diff --git a/app/models/surface-elo.ts b/app/models/surface-elo.ts
index 6267fcf..83258c2 100644
--- a/app/models/surface-elo.ts
+++ b/app/models/surface-elo.ts
@@ -8,7 +8,7 @@
 
 import { database } from "~/database/context";
 import { participantSurfaceElos, seasonParticipantSurfaceElos, seasonParticipants } from "~/database/schema";
-import { eq, sql } from "drizzle-orm";
+import { eq, inArray, sql } from "drizzle-orm";
 
 export type CourtSurface = "hard" | "clay" | "grass";
 
@@ -99,6 +99,45 @@ export async function batchUpsertSurfaceElos(
         updatedAt: sql`excluded.updated_at`,
       },
     });
+
+  // Mirror writes to the canonical participant_surface_elos table.
+  // The simulator reads from canonical, so per-window-only edits would
+  // not affect simulations. Remove the per-window path entirely in Phase 4.
+  const sps = await db
+    .select({ id: seasonParticipants.id, canonicalId: seasonParticipants.participantId })
+    .from(seasonParticipants)
+    .where(inArray(seasonParticipants.id, inputs.map((i) => i.participantId)));
+  const canonicalByInputId = new Map(sps.map((sp) => [sp.id, sp.canonicalId]));
+
+  const canonicalRows = inputs
+    .map((i) => ({
+      canonicalId: canonicalByInputId.get(i.participantId),
+      worldRanking: i.worldRanking ?? null,
+      eloHard: i.eloHard ?? null,
+      eloClay: i.eloClay ?? null,
+      eloGrass: i.eloGrass ?? null,
+    }))
+    .filter((r): r is typeof r & { canonicalId: string } => typeof r.canonicalId === "string");
+
+  if (canonicalRows.length === 0) return;
+
+  await db
+    .insert(participantSurfaceElos)
+    .values(canonicalRows.map(({ canonicalId, ...rest }) => ({
+      participantId: canonicalId,
+      ...rest,
+      updatedAt: now,
+    })))
+    .onConflictDoUpdate({
+      target: [participantSurfaceElos.participantId],
+      set: {
+        worldRanking: sql`excluded.world_ranking`,
+        eloHard: sql`excluded.elo_hard`,
+        eloClay: sql`excluded.elo_clay`,
+        eloGrass: sql`excluded.elo_grass`,
+        updatedAt: sql`excluded.updated_at`,
+      },
+    });
 }
 
 /**