继续按 align-linuxcnc 约束：补极坐标变体源码覆盖，测试通过

test-linuxcnc-source-link.sh

@@ -555,6 +555,9 @@ CNC_SIM_RS274_VAR="$var_file" \
 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_polar_coordinates.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_polar_coordinates.json"
+CNC_SIM_RS274_VAR="$var_file" \
+    "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_polar_coordinate_variants.ngc \
+    >"$output_dir/cnc_sim_linuxcnc_source_polar_coordinate_variants.json"
 polar_coordinate_error_cases=(
     "linuxcnc_polar_g18_error|Cannot use polar coordinate except in G17 plane"
     "linuxcnc_polar_with_x_error|Cannot specify both polar coordinate and X word"
@@ -2122,6 +2125,25 @@ if len(polar_linear_events) != len(expected_polar_linear_ends) or any(
     ]
     raise SystemExit(f"unexpected source-linked polar-coordinate endpoints: {polar_linear_ends!r}")
 
+polar_coordinate_variants = json.loads((OUTPUT_DIR / "cnc_sim_linuxcnc_source_polar_coordinate_variants.json").read_text())
+polar_variant_linear_events = [
+    event
+    for event in polar_coordinate_variants
+    if event["type"] == "linear-feed"
+]
+expected_polar_variant_ends = [(3, 6, 8), (4, 10, 0), (6, 15, 0), (7, 0, 15)]
+if len(polar_variant_linear_events) != len(expected_polar_variant_ends) or any(
+    event["line"] != line or
+    abs(event["end"]["x"] - x) > 1e-9 or
+    abs(event["end"]["y"] - y) > 1e-9
+    for event, (line, x, y) in zip(polar_variant_linear_events, expected_polar_variant_ends)
+):
+    polar_variant_linear_ends = [
+        (event["line"], event["end"]["x"], event["end"]["y"])
+        for event in polar_variant_linear_events
+    ]
+    raise SystemExit(f"unexpected source-linked polar-coordinate variant endpoints: {polar_variant_linear_ends!r}")
+
 predefined = json.loads((OUTPUT_DIR / "cnc_sim_linuxcnc_source_predefined_positions.json").read_text())
 predefined_rapids = [
     (