继续按 align-linuxcnc 约束：补 block reader 源码错误覆盖

结论：覆盖 LinuxCNC interp_read.cc/read_dollar()/read_one_item() 的重复 $、非法起始字符和中途 N word 错误，以及 interp_check.cc/check_m_codes() 的 M 码数量错误；未扩展 smoke。

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

docs/linuxcnc-porting.md

@@ -215,5 +215,6 @@ This matrix tracks LinuxCNC feature coverage for the web/WASM simulator. A featu
 | Parameter expressions and operators | covered for parameter references, source-linked `mod`, `**`, logical, and relational operator precedence, plus LinuxCNC parameter-setting syntax, divide-by-zero, negative-power, malformed `ATAN[]/[]`, unary operation syntax, `read_operation_unary()` unknown-word branches, `read_operation()` binary-operation prefix, unknown operation, and unclosed-expression error paths from `interp_read.cc`/`interp_execute.cc` | `tests/gcode/linuxcnc_parameter_expression_assignment.ngc`, `tests/gcode/linuxcnc_parameter_missing_equal_error.ngc`, `tests/gcode/linuxcnc_parameter_missing_value_error.ngc`, `tests/gcode/linuxcnc_expression_operators.ngc`, `tests/gcode/linuxcnc_divide_by_zero_error.ngc`, `tests/gcode/linuxcnc_negative_power_error.ngc`, `tests/gcode/linuxcnc_atan_missing_slash_error.ngc`, `tests/gcode/linuxcnc_atan_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_unary_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_c_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_e_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_f_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_l_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_r_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_s_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_t_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_default_word_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_a_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_e_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_g_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_l_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_m_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_n_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_o_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_x_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_operation_error.ngc`, `tests/gcode/linuxcnc_unclosed_expression_error.ngc` |
 | Word reader validation | source-linked LinuxCNC reader errors covered for negative `F/G/H/L/M/S/T` values and repeated `A/B/C/D/E/F/H/I/J/K/L/P/Q/R/S/T/U/V/W/X/Y/Z` words from `interp_read.cc` | `tests/gcode/linuxcnc_negative_f_word_error.ngc`, `tests/gcode/linuxcnc_negative_g_code_error.ngc`, `tests/gcode/linuxcnc_negative_h_word_error.ngc`, `tests/gcode/linuxcnc_negative_l_word_error.ngc`, `tests/gcode/linuxcnc_negative_m_code_error.ngc`, `tests/gcode/linuxcnc_negative_s_word_error.ngc`, `tests/gcode/linuxcnc_negative_t_word_error.ngc`, `tests/gcode/linuxcnc_multiple_a_words_error.ngc`, `tests/gcode/linuxcnc_multiple_b_words_error.ngc`, `tests/gcode/linuxcnc_multiple_c_words_error.ngc`, `tests/gcode/linuxcnc_multiple_d_words_error.ngc`, `tests/gcode/linuxcnc_multiple_e_words_error.ngc`, `tests/gcode/linuxcnc_multiple_f_words_error.ngc`, `tests/gcode/linuxcnc_multiple_h_words_error.ngc`, `tests/gcode/linuxcnc_multiple_i_words_error.ngc`, `tests/gcode/linuxcnc_multiple_j_words_error.ngc`, `tests/gcode/linuxcnc_multiple_k_words_error.ngc`, `tests/gcode/linuxcnc_multiple_l_words_error.ngc`, `tests/gcode/linuxcnc_multiple_p_words_error.ngc`, `tests/gcode/linuxcnc_multiple_q_words_error.ngc`, `tests/gcode/linuxcnc_multiple_r_words_error.ngc`, `tests/gcode/linuxcnc_multiple_s_words_error.ngc`, `tests/gcode/linuxcnc_multiple_t_words_error.ngc`, `tests/gcode/linuxcnc_multiple_u_words_error.ngc`, `tests/gcode/linuxcnc_multiple_v_words_error.ngc`, `tests/gcode/linuxcnc_multiple_w_words_error.ngc`, `tests/gcode/linuxcnc_multiple_x_words_error.ngc`, `tests/gcode/linuxcnc_multiple_y_words_error.ngc`, `tests/gcode/linuxcnc_multiple_z_words_error.ngc` |
 | G/M reader validation | source-linked LinuxCNC `read_g()`/`read_m()` errors covered for range checks, unknown code tables, and same-modal-group conflicts from `interp_read.cc` and `interp_array.cc` | `tests/gcode/linuxcnc_g_code_out_of_range_error.ngc`, `tests/gcode/linuxcnc_unknown_g_code_error.ngc`, `tests/gcode/linuxcnc_two_g_codes_same_modal_group_error.ngc`, `tests/gcode/linuxcnc_m_code_greater_199_error.ngc`, `tests/gcode/linuxcnc_unknown_m_code_error.ngc`, `tests/gcode/linuxcnc_two_m_codes_same_modal_group_error.ngc` |
+| Block/item reader validation | source-linked LinuxCNC block reader errors covered for repeated `$`, bad item-start characters, middle-of-line `N` words, and too many M-codes from `interp_read.cc`, `interp_array.cc`, and `interp_check.cc` | `tests/gcode/linuxcnc_multiple_spindle_choice_words_error.ngc`, `tests/gcode/linuxcnc_bad_character_bang_error.ngc`, `tests/gcode/linuxcnc_bad_character_middle_n_word_error.ngc`, `tests/gcode/linuxcnc_too_many_m_codes_error.ngc` |
 | Broader canned cycles `G73`, `G74`, `G82`-`G89` | partially covered: `G73`, `G74`, `G82`, `G83`, `G84`, `G85`, `G86`, `G87`, `G88`, `G89`; smoke parser maps supported cycles across `G17/G18/G19`, including LinuxCNC's special non-XY `G74/G84` tapping argument order and `G87` plane-specific `I/J/K` mapping; native/source regressions now check non-XY `G74/G84/G86/G87/G88` sequences | `tests/gcode/linuxcnc_canned_cycles_extended.ngc`, `tests/gcode/linuxcnc_canned_cycle_planes.ngc`, smoke API regression |
 | Full source-level wasm build | covered for the current wasm-safe RS274 source set, with remaining work focused on broadening browser-hostile dependency replacement and feature coverage | `./build-wasm.sh`, `test-linuxcnc-wasm-runtime-link.sh`, `test-web-wasm-node-smoke.sh`, `test-web-wasm-browser-smoke.sh` |