docs(claude): add Sister Projects section + cross-repo index propagation rule

CLAUDE.md

@@ -15,6 +15,42 @@ The architecture is a two-process design — read `gateway.md` before making str
 
 The worker must do all MXAccess COM calls on its dedicated STA thread, and the STA loop must pump Windows messages (`MsgWaitForMultipleObjectsEx` + `PeekMessage`/`DispatchMessage`) so MXAccess events deliver. A plain blocking queue on an STA is not enough.
 
+## Sister Projects (scadaproj umbrella)
+
+`mxaccessgw` is one of a family of related SCADA / OT / Wonderware / OPC UA **sister
+projects** cloned as sibling directories under `~/Desktop/`. They are **separate repos
+and separate processes**, coupled at runtime over wire protocols (gRPC + OPC UA) — not
+by project/compile references — and share the `ZB.MOM.WW.*` product namespace. **mxaccessgw
+is the linchpin**: the only component that loads 32-bit MXAccess COM, so the others depend
+on it over gRPC rather than touching COM directly.
+
+- **`~/Desktop/scadaproj`** ([`../scadaproj/CLAUDE.md`](../scadaproj/CLAUDE.md)) — the
+  umbrella/index workspace that aggregates the whole family (purpose, location, stack,
+  primary commands per project) and hosts the shared `ZB.MOM.WW.*` libraries, the dev/test
+  GLAuth (`10.100.0.35:3893`, source of truth `scadaproj/infra/glauth/`), and the shared
+  **`ZB.MOM.WW.GalaxyRepository`** package this gateway consumes. **This repo is indexed
+  there** — see the MxAccessGateway entry in `../scadaproj/CLAUDE.md`.
+- **`~/Desktop/OtOpcUa`** (`lmxopcua`, [`../OtOpcUa/CLAUDE.md`](../OtOpcUa/CLAUDE.md)) — OPC
+  UA server whose in-process `GalaxyDriver` **depends on this gateway** for live Galaxy
+  read/write/subscribe and Galaxy Repository browse.
+- **`~/Desktop/ScadaBridge`** ([`../ScadaBridge/CLAUDE.md`](../ScadaBridge/CLAUDE.md)) —
+  distributed SCADA platform whose Data Connection Layer has a dedicated **MxGateway
+  adapter** that talks to this gateway directly (native MxAccess data + A&C alarms),
+  bypassing OtOpcUa.
+- **`~/Desktop/HistorianGateway`** (`historiangw`,
+  [`../HistorianGateway/CLAUDE.md`](../HistorianGateway/CLAUDE.md)) — single-process gRPC
+  sidecar **patterned on this gateway** (session model, dashboard shell, auth interceptor,
+  Galaxy SQL browse) but with no COM / no x86 worker. It also consumes the shared
+  `ZB.MOM.WW.GalaxyRepository` package — the same library mxaccessgw adopted (2026-06-25),
+  so the `galaxy_repository.v1` wire contract is served from one implementation.
+
+**Propagate cross-repo changes to the umbrella index.** When a fact the index records about
+mxaccessgw changes here — remote/push status, the `.proto` contracts (`mxaccess_gateway.proto`,
+`mxaccess_worker.proto`, `galaxy_repository.proto`), the two-process architecture, shared-lib
+consumption, or per-project commands — update the **MxAccessGateway entry in
+[`../scadaproj/CLAUDE.md`](../scadaproj/CLAUDE.md)** in the same change so the umbrella index
+never drifts from this repo. (Mirrors the same rule in the peer repos.)
+
 ## Build, Test, Run
 
 ```powershell