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>
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