Phase 3B: Site I/O & Observability — Communication, DCL, Script/Alarm actors, Health, Event Logging

Communication Layer (WP-1–5):
- 8 message patterns with correlation IDs, per-pattern timeouts
- Central/Site communication actors, transport heartbeat config
- Connection failure handling (no central buffering, debug streams killed)

Data Connection Layer (WP-6–14, WP-34):
- Connection actor with Become/Stash lifecycle (Connecting/Connected/Reconnecting)
- OPC UA + LmxProxy adapters behind IDataConnection
- Auto-reconnect, bad quality propagation, transparent re-subscribe
- Write-back, tag path resolution with retry, health reporting
- Protocol extensibility via DataConnectionFactory

Site Runtime (WP-15–25, WP-32–33):
- ScriptActor/ScriptExecutionActor (triggers, concurrent execution, blocking I/O dispatcher)
- AlarmActor/AlarmExecutionActor (ValueMatch/RangeViolation/RateOfChange, in-memory state)
- SharedScriptLibrary (inline execution), ScriptRuntimeContext (API)
- ScriptCompilationService (Roslyn, forbidden API enforcement, execution timeout)
- Recursion limit (default 10), call direction enforcement
- SiteStreamManager (per-subscriber bounded buffers, fire-and-forget)
- Debug view backend (snapshot + stream), concurrency serialization
- Local artifact storage (4 SQLite tables)

Health Monitoring (WP-26–28):
- SiteHealthCollector (thread-safe counters, connection state)
- HealthReportSender (30s interval, monotonic sequence numbers)
- CentralHealthAggregator (offline detection 60s, online recovery)

Site Event Logging (WP-29–31):
- SiteEventLogger (SQLite, 6 event categories, ISO 8601 UTC)
- EventLogPurgeService (30-day retention, 1GB cap)
- EventLogQueryService (filters, keyword search, keyset pagination)

541 tests pass, zero warnings.

tests/ScadaLink.Communication.Tests/CommunicationServiceTests.cs

@@ -0,0 +1,33 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+
+namespace ScadaLink.Communication.Tests;
+
+/// <summary>
+/// WP-2: Tests for CommunicationService initialization and state.
+/// </summary>
+public class CommunicationServiceTests
+{
+    [Fact]
+    public async Task BeforeInitialization_ThrowsOnUsage()
+    {
+        var options = Options.Create(new CommunicationOptions());
+        var logger = NullLogger<CommunicationService>.Instance;
+        var service = new CommunicationService(options, logger);
+
+        // CommunicationService requires SetCommunicationActor before use
+        await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            service.DeployInstanceAsync("site1",
+                new Commons.Messages.Deployment.DeployInstanceCommand(
+                    "dep1", "inst1", "hash1", "{}", "admin", DateTimeOffset.UtcNow)));
+    }
+
+    [Fact]
+    public void UnsubscribeDebugView_IsTellNotAsk()
+    {
+        // Verify the method signature is void (fire-and-forget Tell pattern)
+        var method = typeof(CommunicationService).GetMethod("UnsubscribeDebugView");
+        Assert.NotNull(method);
+        Assert.Equal(typeof(void), method!.ReturnType);
+    }
+}