feat: add build numbering

kernel/GNUmakefile

@@ -225,6 +225,18 @@ override OBJ += $(addprefix obj-$(ARCH)/,$(NASMFILES:.asm=.asm.o))
 endif
 override HEADER_DEPS := $(addprefix obj-$(ARCH)/,$(CFILES:.c=.c.d) $(CXXFILES:.cpp=.cpp.d) $(OBJCFILES:.mm=.mm.d) $(ASFILES:.S=.S.d))
 
+# Build number. src/Api/BuildNo.hpp holds MONTAUK_BUILD_NUMBER and is included
+# (transitively) only by Api/Syscall.cpp. We regenerate (bump) it whenever any
+# kernel object OR any userspace source changes, so the number embedded in the
+# kernel tracks real rebuilds of the kernel/userspace. Api/Syscall.cpp.o is
+# excluded from the prerequisites to avoid a dependency cycle (it depends on the
+# header), and a clean build bumps exactly once.
+override BUILDNO_HDR := src/Api/BuildNo.hpp
+override BUILDNO_OBJ := obj-$(ARCH)/Api/Syscall.cpp.o
+override PROG_SRC := $(shell find ../programs/src ../programs/include ../programs/lib \
+    -type f \( -name '*.c' -o -name '*.cpp' -o -name '*.h' -o -name '*.hpp' \
+    -o -name '*.S' -o -name '*.asm' \) 2>/dev/null)
+
 # Default target. This must come first, before header dependencies.
 .PHONY: all
 all: bin-$(ARCH)/$(OUTPUT)
@@ -232,6 +244,15 @@ all: bin-$(ARCH)/$(OUTPUT)
 # Include header dependencies.
 -include $(HEADER_DEPS)
 
+# Bump the build number when any kernel object or userspace source is newer.
+$(BUILDNO_HDR): $(filter-out $(BUILDNO_OBJ),$(OBJ)) $(PROG_SRC)
+	../scripts/bump-build.sh $@
+
+# Force Syscall.cpp.o to recompile (and the kernel to relink) in the same pass
+# the header is bumped, so the embedded number always matches BuildNo.hpp even
+# on a clean build (where no .d dependency exists yet).
+$(BUILDNO_OBJ): $(BUILDNO_HDR)
+
 # Link rules for building the C compiler runtime.
 cc-runtime-$(ARCH)/cc-runtime.a: GNUmakefile cc-runtime/*
 	rm -rf cc-runtime-$(ARCH)

kernel/src/Api/BuildNo.hpp

@@ -0,0 +1,15 @@
+/*
+    * BuildNo.hpp
+    * Monotonic kernel build number.
+    *
+    * This file is the source of truth for the build number. It is regenerated
+    * (incremented) by scripts/bump-build.sh whenever the kernel or userspace
+    * sources change, via a rule in kernel/GNUmakefile. Do not edit the number
+    * by hand; the build system manages it.
+    *
+    * Copyright (c) 2026 Daniel Hammer
+*/
+
+#pragma once
+
+#define MONTAUK_BUILD_NUMBER 1

kernel/src/Api/Info.hpp

@@ -7,6 +7,7 @@
 #pragma once
 #include <Sched/Scheduler.hpp>
 
+#include "BuildNo.hpp"
 #include "Syscall.hpp"
 
 namespace Montauk {
@@ -22,7 +23,8 @@ namespace Montauk {
         for (int i = 0; ver[i]; i++) outInfo->osVersion[i] = ver[i];
         outInfo->osVersion[5] = '\0';
 
-        outInfo->apiVersion = 3;
+        outInfo->apiVersion = 4;
         outInfo->maxProcesses = Sched::MaxProcesses;
+        outInfo->buildNumber = MONTAUK_BUILD_NUMBER;
     }
 };

kernel/src/Api/Syscall.hpp

@@ -282,6 +282,7 @@ namespace Montauk {
         char osVersion[32];
         uint32_t    apiVersion;
         uint32_t    maxProcesses;
+        uint32_t    buildNumber;   // monotonic kernel build number (see BuildNo.hpp)
     };
 
     struct NetCfg {