diff --git a/include/memmodel.h b/include/memmodel.h
index 6bc6512..74db7f1 100644
--- a/include/memmodel.h
+++ b/include/memmodel.h
@@ -1,4 +1,4 @@
-/* memmodel.h - the OS-agnostic memory-model contract (the middle layer).
+/* memmodel.h - the OS-agnostic, x86-64 memory-model contract (the middle layer).
  *
  * This is the shared vocabulary between the ENGINE (which turns guest-physical
  * RAM into a usable virtual memory model via x86-64 paging + Windows bring-up)
@@ -6,9 +6,13 @@
  * concept: a handler compiled against this header literally cannot mention an
  * _EPROCESS, a PEB, or an LDR entry.
  *
+ * OS-agnostic, but architecture-bound: the address-space key is the x86-64 CR3
+ * (the PML4 base), shared by any guest OS on x86-64 - it is not portable to an
+ * ISA with a different paging root (e.g. ARM64 TTBR0/1).
+ *
  * Everything here is keyed by a `vmie_mem*` (the opaque physical/paging
- * substrate) plus a `cr3` (the address space). The engine handle `vmie` is
- * never handed to a handler - only `vmie_mem*` + `cr3`.
+ * substrate) plus a `cr3` (the address space). The engine handle is never
+ * handed to a handler - only `vmie_mem*` + `cr3`.
  *
  * Conventions:
  *   - `cr3` is a raw CR3 / DirectoryTableBase value; low flag bits are masked
diff --git a/src/engine/gva.c b/src/engine/gva.c
index 518359f..d1241a1 100644
--- a/src/engine/gva.c
+++ b/src/engine/gva.c
@@ -46,8 +46,8 @@ static int gva_gpa(vmie_mem* m, uintptr_t cr3, uintptr_t va,
 }
 
 /* cold extern translate: GPA of `va` under `cr3`, or -1. Wraps the hot static
- * gva_gpa for cold callers outside this TU (win32 bring-up) without exposing the
- * inlinable hot primitive. Declared in engine-arch.h. */
+ * gva_gpa for cold callers outside this TU without exposing the inlinable hot
+ * primitive. Declared in engine-arch.h. */
 __attribute__((cold))
 int gva_translate(vmie_mem* m, uintptr_t cr3, uintptr_t va, uintptr_t* gpa) {
     return gva_gpa(m, cr3, va, gpa, NULL);
diff --git a/src/engine/include/engine-arch.h b/src/engine/include/engine-arch.h
index a323e65..c317513 100644
--- a/src/engine/include/engine-arch.h
+++ b/src/engine/include/engine-arch.h
@@ -21,15 +21,15 @@
 /* gva_read/gva_write/gva_regions/gva_sweep + gva_sweep_cb and vregion/VR_*
  * are the OS-agnostic contract: declared in memmodel.h, pulled in above. */
 
-/* paging heuristic, shared by the arch walker and the win32 bring-up. Counts
- * present kernel-half PML4 entries under `pml4` (an address-space liveness
- * score). OS-agnostic: const vmie_mem*, no profile/struct vmie. */
+/* paging heuristic, shared by every PT-walking TU. Counts present kernel-half
+ * PML4 entries under `pml4` (an address-space liveness score). OS-agnostic:
+ * const vmie_mem*, no profile, no engine handle. */
 int   khalf_score(const vmie_mem* m, uint64_t pml4) __attribute__((cold));
 
 /* cold extern wrapper over the hot static page-table walk: translate `va` under
  * `cr3` to a GPA (no leaf length). Returns 0 on success, -1 if not present. For
- * cold callers outside gva.c (win32 bring-up); the hot inlinable primitive stays
- * private to gva.c. */
+ * cold callers outside gva.c; the hot inlinable primitive stays private to
+ * gva.c. */
 int   gva_translate(vmie_mem* m, uintptr_t cr3, uintptr_t va, uintptr_t* gpa) __attribute__((cold));
 
 #endif /* VMIE_ENGINE_ARCH_H */