执行 AGENTS align-linuxcnc 加速规则

结论：新增 LinuxCNC source-backed G1 zero-feed 错误覆盖，源码依据为 src/emc/rs274ngc/interp_convert.cc convert_straight()。

测试：./test-native.sh 通过；./test-linuxcnc-source-link.sh 通过。

test-linuxcnc-rs274-native.sh

@@ -496,9 +496,10 @@ for case in "${threading_check_error_cases[@]}"; do
 done
 # Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc
 # convert_straight() and convert_threading_cycle() reject invalid
-# spindle state/selector, rotary-axis motion, and G76 I/J/K geometry
-# before issuing synchronized threading motion.
+# feed/spindle state, spindle selectors, rotary-axis motion, and G76 I/J/K
+# geometry before issuing straight or synchronized threading motion.
 threading_convert_error_cases=(
+    "linuxcnc_g1_zero_feed_error|Cannot do g1 with zero feed rate"
     "linuxcnc_g33_stopped_spindle_error|Spindle not turning in G33"
     "linuxcnc_g33_1_stopped_spindle_error|Spindle not turning in G33.1"
     "linuxcnc_g33_spindle_dollar_out_of_range_error|Invalid spindle (\$) number in G33 move"

test-linuxcnc-source-link.sh

@@ -1080,9 +1080,10 @@ for case in "${threading_check_error_cases[@]}"; do
 done
 # Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc
 # convert_straight() and convert_threading_cycle() reject invalid
-# spindle state/selector, rotary-axis motion, and G76 I/J/K geometry
-# before issuing synchronized threading motion.
+# feed/spindle state, spindle selectors, rotary-axis motion, and G76 I/J/K
+# geometry before issuing straight or synchronized threading motion.
 threading_convert_error_cases=(
+    "linuxcnc_g1_zero_feed_error|Cannot do g1 with zero feed rate"
     "linuxcnc_g33_stopped_spindle_error|Spindle not turning in G33"
     "linuxcnc_g33_1_stopped_spindle_error|Spindle not turning in G33.1"
     "linuxcnc_g33_spindle_dollar_out_of_range_error|Invalid spindle (\$) number in G33 move"

tests/gcode/linuxcnc_g1_zero_feed_error.ngc

@@ -0,0 +1,2 @@
+G21 G90
+G1 X1