diff --git a/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs
index 38762d2..69e3649 100644
--- a/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs
+++ b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs
@@ -68,6 +68,8 @@ public sealed record ElevationCandidate(string StableId, double ModelElevation,
 public sealed record ExistingElevationAnnotation(string StableId, string SourceStableId, string Text, AnnotationPoint Position);
 public sealed record ElevationAnnotationOperation(string StableId, AnnotationOperationKind Kind, string? Text, AnnotationPoint Position, double Rotation, string Layer, string TextStyle, IReadOnlyList<string> Reasons);
 public sealed record ElevationAnnotationPlan(IReadOnlyList<ElevationAnnotationOperation> Operations);
+public sealed record LineConnectionCandidate(string StableId, string LineNumber, Point3Dto FirstEndpoint, Point3Dto SecondEndpoint, Bounds3Dto Bounds, AnnotationPoint Position, double Rotation);
+public sealed record LineConnectionGroup(string LineNumber, IReadOnlyList<LineConnectionCandidate> Members, AnnotationPoint Placement, double Rotation);
 public sealed record LineNumberTextAsset(string Layer, string TextStyle, double Size, string TextValue, Point2Dto Position);
 public sealed record LineNumberLineAsset(string Layer, Point2Dto Start, Point2Dto End);
 public sealed record LineNumberMarkerAsset(string Layer, double MaskScaleFactor, IReadOnlyList<LineNumberTextAsset> Texts, IReadOnlyList<LineNumberLineAsset> Lines);
diff --git a/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Core/LineNumberConnectionPlanner.cs b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Core/LineNumberConnectionPlanner.cs
new file mode 100644
index 0000000..3a5e0d6
--- /dev/null
+++ b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Core/LineNumberConnectionPlanner.cs
@@ -0,0 +1,42 @@
+using PRecAnnot.Abstractions;
+
+namespace PRecAnnot.Core;
+
+public sealed class LineNumberConnectionPlanner
+{
+    public IReadOnlyList<LineConnectionGroup> Build(IEnumerable<LineConnectionCandidate> candidates, double tolerance)
+    {
+        if (tolerance < 0 || double.IsNaN(tolerance) || double.IsInfinity(tolerance)) throw new ArgumentOutOfRangeException(nameof(tolerance));
+        return candidates
+            .Where(value => !string.IsNullOrWhiteSpace(value.LineNumber))
+            .OrderBy(value => value.StableId, StringComparer.Ordinal)
+            .GroupBy(value => value.LineNumber, StringComparer.OrdinalIgnoreCase)
+            .Select(group => BuildGroup(group.Key, group.ToArray(), tolerance))
+            .Where(group => group is not null)
+            .Cast<LineConnectionGroup>()
+            .OrderBy(group => group.LineNumber, StringComparer.OrdinalIgnoreCase)
+            .ToArray();
+    }
+
+    private static LineConnectionGroup? BuildGroup(string number, LineConnectionCandidate[] members, double tolerance)
+    {
+        if (members.Length < 2) return null;
+        var connected = members.Where(first => members.Any(second => !ReferenceEquals(first, second) && Connected(first, second, tolerance))).OrderBy(value => value.StableId, StringComparer.Ordinal).ToArray();
+        if (connected.Length < 2) return null;
+        var anchor = connected[0];
+        return new(number, connected, anchor.Position, anchor.Rotation);
+    }
+
+    private static bool Connected(LineConnectionCandidate first, LineConnectionCandidate second, double tolerance)
+    {
+        if (Distance(first.FirstEndpoint, second.FirstEndpoint) <= tolerance || Distance(first.FirstEndpoint, second.SecondEndpoint) <= tolerance || Distance(first.SecondEndpoint, second.FirstEndpoint) <= tolerance || Distance(first.SecondEndpoint, second.SecondEndpoint) <= tolerance)
+            return true;
+        return ExtentsIntersectionClassifier.Classify(first.Bounds, second.Bounds) is not ExtentsIntersectionType.DoNotIntersect;
+    }
+
+    private static double Distance(Point3Dto first, Point3Dto second)
+    {
+        var x = first.X - second.X; var y = first.Y - second.Y; var z = first.Z - second.Z;
+        return Math.Sqrt(x * x + y * y + z * z);
+    }
+}
diff --git a/Plant3D2026/P_Rec_Annot/tests/PRecAnnot.Core.Tests/LineNumberConnectionPlannerTests.cs b/Plant3D2026/P_Rec_Annot/tests/PRecAnnot.Core.Tests/LineNumberConnectionPlannerTests.cs
new file mode 100644
index 0000000..4f0b856
--- /dev/null
+++ b/Plant3D2026/P_Rec_Annot/tests/PRecAnnot.Core.Tests/LineNumberConnectionPlannerTests.cs
@@ -0,0 +1,29 @@
+using PRecAnnot.Abstractions;
+using PRecAnnot.Core;
+
+namespace PRecAnnot.Core.Tests;
+
+public sealed class LineNumberConnectionPlannerTests
+{
+    [Fact]
+    public void GroupsConnectedSameLineCandidatesInStableOrder()
+    {
+        var a = Candidate("a", "L-1", new(0, 0, 0), new(1, 0, 0));
+        var b = Candidate("b", "l-1", new(1.05, 0, 0), new(2, 0, 0));
+        var c = Candidate("c", "L-2", new(0, 0, 0), new(1, 0, 0));
+        var result = new LineNumberConnectionPlanner().Build([b, c, a], .1);
+        var group = Assert.Single(result);
+        Assert.Equal("L-1", group.LineNumber);
+        Assert.Equal(new[] { "a", "b" }, group.Members.Select(value => value.StableId));
+    }
+
+    [Fact]
+    public void DoesNotGroupDisjointOrSingleLineCandidates()
+    {
+        var a = Candidate("a", "L-1", new(0, 0, 0), new(1, 0, 0));
+        var b = Candidate("b", "L-1", new(10, 0, 0), new(11, 0, 0));
+        Assert.Empty(new LineNumberConnectionPlanner().Build([a, b], .1));
+    }
+
+    private static LineConnectionCandidate Candidate(string id, string line, Point3Dto first, Point3Dto second) => new(id, line, first, second, new(new(Math.Min(first.X, second.X), Math.Min(first.Y, second.Y), Math.Min(first.Z, second.Z)), new(Math.Max(first.X, second.X), Math.Max(first.Y, second.Y), Math.Max(first.Z, second.Z))), new(first.X, first.Y), 0);
+}