docs(handoff): re-characterize gRPC event-row gate — capture-gated, not server-gated

Live SQL ground truth (user-authorized one-time read via SOCKS->SQL relay)
disproves the gate on the open gRPC event-row item. The live 2023 R2 server
IS event-bearing — Runtime.dbo.Events holds 19,356 rows in the last 30 days
(90,944 in 365) — yet the empty-filter gRPC event query still returns zero rows
and long-polls to the deadline over that same window.

So GetNextEventQueryResultBuffer returning nothing is NOT "no events on the
server"; the empty-filter request shape (filter / namespace / event-tag
registration) doesn't match existing rows. The remaining work is a fresh native
gRPC event-query capture of the stock client, not access to a different server.

- handoff.md: rewrite open-item #1 with the SQL numbers + capture-gated framing;
  update the "to move any item" summary to match.
- HistorianGrpcIntegrationTests: correct the event-read test comment (drop the
  false "idle dev box holds no events" rationale; document 19k-events-yet-zero-rows).

No behavior change (test edit is comment-only). Sanitization scan clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B6mcaT2PjRFKcogzp9UkfC

tests/AVEVA.Historian.Client.Tests/HistorianGrpcIntegrationTests.cs

@@ -487,13 +487,19 @@ public sealed class HistorianGrpcIntegrationTests
 
         // Plan #2: ReadEvents over gRPC. The chain runs end-to-end and StartEventQuery succeeds
         // (no InvalidOperationException), but — confirmed live 2026-06-22 — GetNextEventQueryResultBuffer
-        // LONG-POLLS when the query has no rows: the gRPC server blocks to the deadline instead of
-        // returning the synchronous 5-byte code-85 terminal the 2020 WCF op returns. The idle dev box
-        // holds no events, so the orchestrator reaches its no-data terminal with zero rows and (rather
-        // than assert a possibly-false "no events" empty) throws ProtocolEvidenceMissingException.
-        // This pins that current reality and that the chain stays BOUNDED (no multi-minute hang) via
-        // the short registration + poll deadlines. Flip to asserting parsed rows once an event-bearing
-        // 2023 R2 server is available. (Set a small HISTORIAN_GRPC_TIMEOUT to keep this snappy.)
+        // LONG-POLLS and returns zero rows: the gRPC server blocks to the deadline instead of
+        // returning the synchronous 5-byte code-85 terminal the 2020 WCF op returns, so the orchestrator
+        // reaches its no-data terminal with zero rows and (rather than assert a possibly-false "no events"
+        // empty) throws ProtocolEvidenceMissingException.
+        //
+        // IMPORTANT (2026-06-22): the zero rows are NOT "no events on the server". Verified against the
+        // live 2023 R2 box, which holds 19,356 events in the last 30 days (SQL ground truth via the INSQL
+        // linked server, Runtime.dbo.Events). The EMPTY-FILTER gRPC event query simply does not match
+        // them. So the gate here is the empty-filter request shape (filter / namespace / event-tag
+        // registration), NOT data availability — this is capture-gated (needs a native gRPC event-query
+        // capture), not server-gated. Flip to asserting parsed rows once that capture lands and the
+        // request is corrected. The chain stays BOUNDED (no multi-minute hang) via the short
+        // registration + poll deadlines. (Set a small HISTORIAN_GRPC_TIMEOUT to keep this snappy.)
         HistorianClient client = new(BuildOptions(host));
 
         DateTime endUtc = DateTime.UtcNow;