fix: initialize reset transcript files

src/gateway/server.sessions.gateway-server-sessions-a.test.ts

@@ -1111,6 +1111,7 @@ describe("gateway server sessions", () => {
     expect(reset.payload?.entry.modelProvider).toBe("openai");
     expect(reset.payload?.entry.model).toBe("gpt-test-a");
     expect(reset.payload?.entry.contextTokens).toBeUndefined();
+    await expect(fs.stat(reset.payload?.entry.sessionFile as string)).resolves.toBeTruthy();
 
     ws.close();
   });

src/gateway/session-reset-service.ts

@@ -1,4 +1,7 @@
 import { randomUUID } from "node:crypto";
+import fs from "node:fs";
+import path from "node:path";
+import { CURRENT_SESSION_VERSION } from "@mariozechner/pi-coding-agent";
 import { getAcpSessionManager } from "../acp/control-plane/manager.js";
 import { resolveDefaultAgentId } from "../agents/agent-scope.js";
 import { clearBootstrapSnapshot } from "../agents/bootstrap-cache.js";
@@ -387,6 +390,20 @@ export async function performGatewaySessionReset(params: {
     agentId: target.agentId,
     reason: "reset",
   });
+  fs.mkdirSync(path.dirname(next.sessionFile as string), { recursive: true });
+  if (!fs.existsSync(next.sessionFile as string)) {
+    const header = {
+      type: "session",
+      version: CURRENT_SESSION_VERSION,
+      id: next.sessionId,
+      timestamp: new Date().toISOString(),
+      cwd: process.cwd(),
+    };
+    fs.writeFileSync(next.sessionFile as string, `${JSON.stringify(header)}\n`, {
+      encoding: "utf-8",
+      mode: 0o600,
+    });
+  }
   if (hadExistingEntry) {
     await emitSessionUnboundLifecycleEvent({
       targetSessionKey: target.canonicalKey ?? params.key,