diff --git a/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs
index 84c508e..62e7bab 100644
--- a/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs
+++ b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs
@@ -122,6 +122,7 @@ public interface IPlantConnectorPortReader
 {
     PlantConnectorPortReadResult Read(PlantConnectorRelationshipSnapshot connector);
 }
+public sealed record ConnectorViewportEligibility(bool Eligible, Point3Dto? PlacementPoint, string? FailureCode = null);
 public sealed record LineNumberOwnedRow(string SourceStableId, int MarkerNumber, string Text, AnnotationPoint MarkerAttributePosition);
 public sealed record LineNumberRowMutation(string SourceStableId, int PreviousMarkerNumber, int MarkerNumber, string Text, AnnotationPoint? MarkerAttributePosition);
 public sealed record LineNumberTextAsset(string Layer, string TextStyle, double Size, string TextValue, Point2Dto Position);
diff --git a/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Core/ConnectorViewportEligibilityEvaluator.cs b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Core/ConnectorViewportEligibilityEvaluator.cs
new file mode 100644
index 0000000..d1eb8fc
--- /dev/null
+++ b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Core/ConnectorViewportEligibilityEvaluator.cs
@@ -0,0 +1,34 @@
+using PRecAnnot.Abstractions;
+
+namespace PRecAnnot.Core;
+
+// Port of AutoLinenumberConnections.IsOKPrepareAnnotation's geometry gate.
+// The caller performs model-to-paper transformation only after the connector
+// is eligible, preserving legacy model-space containment semantics.
+public sealed class ConnectorViewportEligibilityEvaluator
+{
+    public ConnectorViewportEligibility Evaluate(PlantConnectorPortSnapshot ports, Point3Dto viewDirection, Bounds3Dto viewExtents, double parallelTolerance = 0.1)
+    {
+        if (parallelTolerance < 0) throw new ArgumentOutOfRangeException(nameof(parallelTolerance));
+        if (Parallel(ports.FirstDirection, viewDirection, parallelTolerance) || Parallel(ports.SecondDirection, viewDirection, parallelTolerance))
+            return new(false, null, "CONNECTOR_PORT_PARALLEL_TO_VIEW");
+        if (!Inside(ports.FirstPosition, viewExtents) || !Inside(ports.SecondPosition, viewExtents))
+            return new(false, null, "CONNECTOR_OUTSIDE_VIEW_EXTENTS");
+        // Legacy stores ports[1] as the insertion/model anchor.
+        return new(true, ports.SecondPosition);
+    }
+
+    private static bool Inside(Point3Dto point, Bounds3Dto bounds) =>
+        point.X >= bounds.Minimum.X && point.X <= bounds.Maximum.X &&
+        point.Y >= bounds.Minimum.Y && point.Y <= bounds.Maximum.Y &&
+        point.Z >= bounds.Minimum.Z && point.Z <= bounds.Maximum.Z;
+
+    private static bool Parallel(Point3Dto first, Point3Dto second, double tolerance)
+    {
+        var firstLength = Math.Sqrt(first.X * first.X + first.Y * first.Y + first.Z * first.Z);
+        var secondLength = Math.Sqrt(second.X * second.X + second.Y * second.Y + second.Z * second.Z);
+        if (firstLength == 0 || secondLength == 0) return true;
+        var cosine = Math.Abs((first.X * second.X + first.Y * second.Y + first.Z * second.Z) / (firstLength * secondLength));
+        return 1d - cosine <= tolerance;
+    }
+}
diff --git a/Plant3D2026/P_Rec_Annot/tests/PRecAnnot.Core.Tests/ConnectorViewportEligibilityEvaluatorTests.cs b/Plant3D2026/P_Rec_Annot/tests/PRecAnnot.Core.Tests/ConnectorViewportEligibilityEvaluatorTests.cs
new file mode 100644
index 0000000..fd792aa
--- /dev/null
+++ b/Plant3D2026/P_Rec_Annot/tests/PRecAnnot.Core.Tests/ConnectorViewportEligibilityEvaluatorTests.cs
@@ -0,0 +1,32 @@
+using PRecAnnot.Abstractions;
+using PRecAnnot.Core;
+
+namespace PRecAnnot.Core.Tests;
+
+public sealed class ConnectorViewportEligibilityEvaluatorTests
+{
+    [Fact]
+    public void UsesSecondPortAsLegacyPlacementAnchorWhenBothPortsAreVisible()
+    {
+        var result = new ConnectorViewportEligibilityEvaluator().Evaluate(Ports(new(1, 2, 3), new(4, 5, 6), new(1, 0, 0), new(0, 1, 0)), new(0, 0, 1), Bounds());
+        Assert.True(result.Eligible);
+        Assert.Equal(new Point3Dto(4, 5, 6), result.PlacementPoint);
+    }
+
+    [Fact]
+    public void RejectsPortParallelToViewDirection()
+    {
+        var result = new ConnectorViewportEligibilityEvaluator().Evaluate(Ports(new(), new(), new(0, 0, 1), new(1, 0, 0)), new(0, 0, 1), Bounds());
+        Assert.Equal("CONNECTOR_PORT_PARALLEL_TO_VIEW", result.FailureCode);
+    }
+
+    [Fact]
+    public void RejectsConnectorWhenAnyPortLiesOutsideModelViewExtents()
+    {
+        var result = new ConnectorViewportEligibilityEvaluator().Evaluate(Ports(new(0, 0, 0), new(11, 0, 0), new(1, 0, 0), new(0, 1, 0)), new(0, 0, 1), Bounds());
+        Assert.Equal("CONNECTOR_OUTSIDE_VIEW_EXTENTS", result.FailureCode);
+    }
+
+    private static Bounds3Dto Bounds() => new(new(-10, -10, -10), new(10, 10, 10));
+    private static PlantConnectorPortSnapshot Ports(Point3Dto firstPosition, Point3Dto secondPosition, Point3Dto firstDirection, Point3Dto secondDirection) => new("c", firstPosition, secondPosition, firstDirection, secondDirection);
+}