diff --git a/contracts/cultnet/cultnet.witness-artifact-bundle.schema.json b/contracts/cultnet/cultnet.witness-artifact-bundle.schema.json
index 6dd6971d..936a0a04 100644
--- a/contracts/cultnet/cultnet.witness-artifact-bundle.schema.json
+++ b/contracts/cultnet/cultnet.witness-artifact-bundle.schema.json
@@ -59,6 +59,7 @@
       ],
       "additionalProperties": false,
       "properties": {
+        "id": { "type": "string", "minLength": 1 },
         "role": { "type": "string", "minLength": 1 },
         "schemaId": { "type": "string", "minLength": 1 },
         "schemaVersion": { "type": "string", "minLength": 1 },
@@ -74,6 +75,7 @@
       ],
       "additionalProperties": false,
       "properties": {
+        "id": { "type": "string", "minLength": 1 },
         "role": { "type": "string", "minLength": 1 },
         "uri": { "type": "string", "minLength": 1 },
         "mediaType": { "type": "string", "minLength": 1 },
@@ -92,6 +94,7 @@
       ],
       "additionalProperties": false,
       "properties": {
+        "id": { "type": "string", "minLength": 1 },
         "stage": { "type": "string", "minLength": 1 },
         "startedAt": { "type": "string", "minLength": 1 },
         "completedAt": { "type": "string", "minLength": 1 },
diff --git a/packages/cultnet-py/src/cultnet_py/interop_peer.py b/packages/cultnet-py/src/cultnet_py/interop_peer.py
index ba236686..e6cd4601 100644
--- a/packages/cultnet-py/src/cultnet_py/interop_peer.py
+++ b/packages/cultnet-py/src/cultnet_py/interop_peer.py
@@ -1316,6 +1316,7 @@ def witness_artifact_bundle_schema_json() -> str:
                 "required": ["role", "schemaId"],
                 "additionalProperties": False,
                 "properties": {
+                    "id": {"type": "string", "minLength": 1},
                     "role": {"type": "string", "minLength": 1},
                     "schemaId": {"type": "string", "minLength": 1},
                     "schemaVersion": {"type": "string", "minLength": 1},
@@ -1327,6 +1328,7 @@ def witness_artifact_bundle_schema_json() -> str:
                 "required": ["role", "uri", "mediaType"],
                 "additionalProperties": False,
                 "properties": {
+                    "id": {"type": "string", "minLength": 1},
                     "role": {"type": "string", "minLength": 1},
                     "uri": {"type": "string", "minLength": 1},
                     "mediaType": {"type": "string", "minLength": 1},
@@ -1340,6 +1342,7 @@ def witness_artifact_bundle_schema_json() -> str:
                 "required": ["stage", "startedAt", "completedAt", "latencyMs"],
                 "additionalProperties": False,
                 "properties": {
+                    "id": {"type": "string", "minLength": 1},
                     "stage": {"type": "string", "minLength": 1},
                     "startedAt": {"type": "string", "minLength": 1},
                     "completedAt": {"type": "string", "minLength": 1},
diff --git a/packages/cultnet-py/tests/test_cultnet.py b/packages/cultnet-py/tests/test_cultnet.py
index 475305d3..dc15224b 100644
--- a/packages/cultnet-py/tests/test_cultnet.py
+++ b/packages/cultnet-py/tests/test_cultnet.py
@@ -1870,9 +1870,9 @@ class CultNetTests(unittest.TestCase):
             witness_kind="interop-proof",
             captured_at="2026-06-13T00:00:03Z",
             subject={"documentType": "cultnet.interop-note", "subjectId": "note:python"},
-            contracts=[{"role": "payload", "schemaId": "schema-a"}],
-            artifacts=[{"role": "log", "uri": "cultcache://bundle-1/log", "mediaType": "text/plain"}],
-            timing_witnesses=[{"stage": "roundtrip", "startedAt": "2026-06-13T00:00:03Z", "completedAt": "2026-06-13T00:00:04Z", "latencyMs": 1.0}],
+            contracts=[{"id": "c0e1a2b3c4d5", "role": "payload", "schemaId": "schema-a"}],
+            artifacts=[{"id": "a0e1a2b3c4d5", "role": "log", "uri": "cultcache://bundle-1/log", "mediaType": "text/plain"}],
+            timing_witnesses=[{"id": "e0e1a2b3c4d5", "stage": "roundtrip", "startedAt": "2026-06-13T00:00:03Z", "completedAt": "2026-06-13T00:00:04Z", "latencyMs": 1.0}],
             provenance={"pipelineId": "interop", "runId": "run-1", "runtimeId": "python-test"},
         )
         payload = encode_witness_artifact_bundle_payload(bundle)
@@ -1888,6 +1888,8 @@ class CultNetTests(unittest.TestCase):
         self.assertEqual(slots[2], "2026-06-13T00:00:03Z")
         self.assertEqual(slots[3]["subjectId"], "note:python")
         self.assertEqual(slots[4][0]["schemaId"], "schema-a")
+        self.assertEqual([slots[4][0]["id"], slots[5][0]["id"], slots[6][0]["id"]], ["c0e1a2b3c4d5", "a0e1a2b3c4d5", "e0e1a2b3c4d5"])
+        self.assertEqual(typed_decoded.contracts[0]["id"], "c0e1a2b3c4d5")
         self.assertEqual(slots[5][0]["uri"], "cultcache://bundle-1/log")
         self.assertEqual(slots[6][0]["latencyMs"], 1.0)
         self.assertEqual(slots[7]["runtimeId"], "python-test")
diff --git a/packages/cultnet-ts/test/interop/cultnet-interop.test.ts b/packages/cultnet-ts/test/interop/cultnet-interop.test.ts
index 756ef97d..7eab911f 100644
--- a/packages/cultnet-ts/test/interop/cultnet-interop.test.ts
+++ b/packages/cultnet-ts/test/interop/cultnet-interop.test.ts
@@ -1232,9 +1232,9 @@ test("CultNet TS/Rust/C#/Python peers discover each other and exchange raw state
           schemaVersion: INTEROP_SCHEMA_VERSION,
           schemaId: interopNoteSchemaId,
         },
-        [{ role: "payload", schemaId: interopNoteSchemaId, schemaVersion: INTEROP_SCHEMA_VERSION }],
-        [{ role: "log", uri: "cultcache://bundle:ts-python-witness/log", mediaType: "text/plain" }],
-        [{ stage: "roundtrip", startedAt: "2026-06-13T00:00:03Z", completedAt: "2026-06-13T00:00:04Z", latencyMs: 1 }],
+        [{ id: "c0e1a2b3c4d5", role: "payload", schemaId: interopNoteSchemaId, schemaVersion: INTEROP_SCHEMA_VERSION }],
+        [{ id: "a0e1a2b3c4d5", role: "log", uri: "cultcache://bundle:ts-python-witness/log", mediaType: "text/plain" }],
+        [{ id: "e0e1a2b3c4d5", stage: "roundtrip", startedAt: "2026-06-13T00:00:03Z", completedAt: "2026-06-13T00:00:04Z", latencyMs: 1 }],
         { pipelineId: "interop", runId: "ts-python-witness", runtimeId: "ts-witness", agentId: "ts-agent" },
       ]),
       sourceRuntimeId: "ts-witness",
@@ -1252,6 +1252,7 @@ test("CultNet TS/Rust/C#/Python peers discover each other and exchange raw state
   assert.equal(witnessSlots[1], "interop-proof");
   assert.equal(witnessSlots[3].subjectId, "note:python-peer");
   assert.equal(witnessSlots[7].runtimeId, "ts-witness");
+  assert.deepEqual([witnessSlots[4][0].id, witnessSlots[5][0].id, witnessSlots[6][0].id], ["c0e1a2b3c4d5", "a0e1a2b3c4d5", "e0e1a2b3c4d5"], "element ids cross TS to Python and back");
 
   const expectedPeers = ["csharp-peer", "python-peer", "rust-peer", "ts-peer"];
 
diff --git a/src/GameCult.Networking/CultWitnessArtifactBundle.cs b/src/GameCult.Networking/CultWitnessArtifactBundle.cs
index 045ebfbb..6baa48bb 100644
--- a/src/GameCult.Networking/CultWitnessArtifactBundle.cs
+++ b/src/GameCult.Networking/CultWitnessArtifactBundle.cs
@@ -104,6 +104,10 @@ namespace GameCult.Networking
     [MessagePackObject]
     public sealed class CultWitnessContractPin
     {
+        [Key(4)]
+        [CultElementId]
+        public string Id { get; set; } = string.Empty;
+
         /// <summary>
         /// Gets or sets the contract role inside the bundle.
         /// </summary>
@@ -135,6 +139,10 @@ namespace GameCult.Networking
     [MessagePackObject]
     public sealed class CultWitnessArtifactEntry
     {
+        [Key(6)]
+        [CultElementId]
+        public string Id { get; set; } = string.Empty;
+
         /// <summary>
         /// Gets or sets the artifact role inside the witness bundle.
         /// </summary>
@@ -178,6 +186,10 @@ namespace GameCult.Networking
     [MessagePackObject]
     public sealed class CultWitnessTimingEntry
     {
+        [Key(5)]
+        [CultElementId]
+        public string Id { get; set; } = string.Empty;
+
         /// <summary>
         /// Gets or sets the pipeline stage name.
         /// </summary>