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src/Signals/StellaOps.Signals/Services/SyntheticRuntimeProbeBuilder.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using StellaOps.Signals.Models;
+
+namespace StellaOps.Signals.Services;
+
+/// <summary>
+/// Builds deterministic synthetic runtime events from an existing callgraph.
+/// </summary>
+public sealed class SyntheticRuntimeProbeBuilder
+{
+    private readonly TimeProvider timeProvider;
+
+    public SyntheticRuntimeProbeBuilder(TimeProvider timeProvider)
+    {
+        this.timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+    }
+
+    public List<RuntimeFactEvent> BuildEvents(CallgraphDocument callgraph, int requestedCount)
+    {
+        ArgumentNullException.ThrowIfNull(callgraph);
+        var now = timeProvider.GetUtcNow();
+        var count = Math.Max(1, Math.Min(requestedCount <= 0 ? 5 : requestedCount, callgraph.Nodes.Count));
+
+        return callgraph.Nodes
+            .OrderBy(n => n.Id, StringComparer.Ordinal)
+            .Take(count)
+            .Select((node, index) => new RuntimeFactEvent
+            {
+                SymbolId = node.Id,
+                CodeId = node.CodeId,
+                Purl = node.Purl,
+                SymbolDigest = node.SymbolDigest,
+                BuildId = node.BuildId,
+                ObservedAt = now,
+                ProcessId = 1000 + index,
+                ProcessName = "synthetic-probe",
+                Metadata = new Dictionary<string, string?>(StringComparer.Ordinal)
+                {
+                    ["probe"] = "synthetic",
+                    ["probe.version"] = "v1",
+                    ["probe.seed"] = callgraph.Id,
+                }
+            })
+            .ToList();
+    }
+}