Phase 8: Production readiness — failover tests, security hardening, sandboxing, deployment docs

- WP-1-3: Central/site failover + dual-node recovery tests (17 tests)
- WP-4: Performance testing framework for target scale (7 tests)
- WP-5: Security hardening (LDAPS, JWT key length, no secrets in logs) (11 tests)
- WP-6: Script sandboxing adversarial tests (28 tests, all forbidden APIs)
- WP-7: Recovery drill test scaffolds (5 tests)
- WP-8: Observability validation (structured logs, correlation IDs, metrics) (6 tests)
- WP-9: Message contract compatibility (forward/backward compat) (18 tests)
- WP-10: Deployment packaging (installation guide, production checklist, topology)
- WP-11: Operational runbooks (failover, troubleshooting, maintenance)
92 new tests, all passing. Zero warnings.

src/ScadaLink.Commons/Messages/InboundApi/RouteToInstanceRequest.cs

@@ -0,0 +1,59 @@
+namespace ScadaLink.Commons.Messages.InboundApi;
+
+/// <summary>
+/// Request routed from Inbound API to a site to invoke a script on an instance.
+/// Used by Route.To("instanceCode").Call("scriptName", params).
+/// </summary>
+public record RouteToCallRequest(
+    string CorrelationId,
+    string InstanceUniqueName,
+    string ScriptName,
+    IReadOnlyDictionary<string, object?>? Parameters,
+    DateTimeOffset Timestamp);
+
+/// <summary>
+/// Response from a Route.To() call.
+/// </summary>
+public record RouteToCallResponse(
+    string CorrelationId,
+    bool Success,
+    object? ReturnValue,
+    string? ErrorMessage,
+    DateTimeOffset Timestamp);
+
+/// <summary>
+/// Request to read attribute(s) from a remote instance.
+/// </summary>
+public record RouteToGetAttributesRequest(
+    string CorrelationId,
+    string InstanceUniqueName,
+    IReadOnlyList<string> AttributeNames,
+    DateTimeOffset Timestamp);
+
+/// <summary>
+/// Response containing attribute values from a remote instance.
+/// </summary>
+public record RouteToGetAttributesResponse(
+    string CorrelationId,
+    IReadOnlyDictionary<string, object?> Values,
+    bool Success,
+    string? ErrorMessage,
+    DateTimeOffset Timestamp);
+
+/// <summary>
+/// Request to write attribute(s) on a remote instance.
+/// </summary>
+public record RouteToSetAttributesRequest(
+    string CorrelationId,
+    string InstanceUniqueName,
+    IReadOnlyDictionary<string, string> AttributeValues,
+    DateTimeOffset Timestamp);
+
+/// <summary>
+/// Response confirming attribute writes on a remote instance.
+/// </summary>
+public record RouteToSetAttributesResponse(
+    string CorrelationId,
+    bool Success,
+    string? ErrorMessage,
+    DateTimeOffset Timestamp);