diff --git a/contracts/cultnet/interop/selection-vectors.cs-written.json b/contracts/cultnet/interop/selection-vectors.cs-written.json
index 037f1fe8..8c58a174 100644
--- a/contracts/cultnet/interop/selection-vectors.cs-written.json
+++ b/contracts/cultnet/interop/selection-vectors.cs-written.json
@@ -20,11 +20,11 @@
       "expectedRefusalField": null,
       "expectedEvaluationRefusal": null,
       "expectedIds": [
+        "sha256:9d0bc9aebc3619b07aabf564f98667afde41444c1b866661d777687d443608dc/citer-both-in-target",
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/aa-tie-schema",
-        "sha256:b1f2407d0227a79dcbffdf7ea317f827eec64be38a3f61b7d4e99e81e3b24b42/zz-tie-schema",
-        "sha256:ee192f6526a8f8cdec7044551aa2c8e28c612426766bb270605023bc94e2614d/narrow-citer-accepted"
+        "sha256:b1f2407d0227a79dcbffdf7ea317f827eec64be38a3f61b7d4e99e81e3b24b42/zz-tie-schema"
       ],
-      "matched": 17,
+      "matched": 18,
       "hasNext": true,
       "expectedEdges": []
     },
@@ -51,9 +51,10 @@
       "expectedRefusalField": null,
       "expectedEvaluationRefusal": null,
       "expectedIds": [
-        "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/a-eq"
+        "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/a-eq",
+        "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/dup-key"
       ],
-      "matched": 1,
+      "matched": 2,
       "hasNext": false,
       "expectedEdges": [
         {
@@ -61,6 +62,12 @@
           "role": "Design",
           "toId": "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/a-eq",
           "payloadBase64": null
+        },
+        {
+          "fromId": "sha256:9d0bc9aebc3619b07aabf564f98667afde41444c1b866661d777687d443608dc/citer-both-in-target",
+          "role": "Design",
+          "toId": "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/dup-key",
+          "payloadBase64": null
         }
       ]
     },
@@ -77,10 +84,9 @@
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/tie-mass",
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/-row",
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/\uD83D\uDE02-row",
-        "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/dup-key",
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/aa-tie-schema"
       ],
-      "matched": 8,
+      "matched": 7,
       "hasNext": false,
       "expectedEdges": []
     },
@@ -114,7 +120,7 @@
     },
     {
       "name": "hop_by_role_cites_exact_id",
-      "selectionMessagePackBase64": "iadzY2hlbWFzwKRrZXlzwKZmaWVsZHPApWNpdGVzgqZ0YXJnZXSCqHNjaGVtYUlk2UdzaGEyNTY6ZmYzNWYzZDlkNmRlM2YxMDY2YjkzNjllNzNmZTZjNzY0OGU4ODM2OGQxOGVmYzIyNzVjOTk0NzMwY2Q4NGNmZqlyZWNvcmRLZXmkYS1lcaRyb2xlpkRlc2lnbqVjaXRlZMCqcHJvamVjdGlvbqZoZWFkZXKqZGVzY2VuZGluZ8KlbGltaXTApmN1cnNvcsA=",
+      "selectionMessagePackBase64": "iadzY2hlbWFzwKRrZXlzkadjaXRlci0xpmZpZWxkc8ClY2l0ZXOCpnRhcmdldIKoc2NoZW1hSWTZR3NoYTI1NjpmZjM1ZjNkOWQ2ZGUzZjEwNjZiOTM2OWU3M2ZlNmM3NjQ4ZTg4MzY4ZDE4ZWZjMjI3NWM5OTQ3MzBjZDg0Y2ZmqXJlY29yZEtleaRhLWVxpHJvbGWmRGVzaWdupWNpdGVkwKpwcm9qZWN0aW9upmhlYWRlcqpkZXNjZW5kaW5nwqVsaW1pdMCmY3Vyc29ywA==",
       "asOf": 1,
       "expectedRefusalField": null,
       "expectedEvaluationRefusal": null,
@@ -134,7 +140,7 @@
     },
     {
       "name": "cites_target_by_name_alias",
-      "selectionMessagePackBase64": "iadzY2hlbWFzwKRrZXlzwKZmaWVsZHPApWNpdGVzgqZ0YXJnZXSCqHNjaGVtYUlkqWxlYWZfYS52OalyZWNvcmRLZXmkYS1lcaRyb2xlpkRlc2lnbqVjaXRlZMCqcHJvamVjdGlvbqZoZWFkZXKqZGVzY2VuZGluZ8KlbGltaXTApmN1cnNvcsA=",
+      "selectionMessagePackBase64": "iadzY2hlbWFzwKRrZXlzkadjaXRlci0xpmZpZWxkc8ClY2l0ZXOCpnRhcmdldIKoc2NoZW1hSWSpbGVhZl9hLnY5qXJlY29yZEtleaRhLWVxpHJvbGWmRGVzaWdupWNpdGVkwKpwcm9qZWN0aW9upmhlYWRlcqpkZXNjZW5kaW5nwqVsaW1pdMCmY3Vyc29ywA==",
       "asOf": 1,
       "expectedRefusalField": null,
       "expectedEvaluationRefusal": null,
@@ -249,6 +255,26 @@
         }
       ]
     },
+    {
+      "name": "shared_key_design_resolves_the_first_in_target_candidate_in_row_order",
+      "selectionMessagePackBase64": "iadzY2hlbWFzwKRrZXlzkbRjaXRlci1ib3RoLWluLXRhcmdldKZmaWVsZHPApWNpdGVzgqZ0YXJnZXSCqHNjaGVtYUlk2UdzaGEyNTY6ZmYzNWYzZDlkNmRlM2YxMDY2YjkzNjllNzNmZTZjNzY0OGU4ODM2OGQxOGVmYzIyNzVjOTk0NzMwY2Q4NGNmZqlyZWNvcmRLZXmnZHVwLWtleaRyb2xlpkRlc2lnbqVjaXRlZMCqcHJvamVjdGlvbqZoZWFkZXKqZGVzY2VuZGluZ8KlbGltaXTApmN1cnNvcsA=",
+      "asOf": 1,
+      "expectedRefusalField": null,
+      "expectedEvaluationRefusal": null,
+      "expectedIds": [
+        "sha256:9d0bc9aebc3619b07aabf564f98667afde41444c1b866661d777687d443608dc/citer-both-in-target"
+      ],
+      "matched": 1,
+      "hasNext": false,
+      "expectedEdges": [
+        {
+          "fromId": "sha256:9d0bc9aebc3619b07aabf564f98667afde41444c1b866661d777687d443608dc/citer-both-in-target",
+          "role": "Design",
+          "toId": "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/dup-key",
+          "payloadBase64": null
+        }
+      ]
+    },
     {
       "name": "refuses_empty_schemas_list",
       "selectionMessagePackBase64": "iadzY2hlbWFzkKRrZXlzwKZmaWVsZHPApWNpdGVzwKVjaXRlZMCqcHJvamVjdGlvbqZoZWFkZXKqZGVzY2VuZGluZ8KlbGltaXTApmN1cnNvcsA=",
diff --git a/contracts/cultnet/interop/selection-vectors.fixture.json b/contracts/cultnet/interop/selection-vectors.fixture.json
index 1ba62a9e..7e94fd7b 100644
--- a/contracts/cultnet/interop/selection-vectors.fixture.json
+++ b/contracts/cultnet/interop/selection-vectors.fixture.json
@@ -93,6 +93,13 @@
     },
     {
       "schema": "leaf_a", "key": "aa-tie-schema", "ordinal": 15, "fields": { "kind": "tie-schema", "mass": "1" }
+    },
+    {
+      "//": "R-AO, 2026-09-23: 'dup-key' already carries two rows (leaf_a ordinal 11, leaf_b ordinal 12) - both are in citer's Design role's declared target ([leaf_a, leaf_b], unlike citer_narrow's narrow_ref above, which only ever had one in-target candidate at a shared key). This citer is the first row in this file (hence in both runtimes' row order) to name 'dup-key' through Design, so resolving it must deterministically pick the leaf_a row - the first in-target candidate in the caller's order - never the leaf_b row, in both runtimes.",
+      "schema": "citer",
+      "key": "citer-both-in-target",
+      "ordinal": 16,
+      "references": [ { "role": "Design", "targetKey": "dup-key" } ]
     }
   ]
 }
diff --git a/contracts/cultnet/interop/selection-vectors.rs-written.json b/contracts/cultnet/interop/selection-vectors.rs-written.json
index 36fbab66..a9b635c4 100644
--- a/contracts/cultnet/interop/selection-vectors.rs-written.json
+++ b/contracts/cultnet/interop/selection-vectors.rs-written.json
@@ -16,11 +16,11 @@
       "selectionMessagePackBase64": "g6pwcm9qZWN0aW9upmhlYWRlcqpkZXNjZW5kaW5nw6VsaW1pdAM=",
       "asOf": 1,
       "expectedIds": [
+        "sha256:9d0bc9aebc3619b07aabf564f98667afde41444c1b866661d777687d443608dc/citer-both-in-target",
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/aa-tie-schema",
-        "sha256:b1f2407d0227a79dcbffdf7ea317f827eec64be38a3f61b7d4e99e81e3b24b42/zz-tie-schema",
-        "sha256:ee192f6526a8f8cdec7044551aa2c8e28c612426766bb270605023bc94e2614d/narrow-citer-accepted"
+        "sha256:b1f2407d0227a79dcbffdf7ea317f827eec64be38a3f61b7d4e99e81e3b24b42/zz-tie-schema"
       ],
-      "matched": 17,
+      "matched": 18,
       "hasNext": true,
       "expectedEdges": []
     },
@@ -43,9 +43,10 @@
       "selectionMessagePackBase64": "hKdzY2hlbWFzkdlHc2hhMjU2OmZmMzVmM2Q5ZDZkZTNmMTA2NmI5MzY5ZTczZmU2Yzc2NDhlODgzNjhkMThlZmMyMjc1Yzk5NDczMGNkODRjZmalY2l0ZWSCpHJvbGWmRGVzaWdupmV4aXN0c8OqcHJvamVjdGlvbqZoZWFkZXKqZGVzY2VuZGluZ8I=",
       "asOf": 1,
       "expectedIds": [
-        "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/a-eq"
+        "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/a-eq",
+        "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/dup-key"
       ],
-      "matched": 1,
+      "matched": 2,
       "hasNext": false,
       "expectedEdges": [
         {
@@ -53,6 +54,12 @@
           "role": "Design",
           "toId": "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/a-eq",
           "payloadBase64": null
+        },
+        {
+          "fromId": "sha256:9d0bc9aebc3619b07aabf564f98667afde41444c1b866661d777687d443608dc/citer-both-in-target",
+          "role": "Design",
+          "toId": "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/dup-key",
+          "payloadBase64": null
         }
       ]
     },
@@ -67,10 +74,9 @@
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/tie-mass",
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/-row",
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/😂-row",
-        "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/dup-key",
         "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/aa-tie-schema"
       ],
-      "matched": 8,
+      "matched": 7,
       "hasNext": false,
       "expectedEdges": []
     },
@@ -204,6 +210,24 @@
         }
       ]
     },
+    {
+      "name": "shared_key_design_resolves_the_first_in_target_candidate_in_row_order",
+      "selectionMessagePackBase64": "hKRrZXlzkbRjaXRlci1ib3RoLWluLXRhcmdldKVjaXRlc4KmdGFyZ2V0gqhzY2hlbWFJZNlHc2hhMjU2OmZmMzVmM2Q5ZDZkZTNmMTA2NmI5MzY5ZTczZmU2Yzc2NDhlODgzNjhkMThlZmMyMjc1Yzk5NDczMGNkODRjZmapcmVjb3JkS2V5p2R1cC1rZXmkcm9sZaZEZXNpZ26qcHJvamVjdGlvbqZoZWFkZXKqZGVzY2VuZGluZ8I=",
+      "asOf": 1,
+      "expectedIds": [
+        "sha256:9d0bc9aebc3619b07aabf564f98667afde41444c1b866661d777687d443608dc/citer-both-in-target"
+      ],
+      "matched": 1,
+      "hasNext": false,
+      "expectedEdges": [
+        {
+          "fromId": "sha256:9d0bc9aebc3619b07aabf564f98667afde41444c1b866661d777687d443608dc/citer-both-in-target",
+          "role": "Design",
+          "toId": "sha256:ff35f3d9d6de3f1066b9369e73fe6c7648e88368d18efc2275c994730cd84cff/dup-key",
+          "payloadBase64": null
+        }
+      ]
+    },
     {
       "name": "refuses_empty_schemas_list",
       "selectionMessagePackBase64": "g6dzY2hlbWFzkKpwcm9qZWN0aW9upmhlYWRlcqpkZXNjZW5kaW5nwg==",
diff --git a/packages/cultnet-rs/contracts/cultnet/interop/selection-vectors.fixture.json b/packages/cultnet-rs/contracts/cultnet/interop/selection-vectors.fixture.json
index 1ba62a9e..7e94fd7b 100644
--- a/packages/cultnet-rs/contracts/cultnet/interop/selection-vectors.fixture.json
+++ b/packages/cultnet-rs/contracts/cultnet/interop/selection-vectors.fixture.json
@@ -93,6 +93,13 @@
     },
     {
       "schema": "leaf_a", "key": "aa-tie-schema", "ordinal": 15, "fields": { "kind": "tie-schema", "mass": "1" }
+    },
+    {
+      "//": "R-AO, 2026-09-23: 'dup-key' already carries two rows (leaf_a ordinal 11, leaf_b ordinal 12) - both are in citer's Design role's declared target ([leaf_a, leaf_b], unlike citer_narrow's narrow_ref above, which only ever had one in-target candidate at a shared key). This citer is the first row in this file (hence in both runtimes' row order) to name 'dup-key' through Design, so resolving it must deterministically pick the leaf_a row - the first in-target candidate in the caller's order - never the leaf_b row, in both runtimes.",
+      "schema": "citer",
+      "key": "citer-both-in-target",
+      "ordinal": 16,
+      "references": [ { "role": "Design", "targetKey": "dup-key" } ]
     }
   ]
 }
diff --git a/tests/GameCult.Networking.Tests/SelectionParityVectorTests.cs b/tests/GameCult.Networking.Tests/SelectionParityVectorTests.cs
index b8d1c233..e9a070fc 100644
--- a/tests/GameCult.Networking.Tests/SelectionParityVectorTests.cs
+++ b/tests/GameCult.Networking.Tests/SelectionParityVectorTests.cs
@@ -277,6 +277,16 @@ namespace GameCult.Networking.Tests
                 Keys = new[] { "narrow-citer-accepted" },
                 Cites = new CultNetCitation { Target = new CultNetRecordRef { SchemaId = schemas["leaf_a"].SchemaId, RecordKey = "dup-key" }, Role = "narrow_ref" }
             });
+            // R-AO: "dup-key" has two in-target candidates for citer's Design role (unlike
+            // citer_narrow's narrow_ref above, which only ever had one). citer-both-in-target is the
+            // first row in the fixture file (and so in both runtimes' row order) to name it through
+            // Design - resolution must deterministically pick the first in-target candidate in that
+            // order, the leaf_a row (ordinal 11), never the leaf_b row (ordinal 12) sharing the key.
+            yield return ("shared_key_design_resolves_the_first_in_target_candidate_in_row_order", new CultNetSelection
+            {
+                Keys = new[] { "citer-both-in-target" },
+                Cites = new CultNetCitation { Target = new CultNetRecordRef { SchemaId = schemas["leaf_a"].SchemaId, RecordKey = "dup-key" }, Role = "Design" }
+            });
         }
 
         // R-AF: the shared-key shape's other direction - the only row at the declared edge's key is