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/architecture.md

@@ -18,6 +18,9 @@ The event callback emits normalized `CncSimEvent` records. JavaScript can transf
 
 ## LinuxCNC integration plan
 
+Functional behavior must come from LinuxCNC source code, not independently
+designed project code. See `docs/linuxcnc-source-policy.md`.
+
 1. Build a native `CanonEventSink` that implements all functions declared in `canon.hh`.
 2. Link the sink with `src/emc/rs274ngc` and `src/emc/nml_intf` instead of the task controller.
 3. Stub or remove Python remap support for the first browser target.
@@ -58,10 +61,18 @@ Feature parity needs more than G-code parsing:
 
 ## Five-axis and RTCP
 
-The first RTCP implementation is a geometry kernel, not the full LinuxCNC motion
-controller. It treats programmed XYZ as the tool-center point, applies A/B/C
-orientation to a local tool vector, and computes the compensated pivot/spindle
-point needed to keep the tool tip fixed.
+RTCP pivot events are emitted only for known LinuxCNC switchkins modes. These
+paths must use formulas copied from LinuxCNC source code, not independently
+derived geometry. The current source mapping is:
+
+- `M428` / `XYZBC_TRT`: `linuxcnc/src/emc/kinematics/trtfuncs.c`,
+  `xyzbcKinematicsForward()` and `xyzbcKinematicsInverse()`
+- `M430` / `USERK_IDENTITY`: `linuxcnc/src/emc/kinematics/userkfuncs.c`,
+  delegating to `identityKinematicsForward()` and
+  `identityKinematicsInverse()` in `kins_util.c`
+- The retained `5axiskins` helpers map to
+  `linuxcnc/src/emc/kinematics/5axiskins.c`,
+  `fiveaxis_KinematicsForward()` and `fiveaxis_KinematicsInverse()`
 
 RTCP is opt-in through config JSON. When enabled, the original motion events
 remain programmed tool-tip motion and an additional `rtcp-pivot` event is emitted
@@ -74,7 +85,5 @@ Current files:
 - `core/src/rtcp_kinematics.cpp`
 - `core/tests/rtcp_kinematics_smoke.cpp`
 
-The next integration step is to add machine configuration for rotary topology,
-pivot offsets, tool length sources, and rotation order, then apply RTCP
-compensation while converting LinuxCNC Canon motion events into renderable
-machine/tool-tip trajectories.
+The next integration step is to add more LinuxCNC source-backed kinematics for
+additional switchkins or machine topologies.