fix(page): add cycle/depth guard to recursive tree-traversal CTEs (#207)

getPageBreadCrumbs (ancestor CTE) and forceDelete (descendant CTE) used
withRecursive + unionAll with no CYCLE clause or depth cap. If a parent/child
cycle already exists in the data (e.g. one slipped in via the #7 TOCTOU race),
both queries loop forever — hang / statement timeout. Worse, the move guard
itself runs the ancestor CTE, so a cycle would disable the very guard meant to
prevent it (#207 #8).

Add a depth counter bounded by MAX_PAGE_TREE_DEPTH to both recursive CTEs; the
walk stops at the cap, so a cycle yields a bounded result instead of hanging.
Real page trees are only a few levels deep, so the cap never truncates a
legitimate result. getPageBreadCrumbs selects an explicit column list (not
selectAll) so the internal depth counter never leaks into the breadcrumb shape.

Adds an integration test that seeds an A<->B cycle directly and asserts both
getPageBreadCrumbs and forceDelete return bounded / complete under a short
connection-level statement_timeout instead of hanging.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/test/integration/page-recursive-cte-cycle-guard.int-spec.ts

@@ -0,0 +1,134 @@
+import { CamelCasePlugin, Kysely } from 'kysely';
+import { PostgresJSDialect } from 'kysely-postgres-js';
+import * as postgres from 'postgres';
+import { PageService } from 'src/core/page/services/page.service';
+import {
+  getTestDb,
+  destroyTestDb,
+  createWorkspace,
+  createSpace,
+  createPage,
+  TEST_DATABASE_URL,
+} from './db';
+
+/**
+ * #207 #8 — recursive page-tree CTEs (ancestors in getPageBreadCrumbs,
+ * descendants in forceDelete) must not hang when a parent/child cycle already
+ * exists in the data. Before the fix neither CTE had a CYCLE clause or a depth
+ * cap, so a cycle (e.g. one persisted by the #7 TOCTOU race) made withRecursive
+ * loop forever — and since the move guard itself runs the ancestor CTE, a cycle
+ * would disable the very guard meant to prevent it.
+ *
+ * The fix adds a depth counter bounded by MAX_PAGE_TREE_DEPTH to both CTEs.
+ * These tests seed an A<->B cycle directly (bypassing the guard), then run the
+ * real CTE paths against Postgres with a short connection-level statement_timeout
+ * so a regression (an unbounded CTE) fails fast as a query timeout instead of a
+ * bounded result.
+ */
+describe('recursive page-tree CTEs cycle/depth guard [integration]', () => {
+  // Upper bound on rows the depth-capped CTEs can emit for a 2-node cycle: one
+  // row per depth level 0..MAX. Kept loose so the assertion does not couple to
+  // the exact constant, only to "bounded".
+  const BOUNDED_MAX_ROWS = 20_000;
+
+  let db: Kysely<any>;
+  // Dedicated Kysely whose connections carry a short statement_timeout, so an
+  // unbounded recursive CTE aborts quickly instead of hanging the suite.
+  let timeoutDb: Kysely<any>;
+  let workspaceId: string;
+  let spaceId: string;
+
+  beforeAll(async () => {
+    db = getTestDb();
+    timeoutDb = new Kysely<any>({
+      dialect: new PostgresJSDialect({
+        postgres: postgres(TEST_DATABASE_URL, {
+          max: 2,
+          onnotice: () => {},
+          // Applied to every connection on connect: cap any single statement.
+          connection: { statement_timeout: 4000 },
+          types: {
+            bigint: {
+              to: 20,
+              from: [20, 1700],
+              serialize: (value: number) => value.toString(),
+              parse: (value: string) => Number.parseInt(value),
+            },
+          },
+        }),
+      }),
+      plugins: [new CamelCasePlugin()],
+    });
+    workspaceId = (await createWorkspace(db)).id;
+    spaceId = (await createSpace(db, workspaceId)).id;
+  });
+
+  afterAll(async () => {
+    await timeoutDb.destroy();
+    await destroyTestDb();
+  });
+
+  // Seed two fresh pages and wire them into a direct parent/child cycle,
+  // bypassing PageService.movePage's guard the way the #7 race would.
+  async function seedCycle(): Promise<{ aId: string; bId: string }> {
+    const a = await createPage(db, { workspaceId, spaceId, title: 'cycle-A' });
+    const b = await createPage(db, { workspaceId, spaceId, title: 'cycle-B' });
+    await db
+      .updateTable('pages')
+      .set({ parentPageId: b.id })
+      .where('id', '=', a.id)
+      .execute();
+    await db
+      .updateTable('pages')
+      .set({ parentPageId: a.id })
+      .where('id', '=', b.id)
+      .execute();
+    return { aId: a.id, bId: b.id };
+  }
+
+  function makeService(database: Kysely<any>): PageService {
+    const eventEmitter = { emit: () => true } as any;
+    const attachmentQueue = { add: async () => undefined } as any;
+    return new PageService(
+      undefined as any, // pageRepo (unused by these paths)
+      undefined as any, // pagePermissionRepo
+      undefined as any, // attachmentRepo
+      database as any, // db
+      undefined as any, // storageService
+      attachmentQueue, // attachmentQueue
+      undefined as any, // aiQueue
+      undefined as any, // generalQueue
+      eventEmitter, // eventEmitter
+      undefined as any, // collaborationGateway
+      undefined as any, // watcherService
+      undefined as any, // transclusionService
+    );
+  }
+
+  it('getPageBreadCrumbs returns a bounded result (no hang) when a cycle exists', async () => {
+    const { aId } = await seedCycle();
+    const service = makeService(timeoutDb);
+
+    // Must resolve (the depth cap stops the walk) rather than time out.
+    const crumbs = await service.getPageBreadCrumbs(aId);
+
+    expect(Array.isArray(crumbs)).toBe(true);
+    expect(crumbs.length).toBeGreaterThan(1);
+    expect(crumbs.length).toBeLessThanOrEqual(BOUNDED_MAX_ROWS);
+  });
+
+  it('forceDelete descendant CTE is bounded (no hang) and removes the cyclic pages', async () => {
+    const { aId, bId } = await seedCycle();
+    const service = makeService(timeoutDb);
+
+    // Must complete instead of looping on the descendant CTE.
+    await service.forceDelete(aId, workspaceId);
+
+    const survivors = await db
+      .selectFrom('pages')
+      .select('id')
+      .where('id', 'in', [aId, bId])
+      .execute();
+    expect(survivors).toHaveLength(0);
+  });
+});