fix: retain snapshots for removed workspaces

backend/test/routes-sessions.test.ts

@@ -135,6 +135,41 @@ test("an administrator session listing retains revisions referenced by resumable
   expect(retained).toHaveBeenCalledWith([retainedRevision]);
 });
 
+test("retention scans a removed workspace's retained snapshot", async () => {
+  const retained = vi.fn(async () => {});
+  const removedRevision = "e".repeat(40);
+  const activeSnapshot = "/registry/snapshots/a/other.yaml";
+  const removedSnapshot = "/registry/snapshots/e/removed.yaml";
+  const listRetainedSnapshots = vi.fn(async () => [
+    { id: "other", commit: "a".repeat(40), state: "operational", snapshotPath: activeSnapshot },
+    { id: "removed", commit: removedRevision, state: "operational", snapshotPath: removedSnapshot },
+  ]);
+  const app = buildApp(loadConfig({ AUTH_MODE: "upstream", THT_HARNESS_DIR: "../harness" }), {
+    thtRunner: {
+      withPrincipal: () => ({
+        sessionList: async (snapshotPath: string) => snapshotPath === removedSnapshot
+          ? [{ id: "resumable", status: "closed", archived: false, workspace_revision: removedRevision }]
+          : [],
+      }),
+    } as any,
+    workspaceRegistry: {
+      list: async () => [{ id: "other", commit: "a".repeat(40), state: "operational", snapshotPath: activeSnapshot }],
+      listRetainedSnapshots,
+      reconcileSnapshotRetention: retained,
+    } as any,
+  });
+
+  const response = await app.inject({
+    method: "GET", url: "/sessions?scope=all",
+    headers: { ...aliceHeaders, "x-thoth-is-admin": "1" },
+  });
+
+  expect(response.statusCode).toBe(200);
+  expect(listRetainedSnapshots).toHaveBeenCalledOnce();
+  expect(retained).toHaveBeenCalledWith([removedRevision]);
+  expect(response.json()).toEqual([expect.objectContaining({ id: "resumable" })]);
+});
+
 test("the single local installation listing reconciles its resumable workspace pins", async () => {
   const retained = vi.fn(async () => {});
   const retainedRevision = "d".repeat(40);