fix: keep codex stdio server alive across turns

src/backend/adapter.ts

@@ -1,5 +1,5 @@
 import type { BackendTurnResult, CommandRecord, RunRecord } from "../common/types.js";
-import { runCodexStdioTurn, type CodexStdioTurnOptions } from "./codex-stdio.js";
+import { CodexStdioBackendSession, runCodexStdioTurn, type CodexStdioTurnOptions } from "./codex-stdio.js";
 import { backendProfileSpec } from "../common/backend-profiles.js";
 
 export interface BackendAdapterOptions {
@@ -11,11 +11,30 @@ export interface BackendAdapterOptions {
   env?: NodeJS.ProcessEnv;
 }
 
+export interface BackendSession {
+  runTurn(run: RunRecord, command: CommandRecord, options?: BackendAdapterOptions): Promise<BackendTurnResult>;
+  close(): Promise<BackendTurnResult["events"]>;
+}
+
 export async function runBackendTurn(run: RunRecord, command: CommandRecord, options: BackendAdapterOptions = {}): Promise<BackendTurnResult> {
   const spec = backendProfileSpec(run.backendProfile);
   if (!spec || spec.backendKind !== "codex-app-server-stdio") {
     return { terminalStatus: "failed", failureKind: "backend-failed", failureMessage: `unsupported backendProfile ${run.backendProfile}`, events: [{ type: "error", payload: { failureKind: "backend-failed", backendProfile: run.backendProfile } }] };
   }
+  return runCodexStdioTurn(backendTurnOptions(run, command, options));
+}
+
+export function createBackendSession(run: RunRecord, options: BackendAdapterOptions = {}): BackendSession | null {
+  const spec = backendProfileSpec(run.backendProfile);
+  if (!spec || spec.backendKind !== "codex-app-server-stdio") return null;
+  const session = new CodexStdioBackendSession();
+  return {
+    runTurn: async (nextRun, command, turnOptions = {}) => session.runTurn(backendTurnOptions(nextRun, command, { ...options, ...turnOptions })),
+    close: async () => session.close(),
+  };
+}
+
+export function backendTurnOptions(run: RunRecord, command: CommandRecord, options: BackendAdapterOptions = {}): CodexStdioTurnOptions {
   const prompt = typeof command.payload.prompt === "string" ? command.payload.prompt : JSON.stringify(command.payload);
   const turnOptions: CodexStdioTurnOptions = {
     backendProfile: run.backendProfile,
@@ -33,5 +52,5 @@ export async function runBackendTurn(run: RunRecord, command: CommandRecord, opt
   if (options.env) turnOptions.env = options.env;
   if (options.codexHome) turnOptions.codexHome = options.codexHome;
   if (options.abortSignal) turnOptions.abortSignal = options.abortSignal;
-  return runCodexStdioTurn(turnOptions);
+  return turnOptions;
 }