fix: harden resume and SSE replay

frontend/src/api/sessions.test.ts

@@ -1,6 +1,6 @@
 import { http, HttpResponse } from "msw";
 import { server } from "../test/msw";
-import { createSession, listSessions, prewarmRuntime } from "./sessions";
+import { createSession, listSessions, prewarmRuntime, resumeSession } from "./sessions";
 import {
   renameSession, setSessionGroup, archiveSession, unarchiveSession,
   deleteSession, getSessionDocuments,
@@ -36,6 +36,14 @@ test("listSessions GETs the array", async () => {
   expect(rows[0].id).toBe("s1");
 });
 
+test("resumeSession returns the typed runtime disposition", async () => {
+  server.use(http.post("http://localhost:8787/sessions/s1/resume", () =>
+    HttpResponse.json({ id: "s1", alreadyActive: false })));
+
+  const result: { id: string; alreadyActive: boolean } = await resumeSession("s1");
+  expect(result).toEqual({ id: "s1", alreadyActive: false });
+});
+
 test("renameSession POSTs {name}", async () => {
   let body: unknown = null;
   server.use(http.post("http://localhost:8787/sessions/s1/rename", async ({ request }) => {

frontend/src/api/sessions.ts

@@ -1,5 +1,5 @@
 import { apiFetch } from "./client";
-import type { SessionSummary, SessionDocument, UiResponse } from "./types";
+import type { ResumeSessionResult, SessionSummary, SessionDocument, UiResponse } from "./types";
 
 export const createSession = (i: { question: string; name?: string }) =>
   apiFetch<{ id: string }>("/sessions", { method: "POST", body: JSON.stringify(i) });
@@ -29,7 +29,7 @@ export const closeSession = (id: string) =>
   apiFetch<void>(`/sessions/${id}/close`, { method: "POST" });
 
 export const resumeSession = (id: string) =>
-  apiFetch<void>(`/sessions/${id}/resume`, { method: "POST" });
+  apiFetch<ResumeSessionResult>(`/sessions/${id}/resume`, { method: "POST" });
 
 export const renameSession = (id: string, name: string) =>
   apiFetch<void>(`/sessions/${id}/rename`, { method: "POST", body: JSON.stringify({ name }) });

frontend/src/api/types.ts

@@ -89,7 +89,7 @@ export type StreamEvent =
       };
     }
   | { type: "info"; level?: "info" | "warning" | "error"; text: string }
-  | { type: "system_event"; event: string; [k: string]: unknown };
+  | { type: "system_event"; event: string };
 
 export interface SessionSummary {
   id: string;
@@ -104,6 +104,11 @@ export interface SessionSummary {
   archived: boolean;
 }
 
+export interface ResumeSessionResult {
+  id: string;
+  alreadyActive: boolean;
+}
+
 export interface SessionDocument {
   phase: string;
   key: string;