diff --git a/src/expert-claim/expert-claim.service.ts b/src/expert-claim/expert-claim.service.ts
index 1a6ef96..c70de92 100644
--- a/src/expert-claim/expert-claim.service.ts
+++ b/src/expert-claim/expert-claim.service.ts
@@ -82,6 +82,8 @@ import {
   coerceDamagedPartsMediaToArray,
   normalizeCarPartDamageForExpertReply,
   normalizeDamageSelectedParts,
+  partIdentityKey,
+  partIdentityKeyFromCarPartDamage,
 } from "src/helpers/outer-damage-parts";
 import { ClaimVehicleTypeV2 } from "src/static/outer-car-parts-catalog";
 import { snapshotFromDamageExpert } from "src/helpers/expert-profile-snapshot";
@@ -2639,6 +2641,17 @@ export class ExpertClaimService {
       reply.parts?.length > 0
         ? this.validateAndNormalizeDaghiForExpertReplyV2(reply.parts)
         : [];
+
+    const ownerSelectedParts = normalizeDamageSelectedParts(
+      (claim as any)?.damage?.selectedParts,
+      carTypeSubmit,
+      (claim as any)?.damage?.selectedOuterParts,
+    );
+    const ownerSelectedIdentitySet = new Set(
+      ownerSelectedParts.map((p) => partIdentityKey(p)),
+    );
+    const seenIdentities = new Set<string>();
+
     const processedParts = daghiNormalized.map((p) => {
       let carPartDamage: Record<string, unknown>;
       try {
@@ -2653,7 +2666,31 @@ export class ExpertClaimService {
           }`,
         );
       }
-      return { ...p, carPartDamage };
+
+      const identityKey = partIdentityKeyFromCarPartDamage(carPartDamage);
+      if (!identityKey) {
+        throw new BadRequestException(
+          `Invalid carPartDamage for part ${p.partId}: cannot derive a stable identity (need a catalog id or both name and side).`,
+        );
+      }
+
+      if (
+        ownerSelectedIdentitySet.size > 0 &&
+        !ownerSelectedIdentitySet.has(identityKey)
+      ) {
+        throw new BadRequestException(
+          `Part "${identityKey}" is not in the owner's selected damaged parts; only parts the user picked (or added via objection) can be priced.`,
+        );
+      }
+
+      if (seenIdentities.has(identityKey)) {
+        throw new BadRequestException(
+          `Duplicate part submitted in expert reply: ${identityKey}.`,
+        );
+      }
+      seenIdentities.add(identityKey);
+
+      return { ...p, partId: identityKey, carPartDamage };
     });
 
     const { mixedFactorAndPrice, allFactorLines } = classifyV2ExpertPricingParts(
diff --git a/src/helpers/outer-damage-parts.ts b/src/helpers/outer-damage-parts.ts
index fe904dd..27dd684 100644
--- a/src/helpers/outer-damage-parts.ts
+++ b/src/helpers/outer-damage-parts.ts
@@ -298,6 +298,40 @@ export function partIdentityKey(p: DamageSelectedPartV2): string {
   return `${p.side}|${p.name}`;
 }
 
+/**
+ * Same canonical identity as `partIdentityKey`, but derived directly from a
+ * unified `carPartDamage` snapshot (the shape we persist on
+ * `evaluation.damageExpertReply*.parts[].carPartDamage`).
+ *
+ * Returns `null` when the input cannot produce an identity (no `id`, no
+ * `name`). Callers should treat that as an invalid expert reply line.
+ */
+export function partIdentityKeyFromCarPartDamage(
+  carPartDamage: unknown,
+): string | null {
+  if (
+    !carPartDamage ||
+    typeof carPartDamage !== "object" ||
+    Array.isArray(carPartDamage)
+  ) {
+    return null;
+  }
+  const o = carPartDamage as Record<string, unknown>;
+  const idRaw = o.id;
+  const id =
+    typeof idRaw === "number" && Number.isFinite(idRaw)
+      ? idRaw
+      : typeof idRaw === "string" &&
+          idRaw.trim() &&
+          Number.isFinite(Number(idRaw))
+        ? Number(idRaw)
+        : null;
+  const name = typeof o.name === "string" ? o.name.trim() : "";
+  const side = typeof o.side === "string" ? o.side.trim() : "";
+  if (id == null && !name) return null;
+  return partIdentityKey({ id, name, side, label_fa: "" });
+}
+
 function normPartSegment(s: string): string {
   return String(s ?? "").replace(/[^a-z0-9]/gi, "").toLowerCase();
 }