docs(archreview): R2-06 live gate 5/6 + U-7 retype policy answered

- StorageRateMs bug found+fixed (PR #439); live suite 3/6 -> 5/6
- U-7: EnsureTags is a real upsert; supported-type retype ACCEPTED (Float->Double);
  Int1 not creatable on this histsdk (ProtocolEvidenceMissingException, Int1-only)
- record the observed retype policy in docs/Historian.md (fills the placeholder)

docs/Historian.md

@@ -157,13 +157,25 @@ mapper code change is needed or wanted). Consequences:
 1. **New Boolean tags provision correctly as Int1.** This is the fix arriving as a silent, zero-diff
    semantic change from the bump.
 2. **Pre-bump Boolean tags exist historian-side as Float.** On the next deploy that dispatches provisioning
-   for such a tag, the gateway is asked (via the upsert) to update it to Int1. The AVEVA-side outcome of an
-   in-place analog retype is the one thing the contract does not pin; the candidate behaviors are
-   (i) **accepted with tag versioning** (history preserved under the old version, new writes under Int1),
-   (ii) **accepted as a plain retype**, or (iii) **rejected per-tag** → `TagOperationResult.Success=false`
-   → counted in the provisioner's `failed=N` dispatch tally. Only a live run distinguishes these — see the
-   **retype probe** (`EnsureTags_type_change_outcome_is_observable`) in the [Live /run gate](#live-run-gate).
-   *(This list is replaced with the observed answer after the first live run.)*
+   for such a tag, the gateway is asked (via the upsert) to update it to Int1.
+
+   **Observed live (2026-07-13, real 0.2.0 gateway → real AVEVA historian on `wonder-sql-vd03`, probed via
+   `grpcurl` — archreview R2-06 T12):**
+   - `EnsureTags` is a **real create-or-update upsert** — re-`EnsureTags` of an existing tag at the same type
+     returns `Success=true`.
+   - An **in-place retype between SUPPORTED types is ACCEPTED** — `Float→Double` on an existing tag returns
+     `Success=true` (hypothesis **(ii) accepted as a plain retype**, not rejected).
+   - **BUT `Int1` — the 0.2.0 Boolean target — is *not a creatable type* on this historian's histsdk:**
+     `EnsureTags(Int1)` returns `Success=false, Error="ProtocolEvidenceMissingException"` (the vendored client's
+     "no capture evidence for this type" guard → gRPC `Unimplemented`), both for a fresh tag and as a retype
+     target. A type sweep confirmed it is **Int1-specific**: `Int2/UInt2/Int4/UInt4/Float/Double` all provision
+     `Success=true`; only `Int1` fails.
+   - **Net for a pre-bump Float Boolean tag asked to become Int1:** the provision **fails** (per-tag
+     `Success=false` → `failed=N` tally). It is **neither silently retyped nor data-lost** — the tag stays Float
+     and remains readable; the Int1 provision simply doesn't land until the gateway's histsdk gains `Int1`
+     create-evidence. (Prerequisite for reaching this outcome at all: the provisioner must stamp a **positive
+     `StorageRateMs`** — a `0` made `EnsureTags` throw `ArgumentOutOfRangeException` and fail *every* provision;
+     fixed in `GatewayTagProvisioner`, PR #439.)
 3. **The failure mode is bounded and observable either way.** Provisioning is fire-and-forget and never
    blocks/fails a deploy; a per-tag rejection surfaces only as the tally's `failed` count. Values written to
    a still-Float tag by the recorder remain readable (Float supersets Int1's 0/1 range); nothing is lost