尽快推进：收紧tooldata mmap shim源码锚点

docs/linuxcnc-tooldata-source-map.md

@@ -51,6 +51,17 @@ source-link/shim guard only; it must not add CNC behavior and must not expand th
   `tooldata_db_notify()` must return `0` without side effects while `db_live`
   is false.
 
+## Mmap Backend Boundaries
+
+- `core/wasm_shims/tooldata/tooldata_mmap_backend.cc` must preserve the
+  LinuxCNC `tooldata_mmap.cc` export surface for the mmap creator/user/close lifecycle while using an in-memory replacement for native mmap.
+- The mmap backend must keep the LinuxCNC random-toolchanger flag and
+  `last_index` initialization edges from `tool_mmap_creator()`, and
+  `tooldata_last_index_get()` must preserve the last-index unavailable return.
+- `tool_mmap_user()` must keep LinuxCNC's unavailable mmap failure boundary,
+  and `tool_mmap_close()` must clear the browser-safe in-memory state without
+  adding filesystem mmap behavior.
+
 ## Boundaries
 
 - Tool table files referenced by switchkins INI files are source coverage only;