Wire ApplyScaling, StorageRate; close out write-commands plan

ApplyScaling (HistorianTagDefinition.ApplyScaling):
The EnsT2 trailer's second byte controls server-side scaling — `FE 00`
mirrors MinRaw to MinEU and sets AnalogTag.Scaling=0; `FE 01` persists
distinct MinRaw/MaxRaw and sets Scaling=1. Decoded by toggling
set_ApplyScaling on the native harness and capturing the wire bytes for
both values with identical inputs. The earlier docs claimed
EnsureTagAsync needed a follow-up "UpdateTags" call; the WCF surface has
no such operation — toggling that one byte is the whole fix.

StorageRate (HistorianTagDefinition.StorageRateMs):
Serializer accepts a non-default rate, validated empirically against
the live server which only accepts quantized values
(1000/5000/10000/60000/300000 ms).

EnsureTagAsync upsert semantics:
Second call on the same tag name with different fields succeeds and
updates Description, MinEU, MaxEU, MinRaw, MaxRaw, Scaling in place
(verified by direct SQL inspection in a live test).

Plan + doc closeout:
write-commands-reverse-engineering.md rewritten as a current-state
plan with three workstreams (A doc closeout / B idempotency / C1
StorageRate) and a parallelism table; prior phase notes preserved as
appendix. handoff.md, implementation-status.md, wcf-contract-evidence.md,
README.md updated to remove "writes are out of scope" / non-existent
UpdateTags references and document the actual EnsT2 wire format
including the `FE xx` trailer.

Reverse-engineering harness gains --write-apply-scaling and a SQL
post-check that prints the persisted AnalogTag bounds so future RE
sessions can verify wire→DB causality without leaving the harness.

169/169 tests pass (was 165; +4 new tests covering ApplyScaling,
StorageRate golden bytes, StorageRate live persistence, and
EnsureTagAsync upsert semantics).

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

docs/reverse-engineering/implementation-status.md

@@ -3,13 +3,23 @@
 ## Completed
 
 - Production SDK targets `net10.0` and has no AVEVA binary references.
-- Public API now includes the intended parity surface:
+- Public API includes the full intended parity surface:
   - TCP probe
   - raw, aggregate, at-time, and block history reads
   - event reads
   - tag browse and metadata calls
   - connection, store-forward, and system-parameter status calls
-  - write-back intentionally remains out of scope for this read-only SDK pass
+  - **`EnsureTagAsync`** for analog Float/Double/Int2/Int4/UInt4 with
+    optional `ApplyScaling=true` for distinct MinRaw/MaxRaw persistence
+    (live-verified end-to-end against `localhost`; SQL post-check confirms
+    `AnalogTag.Scaling=1` and distinct raw bounds when the flag is set)
+  - **`DeleteTagAsync`** (live-verified)
+  - **AddS2 (write samples) is architecturally blocked** — server runtime
+    cache only ingests from configured IOServers / Application Server
+    pipelines, not from `HistorianAccess.AddTag`-only flows. Three
+    independent reproduction attempts confirmed the same
+    `129 "Tag not found in cache"` failure even with the real wwTagKey,
+    fresh sessions, and 8s settle waits. Not a protocol gap.
 - Internal protocol scaffolding exists:
   - `HistorianConnection`
   - `HistorianFrameReader`