docs: add requirements generation prompt for LmxProxy project

lmxproxy/REQUIREMENTS_PROMPT.md

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+# LmxProxy Requirements Documentation Prompt
+
+Use this prompt with Claude Code to generate the requirements documentation for the LmxProxy project. Run from the `lmxproxy/` directory.
+
+## Prompt
+
+Create requirements documentation for the LmxProxy project in `docs/requirements/`. Follow the same structure used in the ScadaLink project (`docs/requirements/` in the parent repo) — a high-level requirements doc and per-component breakout documents.
+
+### Context
+
+LmxProxy is a gRPC proxy service that bridges SCADA clients to industrial automation systems (primarily AVEVA/Wonderware System Platform via ArchestrA.MXAccess). It consists of two projects:
+
+1. **ZB.MOM.WW.LmxProxy.Host** — A .NET Framework 4.8 Windows service (Topshelf) that runs on the same machine as System Platform. It connects to MXAccess (COM interop, x86) and exposes a gRPC server for remote SCADA operations (read, write, subscribe, batch operations). It handles session management, API key authentication, TLS, health checks, performance metrics, and subscription management.
+
+2. **ZB.MOM.WW.LmxProxy.Client** — A .NET 10 class library providing a typed gRPC client for consuming the LmxProxy service. It uses protobuf-net.Grpc (code-first, no .proto files). It includes connection management, retry policies, TLS support, streaming extensions, DI integration, and a builder pattern for configuration.
+
+### What to Generate
+
+**1. `docs/requirements/HighLevelReqs.md`** — High-level requirements covering:
+- System purpose and architecture (proxy pattern, why it exists)
+- Deployment model (runs on System Platform machine, clients connect remotely)
+- Communication protocol (gRPC, HTTP/2, code-first and proto-based)
+- Session lifecycle (connect, session ID, disconnect, no idle timeout)
+- Authentication model (API key via metadata header, configurable enforcement)
+- TLS/security model (optional TLS, mutual TLS support, certificate validation)
+- Data model (VTQ — Value/Timestamp/Quality, OPC-style quality codes)
+- Operations (read, read batch, write, write batch, write-and-wait, subscribe)
+- Subscription model (server-streaming, tag-based, sampling interval)
+- Health monitoring and metrics
+- Service hosting (Topshelf Windows service, service recovery)
+- Configuration (appsettings.json sections)
+- Scale considerations
+- Protocol versioning (v1 string-based, v2 OPC UA-aligned typed values)
+
+**2. Component documents** — One `Component-<Name>.md` for each logical component:
+
+- **Component-GrpcServer.md** — The gRPC service implementation (ScadaGrpcService). Session validation, request routing to MxAccessClient, subscription lifecycle, error handling, proto-based serialization.
+
+- **Component-MxAccessClient.md** — The MXAccess COM interop wrapper. Connection lifecycle (Become/Stash-like state machine), tag registration, read/write operations, subscription via advise callbacks, event handling, x86/COM threading constraints. This is the core component.
+
+- **Component-SessionManager.md** — Client session tracking, session creation/destruction, session-to-client mapping, concurrent session limits.
+
+- **Component-Security.md** — API key authentication (ApiKeyService, ApiKeyInterceptor), key file management, role-based permissions (ReadOnly/ReadWrite), TLS certificate management.
+
+- **Component-SubscriptionManager.md** — Tag subscription lifecycle, channel-based update delivery, sampling intervals, backpressure (channel full modes), subscription cleanup on disconnect.
+
+- **Component-Configuration.md** — appsettings.json structure, configuration validation, TLS configuration, service recovery configuration, connection timeouts, retry policies.
+
+- **Component-HealthAndMetrics.md** — Health check service (test tag reads, stale data detection), performance metrics (operation counts, latencies, percentiles), status web server (HTTP status endpoint).
+
+- **Component-ServiceHost.md** — Topshelf service hosting, Program.cs entry point, Serilog logging setup, service install/uninstall, service recovery (Windows SCM restart policies).
+
+- **Component-Client.md** — The LmxProxyClient library. Builder pattern, connection management, retry with Polly, keep-alive pings, streaming extensions, DI registration (ServiceCollectionExtensions), factory pattern, TLS configuration.
+
+- **Component-Protocol.md** — The gRPC protocol specification. Proto definition, code-first contracts (IScadaService), message schemas, VTQ format, quality codes, v1 vs v2 differences.
+
+### Document Structure (per component)
+
+Each component doc must follow this structure exactly:
+```
+# Component: <Name>
+
+## Purpose
+<1-2 sentence description>
+
+## Location
+<Which project(s) and key files>
+
+## Responsibilities
+<Bulleted list of what this component does>
+
+## <Detail sections>
+<Numbered or named sections with specific design details>
+
+## Dependencies
+<What this component depends on>
+
+## Interactions
+<How this component interacts with others>
+```
+
+### Sources
+
+Derive requirements from:
+- The source code in `src/ZB.MOM.WW.LmxProxy.Host/` and `src/ZB.MOM.WW.LmxProxy.Client/`
+- The protocol docs in `docs/lmxproxy_protocol.md` and `docs/lmxproxy_updates.md`
+- The appsettings.json configuration files
+
+### Rules
+
+- Write requirements as design decisions, not aspirational statements. Describe what the system **does**, not what it **should** do.
+- Include specific values from configuration (ports, timeouts, intervals, limits).
+- Cross-reference between documents using component names.
+- Keep the high-level doc focused on system-wide concerns; push implementation details to component docs.
+- Do not invent features not present in the source code.