Auto: s7-d3 — instance-DB / FB parameter resolution

Closes #301

docs/v2/s7.md

@@ -1044,6 +1044,30 @@ The fan-out rejects, with clear errors:
 - Tag with `UdtName` AND `ElementCount > 1` (array-of-UDT belongs in the UDT
   layout, not at the parent-tag level)
 
+### Re-import on UDT / FB-interface edit — caveat
+
+The static-offset model assumes the declared layout matches the runtime
+layout exactly. When the underlying UDT or FB interface changes in TIA Portal
+— a member added, removed, or reordered — the byte offsets shift on the PLC
+side and the cached `S7UdtDefinition` / instance-DB addresses point at the
+wrong member.
+
+**The driver does not auto-detect interface drift.** After any UDT edit or
+multi-instance-FB interface edit on the PLC side, the operator must:
+
+1. Recompile + download the updated program in TIA Portal.
+2. Re-export "Show all tags" CSV from the updated project.
+3. Re-import via `AddTiaCsvImport` (or `import-symbols` CLI) and update the
+   matching `S7UdtDefinition` declarations to mirror the new offsets.
+4. Restart the driver instance (Admin UI → Drivers → Reload).
+
+A stale UDT layout will silently read / write the wrong byte offsets — the
+values will look like valid PLC data but reference whichever member used to
+live at that offset before the edit. The same caveat applies to multi-instance
+FB-instance DBs imported via PR-S7-D3 / [#301](https://github.com/dohertj2/lmxopcua/issues/301);
+see [`docs/drivers/S7-TIA-Import.md` "Re-import on FB-interface edit"](../drivers/S7-TIA-Import.md#re-import-on-fb-interface-edit--caveat)
+for the FB-instance-specific workflow.
+
 ## References
 
 1. Siemens Industry Online Support, *Modbus/TCP Communication between SIMATIC S7-1500 / S7-1200 and Modbus/TCP Controllers with Instructions `MB_CLIENT` and `MB_SERVER`*, Entry ID 102020340, V6 (Feb 2021). https://cache.industry.siemens.com/dl/files/340/102020340/att_118119/v6/net_modbus_tcp_s7-1500_s7-1200_en.pdf