diff --git a/package.json b/package.json
index a8f7b73..2db4c22 100644
--- a/package.json
+++ b/package.json
@@ -15,6 +15,7 @@
     "test:graph-snapshot-schema": "node tests/graph-snapshot-schema.mjs",
     "test:graph-snapshot-upgrade": "node tests/graph-snapshot-upgrade.mjs",
     "test:snapshot-forward-compat": "node tests/snapshot-forward-compat.mjs",
+    "test:luker-snapshot-forward-compat": "node tests/luker-snapshot-forward-compat.mjs",
     "test:reroll-transaction-boundary": "node tests/reroll-transaction-boundary.mjs",
     "test:vector-gate": "node tests/vector-gate.mjs",
     "test:hide-engine": "node tests/hide-engine.mjs",
diff --git a/tests/luker-snapshot-forward-compat.mjs b/tests/luker-snapshot-forward-compat.mjs
new file mode 100644
index 0000000..72cc014
--- /dev/null
+++ b/tests/luker-snapshot-forward-compat.mjs
@@ -0,0 +1,99 @@
+// ST-BME restrained rebirth — Phase 3c Luker sidecar forward-compat tests.
+//
+// Luker stores the graph as a serialized graph blob inside the checkpoint, not as
+// the durable snapshot shape. This test proves the IMPORTANT property: unknown
+// future fields on graph nodes/edges survive a Luker checkpoint round-trip
+// (build -> normalize -> deserialize). It also documents the intentional boundary
+// that the sidecar ENVELOPE metadata (manifest stats, checkpoint meta) is
+// normalized/whitelisted on purpose — those are rebuildable operational metrics,
+// not graph data.
+
+import assert from "node:assert/strict";
+
+import {
+  buildLukerGraphCheckpointV2,
+  normalizeLukerGraphCheckpointV2,
+} from "../graph/graph-persistence.js";
+import {
+  addEdge,
+  addNode,
+  createEdge,
+  createNode,
+  createEmptyGraph,
+  deserializeGraph,
+} from "../graph/graph.js";
+
+// Build a graph and inject unknown FUTURE fields onto a node and an edge.
+const graph = createEmptyGraph();
+const nodeA = addNode(
+  graph,
+  createNode({ type: "char", fields: { name: "恬恬" }, seq: 1 }),
+);
+const nodeB = addNode(
+  graph,
+  createNode({ type: "event", fields: { title: "相遇" }, seq: 2 }),
+);
+// Simulate a future writer adding new fields the current build does not know.
+nodeA.futureNodeField = { trait: "playful", version: 99 };
+const edge = addEdge(
+  graph,
+  createEdge({ fromId: nodeA.id, toId: nodeB.id, relation: "participatesIn" }),
+);
+edge.futureEdgeField = "edge-keep-me";
+
+// 1. Checkpoint round-trip preserves unknown graph record fields.
+const checkpoint = buildLukerGraphCheckpointV2(graph, {
+  revision: 7,
+  chatId: "chat-luker-fc",
+  integrity: "integrity-luker",
+  reason: "test",
+});
+assert.ok(checkpoint, "checkpoint built");
+assert.ok(checkpoint.serializedGraph, "checkpoint carries serialized graph");
+
+const restored = deserializeGraph(checkpoint.serializedGraph);
+const restoredNodeA = restored.nodes.find((n) => n.id === nodeA.id);
+const restoredEdge = restored.edges.find((e) => e.fromId === nodeA.id);
+assert.ok(restoredNodeA, "node survived Luker checkpoint round-trip");
+assert.deepEqual(
+  restoredNodeA.futureNodeField,
+  { trait: "playful", version: 99 },
+  "unknown future node field preserved through Luker checkpoint",
+);
+assert.ok(restoredEdge, "edge survived Luker checkpoint round-trip");
+assert.equal(
+  restoredEdge.futureEdgeField,
+  "edge-keep-me",
+  "unknown future edge field preserved through Luker checkpoint",
+);
+console.log("  ✓ Luker checkpoint preserves unknown future graph record fields");
+
+// 2. normalize re-parse of a checkpoint payload preserves the serialized graph
+// verbatim (so unknown fields inside it are never touched by the envelope layer).
+const reNormalized = normalizeLukerGraphCheckpointV2({
+  ...checkpoint,
+  // A future writer may add an unknown ENVELOPE field. It is intentionally
+  // dropped (rebuildable operational metadata), but graph data must be intact.
+  futureEnvelopeField: "envelope-meta-can-be-dropped",
+});
+assert.equal(
+  reNormalized.serializedGraph,
+  checkpoint.serializedGraph,
+  "serialized graph blob is preserved verbatim by the envelope normalizer",
+);
+const reRestoredNode = deserializeGraph(reNormalized.serializedGraph).nodes.find(
+  (n) => n.id === nodeA.id,
+);
+assert.deepEqual(
+  reRestoredNode.futureNodeField,
+  { trait: "playful", version: 99 },
+  "graph record unknown fields still intact after envelope re-normalize",
+);
+assert.equal(
+  "futureEnvelopeField" in reNormalized,
+  false,
+  "envelope-level unknown metadata is intentionally normalized away (rebuildable)",
+);
+console.log("  ✓ Luker envelope normalize keeps graph data intact while normalizing metadata");
+
+console.log("luker-snapshot-forward-compat tests passed");