[M5] mxaccess-asb: F25 step 9 — Write operation
Closes the highest-value remaining IASBIDataV2 op. With Write landed,
the read+write+subscribe path is functionally complete in-memory.
API additions:
* `MinimalWriteValue { value: AsbVariant }` — carries just the Value
payload. Optional ArrayElementIndex / Comment / HasQT / Status /
Timestamp fields are deferred to a later iteration once a live
capture confirms the WCF DataContract XML form.
* `build_write_request_body(items, values, write_handle)` per
`AsbContracts.cs:181-194`:
```xml
<WriteBasicRequest xmlns="urn:msg.data.asb.iom:2">
<Items><ASBIData>{ItemIdentity[] binary}</ASBIData></Items>
<Values>
<WriteValue><Value><ASBIData>{Variant binary}</ASBIData></Value></WriteValue>
...
</Values>
<WriteHandle>{i32}</WriteHandle>
</WriteBasicRequest>
```
Items array uses the IAsbCustomSerializableType binary fast-path;
each Value's inner Variant also uses the fast-path. WriteHandle is
an Int32 (opaque correlation echoed in PublishWriteComplete).
* `decode_write_response` — per-item Status array (mirrors the
unregister/register pattern).
* `AsbClient::write(items, values, write_handle)` — thin wrapper.
4 new tests:
* `write_request_body_carries_items_values_and_write_handle` — body
shape sanity (WriteHandle = 7 Int32, WriteValue element present).
* `write_request_body_pairs_items_and_values_arrays` — 2 items + 2
values produces 2 WriteValue elements.
* `write_response_round_trips_status_array` — Status decode.
* `write_response_missing_status_fails` — graceful MissingField
error.
Workspace: 695 tests pass (was 691, +4).
Stubbed for next F25 iterations:
* `PublishWriteComplete` — empty request, `ItemWriteComplete[]`
response.
* `DeleteMonitoredItems` — mirrors AddMonitoredItems pattern.
* Optional WriteValue fields (Comment / Timestamp / etc.) once a
live capture confirms the wire-byte layout.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Joseph Doherty
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