feat(sdk-lib-mpc): EddsaRetrofitData type + DKG retrofit constructor + getFirstMessage routing

Add optional `retrofitData` parameter to the `DKG` constructor so parties
can seed a retrofit DKG ceremony from their existing MPCv1 scalar instead
of generating fresh key material.

- Import and store `EddsaRetrofitData` on the `DKG` class instance.
- Constructor gains a 4th optional param: `retrofitData?: EddsaRetrofitData`.
- `getFirstMessage` branches on `this.retrofitData`: when set it calls
  `wasm.ed25519_dkg_round0_import` (ships in WCI-1217) passing the
  party's clamped scalar, aggregate public key, and chain code; otherwise
  it falls through to the existing `ed25519_dkg_round0_process` path.
- Export `EddsaRetrofitData` as a named type from `eddsa-mps/index.ts`
  so callers can import it directly without going through `MPSTypes`.

The `as any` cast on the wasm call-site is intentional and temporary:
`ed25519_dkg_round0_import` will be typed once WCI-1217 lands.

Ticket: WCI-1261
Session-Id: ac4bfdd3-68f2-464c-bb89-a871628f8093
Task-Id: bf6d94d3-a6fd-40c3-9c4a-efc7ffd08fdf

Author: BitGo Agent

modules/sdk-lib-mpc/package.json

@@ -36,7 +36,7 @@
     ]
   },
   "dependencies": {
-    "@bitgo/wasm-mps": "1.10.0",
+    "@bitgo/wasm-mps": "1.12.0",
     "@noble/curves": "1.8.1",
     "@silencelaboratories/dkls-wasm-ll-node": "1.2.0-pre.4",
     "@silencelaboratories/dkls-wasm-ll-web": "1.2.0-pre.4",

modules/sdk-lib-mpc/src/tss/eddsa-mps/dkg.ts

@@ -1,7 +1,7 @@
 import type { MsgState, Share } from '@bitgo/wasm-mps';
 import { encode } from 'cbor-x';
 import crypto from 'crypto';
-import { DeserializedMessage, DeserializedMessages, DkgState, EddsaReducedKeyShare } from './types';
+import { DeserializedMessage, DeserializedMessages, DkgState, EddsaReducedKeyShare, EddsaRetrofitData } from './types';
 
 type NodeWasmer = typeof import('@bitgo/wasm-mps');
 type WebWasmer = typeof import('@bitgo/wasm-mps/web');
@@ -44,13 +44,16 @@ export class DKG {
   private shareChaincode: Buffer | null = null;
   /** Lazily loaded WASM module */
   private wasmMps: WasmMps | null = null;
+  /** Optional MPCv1 retrofit data; when set, round0 uses ed25519_dkg_round0_import */
+  private retrofitData: EddsaRetrofitData | undefined;
 
   protected dkgState: DkgState = DkgState.Uninitialized;
 
-  constructor(n: number, t: number, partyIdx: number) {
+  constructor(n: number, t: number, partyIdx: number, retrofitData?: EddsaRetrofitData) {
     this.n = n;
     this.t = t;
     this.partyIdx = partyIdx;
+    this.retrofitData = retrofitData;
   }
 
   private async loadWasmMps(): Promise<void> {
@@ -124,7 +127,18 @@ export class DKG {
     const wasm = this.getWasmMps();
     let result: MsgState;
     try {
-      result = wasm.ed25519_dkg_round0_process(this.partyIdx, this.decryptionKey!, this.otherPubKeys!, seed);
+      if (this.retrofitData) {
+        result = wasm.ed25519_dkg_round0_import(
+          this.partyIdx,
+          this.decryptionKey!,
+          this.otherPubKeys!,
+          Buffer.from(this.retrofitData.s_i_0, 'hex'),
+          Buffer.from(this.retrofitData.expectedPk, 'hex'),
+          Buffer.from(this.retrofitData.chainCode, 'hex'),
+        );
+      } else {
+        result = wasm.ed25519_dkg_round0_process(this.partyIdx, this.decryptionKey!, this.otherPubKeys!, seed);
+      }
     } catch (err) {
       throw new Error(`Error while creating the first message from party ${this.partyIdx}: ${err}`);
     }

modules/sdk-lib-mpc/src/tss/eddsa-mps/index.ts

@@ -3,3 +3,4 @@ export * as EddsaMPSDsg from './dsg';
 export * as MPSUtil from './util';
 export * as MPSTypes from './types';
 export * as MPSComms from './commsLayer';
+export type { EddsaRetrofitData } from './types';