ATC-009_Modbus_Config_Write_Invalid_Rejected
============================================

Validate invalid external configuration writes are rejected safely.

Execution
---------

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   * - Field
     - Value
   * - Status
     - pass
   * - Test Type
     - functional_acceptance
   * - Last Run At
     - 2026-02-28T17:04:15Z
   * - Last Runner
     - Baseline_Verification

Preconditions
-------------

Writable configuration endpoints are enabled and current valid baseline values are recorded.

Procedure
---------

Attempt invalid writes including out of range and malformed payloads. After each attempt verify rejection response and re-read active configuration values.

Expected Result
---------------

Invalid writes are rejected with no unintended state mutation and previous valid configuration remains active.

Traceability
------------

.. list-table::
   :header-rows: 1

   * - Element Type
     - Referenced Elements
   * - Requirements
     -
       * :doc:`REQ-IFC-004 </generated/requirements/req-ifc-004-d156d04c-89f2-4156-9724-dae00d6c83d7>`