转向直接移植LinuxCNC源程序

结论：明确禁止继续扩展自写 CNC 主体语义，最小 runtime 仅保留为迁移探针；新增 interp_convert.cc 源码直连编译探针，并以最小 emcStatus 状态边界 shim 暴露 native runtime 阻塞点。检查：git diff --check 通过；wasm-port/tests/native/verify_native_probes.sh 通过，linuxcnc_interp_convert_source_probe exitcode=0。

wasm-port/docs/porting-steps-standalone.md

@@ -371,7 +371,18 @@ Current verified progress:
   `interp_convert.cc::convert_straight()` and
   `rs274ngc_return.hh::NCE_CANNOT_DO_G1_WITH_ZERO_FEED_RATE`.
 - This proves the current extracted interpreter slice can parse and execute a
-  simple traverse and feed move through a standalone canonical event sink.
+  small fixture set through a standalone canonical event sink.
+- Important direction change: the minimal wrapper behavior is a migration
+  probe, not the program body. Do not expand it into a separate CNC
+  implementation. The next work must retire hand-written wrapper semantics and
+  move execution through vendored LinuxCNC interpreter source such as
+  `interp_convert.cc`, `interp_read.cc`, `interp_check.cc`, and
+  `interp_execute.cc`.
+- `tools/build_native_probes.sh` now includes
+  `linuxcnc_interp_convert_source_probe`, which directly compiles vendored
+  `interp_convert.cc`. The required `emcStatus` shim is limited to the native
+  status boundary used by `tag_arc()` for machine units; it is not a
+  project-authored CNC behavior implementation.
 
 ## Phase 4: Port INI Parsing Without Editing Upstream
 
@@ -670,9 +681,11 @@ Keep these documents under `wasm-port/docs/`:
 Continue expanding the standalone interpreter core from the verified minimal
 traverse path:
 
-1. replace the temporary minimal `convert_g()` implementation with thin
-   wrappers around more vendored interpreter conversion code,
-2. add `_x`/`_y`/`_z` named parameter fixture coverage and align it with
-   `#5420`/`#5421`/`#5422`,
-3. keep all source changes inside `wasm-port/` and leave `../linuxcnc/`
+1. replace the temporary minimal `convert_g()` implementation with calls into
+   vendored LinuxCNC interpreter conversion code.
+2. identify and shim the native runtime symbols blocking direct compilation of
+   `interp_convert.cc`, `interp_execute.cc`, and related interpreter files.
+3. keep fixture coverage as regression protection while deleting temporary
+   hand-written semantics.
+4. keep all source changes inside `wasm-port/` and leave `../linuxcnc/`
    read-only.