Initial curated itworx-knowledge-hub source from 3b1751d0d9dee551aa6994eee0093704dc334817

src/backend/ItWorx.KnowledgeHub.Application/Decisions/UseCases/GetDecisionUseCase.cs

@@ -0,0 +1,43 @@
+using ItWorx.KnowledgeHub.Application.Knowledge.UseCases;
+using ItWorx.KnowledgeHub.Domain.Decisions;
+
+namespace ItWorx.KnowledgeHub.Application.Decisions.UseCases;
+
+public sealed record DecisionDetailResult(
+    DecisionRecord Decision,
+    PageDetailResult Page,
+    string ETag,
+    DecisionRecord? Supersedes,
+    DecisionRecord? SupersededBy);
+
+/// <summary>Assembles one ADR's full lineage view: its own lifecycle metadata, the
+/// linked page's rendered content, and — resolved by one extra lookup each, never a
+/// duplicated copy — the decision it supersedes and/or is superseded by
+/// (docs/16-runbooks-and-adrs.md: "Links are bidirectional").</summary>
+public sealed class GetDecisionUseCase(IDecisionRepository decisions, GetPageUseCase getPage)
+{
+    public async Task<DecisionDetailResult?> ExecuteAsync(Guid decisionId, CancellationToken cancellationToken)
+    {
+        var decision = await decisions.FindAsync(decisionId, cancellationToken);
+        if (decision is null)
+        {
+            return null;
+        }
+
+        var page = await getPage.ExecuteAsync(decision.PageId, cancellationToken);
+        if (page is null)
+        {
+            return null;
+        }
+
+        var etag = await decisions.GetETagAsync(decisionId, cancellationToken) ?? string.Empty;
+        var supersedes = decision.SupersedesDecisionId is { } supersedesId
+            ? await decisions.FindAsync(supersedesId, cancellationToken)
+            : null;
+        var supersededBy = decision.SupersededByDecisionId is { } supersededById
+            ? await decisions.FindAsync(supersededById, cancellationToken)
+            : null;
+
+        return new DecisionDetailResult(decision, page, etag, supersedes, supersededBy);
+    }
+}