[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>

design/followups.md

@@ -46,7 +46,11 @@ move to `## Resolved` with a date + commit hash.
 
 **Resolves when:** F19-F26 are all closed and the four DoD bullets above pass.
 
-**Cumulative execution log.** F19 + F23 (`ed17c07`); F24 (`7611d9e`); F20 (`9dfd193`); F22 (`43c10a1`); F21 (`5f98558`); F25 step 1 (`25dbd8d`); F25 step 2 (`a2b8989`); F25 step 3 (`c4bf0a0`); F25 step 4 (`1e59249`); F25 step 5 (`9b8133f`); F25 step 6 (`321b796`); F25 step 7 (`1b1ee1e`); F26 step 1 (`8a0f92b`); F26 step 2 (`14bb529`); example rewrite (`c6570dc`); F25 step 8 landed in this commit:
+**Cumulative execution log.** F19 + F23 (`ed17c07`); F24 (`7611d9e`); F20 (`9dfd193`); F22 (`43c10a1`); F21 (`5f98558`); F25 step 1 (`25dbd8d`); F25 step 2 (`a2b8989`); F25 step 3 (`c4bf0a0`); F25 step 4 (`1e59249`); F25 step 5 (`9b8133f`); F25 step 6 (`321b796`); F25 step 7 (`1b1ee1e`); F26 step 1 (`8a0f92b`); F26 step 2 (`14bb529`); example rewrite (`c6570dc`); F25 step 8 (`b543eb1`); F25 step 9 landed in this commit:
+- F25 step 9: Write operation. New `MinimalWriteValue { value: AsbVariant }` carries just the `Value` payload; optional ArrayElementIndex/Comment/HasQT/Status/Timestamp WriteValue fields are deferred to a later iteration once a live capture confirms the WCF DataContract XML form. New `build_write_request_body(items, values, write_handle)` produces the full `WriteBasicRequest` body shape per `AsbContracts.cs:181-194`: Items array uses the IAsbCustomSerializableType binary fast-path (`<Items><ASBIData>{...}</ASBIData></Items>`), each Value's inner `Variant` field also uses the fast-path (`<WriteValue><Value><ASBIData>{...}</ASBIData></Value></WriteValue>`), and WriteHandle is an Int32. New `decode_write_response` returns the per-item Status array. New `client::write(items, values, write_handle)` wrapper. 4 new tests cover Write request body shape (carries Items array, parallel Values array with WriteValue elements, WriteHandle as Int32), parallel-array sizing (2 items + 2 values produces 2 WriteValue elements), Status round-trip, and missing-Status error. Workspace: 695 tests pass (was 691, +4). The IASBIDataV2 read+write+subscribe path is now functionally complete in-memory.
+
+**Earlier slices:**
+- F25 step 8 (commit `b543eb1`):
 - F25 step 8: subscription operations — `CreateSubscription`, `AddMonitoredItems`, `Publish`, `DeleteSubscription`. New `MonitoredItemValue` codec in contracts.rs (`IAsbCustomSerializableType` binary fast-path: ItemIdentity + RuntimeValue + AsbVariant per `cs:1064-1068`). New `MinimalMonitoredItem` request struct exposing only the proven fields (Item, SampleInterval, Buffered) — optional Active/TimeDeadband/ValueDeadband/UserData deferred to a later iteration once a live capture confirms the WCF DataContract XML shape. Per-operation builders, response decoders, and client wrappers follow the established F25 pattern. New `BodyField::Int64Element` variant for the `<SubscriptionId>` / `<MaxQueueSize>` / `<SampleInterval>` primitive fields. The subscription path lifts the `examples/asb-subscribe.rs` "Read-loop" caveat — once wire-byte reconciliation lands, the example can do `create_subscription → add_monitored_items → publish-loop → delete_subscription`. 11 new tests cover MonitoredItemValue round-trip + array, CreateSubscription request body shape + response decode (Int64 + Chars text fallback + missing-field error), AddMonitoredItems request body shape + response decode, DeleteSubscription request body, Publish request + response (with full Status + Values round-trip via the in-memory body synthesis pattern).
 
 **Earlier slices:**