feat(historian-sidecar): live aahClientManaged alarm-event write path (C.1)

SdkAlarmHistorianWriteBackend.WriteBatchAsync replaces the RetryPlease
placeholder with the real entry point — HistorianAccess.AddStreamedValue
(HistorianEvent, out HistorianAccessError) in aahClientManaged, pinned by
decompiling the installed SDK.

The write path opens its own ReadOnly=false connection: the query-side
HistorianDataSource opens ReadOnly sessions and AddStreamedValue fails on
those with WriteToReadOnlyFile. IHistorianConnectionFactory gains a readOnly
parameter (default true, query path unchanged); BuildConnectionArgs is
extracted as a pure helper. HistorianClusterEndpointPicker is shared for
node failover; connection-class errors abort the batch as RetryPlease and
reset the connection, malformed-input codes map to PermanentFail.

Tests: connection-unavailable batch deferral, ClassifyOutcome error-code
table, BuildConnectionArgs read-vs-write shaping (80 pass, 2 rig-skipped).
Live_* round-trip tests stay Skip-gated for the D.1 rollout smoke.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

looseends.md

@@ -16,11 +16,14 @@ remains, plus follow-ups surfaced during the run.
 
 ## Follow-ups surfaced during the run
 
-- **C.1 live SDK binding.** `SdkAlarmHistorianWriteBackend.WriteBatchAsync`
-  (`src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/`) is
-  still a placeholder returning `RetryPlease` for every event, so queued
-  alarm events are retained rather than written. Pinning the real
-  `aahClientManaged` alarm-write entry point is rig-gated — pairs with #20.
+- **~~C.1 live SDK binding.~~** DONE (code). `SdkAlarmHistorianWriteBackend`
+  (`src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/`) now
+  writes via the real entry point `HistorianAccess.AddStreamedValue(HistorianEvent,
+  out error)` in `aahClientManaged`. Two plan corrections found while pinning it:
+  (a) `ArchestrAAlarmsAndEvents.SDK` has no writer — it's a WCF query proxy;
+  (b) writes need their own `ReadOnly=false` connection, not the shared read
+  pool. Remaining: the live-rig write smoke (the `Live_*` tests are still
+  `Skip`-gated) — folds into #20 / D.1.
 
 - **~~#24 Shelve-method routing.~~** DONE. Acknowledge / Confirm already
   routed; OneShotShelve / TimedShelve / Unshelve now route via the native