake any processes blocked on this PID
         for (int i = 0; i < MaxProcesses; i++) {
@@ -672,6 +746,8 @@ namespace Sched {
                 processTable[i].state = ProcessState::Ready;
                 readyCount++;
                 processTable[i].waitingForPid = -1;
+                processTable[i].waitingOnObject = nullptr;
+                processTable[i].sleepUntilTick = 0;
             }
         }
 
@@ -679,15 +755,26 @@ namespace Sched {
 
         // Safe to clean up resources now -- process is not running anywhere.
         WinServer::CleanupProcess(killedPid);
+        Ipc::CleanupProcessSlot(slot, killedPid, proc.pml4Phys);
 
-        if (proc.outBuf) {
+        proc.redirected = false;
-            Memory::g_pfa->Free(proc.outBuf);
+        proc.parentPid = -1;
-            proc.outBuf = nullptr;
+        proc.outBuf = nullptr;
-        }
+        proc.outHead = 0;
-        if (proc.inBuf) {
+        proc.outTail = 0;
-            Memory::g_pfa->Free(proc.inBuf);
+        proc.inBuf = nullptr;
-            proc.inBuf = nullptr;
+        proc.inHead = 0;
-        }
+        proc.inTail = 0;
+        proc.keyHead = 0;
+        proc.keyTail = 0;
+        proc.termCols = 0;
+        proc.termRows = 0;
+        proc.ioOutHandle = -1;
+        proc.ioInHandle = -1;
+        proc.ioKeyHandle = -1;
+        proc.ioWaitsetHandle = -1;
+
+        Ipc::ProcessExitedInSlot(slot, killedPid);
 
         Memory::VMM::Paging::FreeUserHalf(proc.pml4Phys);
 
@@ -727,39 +814,10 @@ namespace Sched {
         // ExitProcess will wake us when the target terminates.
         processTable[slot].state = ProcessState::Blocked;
         processTable[slot].waitingForPid = pid;
+        processTable[slot].waitingOnObject = nullptr;
+        processTable[slot].sleepUntilTick = 0;
         processTable[slot].runningOnCpu = -1;
-
+        SwitchAwayFromBlockedCurrentLocked();
-        // Find next ready process to switch to
-        int next = -1;
-        for (int i = 0; i < MaxProcesses; i++) {
-            if (processTable[i].state == ProcessState::Ready) {
-                next = i;
-                break;
-            }
-        }
-
-        if (next >= 0) {
-            cpu->currentSlot = next;
-            processTable[next].state = ProcessState::Running;
-            readyCount--;
-            processTable[next].runningOnCpu = cpu->cpuIndex;
-            processTable[next].sliceRemaining = TimeSliceMs;
-
-            cpu->kernelRsp = processTable[next].kernelStackTop;
-            cpu->tss->rsp0 = processTable[next].kernelStackTop;
-
-            SchedContextSwitch(&processTable[slot].savedRsp, processTable[next].savedRsp,
-                              processTable[next].pml4Phys,
-                              processTable[slot].fpuState, processTable[next].fpuState);
-            schedLock.Release();
-        } else {
-            // No ready process -- go idle
-            cpu->currentSlot = -1;
-
-            SchedContextSwitch(&processTable[slot].savedRsp, cpu->idleSavedRsp,
-                              GetKernelCR3(), processTable[slot].fpuState, nullptr);
-            schedLock.Release();
-        }
     }
 
     void BlockForSleep(uint64_t ms) {
@@ -772,38 +830,46 @@ namespace Sched {
         schedLock.Acquire();
 
         processTable[slot].state = ProcessState::Blocked;
+        processTable[slot].waitingForPid = -1;
+        processTable[slot].waitingOnObject = nullptr;
         processTable[slot].sleepUntilTick = Timekeeping::GetTicks() + ms;
         processTable[slot].runningOnCpu = -1;
+        SwitchAwayFromBlockedCurrentLocked();
+    }
 
-        int next = -1;
+    void BlockOnObject(void* object, uint64_t timeoutMs) {
+        if (object == nullptr) return;
+
+        auto* cpu = Smp::GetCurrentCpuData();
+        int slot = cpu->currentSlot;
+        if (slot < 0) return;
+
+        schedLock.Acquire();
+        processTable[slot].state = ProcessState::Blocked;
+        processTable[slot].waitingForPid = -1;
+        processTable[slot].waitingOnObject = object;
+        processTable[slot].sleepUntilTick = (timeoutMs > 0)
+            ? (Timekeeping::GetTicks() + timeoutMs)
+            : 0;
+        processTable[slot].runningOnCpu = -1;
+        SwitchAwayFromBlockedCurrentLocked();
+    }
+
+    void WakeObjectWaiters(void* object) {
+        if (object == nullptr) return;
+
+        schedLock.Acquire();
         for (int i = 0; i < MaxProcesses; i++) {
-            if (processTable[i].state == ProcessState::Ready) {
+            if (processTable[i].state != ProcessState::Blocked) continue;
-                next = i;
+            if (processTable[i].waitingOnObject != object) continue;
-                break;
+
-            }
+            processTable[i].waitingOnObject = nullptr;
-        }
+            processTable[i].sleepUntilTick = 0;
-
+            processTable[i].waitingForPid = -1;
-        if (next >= 0) {
+            processTable[i].state = ProcessState::Ready;
-            cpu->currentSlot = next;
+            readyCount++;
-            processTable[next].state = ProcessState::Running;
-            readyCount--;
-            processTable[next].runningOnCpu = cpu->cpuIndex;
-            processTable[next].sliceRemaining = TimeSliceMs;
-
-            cpu->kernelRsp = processTable[next].kernelStackTop;
-            cpu->tss->rsp0 = processTable[next].kernelStackTop;
-
-            SchedContextSwitch(&processTable[slot].savedRsp, processTable[next].savedRsp,
-                              processTable[next].pml4Phys,
-                              processTable[slot].fpuState, processTable[next].fpuState);
-            schedLock.Release();
-        } else {
-            cpu->currentSlot = -1;
-
-            SchedContextSwitch(&processTable[slot].savedRsp, cpu->idleSavedRsp,
-                              GetKernelCR3(), processTable[slot].fpuState, nullptr);
-            schedLock.Release();
         }
+        schedLock.Release();
     }
 
     bool IsAlive(int pid) {

kernel/src/Sched/Scheduler.hpp

@@ -35,7 +35,8 @@ namespace Sched {
         int pid;
         ProcessState state;
         int waitingForPid;     // PID this process is blocked on (-1 if none)
-        uint64_t sleepUntilTick; // Tick deadline for SYS_SLEEP_MS (0 = not sleeping)
+        uint64_t sleepUntilTick; // Tick deadline for sleep/object wait timeout (0 = none)
+        void* waitingOnObject; // IPC/scheduler object this process is blocked on (nullptr if none)
         char name[64];
         uint64_t savedRsp;
         uint64_t stackBase;       // Bottom of allocated kernel stack (lowest address)
@@ -71,6 +72,12 @@ namespace Sched {
         int termCols = 0;
         int termRows = 0;
 
+        // IPC-backed redirected terminal channels
+        int ioOutHandle = -1;
+        int ioInHandle = -1;
+        int ioKeyHandle = -1;
+        int ioWaitsetHandle = -1;
+
         // FPU/SSE state (FXSAVE format, must be 16-byte aligned)
         uint8_t fpuState[512] __attribute__((aligned(16)));
     };
@@ -100,6 +107,13 @@ namespace Sched {
     // Block the current process for the given number of milliseconds.
     void BlockForSleep(uint64_t ms);
 
+    // Block the current process until the given object is signaled or timed out.
+    // timeoutMs == 0 means wait indefinitely.
+    void BlockOnObject(void* object, uint64_t timeoutMs = 0);
+
+    // Wake any processes blocked on the given object.
+    void WakeObjectWaiters(void* object);
+
     // Kill a process by PID. If the process is running on another CPU,
     // sets a kill-pending flag checked on the next timer tick.
     // Returns 0 on success, -1 on failure.

programs/include/Api/Syscall.hpp

@@ -76,6 +76,7 @@ namespace Montauk {
     static constexpr uint64_t SYS_WINPOLL      = 57;
     static constexpr uint64_t SYS_WINENUM      = 58;
     static constexpr uint64_t SYS_WINMAP       = 59;
+    static constexpr uint64_t SYS_WINUNMAP     = 97;
     static constexpr uint64_t SYS_WINSENDEVENT = 60;
     static constexpr uint64_t SYS_WINRESIZE   = 64;
     static constexpr uint64_t SYS_WINSETSCALE = 65;
@@ -126,6 +127,28 @@ namespace Montauk {
     static constexpr uint64_t SYS_FRENAME       = 94;
     static constexpr uint64_t SYS_GETCWD        = 95;
     static constexpr uint64_t SYS_CHDIR         = 96;
+    static constexpr uint64_t SYS_DUPHANDLE     = 98;
+    static constexpr uint64_t SYS_WAIT_HANDLE   = 99;
+    static constexpr uint64_t SYS_STREAM_CREATE = 100;
+    static constexpr uint64_t SYS_STREAM_READ   = 101;
+    static constexpr uint64_t SYS_STREAM_WRITE  = 102;
+    static constexpr uint64_t SYS_MAILBOX_CREATE = 103;
+    static constexpr uint64_t SYS_MAILBOX_SEND   = 104;
+    static constexpr uint64_t SYS_MAILBOX_RECV   = 105;
+    static constexpr uint64_t SYS_WAITSET_CREATE = 106;
+    static constexpr uint64_t SYS_WAITSET_ADD    = 107;
+    static constexpr uint64_t SYS_WAITSET_REMOVE = 108;
+    static constexpr uint64_t SYS_WAITSET_WAIT   = 109;
+    static constexpr uint64_t SYS_PROC_OPEN      = 110;
+    static constexpr uint64_t SYS_SURFACE_CREATE = 111;
+    static constexpr uint64_t SYS_SURFACE_MAP    = 112;
+    static constexpr uint64_t SYS_SURFACE_RESIZE = 113;
+
+    static constexpr uint32_t IPC_SIGNAL_READABLE    = 1u << 0;
+    static constexpr uint32_t IPC_SIGNAL_WRITABLE    = 1u << 1;
+    static constexpr uint32_t IPC_SIGNAL_PEER_CLOSED = 1u << 2;
+    static constexpr uint32_t IPC_SIGNAL_EXITED      = 1u << 3;
+    static constexpr uint32_t IPC_SIGNAL_READY       = 1u << 4;
 
     // Audio control commands (for SYS_AUDIOCTL)
     static constexpr int AUDIO_CTL_SET_VOLUME = 0;
@@ -188,6 +211,11 @@ namespace Montauk {
         uint8_t  buttons;
     };
 
+    struct IpcWaitResult {
+        int32_t index;
+        uint32_t signals;
+    };
+
     // Window server shared types
     struct WinEvent {
         uint8_t type;     // 0=key, 1=mouse, 2=resize, 3=close, 4=scale

programs/include/libc/montauk.h

@@ -79,6 +79,7 @@ extern "C" {
 #define MTK_SYS_WINPOLL         57
 #define MTK_SYS_WINENUM         58
 #define MTK_SYS_WINMAP          59
+#define MTK_SYS_WINUNMAP        97
 #define MTK_SYS_WINSENDEVENT    60
 #define MTK_SYS_PROCLIST        61
 #define MTK_SYS_KILL            62
@@ -99,9 +100,30 @@ extern "C" {
 #define MTK_SYS_GETTZ           91
 #define MTK_SYS_GETCWD          95
 #define MTK_SYS_CHDIR           96
+#define MTK_SYS_DUPHANDLE       98
+#define MTK_SYS_WAIT_HANDLE     99
+#define MTK_SYS_STREAM_CREATE   100
+#define MTK_SYS_STREAM_READ     101
+#define MTK_SYS_STREAM_WRITE    102
+#define MTK_SYS_MAILBOX_CREATE  103
+#define MTK_SYS_MAILBOX_SEND    104
+#define MTK_SYS_MAILBOX_RECV    105
+#define MTK_SYS_WAITSET_CREATE  106
+#define MTK_SYS_WAITSET_ADD     107
+#define MTK_SYS_WAITSET_REMOVE  108
+#define MTK_SYS_WAITSET_WAIT    109
+#define MTK_SYS_PROC_OPEN       110
+#define MTK_SYS_SURFACE_CREATE  111
+#define MTK_SYS_SURFACE_MAP     112
+#define MTK_SYS_SURFACE_RESIZE  113
 
 #define MTK_SOCK_TCP 1
 #define MTK_SOCK_UDP 2
+#define MTK_IPC_SIGNAL_READABLE    (1u << 0)
+#define MTK_IPC_SIGNAL_WRITABLE    (1u << 1)
+#define MTK_IPC_SIGNAL_PEER_CLOSED (1u << 2)
+#define MTK_IPC_SIGNAL_EXITED      (1u << 3)
+#define MTK_IPC_SIGNAL_READY       (1u << 4)
 
 /* Window event types */
 #define MTK_EVENT_KEY    0
@@ -136,6 +158,11 @@ typedef struct {
     uint8_t  buttons;
 } mtk_mouse_state;
 
+typedef struct {
+    int32_t  index;
+    uint32_t signals;
+} mtk_ipc_wait_result;
+
 typedef struct {
     uint8_t type;
     uint8_t _pad[3];
@@ -396,6 +423,78 @@ static inline int mtk_readdir(const char *path, const char **names, int max) {
     return (int)_mtk_syscall3(MTK_SYS_READDIR, (long)path, (long)names, (long)max);
 }
 
+/* ====================================================================
+   Generic IPC
+   ==================================================================== */
+
+static inline int mtk_dup_handle(int handle) {
+    return (int)_mtk_syscall1(MTK_SYS_DUPHANDLE, (long)handle);
+}
+
+static inline uint32_t mtk_wait_handle(int handle, uint32_t wanted_signals, unsigned long timeout_ms) {
+    return (uint32_t)_mtk_syscall3(MTK_SYS_WAIT_HANDLE, (long)handle, (long)wanted_signals, (long)timeout_ms);
+}
+
+static inline int mtk_stream_create(int *out_read_handle, int *out_write_handle, unsigned long capacity) {
+    return (int)_mtk_syscall3(MTK_SYS_STREAM_CREATE, (long)out_read_handle, (long)out_write_handle, (long)capacity);
+}
+
+static inline int mtk_stream_read(int handle, void *buf, int max_len) {
+    return (int)_mtk_syscall3(MTK_SYS_STREAM_READ, (long)handle, (long)buf, (long)max_len);
+}
+
+static inline int mtk_stream_write(int handle, const void *data, int len) {
+    return (int)_mtk_syscall3(MTK_SYS_STREAM_WRITE, (long)handle, (long)data, (long)len);
+}
+
+static inline int mtk_mailbox_create(int *out_send_handle, int *out_recv_handle) {
+    return (int)_mtk_syscall2(MTK_SYS_MAILBOX_CREATE, (long)out_send_handle, (long)out_recv_handle);
+}
+
+static inline int mtk_mailbox_send(int handle, uint32_t msg_type, const void *data,
+                                   uint16_t len, int attach_handle) {
+    return (int)_mtk_syscall5(MTK_SYS_MAILBOX_SEND, (long)handle, (long)msg_type,
+                              (long)data, (long)len, (long)attach_handle);
+}
+
+static inline int mtk_mailbox_recv(int handle, uint32_t *out_msg_type, void *data,
+                                   uint16_t *in_out_len, int *out_attach_handle) {
+    return (int)_mtk_syscall5(MTK_SYS_MAILBOX_RECV, (long)handle, (long)out_msg_type,
+                              (long)data, (long)in_out_len, (long)out_attach_handle);
+}
+
+static inline int mtk_waitset_create(void) {
+    return (int)_mtk_syscall0(MTK_SYS_WAITSET_CREATE);
+}
+
+static inline int mtk_waitset_add(int waitset_handle, int target_handle, uint32_t signals) {
+    return (int)_mtk_syscall3(MTK_SYS_WAITSET_ADD, (long)waitset_handle, (long)target_handle, (long)signals);
+}
+
+static inline int mtk_waitset_remove(int waitset_handle, int index) {
+    return (int)_mtk_syscall2(MTK_SYS_WAITSET_REMOVE, (long)waitset_handle, (long)index);
+}
+
+static inline int mtk_waitset_wait(int waitset_handle, mtk_ipc_wait_result *out_ready, unsigned long timeout_ms) {
+    return (int)_mtk_syscall3(MTK_SYS_WAITSET_WAIT, (long)waitset_handle, (long)out_ready, (long)timeout_ms);
+}
+
+static inline int mtk_proc_open(int pid) {
+    return (int)_mtk_syscall1(MTK_SYS_PROC_OPEN, (long)pid);
+}
+
+static inline int mtk_surface_create(unsigned long byte_size) {
+    return (int)_mtk_syscall1(MTK_SYS_SURFACE_CREATE, (long)byte_size);
+}
+
+static inline void *mtk_surface_map(int handle) {
+    return (void *)_mtk_syscall1(MTK_SYS_SURFACE_MAP, (long)handle);
+}
+
+static inline int mtk_surface_resize(int handle, unsigned long new_size) {
+    return (int)_mtk_syscall2(MTK_SYS_SURFACE_RESIZE, (long)handle, (long)new_size);
+}
+
 /* ====================================================================
    Memory
    ==================================================================== */
@@ -478,6 +577,10 @@ static inline int mtk_win_poll(int id, mtk_win_event *event) {
     return (int)_mtk_syscall2(MTK_SYS_WINPOLL, (long)id, (long)event);
 }
 
+static inline int mtk_win_unmap(int id) {
+    return (int)_mtk_syscall1(MTK_SYS_WINUNMAP, (long)id);
+}
+
 static inline unsigned long mtk_win_resize(int id, int w, int h) {
     return (unsigned long)_mtk_syscall3(MTK_SYS_WINRESIZE, (long)id, (long)w, (long)h);
 }
@@ -486,6 +589,10 @@ static inline int mtk_win_enumerate(mtk_win_info *info, int max) {
     return (int)_mtk_syscall2(MTK_SYS_WINENUM, (long)info, (long)max);
 }
 
+static inline unsigned long mtk_win_map(int id) {
+    return (unsigned long)_mtk_syscall1(MTK_SYS_WINMAP, (long)id);
+}
+
 static inline int mtk_win_setcursor(int id, int cursor) {
     return (int)_mtk_syscall2(MTK_SYS_WINSETCURSOR, (long)id, (long)cursor);
 }

programs/include/montauk/syscall.h

@@ -223,6 +223,62 @@ namespace montauk {
                              (uint64_t)maxLen, (uint64_t)srcIp, (uint64_t)srcPort);
     }
 
+    // Generic IPC
+    inline int dup_handle(int handle) {
+        return (int)syscall1(Montauk::SYS_DUPHANDLE, (uint64_t)handle);
+    }
+    inline uint32_t wait_handle(int handle, uint32_t wantedSignals, uint64_t timeoutMs = ~0ULL) {
+        return (uint32_t)syscall3(Montauk::SYS_WAIT_HANDLE, (uint64_t)handle,
+                                  (uint64_t)wantedSignals, timeoutMs);
+    }
+    inline int stream_create(int* outReadHandle, int* outWriteHandle, uint32_t capacity = 0) {
+        return (int)syscall3(Montauk::SYS_STREAM_CREATE, (uint64_t)outReadHandle,
+                             (uint64_t)outWriteHandle, (uint64_t)capacity);
+    }
+    inline int stream_read(int handle, void* buf, int maxLen) {
+        return (int)syscall3(Montauk::SYS_STREAM_READ, (uint64_t)handle, (uint64_t)buf, (uint64_t)maxLen);
+    }
+    inline int stream_write(int handle, const void* data, int len) {
+        return (int)syscall3(Montauk::SYS_STREAM_WRITE, (uint64_t)handle, (uint64_t)data, (uint64_t)len);
+    }
+    inline int mailbox_create(int* outSendHandle, int* outRecvHandle) {
+        return (int)syscall2(Montauk::SYS_MAILBOX_CREATE, (uint64_t)outSendHandle, (uint64_t)outRecvHandle);
+    }
+    inline int mailbox_send(int handle, uint32_t msgType, const void* data, uint16_t len, int attachHandle = -1) {
+        return (int)syscall5(Montauk::SYS_MAILBOX_SEND, (uint64_t)handle, (uint64_t)msgType,
+                             (uint64_t)data, (uint64_t)len, (uint64_t)(int64_t)attachHandle);
+    }
+    inline int mailbox_recv(int handle, uint32_t* outMsgType, void* data,
+                            uint16_t* inOutLen, int* outAttachHandle = nullptr) {
+        return (int)syscall5(Montauk::SYS_MAILBOX_RECV, (uint64_t)handle, (uint64_t)outMsgType,
+                             (uint64_t)data, (uint64_t)inOutLen, (uint64_t)outAttachHandle);
+    }
+    inline int waitset_create() {
+        return (int)syscall0(Montauk::SYS_WAITSET_CREATE);
+    }
+    inline int waitset_add(int waitsetHandle, int targetHandle, uint32_t signals) {
+        return (int)syscall3(Montauk::SYS_WAITSET_ADD, (uint64_t)waitsetHandle,
+                             (uint64_t)targetHandle, (uint64_t)signals);
+    }
+    inline int waitset_remove(int waitsetHandle, int index) {
+        return (int)syscall2(Montauk::SYS_WAITSET_REMOVE, (uint64_t)waitsetHandle, (uint64_t)index);
+    }
+    inline int waitset_wait(int waitsetHandle, Montauk::IpcWaitResult* outReady, uint64_t timeoutMs = ~0ULL) {
+        return (int)syscall3(Montauk::SYS_WAITSET_WAIT, (uint64_t)waitsetHandle, (uint64_t)outReady, timeoutMs);
+    }
+    inline int proc_open(int pid) {
+        return (int)syscall1(Montauk::SYS_PROC_OPEN, (uint64_t)pid);
+    }
+    inline int surface_create(uint64_t byteSize) {
+        return (int)syscall1(Montauk::SYS_SURFACE_CREATE, byteSize);
+    }
+    inline void* surface_map(int handle) {
+        return (void*)syscall1(Montauk::SYS_SURFACE_MAP, (uint64_t)handle);
+    }
+    inline int surface_resize(int handle, uint64_t newSize) {
+        return (int)syscall2(Montauk::SYS_SURFACE_RESIZE, (uint64_t)handle, newSize);
+    }
+
     // Process management
     inline void waitpid(int pid) { syscall1(Montauk::SYS_WAITPID, (uint64_t)pid); }
 
@@ -435,6 +491,9 @@ namespace montauk {
     inline uint64_t win_map(int id) {
         return (uint64_t)syscall1(Montauk::SYS_WINMAP, (uint64_t)id);
     }
+    inline int win_unmap(int id) {
+        return (int)syscall1(Montauk::SYS_WINUNMAP, (uint64_t)id);
+    }
     inline int win_sendevent(int id, const Montauk::WinEvent* event) {
         return (int)syscall2(Montauk::SYS_WINSENDEVENT, (uint64_t)id, (uint64_t)event);
     }

programs/src/desktop/main.cpp

@@ -390,11 +390,14 @@ bool desktop_poll_external_windows(DesktopState* ds) {
         for (int i = 0; i < ds->window_count; i++) {
             if (ds->windows[i].external && ds->windows[i].ext_win_id == extId) {
                 found = true;
+                bool remapRequested = false;
+                uint64_t currentVa = (uint64_t)(uintptr_t)ds->windows[i].content;
                 if (ds->windows[i].content_w != extWins[e].width ||
                     ds->windows[i].content_h != extWins[e].height) {
                     ds->windows[i].content_w = extWins[e].width;
                     ds->windows[i].content_h = extWins[e].height;
                     ds->windows[i].dirty = true;
+                    remapRequested = true;
                     if (ds->windows[i].state != WIN_MINIMIZED && ds->windows[i].state != WIN_CLOSED) {
                         changed = true;
                     }
@@ -411,12 +414,20 @@ bool desktop_poll_external_windows(DesktopState* ds) {
                     changed = true;
                 }
                 ds->windows[i].ext_cursor = extWins[e].cursor;
-                // Always verify mapping is current. If a window slot was
+
-                // recycled (app exited, new app got same slot), desktopVa
+                if (remapRequested && currentVa != 0) {
-                // was zeroed and Map() returns a new VA. Detect this and
+                    montauk::win_unmap(extId);
-                // update the content pointer to avoid using a stale VA.
+                    ds->windows[i].content = nullptr;
+                    currentVa = 0;
+                }
+
                 uint64_t va = montauk::win_map(extId);
-                if (va != 0 && va != (uint64_t)(uintptr_t)ds->windows[i].content) {
+                if (!remapRequested && va != 0 && va != currentVa) {
+                    montauk::win_unmap(extId);
+                    va = montauk::win_map(extId);
+                }
+
+                if (va != 0 && va != currentVa) {
                     ds->windows[i].content = (uint32_t*)va;
                     ds->windows[i].content_w = extWins[e].width;
                     ds->windows[i].content_h = extWins[e].height;
@@ -508,6 +519,9 @@ bool desktop_poll_external_windows(DesktopState* ds) {
 
         if (!stillExists) {
             // Window gone — remove without freeing content (shared memory)
+            if (ds->windows[i].content != nullptr) {
+                montauk::win_unmap(extId);
+            }
             ds->windows[i].content = nullptr; // prevent free
             gui::desktop_close_window(ds, i);
             changed = true;

programs/src/dhcp/main.cpp

@@ -397,7 +397,9 @@ extern "C" void _start() {
                 }
             }
         }
-        montauk::yield();
+        uint64_t now = montauk::get_milliseconds();
+        if (now >= startMs + 10000) break;
+        montauk::wait_handle(fd, Montauk::IPC_SIGNAL_READABLE, startMs + 10000 - now);
     }
 
     if (!gotOffer) {
@@ -447,7 +449,9 @@ extern "C" void _start() {
                 }
             }
         }
-        montauk::yield();
+        uint64_t now = montauk::get_milliseconds();
+        if (now >= startMs + 10000) break;
+        montauk::wait_handle(fd, Montauk::IPC_SIGNAL_READABLE, startMs + 10000 - now);
     }
 
     montauk::closesocket(fd);

programs/src/fetch/main.cpp

@@ -198,8 +198,14 @@ static int plain_http_exchange(int fd, const char* request, int reqLen,
         if (r > 0) { respLen += r; deadline = montauk::get_milliseconds() + 15000; }
         else if (r < 0) break;
         else {
-            if (montauk::get_milliseconds() >= deadline) break;
+            uint64_t now = montauk::get_milliseconds();
-            montauk::sleep_ms(1);
+            if (now >= deadline) break;
+            uint32_t signals = montauk::wait_handle(
+                fd,
+                Montauk::IPC_SIGNAL_READABLE | Montauk::IPC_SIGNAL_PEER_CLOSED,
+                deadline - now
+            );
+            if (signals == 0 || signals == (uint32_t)-1) break;
         }
     }
     return respLen;

programs/src/httpd/main.cpp

@@ -386,9 +386,17 @@ static void handle_client(int clientFd) {
         } else if (r == 0) {
             break; // Connection closed
         } else {
-            idleCount++;
+            uint32_t signals = montauk::wait_handle(
-            if (idleCount > 500) break; // Timeout
+                clientFd,
-            montauk::yield();
+                Montauk::IPC_SIGNAL_READABLE | Montauk::IPC_SIGNAL_PEER_CLOSED,
+                20
+            );
+            if (signals == 0) {
+                idleCount++;
+                if (idleCount > 500) break;
+            } else if (signals & Montauk::IPC_SIGNAL_PEER_CLOSED) {
+                break;
+            }
         }
     }
     reqBuf[reqLen] = '\0';

programs/src/irc/main.cpp

@@ -1028,7 +1028,9 @@ extern "C" void _start() {
             }
         } else {
             if (!dirty) {
-                montauk::yield();
+                montauk::wait_handle(irc.fd,
+                                     Montauk::IPC_SIGNAL_READABLE | Montauk::IPC_SIGNAL_PEER_CLOSED,
+                                     10);
                 continue;
             }
         }

programs/src/tcpconnect/main.cpp

@@ -187,8 +187,7 @@ extern "C" void _start() {
                 montauk::putchar(ev.ascii);
             }
         } else {
-            // No key and no data -- yield to avoid busy-spinning
+            montauk::wait_handle(fd, Montauk::IPC_SIGNAL_READABLE | Montauk::IPC_SIGNAL_PEER_CLOSED, 10);
-            montauk::yield();
         }
     }