增加当前位置参数fixture验证

结论：新增 position_params fixture，覆盖 Z 轴运动与 #5420/#5421/#5422 当前坐标参数同步；最小 harness 输出当前位置参数，runtime 在直线运动后刷新相对位置参数。检查：git diff --check 通过；wasm-port/tests/native/verify_native_probes.sh 通过。

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

@@ -360,6 +360,11 @@ Current verified progress:
   temporary wrapper behavior is based on LinuxCNC
   `interp_convert.cc::convert_distance_mode()` and
   `interp_convert.cc::convert_straight()`.
+- `tests/fixtures/gcode/position_params.ngc` and
+  `tests/fixtures/canon/position_params.events` cover Z-axis motion plus
+  current-position parameter visibility for `#5420`, `#5421`, and `#5422`.
+  The parameter source basis is LinuxCNC
+  `interp_parameter_def.hh` and `interp_namedparams.cc`.
 - This proves the current extracted interpreter slice can parse and execute a
   simple traverse and feed move through a standalone canonical event sink.
 
@@ -662,7 +667,7 @@ traverse path:
 
 1. replace the temporary minimal `convert_g()` implementation with thin
    wrappers around more vendored interpreter conversion code,
-2. add fixture coverage for `Z` moves and multi-axis current-position
-   parameter updates,
+2. add a negative fixture for `G1` without feed rate to start pinning error
+   semantics,
 3. keep all source changes inside `wasm-port/` and leave `../linuxcnc/`
    read-only.