diff --git a/CLAUDE.md b/CLAUDE.md
index f87255d..2bdb921 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -7,6 +7,8 @@ This project contains design documentation for a distributed SCADA system built
 - `README.md` — Master index with component table and architecture diagrams.
 - `HighLevelReqs.md` — Complete high-level requirements covering all functional areas.
 - `Component-*.md` — Individual component design documents (one per component).
+- `docs/plans/` — Design decision documents from refinement sessions.
+- `AkkaDotNet/` — Akka.NET reference documentation and best practices notes.
 
 There is no source code in this project — only design documentation in markdown.
 
@@ -54,29 +56,87 @@ There is no source code in this project — only design documentation in markdow
 
 ## Key Design Decisions (for context across sessions)
 
+### Architecture & Runtime
 - Instance modeled as Akka actor (Instance Actor) — single source of truth for runtime state.
 - Site Runtime actor hierarchy: Deployment Manager singleton → Instance Actors → Script Actors + Alarm Actors.
-- Script Actors spawn short-lived Script Execution Actors for concurrent execution.
+- Script Actors spawn short-lived Script Execution Actors on a dedicated blocking I/O dispatcher.
 - Alarm Actors are separate peer subsystem from scripts (not inside Script Engine).
 - Shared scripts execute inline as compiled code (no separate actors).
-- Site-wide Akka stream for attribute value and alarm state changes (debug view subscribes to this).
-- Script Engine and Alarm Actors subscribe directly to Instance Actors (not via stream).
+- Site-wide Akka stream for attribute value and alarm state changes with per-subscriber buffering.
+- Instance Actors serialize all state mutations (Akka actor model); concurrent scripts produce interleaved side effects.
+- Staggered Instance Actor startup on failover to prevent reconnection storms.
+- Explicit supervision strategies: Resume for coordinator actors, Stop for short-lived execution actors.
+
+### Data & Communication
 - Data Connection Layer is a clean data pipe — publishes to Instance Actors only.
-- Pre-deployment validation is comprehensive (flattening, script compilation, trigger refs, binding completeness).
-- Data source references are relative paths; connection binding is per-attribute at instance level.
-- System-wide artifact deployment requires explicit Deployment role action.
-- Store-and-forward: fixed retry interval, no max buffer size.
-- Instance lifecycle: enabled/disabled states, deletion supported.
-- Template deletion blocked if instances or child templates reference it.
+- DCL connection actor uses Become/Stash pattern for lifecycle state machine.
+- DCL auto-reconnect at fixed interval; immediate bad quality on disconnect; transparent re-subscribe.
+- DCL write failures returned synchronously to calling script.
+- Tag path resolution retried periodically for devices still booting.
+- Static attribute writes persisted to local SQLite (survive restart/failover, reset on redeployment).
+- All timestamps are UTC throughout the system.
+
+### External Integrations
+- External System Gateway: HTTP/REST only, JSON serialization, API key + Basic Auth.
+- Dual call modes: `ExternalSystem.Call()` (synchronous) and `ExternalSystem.CachedCall()` (store-and-forward on transient failure).
+- Error classification: HTTP 5xx/408/429/connection errors = transient; other 4xx = permanent (returned to script).
+- Notification Service: SMTP with OAuth2 Client Credentials (Microsoft 365) or Basic Auth. BCC delivery, plain text.
+- Inbound API: `POST /api/{methodName}`, `X-API-Key` header, flat JSON, extended type system (Object, List).
+
+### Templates & Deployment
+- Pre-deployment validation includes semantic checks (call targets, argument types, trigger operand types).
+- Composed member addressing uses path-qualified canonical names: `[ModuleInstanceName].[MemberName]`.
+- Override granularity defined per entity type and per field.
+- Template graph acyclicity enforced on save.
+- Flattened configs include a revision hash for staleness detection.
+- Deployment identity: unique deployment ID + revision hash for idempotency.
+- Per-instance operation lock covers all mutating commands (deploy, disable, enable, delete).
+- Site-side apply is all-or-nothing per instance.
+- System-wide artifact version skew across sites is supported.
+- Last-write-wins for concurrent template editing (no optimistic concurrency on templates).
+- Optimistic concurrency on deployment status records.
 - Naming collisions in composed feature modules are design-time errors.
-- Last-write-wins for concurrent template editing.
-- Scripts compiled at site; pre-validated (test compiled) at central.
-- Max recursion depth for script-to-script calls.
-- Alarm on-trigger scripts can call instance scripts; instance scripts cannot call alarm scripts.
-- Audit logging absorbed into Configuration Database component (IAuditService).
+
+### Store-and-Forward
+- Fixed retry interval, no max buffer size. Only transient failures buffered.
+- Async best-effort replication to standby (no ack wait).
+- Messages not cleared on instance deletion.
+- CachedCall idempotency is the caller's responsibility.
+
+### Security & Auth
+- Authentication: direct LDAP bind (username/password), no Kerberos/NTLM. LDAPS/StartTLS required.
+- JWT sessions: HMAC-SHA256 shared symmetric key, 15-minute expiry with sliding refresh, 30-minute idle timeout.
+- LDAP failure: new logins fail; active sessions continue with current roles.
+- Load balancer in front of central UI; JWT + shared Data Protection keys for failover transparency.
+
+### Cluster & Failover
+- Keep-oldest split-brain resolver with `down-if-alone = on`, 15s stable-after.
+- Both nodes are seed nodes. `min-nr-of-members = 1`.
+- Failure detection: 2s heartbeat, 10s threshold. Total failover ~25s.
+- CoordinatedShutdown for graceful singleton handover.
+- Automatic dual-node recovery from persistent storage.
+
+### UI & Monitoring
+- Central UI: Blazor Server (ASP.NET Core + SignalR). Real-time push for debug view, health dashboard, deployment status.
+- Health reports: 30s interval, 60s offline threshold, monotonic sequence numbers, raw error counts per interval.
+- Dead letter monitoring as a health metric.
+- Site Event Logging: 30-day retention, 1GB storage cap, daily purge, paginated queries with keyword search.
+
+### Code Organization
 - Entity classes are persistence-ignorant POCOs in Commons; EF mappings in Configuration Database.
 - Repository interfaces defined in Commons; implementations in Configuration Database.
+- Commons namespace hierarchy: Types/, Interfaces/, Entities/, Messages/ with domain area subfolders.
+- Message contracts follow additive-only evolution rules for version compatibility.
+- Per-component configuration via `appsettings.json` sections bound to options classes (Options pattern).
+- Options classes owned by component projects, not Commons.
+- Host readiness gating: `/health/ready` endpoint, no traffic until operational.
 - EF Core migrations: auto-apply in dev, manual SQL scripts for production.
+- Audit logging absorbed into Configuration Database component (IAuditService).
+
+### Akka.NET Conventions
+- Tell for hot-path internal communication; Ask reserved for system boundaries.
+- Script trust model: forbidden APIs (System.IO, Process, Threading, Reflection, raw network).
+- Application-level correlation IDs on all request/response messages.
 
 ## Tool Usage
 
diff --git a/README.md b/README.md
index 76a6578..85f35ad 100644
--- a/README.md
+++ b/README.md
@@ -4,6 +4,27 @@
 
 This document serves as the master index for the SCADA system design. The system is a centrally-managed, distributed SCADA configuration and deployment platform built on Akka.NET, running across a central cluster and multiple site clusters in a hub-and-spoke topology.
 
+### Technology Stack
+
+| Layer | Technology |
+|-------|-----------|
+| Runtime | .NET, Akka.NET (actors, clustering, remoting, persistence, streams) |
+| Central UI | Blazor Server (ASP.NET Core + SignalR) |
+| Inbound API | ASP.NET Core Web API (REST/JSON) |
+| Central Database | MS SQL Server, Entity Framework Core |
+| Site Storage | SQLite (deployed configs, S&F buffer, event logs) |
+| Authentication | Direct LDAP/AD bind (LDAPS/StartTLS), JWT sessions |
+| Notifications | SMTP with OAuth2 Client Credentials (Microsoft 365) |
+| Hosting | Windows Server, Windows Service |
+| Cluster | Akka.NET Cluster (active/standby, keep-oldest SBR) |
+| Logging | Serilog (structured) |
+
+### Scale
+
+- ~10 site clusters, each with 50–500 machines, 25–75 live tags per machine.
+- Central cluster: 2-node active/standby behind a load balancer.
+- Site clusters: 2-node active/standby, headless (no UI).
+
 ## Document Map
 
 ### Requirements
@@ -13,45 +34,59 @@ This document serves as the master index for the SCADA system design. The system
 
 | # | Component | Document | Description |
 |---|-----------|----------|-------------|
-| 1 | Template Engine | [Component-TemplateEngine.md](Component-TemplateEngine.md) | Template modeling, inheritance, composition, attribute resolution, locking, alarms, flattening, validation, and diff calculation. |
-| 2 | Deployment Manager | [Component-DeploymentManager.md](Component-DeploymentManager.md) | Central-side deployment pipeline: requesting configs, sending to sites, tracking status, system-wide artifact deployment, instance disable/delete. |
-| 3 | Site Runtime | [Component-SiteRuntime.md](Component-SiteRuntime.md) | Site-side actor hierarchy: Deployment Manager singleton, Instance Actors, Script Actors, Alarm Actors, script compilation, shared script library, and the site-wide attribute/alarm Akka stream. |
-| 4 | Data Connection Layer | [Component-DataConnectionLayer.md](Component-DataConnectionLayer.md) | Common data connection interface, OPC UA and custom protocol adapters, subscription management. Publishes tag value updates to Instance Actors. |
-| 5 | Central–Site Communication | [Component-Communication.md](Component-Communication.md) | Akka.NET remoting/cluster topology, message patterns, request routing, and debug streaming. |
-| 6 | Store-and-Forward Engine | [Component-StoreAndForward.md](Component-StoreAndForward.md) | Buffering, retry, parking, application-level replication, and SQLite persistence at sites. |
-| 7 | External System Gateway | [Component-ExternalSystemGateway.md](Component-ExternalSystemGateway.md) | External system definitions, API method invocation, and database connection management. |
-| 8 | Notification Service | [Component-NotificationService.md](Component-NotificationService.md) | Notification lists, email delivery, script API, and store-and-forward integration. |
-| 9 | Central UI | [Component-CentralUI.md](Component-CentralUI.md) | Web-based management interface, workflows, and pages. |
-| 10 | Security & Auth | [Component-Security.md](Component-Security.md) | LDAP/AD authentication, role-based authorization, and site-scoped permissions. |
-| 11 | Health Monitoring | [Component-HealthMonitoring.md](Component-HealthMonitoring.md) | Site health metrics collection (including alarm evaluation errors) and central reporting. |
-| 12 | Site Event Logging | [Component-SiteEventLogging.md](Component-SiteEventLogging.md) | Local operational event logs at sites with central query access. |
-| 13 | Cluster Infrastructure | [Component-ClusterInfrastructure.md](Component-ClusterInfrastructure.md) | Akka.NET cluster setup, active/standby failover, and node management. |
-| 14 | Inbound API | [Component-InboundAPI.md](Component-InboundAPI.md) | Web API for external systems to call in, API key auth, method definitions, script-based implementations. |
-| 15 | Host | [Component-Host.md](Component-Host.md) | Single deployable binary, role-based component registration, Akka.NET bootstrap, and ASP.NET Core hosting for central nodes. |
-| 16 | Commons | [Component-Commons.md](Component-Commons.md) | Shared data types, interfaces, domain entity POCOs, repository interfaces, and message contracts used across all components. |
-| 17 | Configuration Database | [Component-ConfigurationDatabase.md](Component-ConfigurationDatabase.md) | EF Core data access layer, schema ownership, per-component repositories, unit-of-work, audit logging (IAuditService), and migration management for the central MS SQL configuration database. |
+| 1 | Template Engine | [Component-TemplateEngine.md](Component-TemplateEngine.md) | Template modeling, inheritance, composition, path-qualified member addressing, override granularity, locking, alarms, flattening, semantic validation, revision hashing, and diff calculation. |
+| 2 | Deployment Manager | [Component-DeploymentManager.md](Component-DeploymentManager.md) | Central-side deployment pipeline with deployment ID/idempotency, per-instance operation lock, state transition matrix, all-or-nothing site apply, system-wide artifact deployment with per-site status. |
+| 3 | Site Runtime | [Component-SiteRuntime.md](Component-SiteRuntime.md) | Site-side actor hierarchy with explicit supervision strategies, staggered startup, script trust model (constrained APIs), Tell/Ask conventions, concurrency serialization, and site-wide Akka stream with per-subscriber backpressure. |
+| 4 | Data Connection Layer | [Component-DataConnectionLayer.md](Component-DataConnectionLayer.md) | Common data connection interface (OPC UA, custom), Become/Stash connection actor model, auto-reconnect, immediate bad quality on disconnect, transparent re-subscribe, synchronous write failures, tag path resolution retry. |
+| 5 | Central–Site Communication | [Component-Communication.md](Component-Communication.md) | Akka.NET remoting/cluster topology, 8 message patterns with per-pattern timeouts, application-level correlation IDs, transport heartbeat config, message ordering, connection failure behavior. |
+| 6 | Store-and-Forward Engine | [Component-StoreAndForward.md](Component-StoreAndForward.md) | Buffering (transient failures only), fixed-interval retry, parking, async best-effort replication, SQLite persistence at sites. |
+| 7 | External System Gateway | [Component-ExternalSystemGateway.md](Component-ExternalSystemGateway.md) | HTTP/REST + JSON, API key/Basic Auth, per-system timeout, dual call modes (Call/CachedCall), transient/permanent error classification, dedicated blocking I/O dispatcher, ADO.NET connection pooling. |
+| 8 | Notification Service | [Component-NotificationService.md](Component-NotificationService.md) | SMTP with OAuth2 (M365) or Basic Auth, BCC delivery, plain text, transient/permanent SMTP error classification, store-and-forward integration. |
+| 9 | Central UI | [Component-CentralUI.md](Component-CentralUI.md) | Blazor Server with SignalR real-time push, load balancer failover with JWT, all management workflows. |
+| 10 | Security & Auth | [Component-Security.md](Component-Security.md) | Direct LDAP bind (LDAPS/StartTLS), JWT sessions (HMAC-SHA256, 15-min refresh, 30-min idle), role-based authorization, site-scoped permissions. |
+| 11 | Health Monitoring | [Component-HealthMonitoring.md](Component-HealthMonitoring.md) | 30s report interval, 60s offline threshold, monotonic sequence numbers, raw error counts, tag resolution counts, dead letter monitoring. |
+| 12 | Site Event Logging | [Component-SiteEventLogging.md](Component-SiteEventLogging.md) | SQLite storage, 30-day retention + 1GB cap, daily purge, paginated remote queries with keyword search. |
+| 13 | Cluster Infrastructure | [Component-ClusterInfrastructure.md](Component-ClusterInfrastructure.md) | Akka.NET cluster, keep-oldest SBR with down-if-alone, min-nr-of-members=1, 2s/10s/15s failure detection, CoordinatedShutdown, automatic dual-node recovery. |
+| 14 | Inbound API | [Component-InboundAPI.md](Component-InboundAPI.md) | POST /api/{methodName}, X-API-Key header, flat JSON, extended type system (Object/List), script-based implementations, failures-only logging. |
+| 15 | Host | [Component-Host.md](Component-Host.md) | Single deployable binary, role-based component registration, per-component config binding (Options pattern), readiness gating, dead letter monitoring, Akka.NET bootstrap, ASP.NET Core hosting for central. |
+| 16 | Commons | [Component-Commons.md](Component-Commons.md) | Namespace/folder convention (Types/Interfaces/Entities/Messages), shared data types, POCOs, repository interfaces, message contracts with additive-only versioning, UTC timestamp convention. |
+| 17 | Configuration Database | [Component-ConfigurationDatabase.md](Component-ConfigurationDatabase.md) | EF Core data access, per-component repositories, unit-of-work, optimistic concurrency on deployment status, audit logging (IAuditService), migration management. |
+
+### Reference Documentation
+
+- [AkkaDotNet/](AkkaDotNet/) — Akka.NET reference notes covering actors, remoting, clustering, persistence, streams, serialization, hosting, testing, and best practices.
+- [docs/plans/](docs/plans/) — Design decision documents from refinement sessions.
 
 ### Architecture Diagram (Logical)
 
 ```
-┌─────────────────────────────────────────────────────┐
+                    Users (Blazor Server)
+                         │
+                    Load Balancer
+                         │
+┌────────────────────────┼────────────────────────────┐
 │                   CENTRAL CLUSTER                    │
+│              (2-node active/standby)                 │
+│                                                      │
 │  ┌──────────┐ ┌──────────┐ ┌──────────┐            │
 │  │ Template  │ │Deployment│ │ Central  │            │
-│  │ Engine    │ │ Manager  │ │   UI     │            │
+│  │ Engine    │ │ Manager  │ │ UI       │ Blazor Svr │
 │  └──────────┘ └──────────┘ └──────────┘            │
 │  ┌──────────┐ ┌──────────┐ ┌──────────┐            │
-│  │ Security  │ │  Audit   │ │  Health  │            │
-│  │ & Auth    │ │ Logging  │ │ Monitor  │            │
+│  │ Security  │ │  Config  │ │  Health  │            │
+│  │ & Auth    │ │   DB     │ │ Monitor  │            │
+│  │ (JWT/LDAP)│ │ (EF+IAud)│ │          │            │
 │  └──────────┘ └──────────┘ └──────────┘            │
 │  ┌──────────┐                                       │
-│  │ Inbound  │  ◄── External Systems (API key auth)  │
-│  │   API    │                                       │
+│  │ Inbound  │  ◄── External Systems (X-API-Key)     │
+│  │ API      │      POST /api/{method}, JSON         │
 │  └──────────┘                                       │
 │  ┌───────────────────────────────────┐              │
 │  │    Akka.NET Communication Layer   │              │
+│  │  (correlation IDs, per-pattern    │              │
+│  │   timeouts, message ordering)     │              │
 │  └──────────────┬────────────────────┘              │
-│  ┌───────────────────────────────────┐              │
+│  ┌──────────────┴────────────────────┐              │
 │  │    Configuration Database (EF)    │──► MS SQL    │
 │  └───────────────────────────────────┘   (Config DB)│
 │                  │                    Machine Data DB│
@@ -61,18 +96,27 @@ This document serves as the master index for the SCADA system design. The system
      ▼            ▼            ▼
 ┌─────────┐ ┌─────────┐ ┌─────────┐
 │ SITE A  │ │ SITE B  │ │ SITE N  │
+│ (2-node)│ │ (2-node)│ │ (2-node)│
 │ ┌─────┐ │ │ ┌─────┐ │ │ ┌─────┐ │
 │ │Data │ │ │ │Data │ │ │ │Data │ │
 │ │Conn │ │ │ │Conn │ │ │ │Conn │ │
+│ │Layer │ │ │ │Layer │ │ │ │Layer │ │
 │ ├─────┤ │ │ ├─────┤ │ │ ├─────┤ │
 │ │Site │ │ │ │Site │ │ │ │Site │ │
 │ │Runtm│ │ │ │Runtm│ │ │ │Runtm│ │
 │ ├─────┤ │ │ ├─────┤ │ │ ├─────┤ │
 │ │S&F  │ │ │ │S&F  │ │ │ │S&F  │ │
 │ │Engine│ │ │ │Engine│ │ │ │Engine│ │
+│ ├─────┤ │ │ ├─────┤ │ │ ├─────┤ │
+│ │ExtSys│ │ │ │ExtSys│ │ │ │ExtSys│ │
+│ │Gatwy │ │ │ │Gatwy │ │ │ │Gatwy │ │
 │ └─────┘ │ │ └─────┘ │ │ └─────┘ │
 │ SQLite  │ │ SQLite  │ │ SQLite  │
 └─────────┘ └─────────┘ └─────────┘
+     │            │            │
+  OPC UA /     OPC UA /     OPC UA /
+  Custom       Custom       Custom
+  Protocol     Protocol     Protocol
 ```
 
 ### Site Runtime Actor Hierarchy