fix(core): keep workspace runtime available

backend/test/routes-sessions.test.ts

@@ -364,6 +364,65 @@ test("retention scans a removed workspace's retained snapshot", async () => {
   expect(response.json()).toEqual([expect.objectContaining({ id: "resumable" })]);
 });
 
+test("active sessions remain available when retained snapshot discovery is unreadable", async () => {
+  const activeSnapshot = "/registry/snapshots/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa/active.yaml";
+  const retainedFailure = "invalid retained snapshot /registry/snapshots/secret/legacy.yaml";
+  const reconcileSnapshotRetention = vi.fn(async () => {});
+  const subscribed = vi.fn();
+  const warning = vi.spyOn(console, "warn").mockImplementation(() => {});
+  const manifest = {
+    id: "live-session", status: "open", archived: false,
+    workspace_id: "active", workspace_revision: "a".repeat(40),
+  };
+  const app = buildApp(loadConfig({ AUTH_MODE: "upstream", THT_HARNESS_DIR: "../harness" }), {
+    thtRunner: {
+      withPrincipal: () => ({
+        sessionList: async (snapshotPath: string) => {
+          expect(snapshotPath).toBe(activeSnapshot);
+          return [manifest];
+        },
+        sessionShow: async (id: string, snapshotPath?: string) => {
+          if (id === manifest.id && snapshotPath === activeSnapshot) return manifest;
+          throw new Error("session not found");
+        },
+      }),
+    } as any,
+    mgr: { get: () => undefined } as any,
+    hub: {
+      subscribe: (_id: string, _send: unknown, options: { close?: () => void }) => {
+        subscribed();
+        options.close?.();
+        return () => {};
+      },
+    } as any,
+    workspaceRegistry: {
+      listRetainedSnapshots: async () => { throw new Error(retainedFailure); },
+      list: async () => [{
+        id: "active", commit: "a".repeat(40), blob: "b".repeat(40), snapshotPath: activeSnapshot,
+      }],
+      reconcileSnapshotRetention,
+    } as any,
+  });
+
+  try {
+    const list = await app.inject({ method: "GET", url: "/sessions", headers: aliceHeaders });
+    const detail = await app.inject({ method: "GET", url: `/sessions/${manifest.id}`, headers: aliceHeaders });
+    const events = await app.inject({ method: "GET", url: `/sessions/${manifest.id}/events`, headers: aliceHeaders });
+
+    expect(list.statusCode).toBe(200);
+    expect(list.json()).toEqual([expect.objectContaining({ id: manifest.id, active: false })]);
+    expect(detail.statusCode).toBe(200);
+    expect(detail.json()).toMatchObject(manifest);
+    expect(events.statusCode).toBe(200);
+    expect(subscribed).toHaveBeenCalledOnce();
+    expect(reconcileSnapshotRetention).not.toHaveBeenCalled();
+    expect(list.body + detail.body + events.body).not.toContain(retainedFailure);
+  } finally {
+    warning.mockRestore();
+    await app.close();
+  }
+});
+
 test("the single local installation listing reconciles its resumable workspace pins", async () => {
   const retained = vi.fn(async () => {});
   const retainedRevision = "d".repeat(40);