fix(sessions): persist run config on start-failure error session

packages/core/src/sessions/sessionService.ts

@@ -652,6 +652,16 @@ export class SessionService {
     return connectPromise;
   }
 
+  private stampRunConfig(session: AgentSession, params: ConnectParams): void {
+    session.adapter = params.adapter;
+    session.model = params.model;
+    session.executionMode = params.executionMode;
+    session.reasoningLevel = params.reasoningLevel;
+    if (params.initialPrompt?.length) {
+      session.initialPrompt = params.initialPrompt;
+    }
+  }
+
   private async doConnect(params: ConnectParams): Promise<void> {
     const {
       task,
@@ -693,9 +703,7 @@ export class SessionService {
         session.status = "error";
         session.errorMessage =
           "Authentication required. Please sign in to continue.";
-        if (initialPrompt?.length) {
-          session.initialPrompt = initialPrompt;
-        }
+        this.stampRunConfig(session, params);
         this.d.store.setSession(session);
         return;
       }
@@ -784,9 +792,7 @@ export class SessionService {
 
       const taskRunId = latestRun?.id ?? `error-${taskId}`;
       const session = createBaseSession(taskRunId, taskId, taskTitle);
-      if (initialPrompt?.length) {
-        session.initialPrompt = initialPrompt;
-      }
+      this.stampRunConfig(session, params);
       if (latestRun?.log_url) {
         try {
           const { rawEntries } = await this.fetchSessionLogs(

packages/core/src/sessions/sessionServiceRetryConfig.test.ts

@@ -1,4 +1,5 @@
 import type { AgentSession } from "@posthog/shared";
+import type { Task } from "@posthog/shared/domain-types";
 import { describe, expect, it, vi } from "vitest";
 import { SessionService, type SessionServiceDeps } from "./sessionService";
 
@@ -90,3 +91,77 @@ describe("SessionService.clearSessionError retry config", () => {
     );
   });
 });
+
+describe("SessionService.connectToTask start failure", () => {
+  it("persists the run configuration on the error session so retry keeps the model", async () => {
+    const setSession = vi.fn();
+    const deps = {
+      store: {
+        getSessionByTaskId: () => undefined,
+        getSessions: () => ({}),
+        setSession,
+      },
+      log: { info: vi.fn(), warn: vi.fn(), error: vi.fn(), debug: vi.fn() },
+      settings: { customInstructions: "" },
+      DEFAULT_GATEWAY_MODEL: "claude-opus-4-8",
+      // Online for the create-branch check, offline in the catch so the
+      // auto-retry loop is skipped and the stored error session is asserted.
+      getIsOnline: vi
+        .fn<() => boolean>()
+        .mockReturnValueOnce(true)
+        .mockReturnValue(false),
+      trpc: {
+        agent: {
+          start: {
+            mutate: vi
+              .fn()
+              .mockRejectedValue(new Error("session start timeout")),
+          },
+          onSessionIdleKilled: {
+            subscribe: () => ({ unsubscribe: vi.fn() }),
+          },
+        },
+      },
+    } as unknown as SessionServiceDeps;
+
+    const service = new SessionService(deps);
+    vi.spyOn(
+      service as unknown as {
+        getAuthCredentialsStatus: () => Promise<unknown>;
+      },
+      "getAuthCredentialsStatus",
+    ).mockResolvedValue({
+      kind: "ready",
+      auth: {
+        client: { createTaskRun: vi.fn().mockResolvedValue({ id: "run-1" }) },
+        apiHost: "https://app",
+        projectId: 1,
+      },
+    });
+
+    await service.connectToTask({
+      task: {
+        id: "task-1",
+        title: "Test task",
+        description: "Ship the fix",
+        latest_run: null,
+      } as unknown as Task,
+      repoPath: "/repo",
+      initialPrompt: [{ type: "text", text: "Ship the fix" }],
+      executionMode: "auto",
+      adapter: "claude",
+      model: "claude-fable-5",
+      reasoningLevel: "high",
+    });
+
+    const stored = setSession.mock.calls.at(-1)?.[0] as AgentSession;
+    expect(stored.status).toBe("error");
+    expect(stored.model).toBe("claude-fable-5");
+    expect(stored.adapter).toBe("claude");
+    expect(stored.executionMode).toBe("auto");
+    expect(stored.reasoningLevel).toBe("high");
+    expect(stored.initialPrompt).toEqual([
+      { type: "text", text: "Ship the fix" },
+    ]);
+  });
+});