diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0190e6b..db2f9c9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,12 +14,13 @@ jobs:
       build-command: |
         mkdir -p /tmp/space-boot
         command nasm -f bin boot/multiboot.asm -o /tmp/space-boot/trampoline.bin
-        command in compile --path kernel/kernel-root.in --entry kernel_entry --emit boot \
+        command in compile --path kernel/kernel-root.in --entry kernel-entry --emit boot \
           --trampoline /tmp/space-boot/trampoline.bin \
           --target native --target-triple x86_64-unknown-none --linkage static-lib \
           --out /tmp/space-boot/kernel.bin
       test-command: |
         echo "Boot image: $(wc -c < /tmp/space-boot/kernel.bin) bytes"
+        bash scripts/check-spdp-protocol.sh
         bash scripts/check-sci-contract.sh
 
   website:
diff --git a/README.md b/README.md
index 909bfa2..3f40b04 100644
--- a/README.md
+++ b/README.md
@@ -80,6 +80,7 @@ bash scripts/check-terminal-editor.sh # serial editor save test
 bash scripts/check-desktop-visual.sh  # desktop / display visual path
 bash scripts/check-desktop-damage.sh  # moving-window compositor bench
 bash scripts/check-spdp-composite.sh  # SPDP surface-pipeline proof
+bash scripts/check-spdp-protocol.sh    # SPDP wire-format / parser contract
 bash scripts/check-audit-fixes.sh     # kernel-audit hardening assertions
 bash scripts/check-linux-elf.sh       # Linux ELF personality
 bash scripts/check-volume-deep-soak.sh # NVMe volume deep soak
diff --git a/components/display.in b/components/display.in
index 55b1d0a..665b032 100644
--- a/components/display.in
+++ b/components/display.in
@@ -3,8 +3,6 @@ package space.display
 import "../protocol/display.in"
 import "font.in"
 
-const SPDP-OBJ-SURFACE = 5
-
 interface DisplayDevice {
   fn map(phys: Int, size: Int) -> void
   fn present() -> void
@@ -2334,6 +2332,7 @@ fn dsp-init() -> void {
   dsp-surfaces = alloc(DSP-MAX-SURFACES * dsp-surface-size())
   dsp-pools = alloc(DSP-MAX-POOLS * 8)  // array of pool addresses
   dsp-pool-sizes = alloc(DSP-MAX-POOLS * 8) // array of pool sizes (bytes)
+  dsp-msg = alloc(SPDP-MSG-SIZE)
   let i = 0
   while i < DSP-MAX-POOLS {
     store64(dsp-pools + i * 8, 0)
diff --git a/protocol/display.in b/protocol/display.in
index 3e5a9c9..cdd469b 100644
--- a/protocol/display.in
+++ b/protocol/display.in
@@ -1,16 +1,17 @@
 // Space Display Protocol — Wayland-inspired compositor wire format.
 // Objects communicate over channels using a fixed-size message format:
-//   [obj_id(8)][opcode(8)][argc(8)][args...]
-// Each message is exactly 32 bytes (header + up to 3 x 8-byte args).
+//   [obj_id(8)][opcode(8)][arg0(8)][arg1(8)]
+// Each message is exactly 32 bytes (16-byte header + two 8-byte args).
 
 const SPDP-MSG-SIZE = 32
-const SPDP-HEADER-SIZE = 24  // obj_id + opcode + argc
+const SPDP-HEADER-SIZE = 16  // obj_id + opcode
 
 // Object IDs (well-known)
 const SPDP-OBJ-DISPLAY = 1    // global display object
 const SPDP-OBJ-COMPOSITOR = 2 // compositor interface
 const SPDP-OBJ-SHM = 3        // shared memory interface
 const SPDP-OBJ-SEAT = 4       // input seat
+const SPDP-OBJ-SURFACE = 5    // surface object
 
 // Display object opcodes (client → server)
 const SPDP-GET-REGISTRY = 0   // no args
@@ -22,8 +23,8 @@ const SPDP-REGISTRY-GLOBAL = 1  // arg0: obj_id, arg1: interface_addr
 
 // Compositor opcodes
 const SPDP-COMPOSITOR-CREATE-SURFACE = 0  // returns surface_id
-const SPDP-SURFACE-ATTACH = 1             // arg0: surface_id, arg1: buffer_id
-const SPDP-SURFACE-DAMAGE = 2             // arg0: surface_id, arg1: x/w packed
+const SPDP-SURFACE-ATTACH = 1             // arg0: surface_id, arg1: pool_id<<32 | offset
+const SPDP-SURFACE-DAMAGE = 2             // arg0: surface_id, arg1: x<<48|y<<32|w<<16|h
 const SPDP-SURFACE-COMMIT = 3             // arg0: surface_id
 const SPDP-SURFACE-DESTROY = 4            // arg0: surface_id
 
@@ -45,8 +46,8 @@ const SPDP-SEAT-KEYBOARD-KEY = 4   // arg0: time, arg1: key/state packed
 // Surface life cycle:
 //   1. Client sends COMPOSITOR_CREATE_SURFACE → receives surface_id
 //   2. Client creates an SHM pool via SHM_CREATE_POOL
-//   3. Client sends SURFACE_ATTACH(surface_id, buffer_id) to associate buffer
-//   4. Client sends SURFACE_DAMAGE(surface_id, x, y, w, h) to mark dirty region
+//   3. Client sends SURFACE_ATTACH(surface_id, pool_id<<32 | offset)
+//   4. Client sends SURFACE_DAMAGE(surface_id, x<<48|y<<32|w<<16|h) to mark dirty region
 //   5. Client sends SURFACE_COMMIT(surface_id) to present
 //   6. Compositor renders the surface, sends frame callback
 //
diff --git a/scripts/check-spdp-protocol.sh b/scripts/check-spdp-protocol.sh
new file mode 100755
index 0000000..2d99518
--- /dev/null
+++ b/scripts/check-spdp-protocol.sh
@@ -0,0 +1,138 @@
+"exec" "python3" "$0" "$@"
+# check-spdp-protocol.sh — Host-side SPDP wire-format + compositor parse checks.
+# No QEMU / compiler. Run: bash scripts/check-spdp-protocol.sh
+"""Validate protocol/display.in against the compositor's 32-byte SPDP frames.
+
+The kernel parser in components/display.in (dsp-run / dsp-handle-msg) is the
+source of truth: four little-endian u64 words, no argc field.
+"""
+import os, re, struct, sys
+
+passed, failed = 0, 0
+
+def check(label, ok):
+    global passed, failed
+    if ok:
+        print(f"  ok: {label}")
+        passed += 1
+    else:
+        print(f"  FAIL: {label}")
+        failed += 1
+
+def parse_consts(text):
+    found = {}
+    for name, val in re.findall(r"^const (SPDP-[A-Z0-9-]+) = (\d+)", text, re.M):
+        found[name] = int(val)
+    return found
+
+def encode(obj_id, opcode, arg0, arg1):
+    return struct.pack("<QQQQ", obj_id, opcode, arg0, arg1)
+
+def decode(buf):
+    if len(buf) != 32:
+        raise ValueError("SPDP frame must be 32 bytes")
+    return struct.unpack("<QQQQ", buf)
+
+def pack_attach(pool_id, offset):
+    return ((pool_id & 0xFFFFFFFF) << 32) | (offset & 0xFFFFFFFF)
+
+def pack_geometry(x, y, w, h):
+    return ((x & 0xFFFF) << 48) | ((y & 0xFFFF) << 32) | ((w & 0xFFFF) << 16) | (h & 0xFFFF)
+
+def unpack_attach(packed):
+    return (packed >> 32) & 0xFFFFFFFF, packed & 0xFFFFFFFF
+
+def unpack_geometry(packed):
+    return (
+        (packed >> 48) & 0xFFFF,
+        (packed >> 32) & 0xFFFF,
+        (packed >> 16) & 0xFFFF,
+        packed & 0xFFFF,
+    )
+
+def main():
+    here = os.path.dirname(os.path.abspath(__file__))
+    space = os.path.abspath(os.path.join(here, ".."))
+    proto_path = os.path.join(space, "protocol", "display.in")
+    display_path = os.path.join(space, "components", "display.in")
+    ci_path = os.path.join(space, ".github", "workflows", "ci.yml")
+
+    proto = open(proto_path).read()
+    display = open(display_path).read()
+    ci = open(ci_path).read()
+    consts = parse_consts(proto)
+
+    print("[1/4] Protocol constants and frame layout...")
+    check("SPDP-MSG-SIZE == 32", consts.get("SPDP-MSG-SIZE") == 32)
+    check("SPDP-HEADER-SIZE == 16 (obj_id + opcode, no argc)",
+          consts.get("SPDP-HEADER-SIZE") == 16)
+    check("header + two args == message size",
+          consts.get("SPDP-HEADER-SIZE", 0) + 16 == consts.get("SPDP-MSG-SIZE", -1))
+    check("protocol does not reserve an argc word",
+          "argc" not in proto.lower())
+
+    for name, val in [
+        ("SPDP-OBJ-DISPLAY", 1),
+        ("SPDP-OBJ-COMPOSITOR", 2),
+        ("SPDP-OBJ-SHM", 3),
+        ("SPDP-OBJ-SEAT", 4),
+        ("SPDP-OBJ-SURFACE", 5),
+        ("SPDP-COMPOSITOR-CREATE-SURFACE", 0),
+        ("SPDP-SURFACE-ATTACH", 1),
+        ("SPDP-SURFACE-DAMAGE", 2),
+        ("SPDP-SURFACE-COMMIT", 3),
+        ("SPDP-SHM-CREATE-POOL", 0),
+    ]:
+        check(f"{name} == {val}", consts.get(name) == val)
+
+    print("[2/4] Encode/decode packed arguments...")
+    surface = consts.get("SPDP-OBJ-SURFACE", 5)
+    attach_op = consts.get("SPDP-SURFACE-ATTACH", 1)
+    frame = encode(surface, attach_op, 7, pack_attach(3, 0x1000))
+    check("encoded frame is 32 bytes", len(frame) == 32)
+    obj_id, opcode, arg0, arg1 = decode(frame)
+    check("decode obj_id/opcode/arg0", obj_id == surface and opcode == attach_op and arg0 == 7)
+    pool, off = unpack_attach(arg1)
+    check("SURFACE-ATTACH packs pool<<32 | offset", pool == 3 and off == 0x1000)
+
+    gx, gy, gw, gh = unpack_geometry(pack_geometry(100, 100, 64, 64))
+    check("SURFACE-DAMAGE packs x<<48|y<<32|w<<16|h",
+          (gx, gy, gw, gh) == (100, 100, 64, 64))
+
+    # A client that followed the old argc-at-offset-16 layout would put argc in
+    # the word the compositor reads as arg0. That must not be the spec.
+    wrong = struct.pack("<QQQQ", 5, 1, 2, pack_attach(3, 0x1000))  # argc=2 as arg0
+    w_obj, w_op, w_a0, w_a1 = decode(wrong)
+    check("argc-shaped frame is distinguishable from attach(sid=7)",
+          not (w_a0 == 7 and unpack_attach(w_a1) == (3, 0x1000)))
+    check("argc-shaped frame's arg0 is the bogus argc, not surface_id", w_a0 == 2)
+
+    print("[3/4] Compositor parser matches the four-word layout...")
+    check("dsp-run stores word 0 at dsp-msg+0", "store64(dsp-msg + 0, chan-recv(ch))" in display)
+    check("dsp-run stores word 1 at dsp-msg+8", "store64(dsp-msg + 8, chan-recv(ch))" in display)
+    check("dsp-run stores word 2 at dsp-msg+16", "store64(dsp-msg + 16, chan-recv(ch))" in display)
+    check("dsp-run stores word 3 at dsp-msg+24", "store64(dsp-msg + 24, chan-recv(ch))" in display)
+    check("dsp-run loads obj-id from +0", "let obj-id = load64(dsp-msg + 0)" in display)
+    check("dsp-run loads opcode from +8", "let opcode = load64(dsp-msg + 8)" in display)
+    check("dsp-run loads arg0 from +16", "let arg0 = load64(dsp-msg + 16)" in display)
+    check("dsp-run loads arg1 from +24", "let arg1 = load64(dsp-msg + 24)" in display)
+    check("dsp-init allocates the hoisted 32-byte message buffer",
+          "dsp-msg = alloc(SPDP-MSG-SIZE)" in display)
+    check("dsp-handle-msg dispatches SURFACE on SPDP-OBJ-SURFACE",
+          "obj-id == SPDP-OBJ-SURFACE" in display)
+    check("display.in does not re-declare SPDP-OBJ-SURFACE",
+          "const SPDP-OBJ-SURFACE" not in display)
+
+    print("[4/4] CI compile entry matches kernel-entry...")
+    check("ci.yml uses --entry kernel-entry", "--entry kernel-entry" in ci)
+    check("ci.yml does not use C-style kernel_entry", "--entry kernel_entry" not in ci)
+    check("ci.yml runs check-spdp-protocol.sh", "scripts/check-spdp-protocol.sh" in ci)
+
+    print(f"\n=== Results: {passed} passed, {failed} failed ===")
+    if failed:
+        print("FAIL: SPDP protocol/parser contract mismatch.")
+        sys.exit(1)
+    print("PASS: SPDP 32-byte frames match the compositor parser.")
+
+if __name__ == "__main__":
+    main()