Refactor proxy-core surfaces and transformer boundaries (#163)

* refactor: add canonical request contracts

* test: harden transformer boundary contracts

* refactor: adapt protocol transformers to canonical contract

* refactor: add cli profile registry

* refactor: extract provider profiles

* refactor: add conductor and provider executors

* refactor: add models surface

* refactor: migrate responses surface

* refactor: migrate chat surface

* refactor: migrate gemini surface

* refactor: migrate file surfaces

* test: align runtime executor undici mock

* fix: preserve compact SSE closeout payloads

* feat: support all-api-hub v2 backup imports

* fix: aggregate codex oauth SSE final payloads

* fix: harden responses SSE failure handling

src/server/transformers/shared/chatEndpointStrategy.ts

@@ -1,5 +1,5 @@
+import type { Response as UndiciResponse } from 'undici';
 import type { DownstreamFormat } from './normalized.js';
-import type { EndpointAttemptContext, EndpointRecoverResult } from '../../routes/proxy/endpointFlow.js';
 import {
   buildMinimalJsonHeadersForCompatibility,
   isEndpointDispatchDeniedError,
@@ -13,6 +13,18 @@ import {
   shouldRetryNormalizedMessagesBody,
 } from '../anthropic/messages/compatibility.js';
 
+type EndpointAttemptContext = {
+  request: CompatibilityRequest;
+  targetUrl: string;
+  response: UndiciResponse;
+  rawErrText: string;
+};
+
+type EndpointRecoverResult = {
+  upstream: UndiciResponse;
+  upstreamPath: string;
+} | null;
+
 type CompatibilityRequest = {
   endpoint: CompatibilityEndpoint;
   path: string;