From 80668a07bdeb6d96fc3f6adda9a0797e51db7bbb Mon Sep 17 00:00:00 2001
From: Joseph Doherty <dohejw01@gmail.com>
Date: Fri, 24 Jul 2026 05:38:36 -0400
Subject: [PATCH] =?UTF-8?q?feat(health):=200.2.0=20=E2=80=94=20optional=20?=
 =?UTF-8?q?per-entry=20`data`=20+=20Akka=20cluster-view?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Phase 0 of docs/plans/2026-07-22-overview-dashboard-impl-plan.md: give the
canonical health JSON a structured channel so the family overview dashboard can
read each Akka cluster's current leader.

- ZbHealthWriter: optional `"data": {...}` per entry, sourced from
  HealthReportEntry.Data, emitted only when non-empty. Per-property JsonIgnore
  (NOT a global DefaultIgnoreCondition) so `"description": null` still renders —
  payloads from data-less checks stay byte-identical to 0.1.0.
- AkkaClusterHealthCheck: BuildClusterData publishes this node's own view —
  leader (omitted while unknown), selfAddress, selfRoles (sorted), memberCount,
  unreachableCount — on every result path. The startup-safety paths (no
  ActorSystem / cluster inaccessible) stay description-only.
- Tests: writer data emit/omit (raw-JSON assert on the omit case), and a real
  single-node self-joined cluster via Akka.TestKit.Xunit2 for the data values.
  70 tests green (25/39/6).
- Version 0.1.0 -> 0.2.0; 3 packages published to the Gitea feed and
  restore-verified from a scratch consumer, which serves data.leader live.
---
 ZB.MOM.WW.Health/CLAUDE.md                    |  12 +-
 ZB.MOM.WW.Health/Directory.Build.props        |   2 +-
 ZB.MOM.WW.Health/README.md                    |  32 ++++--
 .../AkkaClusterHealthCheck.cs                 |  48 +++++++-
 .../src/ZB.MOM.WW.Health/ZbHealthWriter.cs    |  22 +++-
 .../AkkaClusterDataTests.cs                   | 107 ++++++++++++++++++
 .../AkkaClusterStatusPolicyTests.cs           |   2 +
 .../ZB.MOM.WW.Health.Akka.Tests.csproj        |   1 +
 .../ResponseWriterTests.cs                    |  58 +++++++++-
 ...overview-dashboard-impl-plan.md.tasks.json |  25 ++++
 10 files changed, 281 insertions(+), 28 deletions(-)
 create mode 100644 ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/AkkaClusterDataTests.cs
 create mode 100644 docs/plans/2026-07-22-overview-dashboard-impl-plan.md.tasks.json

diff --git a/ZB.MOM.WW.Health/CLAUDE.md b/ZB.MOM.WW.Health/CLAUDE.md
index 10b2633..f00befc 100644
--- a/ZB.MOM.WW.Health/CLAUDE.md
+++ b/ZB.MOM.WW.Health/CLAUDE.md
@@ -4,7 +4,7 @@ Health-check libraries for the **ZB.MOM.WW SCADA family** (OtOpcUa, MxAccessGate
 
 The library normalizes the three-tier health endpoint convention (`/health/ready`, `/health/active`, `/healthz`) and provides reusable probe implementations so the three sister projects share a common surface without duplicating probe logic.
 
-**Built at 0.1.0. NOT yet adopted by the three apps.** Adoption is tracked in `~/Desktop/scadaproj/components/health/GAPS.md`.
+**Built at 0.2.0 and published to the Gitea NuGet feed. Adopted by all four apps** — adoption is tracked in `~/Desktop/scadaproj/components/health/GAPS.md`.
 
 ---
 
@@ -46,14 +46,14 @@ dotnet test ZB.MOM.WW.Health.slnx
 dotnet pack ZB.MOM.WW.Health.slnx -c Release -o ./artifacts
 ```
 
-All three test assemblies run offline:
+All three test assemblies run offline (the cluster-data tests form a single-node in-process Akka cluster on a loopback port):
 
 | Assembly | Tests |
 |---|---|
-| `ZB.MOM.WW.Health.Tests` | 20 |
-| `ZB.MOM.WW.Health.Akka.Tests` | 32 |
+| `ZB.MOM.WW.Health.Tests` | 25 |
+| `ZB.MOM.WW.Health.Akka.Tests` | 39 |
 | `ZB.MOM.WW.Health.EntityFrameworkCore.Tests` | 6 |
-| **Total** | **58** |
+| **Total** | **70** |
 
 `GeneratePackageOnBuild` is off — pack explicitly with the command above.
 
@@ -61,7 +61,7 @@ All three test assemblies run offline:
 
 ## Status
 
-Built at **0.1.0** and published to the Gitea NuGet feed. **Not yet adopted** by the three apps — adoption is tracked in the component backlog:
+Built at **0.2.0** and published to the Gitea NuGet feed. **Adopted** by all four apps — adoption is tracked in the component backlog:
 
 - `~/Desktop/scadaproj/components/health/GAPS.md` — adoption order, effort, and risk
 
diff --git a/ZB.MOM.WW.Health/Directory.Build.props b/ZB.MOM.WW.Health/Directory.Build.props
index 4b5ab79..88c5a32 100644
--- a/ZB.MOM.WW.Health/Directory.Build.props
+++ b/ZB.MOM.WW.Health/Directory.Build.props
@@ -5,7 +5,7 @@
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <LangVersion>latest</LangVersion>
-    <Version>0.1.0</Version>
+    <Version>0.2.0</Version>
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
     <!-- Emit XML docs so the public API summaries ship inside the packed nupkgs (IntelliSense for
          consumers). CS1591 (missing doc on a public member) is suppressed so undocumented test /
diff --git a/ZB.MOM.WW.Health/README.md b/ZB.MOM.WW.Health/README.md
index 1ff8dc9..eafd782 100644
--- a/ZB.MOM.WW.Health/README.md
+++ b/ZB.MOM.WW.Health/README.md
@@ -30,7 +30,19 @@ MxAccessGateway consumes the core package only — it has no Akka cluster and no
 
 ## Versioning
 
-All three packages are versioned **lockstep** from `Directory.Build.props`. The current release is **0.1.0**. A single version bump in `Directory.Build.props` bumps all three packages simultaneously — consumers should reference the same version for all ZB.MOM.WW.Health packages.
+All three packages are versioned **lockstep** from `Directory.Build.props`. The current release is **0.2.0**. A single version bump in `Directory.Build.props` bumps all three packages simultaneously — consumers should reference the same version for all ZB.MOM.WW.Health packages.
+
+### 0.2.0 — per-entry `data` (additive, non-breaking)
+
+- `ZbHealthWriter` emits an optional `"data": { … }` object per entry, sourced from the check's
+  `HealthCheckResult.Data`, **only when non-empty** — a check that publishes no data produces a
+  byte-identical body to 0.1.0, so every existing consumer is unaffected. Data keys are written
+  verbatim (the camelCase policy applies to the envelope, not to dictionary keys).
+- `AkkaClusterHealthCheck` populates that dictionary with this node's cluster view: `leader`
+  (omitted while unknown), `selfAddress`, `selfRoles`, `memberCount`, `unreachableCount`. The
+  startup-safety paths (no `ActorSystem`, cluster not yet accessible) stay description-only.
+- Consumers gain the leader field on a package bump alone — no application code change, provided the
+  app registers the shared `AkkaClusterHealthCheck`.
 
 ---
 
@@ -42,14 +54,16 @@ dotnet build ZB.MOM.WW.Health.slnx
 dotnet test  ZB.MOM.WW.Health.slnx
 ```
 
-All three test assemblies run with `dotnet test` and require no external dependencies (no running Akka cluster, no database):
+All three test assemblies run with `dotnet test` and require no external dependencies — no database and no
+external cluster (the cluster-data tests form a single-node in-process Akka cluster on a loopback port
+via `Akka.TestKit.Xunit2`):
 
 | Assembly | Tests |
 |---|---|
-| `ZB.MOM.WW.Health.Tests` | 20 |
-| `ZB.MOM.WW.Health.Akka.Tests` | 32 |
+| `ZB.MOM.WW.Health.Tests` | 25 |
+| `ZB.MOM.WW.Health.Akka.Tests` | 39 |
 | `ZB.MOM.WW.Health.EntityFrameworkCore.Tests` | 6 |
-| **Total** | **58** |
+| **Total** | **70** |
 
 ---
 
@@ -62,9 +76,9 @@ dotnet pack ZB.MOM.WW.Health.slnx -c Release -o ./artifacts
 Produces three `.nupkg` files in `artifacts/`:
 
 ```
-ZB.MOM.WW.Health.0.1.0.nupkg
-ZB.MOM.WW.Health.Akka.0.1.0.nupkg
-ZB.MOM.WW.Health.EntityFrameworkCore.0.1.0.nupkg
+ZB.MOM.WW.Health.0.2.0.nupkg
+ZB.MOM.WW.Health.Akka.0.2.0.nupkg
+ZB.MOM.WW.Health.EntityFrameworkCore.0.2.0.nupkg
 ```
 
 `GeneratePackageOnBuild` is off — pack explicitly as above.
@@ -73,7 +87,7 @@ ZB.MOM.WW.Health.EntityFrameworkCore.0.1.0.nupkg
 
 ## Status
 
-**Built at 0.1.0. NOT yet adopted by the three apps.** Adoption is tracked in the component backlog:
+**Built at 0.2.0 and published to the Gitea NuGet feed. Adopted by all four apps** (OtOpcUa, MxAccessGateway, ScadaBridge, HistorianGateway). Adoption is tracked in the component backlog:
 
 - `~/Desktop/scadaproj/components/health/GAPS.md`
 
diff --git a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health.Akka/AkkaClusterHealthCheck.cs b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health.Akka/AkkaClusterHealthCheck.cs
index 302b2b2..bbc0eea 100644
--- a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health.Akka/AkkaClusterHealthCheck.cs
+++ b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health.Akka/AkkaClusterHealthCheck.cs
@@ -44,6 +44,7 @@ public sealed class AkkaClusterHealthCheck : IHealthCheck
             return Task.FromResult(HealthCheckResult.Degraded("ActorSystem not yet available."));
 
         MemberStatus status;
+        IReadOnlyDictionary<string, object> data;
         try
         {
             // Cluster.Get(system).SelfMember can throw while the ActorSystem exists but the cluster
@@ -51,7 +52,9 @@ public sealed class AkkaClusterHealthCheck : IHealthCheck
             // ConfigurationException). The spec's startup-safety rule maps this to Degraded, not an
             // escaping exception (which the host would record as Unhealthy and pull the node from
             // rotation).
-            status = Cluster.Get(system).SelfMember.Status;
+            var cluster = Cluster.Get(system);
+            status = cluster.SelfMember.Status;
+            data = BuildClusterData(cluster);
         }
         catch (Exception ex) when (ex is not OperationCanceledException)
         {
@@ -62,10 +65,47 @@ public sealed class AkkaClusterHealthCheck : IHealthCheck
         var description = $"Akka cluster member status: {status}";
         var result = health switch
         {
-            HealthStatus.Healthy   => HealthCheckResult.Healthy(description),
-            HealthStatus.Degraded  => HealthCheckResult.Degraded(description),
-            _                      => HealthCheckResult.Unhealthy(description),
+            HealthStatus.Healthy   => HealthCheckResult.Healthy(description, data),
+            HealthStatus.Degraded  => HealthCheckResult.Degraded(description, data: data),
+            _                      => HealthCheckResult.Unhealthy(description, data: data),
         };
         return Task.FromResult(result);
     }
+
+    /// <summary>
+    /// Projects this node's view of the cluster into the check's <c>data</c> dictionary.
+    /// </summary>
+    /// <param name="cluster">The cluster extension for the local <see cref="ActorSystem"/>.</param>
+    /// <returns>
+    /// JSON-friendly values only (string / int / string[]), so the canonical health writer can emit
+    /// them verbatim: <c>leader</c> (omitted while the leader is unknown, e.g. pre-join or during
+    /// convergence), <c>selfAddress</c>, <c>selfRoles</c> (sorted for a stable payload),
+    /// <c>memberCount</c>, <c>unreachableCount</c>.
+    /// </returns>
+    /// <remarks>
+    /// This is deliberately each node's <em>own</em> view rather than an authoritative fleet answer —
+    /// a consumer that reads it from several members of the same cluster can compare them, and a
+    /// disagreement is a split-brain tell.
+    /// </remarks>
+    internal static IReadOnlyDictionary<string, object> BuildClusterData(Cluster cluster)
+    {
+        ArgumentNullException.ThrowIfNull(cluster);
+
+        var state = cluster.State;
+        var data = new Dictionary<string, object>(StringComparer.Ordinal)
+        {
+            ["selfAddress"] = cluster.SelfAddress.ToString(),
+            ["selfRoles"] = cluster.SelfMember.Roles.OrderBy(static r => r, StringComparer.Ordinal).ToArray(),
+            ["memberCount"] = state.Members.Count,
+            ["unreachableCount"] = state.Unreachable.Count,
+        };
+
+        // Omitted rather than emitted as null: a missing key reads as "this node does not know yet",
+        // which is exactly the pre-join / mid-convergence state.
+        var leader = state.Leader;
+        if (leader is not null)
+            data["leader"] = leader.ToString();
+
+        return data;
+    }
 }
diff --git a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthWriter.cs b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthWriter.cs
index 8aa41a1..91a835a 100644
--- a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthWriter.cs
+++ b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthWriter.cs
@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Diagnostics.HealthChecks;
 
@@ -16,15 +17,18 @@ namespace ZB.MOM.WW.Health;
 ///   "status": "Healthy|Degraded|Unhealthy",
 ///   "totalDurationMs": 12.34,
 ///   "entries": {
-///     "&lt;name&gt;": { "status": "...", "description": "...", "durationMs": 1.23 }
+///     "&lt;name&gt;": { "status": "...", "description": "...", "durationMs": 1.23, "data": { ... } }
 ///   }
 /// }
 /// </code>
 /// The <c>description</c> key is always present; when a check supplies no description it is emitted
 /// as JSON <c>null</c> (not omitted), matching the spec example and the <c>HealthChecks.UI.Client</c>
-/// shape. The HTTP status code is left to the ASP.NET Core health-checks middleware (Healthy/Degraded
-/// → 200, Unhealthy → 503); this writer only renders the body and sets
-/// <c>Content-Type: application/json</c>.
+/// shape. The <c>data</c> key is the opposite: it is emitted only when the check supplied a non-empty
+/// <see cref="HealthCheckResult.Data"/> dictionary, so payloads from checks that publish no data stay
+/// byte-identical to the pre-0.2.0 shape. Its keys are written verbatim (the camelCase naming policy
+/// applies to the envelope properties, not to dictionary keys). The HTTP status code is left to the
+/// ASP.NET Core health-checks middleware (Healthy/Degraded → 200, Unhealthy → 503); this writer only
+/// renders the body and sets <c>Content-Type: application/json</c>.
 /// </remarks>
 public static class ZbHealthWriter
 {
@@ -60,6 +64,10 @@ public static class ZbHealthWriter
                     Status = e.Value.Status.ToString(),
                     Description = e.Value.Description,
                     DurationMs = e.Value.Duration.TotalMilliseconds,
+                    // HealthReportEntry.Data is never null (empty when the check set none); mapping
+                    // empty → null is what drops the key entirely, keeping data-less payloads
+                    // byte-identical to the pre-0.2.0 shape.
+                    Data = e.Value.Data.Count > 0 ? e.Value.Data : null,
                 }),
         };
 
@@ -78,5 +86,11 @@ public static class ZbHealthWriter
         public string Status { get; init; } = string.Empty;
         public string? Description { get; init; }
         public double DurationMs { get; init; }
+
+        // Per-property ignore, deliberately NOT a global DefaultIgnoreCondition: the writer must keep
+        // emitting "description": null (see SerializerOptions above) while omitting "data" entirely
+        // when a check publishes none.
+        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+        public IReadOnlyDictionary<string, object>? Data { get; init; }
     }
 }
diff --git a/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/AkkaClusterDataTests.cs b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/AkkaClusterDataTests.cs
new file mode 100644
index 0000000..bd1ab9a
--- /dev/null
+++ b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/AkkaClusterDataTests.cs
@@ -0,0 +1,107 @@
+using Akka.Actor;
+using Akka.Cluster;
+using Akka.TestKit.Xunit2;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using ZB.MOM.WW.Health.Akka;
+
+namespace ZB.MOM.WW.Health.Akka.Tests;
+
+/// <summary>
+/// Covers the cluster-view <c>data</c> dictionary that <see cref="AkkaClusterHealthCheck"/> publishes
+/// from 0.2.0 on (consumed by the family overview dashboard to show each cluster's current leader).
+/// Uses a real single-node self-joined cluster via <see cref="TestKit"/> — the values come off
+/// <see cref="Cluster"/>, which cannot be faked, so a formed cluster is the only honest fixture.
+/// </summary>
+public sealed class AkkaClusterDataTests : TestKit
+{
+    private const string ClusterConfig = """
+        akka {
+          actor.provider = cluster
+          remote.dot-netty.tcp {
+            hostname = "127.0.0.1"
+            port = 0
+          }
+          cluster {
+            roles = ["driver", "admin"]
+            # Keep the single-node self-join deterministic and fast in-test.
+            min-nr-of-members = 1
+          }
+        }
+        """;
+
+    private static readonly TimeSpan FormationTimeout = TimeSpan.FromSeconds(30);
+
+    public AkkaClusterDataTests()
+        : base(ClusterConfig, nameof(AkkaClusterDataTests))
+    {
+    }
+
+    /// <summary>Self-joins the test node and waits until it is Up with a converged leader.</summary>
+    private Cluster FormSingleNodeCluster()
+    {
+        var cluster = Cluster.Get(Sys);
+        cluster.Join(cluster.SelfAddress);
+        AwaitCondition(
+            () => cluster.SelfMember.Status == MemberStatus.Up && cluster.State.Leader is not null,
+            FormationTimeout);
+        return cluster;
+    }
+
+    [Fact]
+    public void BuildClusterData_SingleNodeCluster_ReportsSelfAsLeader()
+    {
+        var cluster = FormSingleNodeCluster();
+
+        var data = AkkaClusterHealthCheck.BuildClusterData(cluster);
+
+        Assert.Equal(cluster.SelfAddress.ToString(), Assert.IsType<string>(data["leader"]));
+        Assert.Equal(cluster.SelfAddress.ToString(), Assert.IsType<string>(data["selfAddress"]));
+        Assert.Equal(1, Assert.IsType<int>(data["memberCount"]));
+        Assert.Equal(0, Assert.IsType<int>(data["unreachableCount"]));
+    }
+
+    [Fact]
+    public void BuildClusterData_RolesRoundTripSorted()
+    {
+        var cluster = FormSingleNodeCluster();
+
+        var roles = Assert.IsType<string[]>(AkkaClusterHealthCheck.BuildClusterData(cluster)["selfRoles"]);
+
+        // Sorted, so the payload is stable across restarts; the configured roles survive verbatim.
+        Assert.Equal(new[] { "admin", "driver" }, roles);
+    }
+
+    [Fact]
+    public async Task CheckHealth_FormedCluster_HealthyResultCarriesClusterData()
+    {
+        var cluster = FormSingleNodeCluster();
+        var provider = new ServiceCollection().AddSingleton(Sys).BuildServiceProvider();
+        var check = new AkkaClusterHealthCheck(provider, AkkaClusterStatusPolicy.Default);
+
+        var result = await check.CheckHealthAsync(NewContext(check));
+
+        Assert.Equal(HealthStatus.Healthy, result.Status);
+        Assert.Equal(cluster.SelfAddress.ToString(), result.Data["leader"]);
+        Assert.Equal(1, result.Data["memberCount"]);
+    }
+
+    [Fact]
+    public async Task CheckHealth_NoActorSystem_CarriesNoData()
+    {
+        // The startup-safety paths stay description-only: an empty data dictionary is what makes the
+        // writer omit the "data" key entirely, so a not-yet-started node's payload is unchanged.
+        var provider = new ServiceCollection().BuildServiceProvider();
+        var check = new AkkaClusterHealthCheck(provider, AkkaClusterStatusPolicy.Default);
+
+        var result = await check.CheckHealthAsync(NewContext(check));
+
+        Assert.Equal(HealthStatus.Degraded, result.Status);
+        Assert.Empty(result.Data);
+    }
+
+    private static HealthCheckContext NewContext(IHealthCheck check) => new()
+    {
+        Registration = new HealthCheckRegistration("akka-cluster", check, HealthStatus.Unhealthy, tags: null),
+    };
+}
diff --git a/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/AkkaClusterStatusPolicyTests.cs b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/AkkaClusterStatusPolicyTests.cs
index 0c8bd10..f02bc97 100644
--- a/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/AkkaClusterStatusPolicyTests.cs
+++ b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/AkkaClusterStatusPolicyTests.cs
@@ -88,6 +88,8 @@ public sealed class AkkaClusterStatusPolicyTests
             var result = await check.CheckHealthAsync(NewContext(check));
 
             Assert.Equal(HealthStatus.Degraded, result.Status);
+            // No cluster to describe → no data, so the emitted payload stays the pre-0.2.0 shape.
+            Assert.Empty(result.Data);
         }
         finally
         {
diff --git a/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/ZB.MOM.WW.Health.Akka.Tests.csproj b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/ZB.MOM.WW.Health.Akka.Tests.csproj
index a858d74..e54e7eb 100644
--- a/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/ZB.MOM.WW.Health.Akka.Tests.csproj
+++ b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Akka.Tests/ZB.MOM.WW.Health.Akka.Tests.csproj
@@ -5,6 +5,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Akka.TestKit.Xunit2" />
     <PackageReference Include="coverlet.collector" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" />
     <PackageReference Include="xunit" />
diff --git a/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Tests/ResponseWriterTests.cs b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Tests/ResponseWriterTests.cs
index 0e9bd6b..d099ec9 100644
--- a/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Tests/ResponseWriterTests.cs
+++ b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Tests/ResponseWriterTests.cs
@@ -22,8 +22,11 @@ public sealed class ResponseWriterTests
     {
         private readonly HealthCheckResult _result;
 
-        public StubHealthCheck(HealthStatus status, string? description = null) =>
-            _result = new HealthCheckResult(status, description);
+        public StubHealthCheck(
+            HealthStatus status,
+            string? description = null,
+            IReadOnlyDictionary<string, object>? data = null) =>
+            _result = new HealthCheckResult(status, description, exception: null, data: data);
 
         public Task<HealthCheckResult> CheckHealthAsync(
             HealthCheckContext context,
@@ -31,12 +34,14 @@ public sealed class ResponseWriterTests
     }
 
     private static async Task<HttpResponseMessage> GetReadyAsync(
-        HealthStatus status, string? description = "db reachable")
+        HealthStatus status,
+        string? description = "db reachable",
+        IReadOnlyDictionary<string, object>? data = null)
     {
         var builder = WebApplication.CreateBuilder();
         builder.WebHost.UseTestServer();
         builder.Services.AddHealthChecks()
-            .AddCheck("db", new StubHealthCheck(status, description), tags: new[] { ZbHealthTags.Ready });
+            .AddCheck("db", new StubHealthCheck(status, description, data), tags: new[] { ZbHealthTags.Ready });
 
         await using var app = builder.Build();
         app.MapZbHealth();
@@ -84,6 +89,51 @@ public sealed class ResponseWriterTests
         Assert.Equal(JsonValueKind.Null, description.ValueKind);
     }
 
+    [Fact]
+    public async Task ReadyEndpoint_EntryWithData_EmitsDataObject_WithVerbatimKeys()
+    {
+        // The envelope properties are camelCased by the naming policy, but a check's own data keys are
+        // dictionary keys and must survive verbatim — the dashboard reads them by exact name
+        // (entries["akka-cluster"].data.leader), so a naming policy applied here would silently break
+        // the contract. Values may be any JSON-friendly type (string / int / string[]).
+        var data = new Dictionary<string, object>
+        {
+            ["leader"] = "akka.tcp://sys@node-1:4053",
+            ["memberCount"] = 2,
+            ["selfRoles"] = new[] { "driver", "site-a" },
+        };
+
+        var response = await GetReadyAsync(HealthStatus.Healthy, data: data);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        using var doc = JsonDocument.Parse(await response.Content.ReadAsStringAsync());
+        var entryData = doc.RootElement.GetProperty("entries").GetProperty("db").GetProperty("data");
+
+        Assert.Equal("akka.tcp://sys@node-1:4053", entryData.GetProperty("leader").GetString());
+        Assert.Equal(2, entryData.GetProperty("memberCount").GetInt32());
+        Assert.Equal(
+            new[] { "driver", "site-a" },
+            entryData.GetProperty("selfRoles").EnumerateArray().Select(static e => e.GetString()).ToArray());
+    }
+
+    [Fact]
+    public async Task ReadyEndpoint_EntryWithoutData_OmitsDataKeyEntirely()
+    {
+        // The 0.2.0 non-breaking invariant: a check that publishes no data must produce exactly the
+        // pre-0.2.0 body. Asserted on the raw JSON string so a `"data": null` regression (which
+        // TryGetProperty would still accept as "present") fails here.
+        var response = await GetReadyAsync(HealthStatus.Healthy);
+
+        var body = await response.Content.ReadAsStringAsync();
+
+        Assert.DoesNotContain("\"data\"", body, StringComparison.Ordinal);
+
+        using var doc = JsonDocument.Parse(body);
+        var db = doc.RootElement.GetProperty("entries").GetProperty("db");
+        Assert.False(db.TryGetProperty("data", out _), "data key must be absent when the check set none");
+    }
+
     [Fact]
     public async Task ReadyEndpoint_Degraded_Returns200_WithDegradedStatus()
     {
diff --git a/docs/plans/2026-07-22-overview-dashboard-impl-plan.md.tasks.json b/docs/plans/2026-07-22-overview-dashboard-impl-plan.md.tasks.json
new file mode 100644
index 0000000..b97e240
--- /dev/null
+++ b/docs/plans/2026-07-22-overview-dashboard-impl-plan.md.tasks.json
@@ -0,0 +1,25 @@
+{
+  "plan": "docs/plans/2026-07-22-overview-dashboard-impl-plan.md",
+  "tasks": [
+    { "id": "1",  "subject": "0.1 Health writer: optional per-entry `data` object", "status": "pending", "blockedBy": [] },
+    { "id": "2",  "subject": "0.2 AkkaClusterHealthCheck: populate cluster-view data", "status": "pending", "blockedBy": [] },
+    { "id": "3",  "subject": "0.3 Health 0.2.0: version, test, pack, publish, verify", "status": "pending", "blockedBy": ["1", "2"] },
+    { "id": "4",  "subject": "1.1 ScadaBridge: bump Health packages to 0.2.0", "status": "pending", "blockedBy": ["3"] },
+    { "id": "5",  "subject": "1.2 ScadaBridge: site health checks (akka-cluster, localdb, active-node)", "status": "pending", "blockedBy": ["4"] },
+    { "id": "6",  "subject": "1.3 ScadaBridge: map MapZbHealth on the site pipeline", "status": "pending", "blockedBy": ["5"] },
+    { "id": "7",  "subject": "1.4 ScadaBridge: site health tests", "status": "pending", "blockedBy": ["6"] },
+    { "id": "8",  "subject": "2.1 OtOpcUa: verify `akka` check is the shared AkkaClusterHealthCheck", "status": "pending", "blockedBy": [] },
+    { "id": "9",  "subject": "2.2 OtOpcUa: bump Health to 0.2.0", "status": "pending", "blockedBy": ["3", "8"] },
+    { "id": "10", "subject": "2.3 Alignment bumps: mxgw + HistorianGateway Health 0.2.0", "status": "pending", "blockedBy": ["3"] },
+    { "id": "11", "subject": "3.1 Overview: scaffold project", "status": "pending", "blockedBy": ["3"] },
+    { "id": "12", "subject": "3.2 Overview: registry options + validation", "status": "pending", "blockedBy": ["11"] },
+    { "id": "13", "subject": "3.3 Overview: health client + status model", "status": "pending", "blockedBy": ["11"] },
+    { "id": "14", "subject": "3.4 Overview: poller + snapshot store", "status": "pending", "blockedBy": ["12", "13"] },
+    { "id": "15", "subject": "3.5 Overview: leader aggregation", "status": "pending", "blockedBy": ["13"] },
+    { "id": "16", "subject": "3.6 Overview: UI (ThemeShell, Overview page, InstanceCard)", "status": "pending", "blockedBy": ["14", "15"] },
+    { "id": "17", "subject": "3.7 Overview: self-observability", "status": "pending", "blockedBy": ["14"] },
+    { "id": "18", "subject": "3.8 Overview: tests", "status": "pending", "blockedBy": ["16", "17"] },
+    { "id": "19", "subject": "3.9 Overview: config + docker", "status": "pending", "blockedBy": ["17"] },
+    { "id": "20", "subject": "4 Live acceptance (design §9)", "status": "pending", "blockedBy": ["7", "9", "18", "19"] }
+  ]
+}