继续按 align-linuxcnc 约束：补 O-word 执行错误源码覆盖

结论：新增重复/未匹配 O-word label 和 out-of-context return/endsub 的 source-link 断言；依据 LinuxCNC interp_o_word.cc，未扩展 smoke。

test-linuxcnc-source-link.sh

@@ -893,6 +893,28 @@ for case in "${oword_reader_error_cases[@]}"; do
     fi
     grep -q "$expected" "$output_dir/cnc_sim_linuxcnc_source_$fixture.err"
 done
+# Source basis: LinuxCNC src/emc/rs274ngc/interp_o_word.cc
+# convert_control_functions() rejects unmatched, duplicate, and
+# out-of-context O-word control labels during execution.
+oword_execution_error_cases=(
+    "linuxcnc_oword_endsub_without_sub_error|not in a subroutine definition"
+    "linuxcnc_oword_return_without_sub_error|not in a subroutine definition"
+    "linuxcnc_oword_duplicate_if_label_error|duplicate O-word label"
+    "linuxcnc_oword_elseif_undefined_label_error|undefined O-word label"
+    "linuxcnc_oword_break_undefined_label_error|undefined O-word label"
+    "linuxcnc_oword_endrepeat_no_matching_repeat_error|no matching label"
+)
+for case in "${oword_execution_error_cases[@]}"; do
+    fixture=${case%%|*}
+    expected=${case#*|}
+    if CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
+        "$build_dir/linuxcnc_rs274_source_dump" "tests/gcode/$fixture.ngc" \
+        >"$output_dir/cnc_sim_linuxcnc_source_$fixture.json" 2>"$output_dir/cnc_sim_linuxcnc_source_$fixture.err"; then
+        echo "expected $fixture.ngc to fail" >&2
+        exit 1
+    fi
+    grep -q "$expected" "$output_dir/cnc_sim_linuxcnc_source_$fixture.err"
+done
 # Source basis: LinuxCNC src/emc/rs274ngc/interp_read.cc read_text()
 # rejects EOF without the matching percent/program end and overlong file
 # lines; read_n_number() rejects malformed N-line numbers through