fix(coding): preserve runtime model and failure contracts

electron/coding-runtime/in-memory-conversation-runtime.ts

@@ -2,8 +2,6 @@ import type {
   CodingConversationRuntime,
   CodingRuntimeCommand,
   CodingRuntimeDiagnostics,
-  CodingRuntimeErrorCode,
-  CodingRuntimePublicError,
   ConversationModelState,
   ConversationInteraction,
   ConversationInteractionResponse,
@@ -22,22 +20,14 @@ import type {
   SetConversationModelInput,
   SetThinkingLevelInput,
 } from './contracts';
+import { CodingRuntimeContractError } from './runtime-errors';
+export { CodingRuntimeContractError } from './runtime-errors';
 import {
   createConversationReducerState,
   reduceConversationPatch,
   type ConversationReducerState,
 } from './conversation-reducer';
 
-export class CodingRuntimeContractError extends Error {
-  readonly publicError: CodingRuntimePublicError;
-
-  constructor(code: CodingRuntimeErrorCode, message: string, recoverable: boolean) {
-    super(message);
-    this.name = 'CodingRuntimeContractError';
-    this.publicError = { code, message, recoverable };
-  }
-}
-
 export interface InMemoryConversationRuntimeOptions {
   snapshots?: ConversationSnapshot[];
   commands?: CodingRuntimeCommand[];