按建议，继续工作

结论：已新增 G53 机床坐标正向 fixture 和增量模式拒绝 fixture，固定 vendored LinuxCNC find_ends()/convert_straight() 行为；native probe 全量验证通过。

wasm-port/docs/scope-and-baseline.md

@@ -40,6 +40,7 @@ G-code fixture coverage includes:
 - position parameters
 - canned cycles
 - coordinate offsets
+- G53 machine-coordinate motion
 - feed and motion control modes
 - cutter compensation motion
 - probe semantics
@@ -58,6 +59,7 @@ Negative fixture coverage includes:
 - arc radius mismatch
 - zero-radius arc
 - cutter compensation plane-change rejection
+- G53 incremental-mode rejection
 - read-only named parameter writes
 - read-only numbered parameter writes
 - missing tool