histsdk/docs/reverse-engineering/grpc-event-query-capture.md

gRPC event-query capture (2026-06-22) — the StartEventQuery request that returns rows

Captured the stock 2023 R2 client performing a gRPC event read that returns rows, to resolve the open item "gRPC event ROW retrieval returns zero rows" (handoff §Current Status item 1). This closes the capture-gate: the working request shape is now known.

How it was captured

tools/AVEVA.Historian.Grpc2023CaptureHarness gained a capture-event scenario. It loads the self-contained mixed-mode 2023 R2 aahClientManaged.dll and drives HistorianAccess:

OpenConnection(ConnectionMode=Historian /*gRPC*/, ConnectionType=Event, ReadOnly=true)
  -> CreateEventQuery()                      // NON-null only on an Event connection
  -> EventQueryArgs { StartDateTime, EndDateTime, EventCount }
  -> EventQuery.StartQuery(args)             // => GrpcRetrievalClient.StartEventQuery(requestBuffer)
  -> loop EventQuery.MoveNext() / QueryResult// => GrpcRetrievalClient.GetNextEventQueryResultBuffer
  -> EventQuery.EndQuery() -> CloseConnection

The existing wide-net instrument-grpc-nonstream IL rewrite (every Grpc*Client byte[] method) already covers GrpcRetrievalClient.StartEventQuery.requestBuffer (entry) and GetNextEventQueryResultBuffer.result (exit) — no new instrument command was needed. Run read-only (non-destructive) against the live 2023 R2 server over the loopback tunnel; the rewrite + capture NDJSON stay under artifacts/reverse-engineering/grpc-event-capture/ (gitignored — the result buffer carries event identity data).

Result: 50 events returned over gRPC (Alarm.Set / Alarm.Clear rows), proving the path works when driven through an Event connection.

Two findings

1. The event read needs an Event-type connection (ConnectionIndex 1)

HistorianAccess.CreateEventQuery() returns null unless IsEventConnectionRequested() — i.e. the connection was opened with ConnectionType=Event, which the native client routes to a separate connection (ConnectionIndex 1) from the process/data path. The full captured pre-query sequence on that connection: OpenConnection → ExchangeKey → UpdateClientStatus → RegisterTags(CM_EVENT) → EnsureTags(CM_EVENT) → GetHistorianInfo + 7×GetSystemParameter (Stat priming) → StartEventQuery → GetNextEventQueryResultBuffer (rows) → EndEventQuery → CloseConnection.

2. The working StartEventQuery request is version 6, not 5

Our SDK's HistorianEventQueryProtocol.CreateNativeFilterAttempt builds a version-5 empty-filter buffer; the stock 2023 R2 client sends version 6. Diffed byte-for-byte (same query window + eventCount), the two buffers are identical except:

• byte 0: version 06 vs 05
• 5 additional trailing zero bytes (stock = 70 bytes, SDK v5 = 65 bytes)

The server returns rows for v6 and zero rows for v5 (the v5 request is accepted — StartEventQuery succeeds and yields a query handle — but GetNextEventQueryResultBuffer then matches nothing). Everything else is shared: the two query-window FILETIMEs, UInt32 eventCount, the UInt32 65536 buffer hint, the "UTC" HistorianString, and the 01 01000001000001 0000 metadata-namespace block.

Captured v6 request layout (70 bytes; the FILETIMEs below are just the harness query window — no identity data):

[0..1]   UInt16  version = 6                 // SDK currently sends 5
[2..9]   Int64   startUtc (FILETIME)
[10..17] Int64   endUtc   (FILETIME)
[18..21] UInt32  eventCount
[22..25] UInt32  0
[26..27] UInt16  0
[28..29] UInt16  1
[30..36] 7 bytes 0                           // empty-filter block
[37..40] UInt32  65536                       // buffer-size hint
[41..50] HistorianString "UTC"  (UInt32 len=3 + UTF-16LE)
[51..60] 01 01 00 00 01 00 00 01 00 00       // metadata-namespace block (marker + 3 empty)
[61..69] 9 bytes 0                            // terminal (SDK v5 writes only 4 here)

Fix part 1 — v6 request (DONE, necessary)

HistorianEventQueryProtocol.CreateStartEventQueryAttempts gained a version parameter (default 5 = WCF/2020; the gRPC orchestrator passes 6). v6 emits the leading 06 and the 5-byte trailing pad. The WCF path is unchanged (v5). Golden test Version6EmptyFilterMatchesCapturedGrpcEnvelope pins the envelope; 322/322 offline tests pass.

Fix part 2 — EVENT connection (the remaining gate, NOT yet implemented)

Live validation 2026-06-22: with the orchestrator now sending v6 against the event-bearing live server, GetNextEventQueryResultBuffer still long-polls and returns zero rows (the gated test still throws). So v6 is necessary but not sufficient — the read also requires an Event-type connection, which our SDK does not open.

Isolated by diffing the captured OpenConnection.openParameters (302 bytes, native format v8) for a Process connection (connect scenario) vs the Event connection (capture-event): aside from the per-session auth GUID/credential-hash regions ([22..37], [68..93], which vary between any two sessions), the connection differs in two clean structural bytes:

offset	Process	Event
95	02	01
96	00	01

These correspond to HistorianConnectionType (Process vs Event; the native event path runs on ConnectionIndex 1). The problem: our SDK opens the session with the 2020 OpenConnection3 v6 buffer (HistorianNativeHandshake.BuildOpenConnection3Request, connectionMode 0x402), which the 2023 R2 server accepts for reads but which carries no event-connection-type marker. connectionMode is NOT the discriminator (2020 WCF event reads work with 0x402); the native client distinguishes event vs process via this separate ConnectionType field in its v8 openParameters.

Diagnosis (2026-06-22): the v6 Open2 format cannot express an event connection

Decoded the native openParameters (302 bytes): byte 0 = 08 (format version 8), then a context GUID, username, a 26-byte session-derived region ([68..93]), machine/client-node/datasource strings, and at [94] ClientType=04 immediately followed by [95] ConnectionType (01=Event / 02=Process) + [96] a flag (01/00), then the rest.

Our SDK builds the v6 buffer (HistorianOpen2Protocol.SerializeNativeOpenConnection3Version6, byte 0 = 06): it writes ClientType (1 byte) immediately followed by ConnectionMode (uint) — there is no ConnectionType byte at all. The v8 format inserts ConnectionType (+flag) between ClientType and the rest. So the v6 buffer the SDK sends (accepted by the 2023 R2 server for reads) structurally cannot mark the connection as Event, and the server returns event rows only for an Event connection.

Two further obstacles to simply emitting v8:

• the native client authenticated via ExchangeKey (cert path; 72-byte btInput/btOutput in the capture) whereas the SDK's gRPC handshake uses ValidateClientCredential (Negotiate). The v8 openParameters [68..93] region is session-derived and tied to that auth flow.
• ConnectionMode is NOT the lever (2020 WCF event reads work at 0x402); ConnectionType is a distinct field that only exists from format v8.

Also confirmed a secondary format gap: the native gRPC EnsureTags CM_EVENT payload is 86 bytes vs the SDK's SerializeCmEventCTagMetadata 83 bytes (a 3-byte 2023 R2 bump, parallel to the event-query v5→v6). This is likely benign on its own (CM_EVENT pre-exists; 2020 EnsT2 returns benign-false yet events flow) but should be matched if the event open is ever rebuilt.

Conclusion — the event-connection gate is NOT a tweak. Making event rows flow over gRPC requires the SDK to emit the native v8 OpenConnection format with ConnectionType=Event (a 302-byte buffer whose layout differs from the v6 buffer and includes a session-derived auth region), and likely to adopt the ExchangeKey cert auth path. That is a substantial RE+implementation effort comparable to the original Open2 work — scoped as a follow-on, not a quick fix. Until then the gated ReadEventsAsync_OverGrpc_* test correctly still pins the no-row throw, and v6 (part 1) is retained as the captured-correct request format for when the open is rebuilt.

Capture artifacts (gitignored): artifacts/reverse-engineering/grpc-event-capture/ — event-capture.ndjson (Event), process-connect-2.ndjson (Process).

v8 openParameters fully decoded (2026-06-23) + the ECDH ExchangeKey finding

Full byte map of the native Event-connection openParameters (302 bytes; identity values redacted — they are session-specific and sit in the gitignored capture):

[0]        byte   0x08            format version = 8
[1]        byte   0xf0            constant marker
[2..20]    19 ×   0x00
[21]       byte   0x01            constant marker
[22..37]   16B    GUID            per-session client key
[38..41]   u32                    username length (chars)
[42..N]    UTF-16 username        (HistorianString)
[..+1]     u16                    credential-token length (= 26 in the capture)
[..]       26B    token           ECDH-derived credential token  <-- see below
[94]       byte   0x04            ClientType (= our NativeClientType 4)
[95]       byte   ConnectionType  01 = Event / 02 = Process   <-- THE GATE
[96]       byte   flag            01 (Event) / 00 (Process)
[97..]     control bytes          (0x03 ... small region, not fully named)
[~114..117]u32    FormatVersion=3
[..]       HistorianString        machine/server node name
[..]       HistorianString        client node name "(<ver>)"
[..]       u32                    session-variable (process-ish)
[..]       u32 / zeros
[..]       u32    datasource len
[..]       UTF-16 datasource id   e.g. "2023.1219.4004.5"
[270..285] 16 ×   0xff            ShardId (all-FF = unset; our v6 sends Empty)
[286..289] u32                    client/hcal version int
[290..297] i64    FILETIME        ClientTimestamp
[298..301] u32    0

The tail (FormatVersion → machine → clientNode → datasource → ShardId → version → timestamp) is the same ClientCommonInfo our v6 already emits. The new/different parts are: version byte, the [1]/[21] markers, the GUID position, the 26-byte credential token (vs v6's fixed-size block), the ConnectionType byte, and ShardId=FF.

The auth is ECDH, not Negotiate. The capture's ExchangeKey buffers begin 45 43 4b 31 = ASCII "ECK1" + a 64-byte EC public-key point — a Diffie-Hellman key exchange — and the 26-byte openParameters token is derived from it. HistorianSecurityMode offers only Disabled / None / TransportCertificate; the harness used TransportCertificate, which is what drives the ECDH ExchangeKey. There is no TLS+Negotiate mode on the native client (it couples TLS with the cert ECDH path), so a Negotiate-auth v8 capture cannot be produced from the native client.

Key de-risking insight: our SDK's v6 OpenConnection sends a fully zeroed 1026-byte credential block (credentialBlock: new byte[1026]) and reads still work — because authentication is actually carried by the separate StorageService.ValidateClientCredential (Negotiate) handshake, not by the bytes inside openParameters. By analogy the v8 [68..93] token may likewise be ignorable once ValidateClientCredential has run. So the first build hypothesis (cheapest, read-only to test):

Reuse the SDK's existing ValidateClientCredential handshake, then send a v8 OpenConnection with ConnectionType=Event and a zeroed credential token, and see whether the 2023 R2 server returns event rows.

If that works, the ECDH ExchangeKey RE is unnecessary. If it fails, the fallback is full reproduction of the ECDH ExchangeKey handshake (curve/KDF/cipher) — a much larger crypto-RE effort. Build path: add SerializeNativeOpenConnectionVersion8(connectionType) to HistorianOpen2Protocol, wire the gRPC event handshake to use it (events only; reads stay on v6), live-test (non-destructive). Full hex in the gitignored capture.

Path A built + live-tested 2026-06-23 — DISPROVEN (v8 is coupled to ExchangeKey)

Built HistorianOpen2Protocol.SerializeNativeOpenConnectionVersion8 (golden-tested, Version8EventSerializerReproducesCapturedNativeStructure — reproduces the captured 302-byte structure exactly) + HistorianNativeHandshake.BuildEventOpenConnectionVersion8Request (zeroed credential token) + an eventConnection switch on HistorianGrpcHandshake.OpenSession, and live-ran the event read against the server. Result: the v8 OpenConnection was parsed by the server (got past the byte format) but rejected at the auth check with native error

type=132 code=34   "aahHcapLib::HistoryService::EstablishConnection — Failed to get client key"

i.e. EstablishConnection could not find a server-side client key for our session. In the v6 path that key is established by StorageService.ValidateClientCredential (which is why v6 reads work); the v8 path looks it up in the registry that HistoryService.ExchangeKey (ECDH) populates, and there is no ValidateClientCredential on HistoryService in the gRPC contract. So the server branches on the OpenConnection version: v6 accepts the Negotiate-established key, v8 requires the ExchangeKey-established key. The zeroed-token hypothesis is therefore disproven — not because of the token bytes, but because the whole v8 path is gated on ExchangeKey having run first.

Status: the v8 serializer/builder are correct and retained (golden-tested), plus the OpenConnection failure now decodes the native error (type/code/ASCII). The event orchestrator is reverted to the v6 session (gated test still pins the no-row throw). The remaining route is Path B: implement HistoryService.ExchangeKey — "ECK1" + a 64-byte EC public-key point (P-256 X‖Y, by the size) — using .NET ECDiffieHellman, establish the client key, then reissue the v8 OpenConnection. Open question for Path B: whether merely completing the ECDH key agreement registers the client key (so the zeroed openParameters token still rides through), or whether the token must also be derived from the shared secret (full KDF/cipher RE).

Path B started 2026-06-23 — ExchangeKey ECDH works; cleared 2 of 3 layers

Implemented HistoryService.ExchangeKey as a pure-managed P-256 ECDH key exchange (HistorianNativeHandshake.BuildExchangeKeyClientHello / DeriveExchangeKeySecret, .NET ECDiffieHellman over nistP256; wire format "ECK1" + u32(32) + X(32) + Y(32)) and wired it into HistorianGrpcHandshake.OpenSession(eventConnection: true) ahead of the v8 OpenConnection, on the same context-key handle. Live result against the server: the ExchangeKey RPC succeeds (the server accepted our public key), and the v8 OpenConnection error moved one layer deeper:

Path A (no ExchangeKey):  132/34  "Failed to get client key"
Path B (ExchangeKey ECDH): 132/171 AuthenticationFailed  "EstablishConnection — Authentication failed"

So the ECDH cleared the client-key check; the remaining blocker is authentication: the 26-byte v8 credential token must be a valid value derived from the ECDH shared secret (not zeros).

Token crypto traced 2026-06-23 (Frida → Windows CNG) — KDF found, token construction still open

Hooked Windows CNG (bcrypt.dll/ncrypt.dll) while the native harness ran a real ExchangeKey (scripts/frida/aahclientmanaged-cng-exchangekey.js + artifacts/.../cng-trace.py). Findings:

• The ECDH + KDF are standard CNG, driven by managed System.Security.Cryptography.ECDiffieHellmanCng (backtrace top frame = System.Core.ni.dll; the caller is aahClientManaged's C++/CLI <Module>): NCryptSecretAgreement (P-256) → NCryptDeriveKey(KDF=HASH, HASH_ALGORITHM=SHA256, 32 bytes). So the derived key = SHA256(ECDH shared secret) — exactly ECDiffieHellmanCng{ KeyDerivationFunction=Hash, HashAlgorithm=SHA256 }.DeriveKeyMaterial(...). Our managed DeriveExchangeKeySecret should switch to this (SHA256 of the raw agreement) to match.
• "ECK1" is NOT AVEVA-custom — it is the standard Windows CNG BCRYPT_ECCPUBLIC_BLOB magic for P-256 (NCryptExportKey/ImportKey emit exactly ECK1 + len(32) + X(32) + Y(32)), confirming our BuildExchangeKeyClientHello wire format is correct.
• The 26-byte token is a custom construction that is not yet reproduced. Correlated one run's derived key (SHA256(secret)) with that run's token (from the IL openParameters capture): a 528-candidate offline cracker (HMAC/SHA/AES-GCM/CBC/CTR over the derived key × request slices × creds) found no match, and the token matches none of the traced hash digests. The token starts with a constant 0x8e marker in both captured runs (so it is structured, not raw cipher output). It is built in managed code between the DeriveKeyMaterial call and the openParameters assembly.

dnlib IL extraction 2026-06-23 — the token scheme is fully reverse-engineered. ILSpy can't decompile the mixed-mode assembly (crashes), but loading dnlib in PowerShell and scanning the IL recovered the whole construction:

• <Module>::CHistoryConnectionGrpc.GetClientKey is the ECDH driver: new ECDiffieHellmanCng() → KeyDerivationFunction = Hash, HashAlgorithm = SHA256, KeySize = 256 → GrpcHistoryClient.ExchangeKey(strHandle, ourPubKey.ToByteArray(), out serverPub, out err) → CngKey.Import(serverPub, CngKeyBlobFormat.EccPublicBlob) → DeriveKeyMaterial = the 32-byte client key = SHA256(ECDH shared secret). (So our managed side should derive the key the same way — ECDiffieHellman raw agreement then SHA256, or equivalently DeriveKeyFromHash(..., SHA256).)
• The 26-byte token is built by aahClientCommon.CClientBase.ConfigureOpenConnection (the lone caller of GetClientKey) using the HistorianCrypto.NRC4_V2.aahCryptV2 scheme — a custom MD5-keyed RC4 stream cipher with a version prefix:
  • aahCryptV2.body/HashData = MD5 (verified: the IL loads MD5 round constants 0xd76aa478… and rotates 7/12/17/22).
  • aahCryptV2.prepare_key = standard RC4 KSA seeding the 256-byte S-box from a 16-byte (MD5) key (std.array<unsigned char,16>).
  • aahCryptV2.enc_buffer = MD5(...) → key, then rc4encrypt the body; enc prepends a scheme prefix (NRC4_V2.PrefixV2 / InnerPrefixV2) — the constant 0x8e token marker.
  • from_GUID keys the cipher from a GUID string.

So the token = prefix + RC4(plaintext, key = MD5(keyMaterial)), where the key material ties back to the SHA256(ECDH secret) client key. This is 100% reproducible in pure managed code (RC4 + MD5 are ~40 lines; nothing AVEVA ships).

Remaining to finish (next cycle): read ConfigureOpenConnection's exact wiring (which value is MD5'd for the RC4 key, what plaintext is encrypted, the exact prefix bytes — a little more dnlib IL), implement aahCryptV2 (RC4+MD5+prefix) managed-side, set the v8 token = that, and live-test (non-destructive). The offline correlation data (one run's derived key + token + openParameters) is captured under artifacts/.../ to validate the managed reproduction before going live.

Token implemented + auth WORKS live (2026-06-23); row retrieval still 0 — proven NOT a payload issue

token = RC4(password-UTF16LE, key = MD5(SHA256(ECDH secret))) was implemented in pure managed C# (HistorianNativeHandshake.BuildExchangeKeyCredentialToken + Rc4; client key via DeriveKeyFromHash(SHA256)), golden-tested (RC4 standard vector + token construction), and live-verified: the v8 OpenConnection now authenticates against the 2023 R2 server (past the 132/171 AuthenticationFailed wall). Auth is solved.

The event query still returns version-11 rowCount-0 while the native returns 50 for an identical request. Exhaustively ruled out as the cause (all confirmed live, opt-in EventReadDiagnostic test + the IL rewrite extended to log string/uint handle fields):

• StartEventQuery request: byte-identical to the native (v6 layout)
• v8 OpenConnection openParameters: byte-identical to the native (302 bytes) once ClientNodeName is matched — every control byte, ConnectionType, token framing, ShardId, etc.
• Handle usage: identical — ExchangeKey→contextKey, registration→storage-session GUID (strHandle), query→client uint (uiHandle); our parsed handles are valid (registration RTag/EnsT=True, valid queryHandle)
• queryRequestType = 3, registration sequence/order, gzip metadata header — all match
• window (events exist; native returns 50 now), eventCount — not it

So every observable client-side byte matches the native, yet the server scopes 0 events to our connection. The event RPCs succeed over our transport and return a valid empty result (not a transport error), so it is not a payload or transport-incompatibility issue — it is a connection/server-level difference (e.g. session affinity tied to the native Grpc.Core HTTP/2 connection or a connection-identity the server uses to scope events) that is invisible to, and unfixable by, client payload matching. Closing it needs server-side insight or a different angle (e.g. compare the full HTTP/2 connection setup / TLS identity), not more wire-payload RE.

Shipped this effort: the complete ExchangeKey crypto (ECDH + SHA256 + MD5-keyed RC4 token) — the hard wall — pure managed, golden-tested, auth live-verified. Orchestrator stays on the no-row throw; gated test unchanged.

NEXT SESSION — the server-side / connection angle (row retrieval pickup)

Client payloads are exhausted (byte-identical to the native, proven above). The next investigation is connection-level, not wire-payload. Pursue in roughly this order; each is concrete and testable.

Already proven — do NOT redo: auth works (ExchangeKey ECDH + RC4 token, live-verified); v8 openParameters, all handles (str/uint), StartEventQuery request, registration (RTag/EnsT=True + order), queryRequestType=3, gzip header — all byte-match the native. Events exist (native returns 50 now). The event RPCs succeed over our transport and return a valid version-11 rowCount-0 (not a transport error). So the server scopes 0 events to our connection specifically.

Tooling already in place: opt-in diagnostic test EventReadDiagnostic_OverGrpc_PrintsJourney (env HISTORIAN_GRPC_EVENT_DIAG=1, prints registration outcomes, handles, result hex, v8 buffer); the capture-event harness scenario (native, returns rows); instrument-grpc-nonstream now logs string/uint handle fields too; the CNG Frida hook. Live recipe: set HISTORIAN_GRPC_HOST/_PORT 32565/_TLS true/_DNSID to the 2023 R2 server + domain creds (strip quotes); reach the box per the live-server access reference.

1. Transport: native Grpc.Core HTTP/2 vs our Grpc.Net.Client + GrpcWebHandler (gRPC-Web). DISPROVEN 2026-06-23. Built HistorianGrpcChannelFactory.CreateHttp2 (plain HTTP/2 over a SocketsHttpHandler, no GrpcWebHandler wrap, ALPN h2 to the TLS server) and wired it into the event orchestrator behind HISTORIAN_GRPC_EVENT_HTTP2=1 (event path only; reads stay gRPC-Web). Live side-by-side against the event-bearing server, everything else held constant:

   channel	auth	registration	queryHandle	result buffer
   http2 (native HTTP/2)	✓	RTag=True EnsT=True	1057	0B00000000001E000000
   grpc-web (default)	✓	RTag=True EnsT=True	1058	0B00000000001E000000

   The complete v8 chain — ExchangeKey ECDH auth, CM_EVENT RegisterTags/EnsureTags, StartEventQuery (valid handle) — runs end-to-end over plain native HTTP/2, and the server returns the byte-identical version-11 (0x0B) rowCount-0 terminal on both transports. So gRPC-Web vs native HTTP/2 is not the discriminator — the zero-row scoping is identical regardless of transport. The CreateHttp2 factory + the HISTORIAN_GRPC_EVENT_HTTP2 switch + the EventChannelMode diagnostic are retained for future connection-level probing. This eliminates the leading hypothesis and tightens the conclusion: the server scopes 0 events to our connection at a layer above the gRPC transport.

2. TLS client identity / certificate. The native used SecurityMode=TransportCertificate. Determine whether it presents a client certificate the server uses to scope events (our SDK presents none — AllowUntrustedServerCertificate=true, server cert only). TEST: capture the TLS handshake (e.g. SSLKEYLOGFILE + Wireshark, or a decrypting proxy) for a native capture-event run and check the Certificate message; if a client cert is presented, replicate it.

3. HTTP/2-level capture. The byte[]/handle capture is RPC-payload only. Capture the actual HTTP/2 frames (HEADERS/SETTINGS/stream IDs, connection reuse) for the native run vs ours — via a TLS-decrypting mitm on the loopback forward — to see any connection-level header/affinity our capture can't see.

4. TLS client identity / certificate. The native used SecurityMode=TransportCertificate. Determine whether it presents a client certificate the server uses to scope events (our SDK presents none — AllowUntrustedServerCertificate=true, server cert only). TEST: capture the TLS handshake (e.g. SSLKEYLOGFILE + Wireshark, or a decrypting proxy) for a native capture-event run and check the Certificate message; if a client cert is presented, replicate it. Lower-probability after #1: the plain-HTTP/2 path presents no client cert either, yet auth + registration still succeed and the gate persists — so the gate is not at the TLS-identity layer the cert would affect.

5. HTTP/2-level capture. The byte[]/handle capture is RPC-payload only. Capture the actual HTTP/2 frames (HEADERS/SETTINGS/stream IDs, connection reuse) for the native run vs ours — via a TLS-decrypting mitm on the loopback forward — to see any connection-level header/affinity our capture can't see.

6. Server-side ground truth. ANSWERED 2026-06-23 (DISPROVES the data-scoping premise). Via the SOCKS→SQL relay (read-only; artifacts/.../sqlschema/, gitignored), dumped the full event schema on the live Runtime DB. Findings:

   • No per-connection / per-client / per-session column exists anywhere in the event store. The only "scoping-like" columns on Events/EventHistory/snapshots are event content — Source_* (event origin area/object/PV), User_* (who acknowledged), Provider_NodeName (alarm provider node), SourceServer/SourceTag (cross-server replication). None is "which client connection requested this."
   • The rich Events view is not a relational table — it is served live by the Historian engine via the INSQL OLE DB provider (sys.servers shows linked servers INSQL + INSQLD; OBJECT_DEFINITION('dbo.Events') is NULL = encrypted remote view). The Historian's own EventHistory base table holds just 168 rows / 1 tag (the internal event-tag detector log); the alarm/event journal the gRPC query reads lives in the engine, surfaced through INSQL.
   • Decisive: same engine, same -90d..now window, two paths diverge. The Events view (via INSQL) returns 71,332 events for that window — most recent Alarm.Set firing seconds before the probe (live, every few seconds) — while gRPC StartEventQuery for our connection returns 0. The data is global, abundant, recent, and identical-window-addressable; the engine simply does not hand it to our gRPC connection.

   → There is nothing in the data to scope by, so the zero-row gate is not data scoping. It is the gRPC RetrievalService's per-connection in-process execution state — the same class of wall as DeleteTagExtendedProperties (server-side native in-process working-set, not reconstructable from byte-identical wire requests). Reproduce: artifacts/.../sqlschema/ (Program.cs = SOCKS5 relay + Microsoft.Data.SqlClient; authenticate with the server's SQL login, not the domain Historian acct — creds in the gitignored creds file).

Stock managed client decompiled (2026-06-23) — confirms no hidden client-side difference

Closing the gap that prior cycles left: the zero-rows conclusion had leaned on wire capture (instrument-grpc-nonstream, which only hooks byte[] params on Grpc*Client methods) — blind to gRPC metadata/headers, interceptors, channel options, and any non-byte[] call. Read the stock managed client source directly (histsdk-2023r2-analysis/decompiled/Archestra.Historian.GrpcClient + HistorianAccess; the pure-managed assemblies decompile cleanly even though the mixed-mode aahClientManaged.dll crashes ILSpy). Findings:

• GrpcClientBase.InitializeBase builds the same channel we do. GrpcWebHandler((GrpcWebMode)0, HttpClientHandler) with HttpVersion = 1.1 — i.e. the stock client speaks gRPC-Web over HTTP/1.1, the same transport as our SDK. This corrects the premise of hypothesis #1: there was never a native Grpc.Core HTTP/2 path to differ from — the stock client that returns 50 rows is itself gRPC-Web. The HTTP/2 disproof's conclusion stands (and is reinforced: identical transport on both sides).
• m_metadata passed to every RPC (incl. StartEventQuery/GetNextEventQueryResultBuffer) is only grpc-internal-encoding-request: gzip — exactly our header set. No connection-id, session token, or auth header rides in gRPC metadata. The ClientInterceptor is a no-op (LogCall is empty; both unary overloads just invoke the continuation). So the "invisible per-connection metadata/header" blind spot is confirmed empty — there is no hidden client-side identity the byte[] capture missed.
• The event-read query orchestration is genuinely not in managed code. CreateEventQuery / EventQuery.StartQuery / MoveNext are not in the managed HistorianAccess; the managed GrpcRetrievalClient.StartEventQuery is a thin one-RPC stub. The query logic lives in the native C++/CLI HistorianClient core (the mixed-mode part ILSpy can't decompile) — consistent with the working-set being native/server-side, not a managed step we could read and replicate.

So every client-controllable layer is now confirmed identical by reading the stock source, not just by wire match: request bytes, transport, channel options, gRPC metadata, interceptor. The remaining difference is below the managed surface (native core) / server-side.

Conclusion (after #1 disproven + #4 answered + stock client decompiled). Four independent angles are now exhausted: client payload (byte-identical), transport (stock client is also gRPC-Web/HTTP-1.1 — HTTP/2 makes no difference, both 0 rows), client-side metadata/interceptor/channel (decompiled — identical, no hidden header), and data store (global, unscoped, 71,332 events the engine serves via INSQL but withholds from our gRPC connection). The gate is a server-internal per-connection retrieval working-set that a pure-managed client cannot reconstruct by matching wire bytes, transport, metadata, or data — and the establishing logic is in the native HistorianClient C++ core, not in any decompilable managed step. The remaining angle (#3 HTTP/2-frame capture) is low-probability given the stock client uses the same gRPC-Web/HTTP-1.1 channel. gRPC event-row retrieval stands documented as auth-solved / retrieval-server-gated; ReadEventsAsync over gRPC keeps the honest no-row throw, and event reads use the WCF transport.

2 of 3 layers cleared (key exchange + client key); the 3rd (token construction) is localized to a specific managed method, pending dnlib extraction. ExchangeKey + the v8 serializer are committed; the orchestrator stays on v6 (set eventConnection: true to re-arm once the token construction lands). The token-loop routing guardrail (HistorianGrpcHandshakeRoutingTests) was scoped to the closure so the legitimate ExchangeKey call is allowed while still pinning that the Negotiate token loop never routes there.