feat(ai-chat): durable detached agent runs — phase 1 (#184/#234)

Squashed for a clean rebase onto develop (was 19 commits; the reviewer approved
the net diff at fb246080). Detaches an agent run from the HTTP request/browser
window: a run is a first-class lifecycle object (ai_chat_runs), a browser
disconnect no longer kills it, a concurrent-run insert-gate prevents double runs,
and a reopened chat live-follows a still-running run via a polled observer merge.

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

apps/server/src/database/database.module.ts

@@ -31,6 +31,7 @@ import { FavoriteRepo } from '@docmost/db/repos/favorite/favorite.repo';
 import { TemplateRepo } from '@docmost/db/repos/template/template.repo';
 import { AiChatRepo } from '@docmost/db/repos/ai-chat/ai-chat.repo';
 import { AiChatMessageRepo } from '@docmost/db/repos/ai-chat/ai-chat-message.repo';
+import { AiChatRunRepo } from '@docmost/db/repos/ai-chat/ai-chat-run.repo';
 import { AiChatPageSnapshotRepo } from '@docmost/db/repos/ai-chat/ai-chat-page-snapshot.repo';
 import { AiProviderCredentialsRepo } from '@docmost/db/repos/ai-chat/ai-provider-credentials.repo';
 import { AiMcpServerRepo } from '@docmost/db/repos/ai-chat/ai-mcp-server.repo';
@@ -105,6 +106,7 @@ import { normalizePostgresUrl } from '../common/helpers';
     TemplateRepo,
     AiChatRepo,
     AiChatMessageRepo,
+    AiChatRunRepo,
     AiChatPageSnapshotRepo,
     AiProviderCredentialsRepo,
     AiMcpServerRepo,
@@ -139,6 +141,7 @@ import { normalizePostgresUrl } from '../common/helpers';
     TemplateRepo,
     AiChatRepo,
     AiChatMessageRepo,
+    AiChatRunRepo,
     AiChatPageSnapshotRepo,
     AiProviderCredentialsRepo,
     AiMcpServerRepo,

apps/server/src/database/migrations/20260627T130000-ai-chat-runs.ts

@@ -0,0 +1,106 @@
+import { type Kysely, sql } from 'kysely';
+
+/**
+ * `ai_chat_runs` — the agent RUN as a first-class, server-side lifecycle object
+ * (#184 phase 1: autonomous agent runs detached from the browser window).
+ *
+ * Until now an agent turn lived ONLY as long as the HTTP request was open
+ * (`res.hijack()` in ai-chat.controller.ts); a browser disconnect aborted it.
+ * This table makes a turn a persistent object the server owns: it is created
+ * when a run starts (inserted directly as 'running' in phase 1 — 'pending' is
+ * only this column's default + a reserved value, never written by code yet) and
+ * advances to succeeded|failed|aborted, surviving the subscriber (browser) going
+ * away when it settles. The DB is the source of
+ * truth — a later client reconnects/sees the result by reading this row plus the
+ * assistant message it projects (`assistant_message_id`).
+ *
+ * The assistant message row (#183 step-granular durability) is the PROJECTION of
+ * a run's output; this row is the run's LIFECYCLE. They are linked by
+ * `assistant_message_id` (SET NULL if the message is later pruned).
+ *
+ * `status`  : 'pending' | 'running' | 'succeeded' | 'failed' | 'aborted'.
+ * `trigger` : 'user' | 'autostart' | 'schedule' | 'api' | 'continue' — only
+ *             'user' is produced in phase 1; the others are reserved for the
+ *             autonomy triggers deferred to phase 2 so they need no later
+ *             migration.
+ *
+ * ONE ACTIVE RUN PER CHAT is enforced by a partial unique index on `chat_id`
+ * WHERE status IN ('pending','running'): an autonomous run and a user run can
+ * never trample each other on the same chat. Settled runs (succeeded/failed/
+ * aborted) are excluded from the index so a chat can accumulate any number of
+ * historical runs.
+ */
+export async function up(db: Kysely<any>): Promise<void> {
+  await db.schema
+    .createTable('ai_chat_runs')
+    .ifNotExists()
+    .addColumn('id', 'uuid', (col) =>
+      col.primaryKey().defaultTo(sql`gen_uuid_v7()`),
+    )
+    .addColumn('chat_id', 'uuid', (col) =>
+      col.references('ai_chats.id').onDelete('cascade').notNull(),
+    )
+    .addColumn('workspace_id', 'uuid', (col) =>
+      col.references('workspaces.id').onDelete('cascade').notNull(),
+    )
+    // The human who triggered the run (audit). SET NULL on user deletion so the
+    // run history outlives its author; NULL is also the natural value for a
+    // future system/cron/api trigger with no human actor.
+    .addColumn('created_by', 'uuid', (col) =>
+      col.references('users.id').onDelete('set null'),
+    )
+    // The assistant message this run materializes (the #183 projection). SET NULL
+    // if that message row is later deleted; nullable because the run row is
+    // created a moment BEFORE the assistant row is seeded.
+    .addColumn('assistant_message_id', 'uuid', (col) =>
+      col.references('ai_chat_messages.id').onDelete('set null'),
+    )
+    .addColumn('trigger', 'varchar(20)', (col) =>
+      col.notNull().defaultTo('user'),
+    )
+    .addColumn('status', 'varchar(20)', (col) =>
+      col.notNull().defaultTo('pending'),
+    )
+    // Terminal error message for a failed run (provider/transport cause),
+    // mirroring the assistant message's metadata.error.
+    .addColumn('error', 'text', (col) => col)
+    // Number of agent steps finished so far (kept monotonic with the projection).
+    .addColumn('step_count', 'integer', (col) => col.notNull().defaultTo(0))
+    // Set when an EXPLICIT user stop is requested (distinct from a mere browser
+    // disconnect, which never stops a run). The runner aborts the turn and the
+    // run settles as 'aborted'.
+    .addColumn('stop_requested_at', 'timestamptz', (col) => col)
+    .addColumn('started_at', 'timestamptz', (col) => col)
+    .addColumn('finished_at', 'timestamptz', (col) => col)
+    .addColumn('created_at', 'timestamptz', (col) =>
+      col.notNull().defaultTo(sql`now()`),
+    )
+    .addColumn('updated_at', 'timestamptz', (col) =>
+      col.notNull().defaultTo(sql`now()`),
+    )
+    .execute();
+
+  // Reconnect / "latest run for this chat" reads hit chat_id first.
+  await db.schema
+    .createIndex('ai_chat_runs_chat_id_idx')
+    .ifNotExists()
+    .on('ai_chat_runs')
+    .column('chat_id')
+    .execute();
+
+  // One ACTIVE run per chat (advisory at the DB level): a second pending/running
+  // run on the same chat is rejected, so a user turn and an autonomous turn can
+  // never race on the same chat. Partial so settled runs do not collide.
+  await db.schema
+    .createIndex('ai_chat_runs_one_active_per_chat')
+    .ifNotExists()
+    .on('ai_chat_runs')
+    .column('chat_id')
+    .unique()
+    .where(sql.ref('status'), 'in', sql`('pending','running')`)
+    .execute();
+}
+
+export async function down(db: Kysely<any>): Promise<void> {
+  await db.schema.dropTable('ai_chat_runs').execute();
+}

apps/server/src/database/repos/ai-chat/ai-chat-message.repo.ts

@@ -121,6 +121,23 @@ export class AiChatMessageRepo {
     return rows.reverse();
   }
 
+  /** Fetch a single message by id + workspace (e.g. a run's projection row for
+   *  the #184 reconnect read). Returns undefined when nothing matches. */
+  async findById(
+    id: string,
+    workspaceId: string,
+    trx?: KyselyTransaction,
+  ): Promise<AiChatMessage | undefined> {
+    const db = dbOrTx(this.db, trx);
+    return db
+      .selectFrom('aiChatMessages')
+      .select(this.baseFields)
+      .where('id', '=', id)
+      .where('workspaceId', '=', workspaceId)
+      .where('deletedAt', 'is', null)
+      .executeTakeFirst();
+  }
+
   async insert(
     insertable: InsertableAiChatMessage,
     trx?: KyselyTransaction,

apps/server/src/database/repos/ai-chat/ai-chat-run.repo.spec.ts

@@ -0,0 +1,82 @@
+import { AiChatRunRepo, SWEEP_RUN_STALE_MS } from './ai-chat-run.repo';
+import type { KyselyDB } from '../../types/kysely.types';
+
+/**
+ * Unit coverage for AiChatRunRepo.sweepRunning over a chainable builder mock (no
+ * live DB). The F1 invariant under test (DECISION C): the BOOT sweep is
+ * UNCONDITIONAL — it adds NO `updatedAt <` predicate, so a fresh 'running' run
+ * (updatedAt = now) IS settled rather than skipped by a staleness window. The
+ * window is added ONLY when an explicit `staleMs` is supplied (the future phase-2
+ * multi-instance timer sweep). We assert the EXACT predicates the spec mandates.
+ */
+describe('AiChatRunRepo.sweepRunning', () => {
+  type Recorded = {
+    table?: string;
+    set?: Record<string, unknown>;
+    wheres: Array<[string, string, unknown]>;
+    returning?: string;
+  };
+
+  function makeDb(swept: Array<{ id: string }>): {
+    db: KyselyDB;
+    rec: Recorded;
+  } {
+    const rec: Recorded = { wheres: [] };
+    const builder: Record<string, unknown> = {};
+    builder.set = (v: Record<string, unknown>) => {
+      rec.set = v;
+      return builder;
+    };
+    builder.where = (col: string, op: string, val: unknown) => {
+      rec.wheres.push([col, op, val]);
+      return builder;
+    };
+    builder.returning = (col: string) => {
+      rec.returning = col;
+      return builder;
+    };
+    builder.execute = () => Promise.resolve(swept);
+    const db = {
+      updateTable: (table: string) => {
+        rec.table = table;
+        return builder;
+      },
+    } as unknown as KyselyDB;
+    return { db, rec };
+  }
+
+  it('F1: the boot sweep (no staleMs) is UNCONDITIONAL — only a status filter, NO updatedAt window', async () => {
+    const { db, rec } = makeDb([{ id: 'r1' }, { id: 'r2' }]);
+    const repo = new AiChatRunRepo(db);
+
+    const swept = await repo.sweepRunning();
+
+    expect(swept).toBe(2);
+    expect(rec.table).toBe('aiChatRuns');
+    // The status filter is always present...
+    expect(rec.wheres).toContainEqual([
+      'status',
+      'in',
+      expect.arrayContaining(['pending', 'running']),
+    ]);
+    // ...but a fresh 'running' run (updatedAt = now) must NOT be skipped: no
+    // updatedAt predicate at all on the boot path.
+    expect(rec.wheres.some(([col]) => col === 'updatedAt')).toBe(false);
+    // It flips to 'aborted' and stamps finishedAt.
+    expect(rec.set).toEqual(
+      expect.objectContaining({ status: 'aborted', finishedAt: expect.any(Date) }),
+    );
+  });
+
+  it('phase-2 path: an explicit staleMs reintroduces the updatedAt window', async () => {
+    const { db, rec } = makeDb([]);
+    const repo = new AiChatRunRepo(db);
+
+    await repo.sweepRunning({ staleMs: SWEEP_RUN_STALE_MS });
+
+    const updatedAtWhere = rec.wheres.find(([col]) => col === 'updatedAt');
+    expect(updatedAtWhere).toBeDefined();
+    expect(updatedAtWhere![1]).toBe('<');
+    expect(updatedAtWhere![2]).toBeInstanceOf(Date);
+  });
+});

apps/server/src/database/repos/ai-chat/ai-chat-run.repo.ts

@@ -0,0 +1,212 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { InjectKysely } from 'nestjs-kysely';
+import { sql } from 'kysely';
+import { KyselyDB, KyselyTransaction } from '../../types/kysely.types';
+import { dbOrTx } from '../../utils';
+import {
+  AiChatRun,
+  InsertableAiChatRun,
+} from '@docmost/db/types/entity.types';
+
+// Statuses that count as "the run is still live" (an autonomous and a user run
+// must never both be live on one chat — enforced by the partial unique index and
+// checked here for friendly 409s before the insert races the constraint).
+export const ACTIVE_RUN_STATUSES = ['pending', 'running'] as const;
+
+// Crash-recovery sweep recency threshold (mirrors AiChatMessageRepo.sweepStreaming,
+// #183): when a staleness window is supplied, a 'running'/'pending' run is only
+// swept to 'aborted' once it has been UNTOUCHED for this long, so a sibling
+// replica's boot-sweep can never abort a run another replica is actively
+// executing. The runner bumps `updatedAt` on every step, so a live run never
+// matches. PHASE 1 is single-process and the boot sweep passes NO window (every
+// dangling run is settled unconditionally — see sweepRunning / F1). This constant
+// is the window to reintroduce for the phase-2 multi-instance timer sweep.
+export const SWEEP_RUN_STALE_MS = 10 * 60 * 1000; // 10 minutes
+
+/**
+ * Repository for `ai_chat_runs` (#184 phase 1): the agent run as a first-class,
+ * server-side lifecycle object detached from the HTTP request. The run row is the
+ * point a client subscribes/reconnects to (by `id` or by chat); the assistant
+ * message it links to (`assistantMessageId`) is the #183 projection of its output.
+ */
+@Injectable()
+export class AiChatRunRepo {
+  private readonly logger = new Logger(AiChatRunRepo.name);
+
+  private baseFields: Array<keyof AiChatRun> = [
+    'id',
+    'chatId',
+    'workspaceId',
+    'createdBy',
+    'assistantMessageId',
+    'trigger',
+    'status',
+    'error',
+    'stepCount',
+    'stopRequestedAt',
+    'startedAt',
+    'finishedAt',
+    'createdAt',
+    'updatedAt',
+  ];
+
+  constructor(@InjectKysely() private readonly db: KyselyDB) {}
+
+  async insert(
+    insertable: InsertableAiChatRun,
+    trx?: KyselyTransaction,
+  ): Promise<AiChatRun> {
+    const db = dbOrTx(this.db, trx);
+    return db
+      .insertInto('aiChatRuns')
+      .values(insertable)
+      .returning(this.baseFields)
+      .executeTakeFirst();
+  }
+
+  async findById(
+    id: string,
+    workspaceId: string,
+    trx?: KyselyTransaction,
+  ): Promise<AiChatRun | undefined> {
+    const db = dbOrTx(this.db, trx);
+    return db
+      .selectFrom('aiChatRuns')
+      .select(this.baseFields)
+      .where('id', '=', id)
+      .where('workspaceId', '=', workspaceId)
+      .executeTakeFirst();
+  }
+
+  /** The currently-active (pending|running) run for a chat, if any. At most one
+   *  exists thanks to the partial unique index. */
+  async findActiveByChat(
+    chatId: string,
+    workspaceId: string,
+    trx?: KyselyTransaction,
+  ): Promise<AiChatRun | undefined> {
+    const db = dbOrTx(this.db, trx);
+    return db
+      .selectFrom('aiChatRuns')
+      .select(this.baseFields)
+      .where('chatId', '=', chatId)
+      .where('workspaceId', '=', workspaceId)
+      .where('status', 'in', ACTIVE_RUN_STATUSES as unknown as string[])
+      .executeTakeFirst();
+  }
+
+  /** The most-recent run for a chat (active or settled) — the reconnect target. */
+  async findLatestByChat(
+    chatId: string,
+    workspaceId: string,
+    trx?: KyselyTransaction,
+  ): Promise<AiChatRun | undefined> {
+    const db = dbOrTx(this.db, trx);
+    return db
+      .selectFrom('aiChatRuns')
+      .select(this.baseFields)
+      .where('chatId', '=', chatId)
+      .where('workspaceId', '=', workspaceId)
+      .orderBy('createdAt', 'desc')
+      .orderBy('id', 'desc')
+      .limit(1)
+      .executeTakeFirst();
+  }
+
+  /**
+   * Patch a run by id + workspace; always bumps `updatedAt`. Used for every
+   * lifecycle transition (mark running, link the assistant message, bump
+   * step_count, finalize succeeded/failed/aborted). Returns the updated row or
+   * undefined when nothing matched (e.g. a foreign workspace).
+   */
+  async update(
+    id: string,
+    workspaceId: string,
+    patch: Partial<{
+      status: string;
+      error: string | null;
+      stepCount: number;
+      assistantMessageId: string | null;
+      stopRequestedAt: Date | null;
+      startedAt: Date | null;
+      finishedAt: Date | null;
+    }>,
+    trx?: KyselyTransaction,
+  ): Promise<AiChatRun | undefined> {
+    const db = dbOrTx(this.db, trx);
+    return db
+      .updateTable('aiChatRuns')
+      .set({ ...(patch as Record<string, unknown>), updatedAt: new Date() })
+      .where('id', '=', id)
+      .where('workspaceId', '=', workspaceId)
+      .returning(this.baseFields)
+      .executeTakeFirst();
+  }
+
+  /**
+   * Mark an EXPLICIT stop request on an active run (distinct from a browser
+   * disconnect, which never stops a run). Stamps `stop_requested_at` ONLY while
+   * the run is still active, so a late stop on an already-settled run is a no-op.
+   * Returns the row when a stop was recorded, else undefined (nothing active).
+   */
+  async markStopRequested(
+    id: string,
+    workspaceId: string,
+    trx?: KyselyTransaction,
+  ): Promise<AiChatRun | undefined> {
+    const db = dbOrTx(this.db, trx);
+    return db
+      .updateTable('aiChatRuns')
+      .set({ stopRequestedAt: new Date(), updatedAt: new Date() })
+      .where('id', '=', id)
+      .where('workspaceId', '=', workspaceId)
+      .where('status', 'in', ACTIVE_RUN_STATUSES as unknown as string[])
+      .returning(this.baseFields)
+      .executeTakeFirst();
+  }
+
+  /**
+   * Crash-recovery sweep (mirrors AiChatMessageRepo.sweepStreaming): flip every
+   * run still left pending/running — a run whose process died before reaching a
+   * terminal status — to 'aborted', stamping `finished_at`. Returns the number
+   * swept. Workspace-wide on purpose (a crash can dangle runs in any workspace).
+   *
+   * F1 (DECISION C): the BOOT sweep is UNCONDITIONAL — it passes no `staleMs`, so
+   * EVERY dangling run is settled regardless of how recently it was touched. On a
+   * fresh single-process boot any pending|running run is definitionally hung (no
+   * runner is alive to own it), so a fast restart (deploy/OOM within minutes of
+   * the last step) no longer leaves a run stuck 'running' forever — which would
+   * make the one-active-run gate 409 every future turn in that chat.
+   *
+   * The optional `staleMs` window is reintroduced ONLY for the future phase-2
+   * multi-instance timer sweep (see {@link SWEEP_RUN_STALE_MS}): there a booting
+   * replica must NOT abort a run another replica is actively executing, so it
+   * sweeps only runs UNTOUCHED past the window. Phase 1 is single-process, so the
+   * boot path supplies no window.
+   */
+  async sweepRunning(
+    opts: { staleMs?: number } = {},
+    trx?: KyselyTransaction,
+  ): Promise<number> {
+    const db = dbOrTx(this.db, trx);
+    const now = new Date();
+    let query = db
+      .updateTable('aiChatRuns')
+      .set({
+        status: 'aborted',
+        finishedAt: now,
+        updatedAt: now,
+        error: sql`coalesce(error, ${'Run interrupted by a server restart.'})`,
+      })
+      .where('status', 'in', ACTIVE_RUN_STATUSES as unknown as string[]);
+    // Multi-instance (phase 2) only: skip runs touched within the window so a
+    // sibling replica's live run is never aborted. Omitted on the phase-1 boot
+    // sweep -> unconditional.
+    if (typeof opts.staleMs === 'number') {
+      const staleBefore = new Date(now.getTime() - opts.staleMs);
+      query = query.where('updatedAt', '<', staleBefore);
+    }
+    const rows = await query.returning('id').execute();
+    return rows.length;
+  }
+}

apps/server/src/database/types/db.d.ts

@@ -647,6 +647,35 @@ export interface AiChatMessages {
   deletedAt: Timestamp | null;
 }
 
+// The agent RUN as a first-class server-side lifecycle object (#184 phase 1).
+// Mirrors migration 20260627T130000-ai-chat-runs.ts. A run is created when an
+// agent turn starts and survives the browser disconnecting; the DB is the source
+// of truth a later client reconnects to. `assistantMessageId` links to the #183
+// projection row (the assistant message this run materializes).
+export interface AiChatRuns {
+  id: Generated<string>;
+  chatId: string;
+  workspaceId: string;
+  // SET NULL on user deletion (the run history outlives its author); also NULL
+  // for a future non-human trigger (cron/api).
+  createdBy: string | null;
+  // The assistant message this run materializes; SET NULL if it is pruned.
+  assistantMessageId: string | null;
+  // 'user' | 'autostart' | 'schedule' | 'api' | 'continue' (only 'user' is
+  // produced in phase 1; the rest are reserved for the deferred autonomy triggers).
+  trigger: Generated<string>;
+  // 'pending' | 'running' | 'succeeded' | 'failed' | 'aborted'.
+  status: Generated<string>;
+  error: string | null;
+  stepCount: Generated<number>;
+  // Set when an EXPLICIT user stop is requested (distinct from a disconnect).
+  stopRequestedAt: Timestamp | null;
+  startedAt: Timestamp | null;
+  finishedAt: Timestamp | null;
+  createdAt: Generated<Timestamp>;
+  updatedAt: Generated<Timestamp>;
+}
+
 // Per-(chat,page) snapshot of the open page's Markdown at the END of the agent's
 // previous turn (#274). Mirrors migration 20260702T120000-ai-chat-page-snapshot.ts.
 // The next turn diffs the CURRENT Markdown against `contentMd` to surface edits a
@@ -683,6 +712,7 @@ export interface DB {
   aiAgentRoles: AiAgentRoles;
   aiChats: AiChats;
   aiChatMessages: AiChatMessages;
+  aiChatRuns: AiChatRuns;
   aiChatPageSnapshots: AiChatPageSnapshots;
   apiKeys: ApiKeys;
   attachments: Attachments;

apps/server/src/database/types/entity.types.ts

@@ -3,6 +3,7 @@ import {
   AiAgentRoles,
   AiChats,
   AiChatMessages,
+  AiChatRuns,
   AiChatPageSnapshots,
   Attachments,
   Comments,
@@ -56,10 +57,12 @@ export type UpdatableAiChat = Updateable<Omit<AiChats, 'id'>>;
 // full-text search. It is omitted from the public type so it never leaks
 // into HTTP responses or the chat history fed to the language model.
 export type AiChatMessage = Omit<Selectable<AiChatMessages>, 'tsv'>;
-export type InsertableAiChatMessage = Omit<
-  Insertable<AiChatMessages>,
-  'tsv'
->;
+export type InsertableAiChatMessage = Omit<Insertable<AiChatMessages>, 'tsv'>;
+
+// AI Chat Run (#184 phase 1): the agent run as a first-class lifecycle object,
+// detached from the HTTP request / browser window.
+export type AiChatRun = Selectable<AiChatRuns>;
+export type InsertableAiChatRun = Insertable<AiChatRuns>;
 
 // AI Chat Page Snapshot (#274): per-(chat,page) Markdown snapshot taken at the
 // end of the agent's previous turn, diffed against the current page next turn to
@@ -214,11 +217,14 @@ export type UpdatableFavorite = Updateable<Omit<Favorites, 'id'>>;
 // Page Transclusion
 export type PageTransclusion = Selectable<PageTransclusions>;
 export type InsertablePageTransclusion = Insertable<PageTransclusions>;
-export type UpdatablePageTransclusion = Updateable<Omit<PageTransclusions, 'id'>>;
+export type UpdatablePageTransclusion = Updateable<
+  Omit<PageTransclusions, 'id'>
+>;
 
 // Page Transclusion Reference
 export type PageTransclusionReference = Selectable<PageTransclusionReferences>;
-export type InsertablePageTransclusionReference = Insertable<PageTransclusionReferences>;
+export type InsertablePageTransclusionReference =
+  Insertable<PageTransclusionReferences>;
 export type UpdatablePageTransclusionReference = Updateable<
   Omit<PageTransclusionReferences, 'id'>
 >;
@@ -288,7 +294,9 @@ export type UpdatablePagePermission = Updateable<Omit<_PagePermissions, 'id'>>;
 // Page Verification
 export type PageVerification = Selectable<_PageVerifications>;
 export type InsertablePageVerification = Insertable<_PageVerifications>;
-export type UpdatablePageVerification = Updateable<Omit<_PageVerifications, 'id'>>;
+export type UpdatablePageVerification = Updateable<
+  Omit<_PageVerifications, 'id'>
+>;
 
 // Page Verifier
 export type PageVerifier = Selectable<_PageVerifiers>;