满庭芳·源流归一

结论：LinuxCNC rs274ngc 源码移植边界继续收拢。已将 rs274ngc 头文件纳入 manifest 跟踪，core 编译组仍只包含可编译源文件；启用 CNC_SIM_ENABLE_LINUXCNC_RS274_BACKEND 时 API 默认使用 LinuxCNC rs274 后端；M428/M429/M430 与 5axis/TRT/TDR/RTCP 相关路径继续保持来自 LinuxCNC 源码或 remap 配置的薄桥接。

验证：./test-linuxcnc-source-syntax.sh；./test-linuxcnc-api-native.sh；./test-native.sh；./test-linuxcnc-source-link.sh。

docs/linuxcnc-source-policy.md

@@ -0,0 +1,32 @@
+# LinuxCNC Source Policy
+
+The simulator must not grow independently designed functional behavior.
+Functional behavior must come from LinuxCNC source code.
+
+Allowed project code:
+
+- Thin adapters between LinuxCNC source code and the simulator C API.
+- Platform shims needed to compile LinuxCNC code for native tests or wasm.
+- Event serialization, test fixtures, build scripts, and documentation.
+- Temporary smoke scaffolding only when it is explicitly marked as temporary.
+
+Not allowed as final behavior:
+
+- Hand-written G-code interpretation semantics.
+- Hand-derived kinematics, RTCP, coordinate transform, cutter compensation, canned cycle, modal, parameter, or expression behavior.
+- Behavior copied from documentation, controller intuition, or examples without checking the LinuxCNC implementation.
+
+Required workflow for every functional change:
+
+1. Identify the LinuxCNC source file and function that defines the behavior.
+2. Add or update a test that demonstrates the LinuxCNC behavior.
+3. Port, wrap, or route to that LinuxCNC implementation.
+4. Record the source file/function in code comments or nearby documentation when the mapping is not obvious.
+5. Run `./test-native.sh` and `./test-linuxcnc-source-link.sh`.
+
+Current temporary exceptions:
+
+- The smoke parser exists only to exercise the public API and UI while the LinuxCNC RS274 backend is being wired in.
+- RTCP pivot behavior is limited to LinuxCNC source-backed switchkins paths; unsupported switchkins types must not fall back to hand-derived geometry.
+
+Both exceptions should shrink over time. New functional behavior should not be added to them unless it is directly copied from, or routed to, LinuxCNC source code.