继续按 align-linuxcnc 约束：补 G 代码校验错误源码覆盖，测试通过

test-linuxcnc-source-link.sh

@@ -641,6 +641,30 @@ for case in "${enhance_block_error_cases[@]}"; do
     fi
     grep -Fq "$expected" "$output_dir/cnc_sim_linuxcnc_source_$fixture.err"
 done
+# Source basis: LinuxCNC src/emc/rs274ngc/interp_check.cc
+# check_g_codes() rejects invalid modal-0 combinations for G4, G10, and G53
+# before convert_g() executes motion or coordinate updates.
+check_g_code_error_cases=(
+    "linuxcnc_g4_missing_p_error|Dwell time missing with g4"
+    "linuxcnc_g4_arc_p_conflict_error|G4 not allowed with G2 or G3 because they both use P"
+    "linuxcnc_g10_invalid_l_error|Line with G10 does not have L0, L1, L10, L11, L2, or L20"
+    "linuxcnc_g10_p_non_integer_error|P value not an integer with G10"
+    "linuxcnc_g10_l2_p_out_of_range_error|P value out of range (0-9) with G10 L2"
+    "linuxcnc_g10_l1_p_out_of_range_error|P value out of range with G10 L1"
+    "linuxcnc_g53_arc_error|Must use g0 or g1 with g53"
+    "linuxcnc_g53_incremental_error|Cannot use g53 incremental"
+)
+for case in "${check_g_code_error_cases[@]}"; do
+    fixture=${case%%|*}
+    expected=${case#*|}
+    if CNC_SIM_RS274_VAR="$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 $fixture.ngc to fail" >&2
+        exit 1
+    fi
+    grep -Fq "$expected" "$output_dir/cnc_sim_linuxcnc_source_$fixture.err"
+done
 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_predefined_positions.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_predefined_positions.json"