diff --git a/app/models/__tests__/surface-elo.test.ts b/app/models/__tests__/surface-elo.test.ts
index 307a87a..017543b 100644
--- a/app/models/__tests__/surface-elo.test.ts
+++ b/app/models/__tests__/surface-elo.test.ts
@@ -42,10 +42,10 @@ describe("getSurfaceEloMap", () => {
     expect(result.size).toBe(0);
   });
 
-  it("returns a Map keyed by participantId", async () => {
+  it("returns a Map keyed by seasonParticipantId", async () => {
     mockDb.where.mockResolvedValue([
-      { participantId: "p1", worldRanking: 1, eloHard: 1800, eloClay: 1700, eloGrass: 1600 },
-      { participantId: "p2", worldRanking: null, eloHard: null, eloClay: 1750, eloGrass: null },
+      { seasonParticipantId: "p1", worldRanking: 1, eloHard: 1800, eloClay: 1700, eloGrass: 1600 },
+      { seasonParticipantId: "p2", worldRanking: null, eloHard: null, eloClay: 1750, eloGrass: null },
     ]);
     const result = await getSurfaceEloMap("season-1");
     expect(result.size).toBe(2);
@@ -55,7 +55,7 @@ describe("getSurfaceEloMap", () => {
 
   it("preserves null surface Elos (does not coerce to 0)", async () => {
     mockDb.where.mockResolvedValue([
-      { participantId: "p1", worldRanking: null, eloHard: null, eloClay: null, eloGrass: null },
+      { seasonParticipantId: "p1", worldRanking: null, eloHard: null, eloClay: null, eloGrass: null },
     ]);
     const result = await getSurfaceEloMap("season-1");
     const entry = result.get("p1");
@@ -72,7 +72,13 @@ describe("batchUpsertSurfaceElos", () => {
     expect(mockDb.insert).not.toHaveBeenCalled();
   });
 
-  it("calls insert with the correct values", async () => {
+  it("calls insert with the correct values on the per-window table", async () => {
+    // The function first upserts to the per-window table, then reads
+    // season_participants for canonical-id lookup. Make the follow-up select
+    // return empty so the canonical write path short-circuits and we only
+    // observe the per-window insert in this assertion.
+    mockDb.where.mockResolvedValue([]);
+
     const inputs = [
       { participantId: "p1", sportsSeasonId: "s1", worldRanking: 1, eloHard: 1800, eloClay: 1700, eloGrass: 1600 },
       { participantId: "p2", sportsSeasonId: "s1", worldRanking: null, eloHard: null, eloClay: 1750, eloGrass: undefined },
@@ -95,11 +101,36 @@ describe("batchUpsertSurfaceElos", () => {
   });
 
   it("uses onConflictDoUpdate for upsert behaviour", async () => {
+    mockDb.where.mockResolvedValue([]); // no canonical links; only per-window write
+
     await batchUpsertSurfaceElos([
       { participantId: "p1", sportsSeasonId: "s1", worldRanking: 5, eloHard: 2000 },
     ]);
     expect(mockDb.onConflictDoUpdate).toHaveBeenCalledOnce();
   });
+
+  it("mirrors writes to canonical participant_surface_elos when linked", async () => {
+    // season_participants lookup returns canonical links for p1 only.
+    mockDb.where.mockResolvedValue([
+      { id: "p1", canonicalId: "canon-1" },
+    ]);
+
+    await batchUpsertSurfaceElos([
+      { participantId: "p1", sportsSeasonId: "s1", worldRanking: 5, eloHard: 2000 },
+    ]);
+
+    // One per-window insert, one canonical insert → two inserts total.
+    expect(mockDb.insert).toHaveBeenCalledTimes(2);
+    expect(mockDb.onConflictDoUpdate).toHaveBeenCalledTimes(2);
+
+    const canonicalValues = mockDb.values.mock.calls[1][0] as Array<{
+      participantId: string;
+      eloHard: number | null;
+    }>;
+    expect(canonicalValues).toHaveLength(1);
+    expect(canonicalValues[0].participantId).toBe("canon-1");
+    expect(canonicalValues[0].eloHard).toBe(2000);
+  });
 });
 
 describe("getSurfaceElosForSeason", () => {