feat(portal-bff): admin audit-log read endpoint + audit_reader-locked path (#132)

## Summary

First real consumer of the admin module — `GET /api/admin/audit`, the paginated audit-log viewer named in [ADR-0020](docs/decisions/0020-portal-admin-app.md)'s v1 catalogue. Gated by `@RequireAdmin`, reads through the `audit_reader` Postgres role only, and emits `admin.audit.query` on every call as the "fishing expedition" deterrent ADR-0020 calls out (§"Read actions are also captured … to deter fishing expeditions"). This is the BFF half of the audit-viewer chantier — the SPA screen lands later.

## What ships

### [`AuditReader`](apps/portal-bff/src/admin/audit-reader.service.ts)

- Wraps every read in a transaction whose first statement is `SET LOCAL ROLE audit_reader`. Symmetric with `AuditWriter`'s `SET LOCAL ROLE audit_writer`: the runtime role contract holds even when the BFF connection is otherwise privileged. UPDATE / INSERT / DELETE on `audit.events` fail at the Postgres level regardless of what gets through the application layer.
- Parameterised SELECT only — filter values flow into `$queryRawUnsafe`'s positional params, never concatenated into the SQL string. Subject-prefix filter uses `LIKE` with explicit `ESCAPE '\\'` and escapes `%` / `_` / `\` in the literal so an admin-side wildcard can't masquerade as a meta-character.
- COUNT(\*) + `LIMIT` / `OFFSET` pagination. Ordering is `created_at DESC, id DESC` for deterministic page boundaries on identical timestamps (UUIDs break ties).
- Hard caps `limit` at `MAX_LIMIT` (200) even if a caller bypasses the DTO — defense in depth on the BFF's event loop.

### [`AdminAuditQueryDto`](apps/portal-bff/src/admin/audit-query.dto.ts)

| Filter | Type | Notes |
| --- | --- | --- |
| `eventType` | string ≤128 | Exact match (e.g. `auth.sign_in`). |
| `actorIdHash` | string ≤128 | Exact match on the salted hash from the writer. |
| `audience` | enum | `workforce` \| `customer`. |
| `outcome` | enum | `success` \| `failure` \| `denied`. |
| `subjectPrefix` | string ≤128 | `LIKE 'prefix%'`, escaped literal. |
| `createdAtFrom` | ISO-8601 | Inclusive lower bound. |
| `createdAtTo` | ISO-8601 | Exclusive upper bound. |
| `limit` | int 1..200 | Default **50**. |
| `offset` | int ≥0 | Default **0**. |

Bound through Nest's global `ValidationPipe` — unknown query keys are rejected by `forbidNonWhitelisted` (defends against query-string smuggling), `transform: true` coerces numeric strings into numbers.

### [`AdminAuditController`](apps/portal-bff/src/admin/admin-audit.controller.ts)

`@Controller('admin/audit')` + `@RequireAdmin()` at the class level. The handler:

1. Calls `AuditReader.findEvents(filters)`.
2. Emits `admin.audit.query` with `{ filters, resultCount }` so a reviewer can see exactly what the admin searched for and how many rows came back.
3. Returns the page to the SPA.

`@RequireMfa({ freshness: 600 })` is **intentionally not applied** in v1: the admin surface already sits behind a freshly-MFA'd session at sign-in (per ADR-0020), and the per-query audit row is the deterrent. Adding `@RequireMfa` later is a one-line change — that's why the decorator was designed-in by PR #128.

### [`AuditWriter.adminAuditQuery()`](apps/portal-bff/src/audit/audit.service.ts)

New typed method using `outcome=success`. The read **happened** regardless of whether it matched rows; row count lives in `resultCount`. An `outcome=denied` from this surface is reserved for the day we add per-row authZ.

## Operational notes

- **Dev pool, `SET LOCAL ROLE` pattern** (per [ADR-0018](docs/decisions/0018-environment-configuration-strategy.md)): the BFF talks to Postgres on the shared `DATABASE_URL` pool and switches role per-transaction. In production the audit-write pool is already split via `AUDIT_DATABASE_URL`; a dedicated `audit_reader`-only pool is a future follow-up if read-side isolation is desired (the role-locking on the shared pool already prevents privilege bleed at the Postgres level).
- COUNT(\*) is fine at v1 audit volume; if the table grows past a few million rows we'll switch to keyset pagination and drop the total.

## Test plan

- [x] `pnpm nx test portal-bff` — **308 specs pass** (was 278; +30: AuditReader 10, AdminAuditController 6, AuditWriter typed event 2, DTO validation 12).
- [x] `pnpm exec nx affected -t format:check lint test build --base=origin/main` — clean (the pre-existing `_res` / `_next` warnings in `rate-limit.middleware.ts` are unrelated).
- [x] SQL-injection probe via fixture (`'; DROP TABLE events; --` as `eventType`) — value lands in the params array, SQL stays templated.
- [x] LIKE escaping verified: `%`, `_`, `\` in `subjectPrefix` are escaped to their literal form.
- [ ] e2e — pending the admin SPA + at least one `admin` Entra role assignment. Once both exist: `curl --cookie 'portal_admin_session=…' /api/admin/audit?eventType=auth.sign_in&limit=10` returns the most recent sign-ins and `psql` shows the matching `admin.audit.query` row in `audit.events`.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #132

apps/portal-bff/src/admin/admin-audit.controller.spec.ts

@@ -0,0 +1,100 @@
+import type { Request } from 'express';
+import { AdminAuditController } from './admin-audit.controller';
+import type { AdminAuditQueryDto } from './audit-query.dto';
+import type { AuditReader, AdminAuditPage } from './audit-reader.service';
+import type { AuditWriter } from '../audit/audit.service';
+
+const PAGE: AdminAuditPage = {
+  items: [
+    {
+      id: '11111111-1111-1111-1111-111111111111',
+      createdAt: '2026-05-13T10:30:00.000Z',
+      eventType: 'auth.sign_in',
+      audience: 'workforce',
+      actorIdHash: 'hash(jane)',
+      traceId: 'trace-abc',
+      subject: 'session:sid-1',
+      outcome: 'success',
+      payload: { amr: ['pwd', 'mfa'] },
+    },
+  ],
+  total: 1,
+  limit: 50,
+  offset: 0,
+};
+
+function makeReq(user?: { oid: string }): Request {
+  return { session: user !== undefined ? { user } : {} } as unknown as Request;
+}
+
+function makeFixture() {
+  const auditReader = {
+    findEvents: jest.fn().mockResolvedValue(PAGE),
+  };
+  const auditWriter = {
+    adminAuditQuery: jest.fn().mockResolvedValue(undefined),
+  };
+  const controller = new AdminAuditController(
+    auditReader as unknown as AuditReader,
+    auditWriter as unknown as AuditWriter,
+  );
+  return { controller, auditReader, auditWriter };
+}
+
+describe('AdminAuditController.list', () => {
+  it('returns the page from AuditReader', async () => {
+    const { controller } = makeFixture();
+    const page = await controller.list(makeReq({ oid: 'admin-oid' }), {} as AdminAuditQueryDto);
+    expect(page).toBe(PAGE);
+  });
+
+  it('forwards the validated DTO to AuditReader as-is', async () => {
+    const { controller, auditReader } = makeFixture();
+    const filters: AdminAuditQueryDto = {
+      eventType: 'auth.sign_in',
+      audience: 'workforce',
+      createdAtFrom: '2026-05-01T00:00:00.000Z',
+      limit: 100,
+      offset: 0,
+    };
+    await controller.list(makeReq({ oid: 'admin-oid' }), filters);
+    expect(auditReader.findEvents).toHaveBeenCalledWith(filters);
+  });
+
+  it('emits admin.audit.query with the filters + result count as deterrent', async () => {
+    const { controller, auditWriter } = makeFixture();
+    const filters: AdminAuditQueryDto = { eventType: 'auth.sign_in', limit: 50 };
+    await controller.list(makeReq({ oid: 'admin-oid' }), filters);
+    expect(auditWriter.adminAuditQuery).toHaveBeenCalledWith({
+      actor: { oid: 'admin-oid' },
+      filters: { eventType: 'auth.sign_in', limit: 50 },
+      resultCount: PAGE.items.length,
+    });
+  });
+
+  it('captures an empty filter object verbatim (the admin asked for everything)', async () => {
+    const { controller, auditWriter } = makeFixture();
+    await controller.list(makeReq({ oid: 'admin-oid' }), {} as AdminAuditQueryDto);
+    expect(auditWriter.adminAuditQuery).toHaveBeenCalledWith(
+      expect.objectContaining({ filters: {} }),
+    );
+  });
+
+  it('still returns the page when there is no session.user (defensive — guard should have caught it)', async () => {
+    const { controller, auditWriter } = makeFixture();
+    const page = await controller.list(makeReq(), {} as AdminAuditQueryDto);
+    expect(page).toBe(PAGE);
+    // No actor → no audit row. The guard is the primary gate; this
+    // branch exists so a misconfiguration doesn't crash with a
+    // misleading error.
+    expect(auditWriter.adminAuditQuery).not.toHaveBeenCalled();
+  });
+
+  it('propagates audit write failures (blocking per ADR-0013)', async () => {
+    const { controller, auditWriter } = makeFixture();
+    auditWriter.adminAuditQuery.mockRejectedValueOnce(new Error('audit_writer denied'));
+    await expect(
+      controller.list(makeReq({ oid: 'admin-oid' }), {} as AdminAuditQueryDto),
+    ).rejects.toThrow('audit_writer denied');
+  });
+});

apps/portal-bff/src/admin/admin-audit.controller.ts

@@ -0,0 +1,58 @@
+import { Controller, Get, Query, Req } from '@nestjs/common';
+import type { Request } from 'express';
+import { AuditWriter } from '../audit/audit.service';
+import { AdminAuditQueryDto } from './audit-query.dto';
+import { AuditReader, type AdminAuditPage } from './audit-reader.service';
+import { RequireAdmin } from './require-admin.decorator';
+
+/**
+ * `GET /api/admin/audit` — paginated audit-log viewer per
+ * ADR-0020's v1 admin module catalogue. Reads `audit.events` via
+ * the `audit_reader` Postgres role (locked inside the `AuditReader`
+ * service), shapes the result for SPA consumption, and emits an
+ * `admin.audit.query` row so the read itself is auditable per
+ * ADR-0020 §"Read actions are also captured … to deter fishing
+ * expeditions".
+ *
+ * The query DTO (`AdminAuditQueryDto`) carries every supported
+ * filter + pagination knob; Nest's global ValidationPipe rejects
+ * unknown keys before they reach this handler.
+ *
+ * `@RequireAdmin()` at the class level gates the route on the
+ * `admin` Entra app role per ADR-0020 §"Auth — same Entra ID".
+ * `@RequireMfa()` is not applied here in v1: the entire admin
+ * surface already sits behind a freshly-MFA'd session at the
+ * sign-in entry, and the audit row itself is the per-query
+ * deterrent. A future security review can layer `@RequireMfa`
+ * with a tighter freshness here without touching this code's
+ * shape — that's exactly why the decorator was designed-in.
+ */
+@Controller('admin/audit')
+@RequireAdmin()
+export class AdminAuditController {
+  constructor(
+    private readonly auditReader: AuditReader,
+    private readonly audit: AuditWriter,
+  ) {}
+
+  @Get()
+  async list(@Req() req: Request, @Query() filters: AdminAuditQueryDto): Promise<AdminAuditPage> {
+    const page = await this.auditReader.findEvents(filters);
+
+    // Guard guarantees `req.session.user`; we still defensively
+    // narrow rather than assert — the audit emission is what
+    // makes this read auditable, so if we somehow get here without
+    // an actor we should still surface the read (with no actor
+    // hash) rather than silently swallow it.
+    const actorOid = req.session.user?.oid;
+    if (actorOid !== undefined) {
+      await this.audit.adminAuditQuery({
+        actor: { oid: actorOid },
+        filters: { ...filters },
+        resultCount: page.items.length,
+      });
+    }
+
+    return page;
+  }
+}

apps/portal-bff/src/admin/admin.module.ts

@@ -1,8 +1,10 @@
 import { Module } from '@nestjs/common';
 import { AuthModule } from '../auth/auth.module';
+import { AdminAuditController } from './admin-audit.controller';
 import { AdminAuthController } from './admin-auth.controller';
 import { AdminController } from './admin.controller';
 import { AdminRoleGuard } from './admin-role.guard';
+import { AuditReader } from './audit-reader.service';
 
 /**
  * `AdminModule` — root of the `/api/admin/*` surface per ADR-0020.
@@ -28,7 +30,7 @@ import { AdminRoleGuard } from './admin-role.guard';
  */
 @Module({
   imports: [AuthModule],
-  controllers: [AdminController, AdminAuthController],
+  controllers: [AdminController, AdminAuthController, AdminAuditController],
-  providers: [AdminRoleGuard],
+  providers: [AdminRoleGuard, AuditReader],
 })
 export class AdminModule {}

apps/portal-bff/src/admin/audit-query.dto.spec.ts

@@ -0,0 +1,77 @@
+import { ValidationPipe } from '@nestjs/common';
+import { AdminAuditQueryDto, MAX_LIMIT } from './audit-query.dto';
+
+/**
+ * Spec exercises the DTO through Nest's `ValidationPipe` with the
+ * same options the BFF wires in `main.ts` (`whitelist`,
+ * `forbidNonWhitelisted`, `transform`) — the test is therefore a
+ * close stand-in for how the controller will see the parsed query
+ * at runtime.
+ */
+const pipe = new ValidationPipe({
+  whitelist: true,
+  forbidNonWhitelisted: true,
+  transform: true,
+});
+
+async function transform(input: unknown): Promise<AdminAuditQueryDto> {
+  return (await pipe.transform(input, {
+    type: 'query',
+    metatype: AdminAuditQueryDto,
+  })) as AdminAuditQueryDto;
+}
+
+describe('AdminAuditQueryDto', () => {
+  it('accepts an empty query (every filter is optional)', async () => {
+    await expect(transform({})).resolves.toEqual({});
+  });
+
+  it('coerces numeric strings (URL query format) into numbers', async () => {
+    const out = await transform({ limit: '25', offset: '100' });
+    expect(out.limit).toBe(25);
+    expect(out.offset).toBe(100);
+  });
+
+  it('rejects a limit above MAX_LIMIT', async () => {
+    await expect(transform({ limit: String(MAX_LIMIT + 1) })).rejects.toThrow();
+  });
+
+  it('rejects a negative offset', async () => {
+    await expect(transform({ offset: '-1' })).rejects.toThrow();
+  });
+
+  it('rejects a non-integer limit', async () => {
+    await expect(transform({ limit: '12.5' })).rejects.toThrow();
+  });
+
+  it('accepts each valid audience enum value', async () => {
+    await expect(transform({ audience: 'workforce' })).resolves.toMatchObject({
+      audience: 'workforce',
+    });
+    await expect(transform({ audience: 'customer' })).resolves.toMatchObject({
+      audience: 'customer',
+    });
+  });
+
+  it('rejects an unknown audience', async () => {
+    await expect(transform({ audience: 'visitor' })).rejects.toThrow();
+  });
+
+  it('accepts each valid outcome enum value', async () => {
+    for (const outcome of ['success', 'failure', 'denied']) {
+      await expect(transform({ outcome })).resolves.toMatchObject({ outcome });
+    }
+  });
+
+  it('rejects an ISO-8601 createdAtFrom that is not well-formed', async () => {
+    await expect(transform({ createdAtFrom: 'not-a-date' })).rejects.toThrow();
+  });
+
+  it('rejects an unknown query key (forbidNonWhitelisted)', async () => {
+    await expect(transform({ password: 'leak' })).rejects.toThrow();
+  });
+
+  it('rejects an over-long eventType (MaxLength guard)', async () => {
+    await expect(transform({ eventType: 'a'.repeat(129) })).rejects.toThrow();
+  });
+});

apps/portal-bff/src/admin/audit-query.dto.ts

@@ -0,0 +1,98 @@
+import { Type } from 'class-transformer';
+import {
+  IsEnum,
+  IsInt,
+  IsISO8601,
+  IsOptional,
+  IsString,
+  Max,
+  MaxLength,
+  Min,
+} from 'class-validator';
+
+/**
+ * Query parameters accepted by `GET /api/admin/audit`. Bound from
+ * the URL via Nest's `@Query()` + the global `ValidationPipe`
+ * (whitelist + forbidNonWhitelisted + transform). Unknown keys are
+ * rejected at the pipe — saves the controller from having to vet
+ * them and shrinks the attack surface for query-string smuggling.
+ *
+ * Pagination is offset/limit, kept simple in v1:
+ *   - `limit` defaults to 50 and is capped at {@link MAX_LIMIT} (200)
+ *     so a single request can't pull tens of thousands of rows in
+ *     one trip and stall the BFF's event loop on JSON serialisation.
+ *   - `offset` defaults to 0. For deeper pagination the SPA should
+ *     refine the date-range filter rather than walking thousands of
+ *     offsets — Postgres' offset pagination performance degrades
+ *     past a few thousand rows.
+ *
+ * Filters all OR-compose nothing — each is an additional AND clause.
+ * They are deliberately exact-match except `subjectPrefix` (which
+ * uses `LIKE 'prefix%'`) because the existing event catalogue uses
+ * structured prefixes like `session:<sid>` or `route:GET /api/...`.
+ */
+export const MAX_LIMIT = 200;
+export const DEFAULT_LIMIT = 50;
+
+/** Subset of `AuditAudience` accepted by the filter. */
+const AUDIT_AUDIENCES = ['workforce', 'customer'] as const;
+type AuditAudienceFilter = (typeof AUDIT_AUDIENCES)[number];
+
+/** Subset of `AuditOutcome` accepted by the filter. */
+const AUDIT_OUTCOMES = ['success', 'failure', 'denied'] as const;
+type AuditOutcomeFilter = (typeof AUDIT_OUTCOMES)[number];
+
+export class AdminAuditQueryDto {
+  @IsOptional()
+  @IsString()
+  @MaxLength(128)
+  eventType?: string;
+
+  @IsOptional()
+  @IsString()
+  @MaxLength(128)
+  actorIdHash?: string;
+
+  @IsOptional()
+  @IsEnum(AUDIT_AUDIENCES)
+  audience?: AuditAudienceFilter;
+
+  @IsOptional()
+  @IsEnum(AUDIT_OUTCOMES)
+  outcome?: AuditOutcomeFilter;
+
+  /**
+   * Prefix match on the `subject` column. Matches the
+   * structured-prefix convention used by the event catalogue —
+   * e.g. `session:` to find every event tied to a particular
+   * session, or `GET /api/admin/` to find every denied admin
+   * access attempt.
+   */
+  @IsOptional()
+  @IsString()
+  @MaxLength(128)
+  subjectPrefix?: string;
+
+  /** ISO-8601 lower bound on `created_at` (inclusive). */
+  @IsOptional()
+  @IsISO8601()
+  createdAtFrom?: string;
+
+  /** ISO-8601 upper bound on `created_at` (exclusive). */
+  @IsOptional()
+  @IsISO8601()
+  createdAtTo?: string;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  @Min(1)
+  @Max(MAX_LIMIT)
+  limit?: number;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  @Min(0)
+  offset?: number;
+}

apps/portal-bff/src/admin/audit-reader.service.spec.ts

@@ -0,0 +1,181 @@
+import { Test } from '@nestjs/testing';
+import { PrismaService } from 'nestjs-prisma';
+import type { AdminAuditQueryDto } from './audit-query.dto';
+import { AuditReader, type AdminAuditEventDto } from './audit-reader.service';
+
+interface MockTx {
+  $executeRawUnsafe: jest.Mock;
+  $queryRawUnsafe: jest.Mock;
+}
+
+interface MockPrisma {
+  $transaction: jest.Mock;
+  tx: MockTx;
+}
+
+function buildMocks(opts?: {
+  countRows?: Array<{ count: bigint }>;
+  selectRows?: unknown[];
+}): MockPrisma {
+  const tx: MockTx = {
+    $executeRawUnsafe: jest.fn().mockResolvedValue(0),
+    $queryRawUnsafe: jest
+      .fn()
+      // First $queryRawUnsafe call is the COUNT; second is the SELECT.
+      .mockResolvedValueOnce(opts?.countRows ?? [{ count: 0n }])
+      .mockResolvedValueOnce(opts?.selectRows ?? []),
+  };
+  return {
+    tx,
+    $transaction: jest.fn(async (fn: (tx: MockTx) => Promise<unknown>) => fn(tx)),
+  };
+}
+
+async function createSubject(prisma: MockPrisma): Promise<AuditReader> {
+  const moduleRef = await Test.createTestingModule({
+    providers: [AuditReader, { provide: PrismaService, useValue: prisma }],
+  }).compile();
+  return moduleRef.get(AuditReader);
+}
+
+const ROW = {
+  id: '11111111-1111-1111-1111-111111111111',
+  created_at: new Date('2026-05-13T10:30:00.000Z'),
+  event_type: 'admin.audit.query',
+  audience: 'workforce',
+  actor_id_hash: 'hash(admin)',
+  trace_id: 'trace-abc',
+  subject: null,
+  outcome: 'success',
+  payload: { filters: {}, resultCount: 0 },
+};
+
+describe('AuditReader.findEvents', () => {
+  it('locks the transaction to audit_reader before SELECT', async () => {
+    const prisma = buildMocks();
+    const reader = await createSubject(prisma);
+
+    await reader.findEvents({});
+
+    const setRoleCalls = prisma.tx.$executeRawUnsafe.mock.calls;
+    expect(setRoleCalls[0]?.[0]).toBe('SET LOCAL ROLE audit_reader');
+  });
+
+  it('issues a COUNT(*) then a SELECT in the same transaction', async () => {
+    const prisma = buildMocks({ countRows: [{ count: 42n }], selectRows: [ROW] });
+    const reader = await createSubject(prisma);
+
+    const page = await reader.findEvents({});
+
+    expect(prisma.$transaction).toHaveBeenCalledTimes(1);
+    const queries = prisma.tx.$queryRawUnsafe.mock.calls;
+    expect(queries[0]?.[0]).toMatch(/SELECT COUNT\(\*\)::bigint AS count FROM "audit"\."events"/);
+    expect(queries[1]?.[0]).toMatch(/SELECT id, created_at, event_type, audience/);
+    expect(page.total).toBe(42);
+    expect(page.items).toHaveLength(1);
+  });
+
+  it('projects rows into the SPA-facing shape (ISO timestamp + null payload tolerance)', async () => {
+    const prisma = buildMocks({
+      selectRows: [{ ...ROW, payload: null }, ROW],
+    });
+    const reader = await createSubject(prisma);
+    const page = await reader.findEvents({});
+    const first = page.items[0] as AdminAuditEventDto;
+    expect(first.createdAt).toBe('2026-05-13T10:30:00.000Z');
+    expect(first.payload).toBeNull();
+    const second = page.items[1] as AdminAuditEventDto;
+    expect(second.payload).toEqual({ filters: {}, resultCount: 0 });
+  });
+
+  it('emits no WHERE clause when no filter is provided', async () => {
+    const prisma = buildMocks();
+    const reader = await createSubject(prisma);
+    await reader.findEvents({});
+    const countSql = prisma.tx.$queryRawUnsafe.mock.calls[0]?.[0] as string;
+    expect(countSql).not.toMatch(/WHERE/);
+  });
+
+  it('orders by created_at DESC, id DESC for deterministic pagination', async () => {
+    const prisma = buildMocks();
+    const reader = await createSubject(prisma);
+    await reader.findEvents({});
+    const selectSql = prisma.tx.$queryRawUnsafe.mock.calls[1]?.[0] as string;
+    expect(selectSql).toMatch(/ORDER BY created_at DESC, id DESC/);
+  });
+
+  it('passes filter values as positional parameters (never inlined into SQL)', async () => {
+    const prisma = buildMocks();
+    const reader = await createSubject(prisma);
+
+    await reader.findEvents({
+      eventType: "admin.audit.query'; DROP TABLE events; --",
+      audience: 'workforce',
+    });
+
+    const countCall = prisma.tx.$queryRawUnsafe.mock.calls[0] ?? [];
+    const sql = countCall[0] as string;
+    const params = countCall.slice(1);
+    expect(sql).toContain('$1');
+    expect(sql).toContain('$2');
+    expect(sql).not.toContain('DROP TABLE');
+    expect(params).toEqual(["admin.audit.query'; DROP TABLE events; --", 'workforce']);
+  });
+
+  it('casts enum filters through the proper enum types in SQL', async () => {
+    const prisma = buildMocks();
+    const reader = await createSubject(prisma);
+    await reader.findEvents({ audience: 'workforce', outcome: 'denied' });
+    const sql = prisma.tx.$queryRawUnsafe.mock.calls[0]?.[0] as string;
+    expect(sql).toMatch(/audience = \$\d+::"audit"\."AuditAudience"/);
+    expect(sql).toMatch(/outcome = \$\d+::"audit"\."AuditOutcome"/);
+  });
+
+  it('uses LIKE with ESCAPE for subjectPrefix and escapes %/_ in the literal', async () => {
+    const prisma = buildMocks();
+    const reader = await createSubject(prisma);
+    await reader.findEvents({ subjectPrefix: 'session:abc%_' });
+    const countCall = prisma.tx.$queryRawUnsafe.mock.calls[0] ?? [];
+    const sql = countCall[0] as string;
+    const params = countCall.slice(1) as string[];
+    expect(sql).toMatch(/subject LIKE \$\d+ ESCAPE '\\'/);
+    expect(params[0]).toBe('session:abc\\%\\_%');
+  });
+
+  it('translates createdAt ISO strings to Date instances in the params', async () => {
+    const prisma = buildMocks();
+    const reader = await createSubject(prisma);
+    await reader.findEvents({
+      createdAtFrom: '2026-05-01T00:00:00.000Z',
+      createdAtTo: '2026-05-13T23:59:59.999Z',
+    });
+    const params = prisma.tx.$queryRawUnsafe.mock.calls[0]?.slice(1) as unknown[];
+    expect(params[0]).toBeInstanceOf(Date);
+    expect((params[0] as Date).toISOString()).toBe('2026-05-01T00:00:00.000Z');
+    expect((params[1] as Date).toISOString()).toBe('2026-05-13T23:59:59.999Z');
+  });
+
+  it('applies the default limit (50) and offset (0) when not provided', async () => {
+    const prisma = buildMocks();
+    const reader = await createSubject(prisma);
+    const page = await reader.findEvents({});
+    const selectCall = prisma.tx.$queryRawUnsafe.mock.calls[1] ?? [];
+    // The last two params are LIMIT and OFFSET in that order.
+    const params = selectCall.slice(1) as unknown[];
+    expect(params[params.length - 2]).toBe(50);
+    expect(params[params.length - 1]).toBe(0);
+    expect(page.limit).toBe(50);
+    expect(page.offset).toBe(0);
+  });
+
+  it('caps limit at MAX_LIMIT (200) even if a caller bypasses the DTO', async () => {
+    const prisma = buildMocks();
+    const reader = await createSubject(prisma);
+    // Direct service call with limit above the ceiling — simulates
+    // a future caller (worker, batch job) that doesn't pass
+    // through the controller's ValidationPipe.
+    await reader.findEvents({ limit: 1000 } as AdminAuditQueryDto);
+    const params = prisma.tx.$queryRawUnsafe.mock.calls[1]?.slice(1) as unknown[];
+    expect(params[params.length - 2]).toBe(200);
+  });
+});

apps/portal-bff/src/admin/audit-reader.service.ts

@@ -0,0 +1,198 @@
+import { Injectable } from '@nestjs/common';
+import { PrismaService } from 'nestjs-prisma';
+import { DEFAULT_LIMIT, MAX_LIMIT, type AdminAuditQueryDto } from './audit-query.dto';
+
+/**
+ * A single audit row projected for SPA consumption. Naming matches
+ * the `AuditEvent` Prisma model but exposes ISO-string timestamps
+ * (`created_at` → ISO 8601) and `Record<string, unknown>` payloads —
+ * the SPA shouldn't have to know about Prisma `Json` runtime
+ * shapes.
+ */
+export interface AdminAuditEventDto {
+  readonly id: string;
+  readonly createdAt: string;
+  readonly eventType: string;
+  readonly audience: string;
+  readonly actorIdHash: string | null;
+  readonly traceId: string | null;
+  readonly subject: string | null;
+  readonly outcome: string;
+  readonly payload: Record<string, unknown> | null;
+}
+
+export interface AdminAuditPage {
+  readonly items: readonly AdminAuditEventDto[];
+  /**
+   * Total rows matching the filter, ignoring `limit` / `offset`.
+   * COUNT(*) on the filtered set — fine at v1 audit volume; if the
+   * table grows past a few million rows we'll switch to keyset
+   * pagination and drop the total.
+   */
+  readonly total: number;
+  readonly limit: number;
+  readonly offset: number;
+}
+
+/**
+ * Raw shape returned by the underlying `$queryRawUnsafe`. Postgres
+ * returns timestamps as `Date` and json columns as already-parsed
+ * objects; the projection in {@link toDto} normalises both into
+ * SPA-friendly types.
+ */
+interface RawAuditRow {
+  id: string;
+  created_at: Date;
+  event_type: string;
+  audience: string;
+  actor_id_hash: string | null;
+  trace_id: string | null;
+  subject: string | null;
+  outcome: string;
+  payload: Record<string, unknown> | null;
+}
+
+/**
+ * `AuditReader` — single entry point for ADR-0013 audit-log reads.
+ *
+ * Contract
+ * --------
+ * - **Always runs under `audit_reader`.** Every query is wrapped in
+ *   a transaction whose first statement is `SET LOCAL ROLE
+ *   audit_reader`. That role has SELECT-only on `audit.events`
+ *   (per the migration that created the schema); UPDATE / INSERT /
+ *   DELETE all fail at the Postgres level even when the BFF's
+ *   connection is otherwise privileged. The role resets at
+ *   transaction end. Mirrors the `AuditWriter`'s role-locking
+ *   posture for symmetry.
+ *
+ * - **Parameterised SQL only.** Filter values flow into the
+ *   `$queryRawUnsafe` parameter array, never concatenated into the
+ *   SQL string — defends against admin-side SQL injection through
+ *   the audit-viewer filter form.
+ *
+ * - **No PII redaction here.** The payload JSON is returned as-is
+ *   to admin callers. Per ADR-0013, redaction is the writer's
+ *   responsibility; what landed in the row is what comes out. The
+ *   admin role is the trust boundary.
+ */
+@Injectable()
+export class AuditReader {
+  constructor(private readonly prisma: PrismaService) {}
+
+  async findEvents(filters: AdminAuditQueryDto): Promise<AdminAuditPage> {
+    const limit = filters.limit ?? DEFAULT_LIMIT;
+    const offset = filters.offset ?? 0;
+    // Hard cap at the DTO ceiling even if a future caller bypasses
+    // the ValidationPipe — defense in depth.
+    const safeLimit = Math.min(limit, MAX_LIMIT);
+
+    const { whereSql, params } = buildWhere(filters);
+
+    return this.prisma.$transaction(async (tx) => {
+      await tx.$executeRawUnsafe(`SET LOCAL ROLE audit_reader`);
+
+      const totalRows = await tx.$queryRawUnsafe<Array<{ count: bigint }>>(
+        `SELECT COUNT(*)::bigint AS count FROM "audit"."events" ${whereSql}`,
+        ...params,
+      );
+      const total = Number(totalRows[0]?.count ?? 0n);
+
+      // Ordering is `created_at DESC, id DESC` so the SPA gets the
+      // newest events first (typical audit-viewer expectation) and
+      // ties on identical timestamps break deterministically on the
+      // uuid — preventing pagination drift if two events share a
+      // microsecond.
+      //
+      // Postgres parameter numbering continues from the WHERE clause
+      // (`params.length`), so LIMIT lands at `$N+1` and OFFSET at
+      // `$N+2`.
+      const items = await tx.$queryRawUnsafe<RawAuditRow[]>(
+        `SELECT id, created_at, event_type, audience, actor_id_hash,
+                trace_id, subject, outcome, payload
+         FROM "audit"."events"
+         ${whereSql}
+         ORDER BY created_at DESC, id DESC
+         LIMIT $${params.length + 1}
+         OFFSET $${params.length + 2}`,
+        ...params,
+        safeLimit,
+        offset,
+      );
+
+      return {
+        items: items.map(toDto),
+        total,
+        limit: safeLimit,
+        offset,
+      };
+    });
+  }
+}
+
+/**
+ * Build the parameterised WHERE clause + the matching positional
+ * parameter array. Every filter is optional; missing filters drop
+ * out of the SQL so the planner can pick the cheapest index.
+ */
+function buildWhere(filters: AdminAuditQueryDto): { whereSql: string; params: unknown[] } {
+  const clauses: string[] = [];
+  const params: unknown[] = [];
+
+  if (filters.eventType !== undefined) {
+    params.push(filters.eventType);
+    clauses.push(`event_type = $${params.length}`);
+  }
+  if (filters.actorIdHash !== undefined) {
+    params.push(filters.actorIdHash);
+    clauses.push(`actor_id_hash = $${params.length}`);
+  }
+  if (filters.audience !== undefined) {
+    params.push(filters.audience);
+    clauses.push(`audience = $${params.length}::"audit"."AuditAudience"`);
+  }
+  if (filters.outcome !== undefined) {
+    params.push(filters.outcome);
+    clauses.push(`outcome = $${params.length}::"audit"."AuditOutcome"`);
+  }
+  if (filters.subjectPrefix !== undefined) {
+    // `LIKE` with a literal escape so a `%` in the prefix doesn't
+    // act as a wildcard. The prefix bound is concatenated *to a
+    // parameter*, never to the SQL string — the parameter is the
+    // already-escaped literal followed by `%`.
+    params.push(`${escapeLikeLiteral(filters.subjectPrefix)}%`);
+    clauses.push(`subject LIKE $${params.length} ESCAPE '\\'`);
+  }
+  if (filters.createdAtFrom !== undefined) {
+    params.push(new Date(filters.createdAtFrom));
+    clauses.push(`created_at >= $${params.length}`);
+  }
+  if (filters.createdAtTo !== undefined) {
+    params.push(new Date(filters.createdAtTo));
+    clauses.push(`created_at < $${params.length}`);
+  }
+
+  const whereSql = clauses.length > 0 ? `WHERE ${clauses.join(' AND ')}` : '';
+  return { whereSql, params };
+}
+
+function escapeLikeLiteral(raw: string): string {
+  // `\` first, then the two LIKE meta-characters. Order matters —
+  // if `%`/`_` were escaped first their inserted `\` would be
+  // double-escaped on the second pass.
+  return raw.replace(/\\/g, '\\\\').replace(/%/g, '\\%').replace(/_/g, '\\_');
+}
+
+function toDto(row: RawAuditRow): AdminAuditEventDto {
+  return {
+    id: row.id,
+    createdAt: row.created_at.toISOString(),
+    eventType: row.event_type,
+    audience: row.audience,
+    actorIdHash: row.actor_id_hash,
+    traceId: row.trace_id,
+    subject: row.subject,
+    outcome: row.outcome,
+    payload: row.payload,
+  };
+}

apps/portal-bff/src/audit/audit.service.spec.ts

@@ -316,6 +316,44 @@ describe('AuditWriter — typed event methods', () => {
     });
   });
 
+  describe('adminAuditQuery()', () => {
+    it('records admin.audit.query (success) with filters + resultCount in payload', async () => {
+      const { writer, prisma, hashUserId } = await createSubject();
+      await writer.adminAuditQuery({
+        actor: { oid: 'admin-oid' },
+        filters: { eventType: 'auth.sign_in', limit: 50 },
+        resultCount: 12,
+      });
+      expect(hashUserId.hash).toHaveBeenCalledWith('admin-oid');
+      const row = extractInsertedRow(prisma);
+      expect(row.eventType).toBe('admin.audit.query');
+      expect(row.audience).toBe('workforce');
+      expect(row.outcome).toBe('success');
+      expect(row.actorIdHash).toBe('hash(admin-oid)');
+      // `subject` is left null — the event is system-wide on the
+      // audit log itself, not tied to a specific entity URI.
+      expect(row.subject).toBeNull();
+      expect(row.payloadJson).toBe(
+        JSON.stringify({
+          filters: { eventType: 'auth.sign_in', limit: 50 },
+          resultCount: 12,
+        }),
+      );
+    });
+
+    it('persists an empty filters object verbatim (the admin asked for everything)', async () => {
+      const { writer, prisma } = await createSubject();
+      await writer.adminAuditQuery({
+        actor: { oid: 'admin-oid' },
+        filters: {},
+        resultCount: 0,
+      });
+      expect(extractInsertedRow(prisma).payloadJson).toBe(
+        JSON.stringify({ filters: {}, resultCount: 0 }),
+      );
+    });
+  });
+
   describe('mfaRequired()', () => {
     it('records auth.mfa_required (denied) with reason + freshnessSeconds in payload', async () => {
       const { writer, prisma, hashUserId } = await createSubject();

apps/portal-bff/src/audit/audit.service.ts

@@ -4,6 +4,7 @@ import { ClsService } from 'nestjs-cls';
 import { PrismaService } from 'nestjs-prisma';
 import type {
   AdminAccessDeniedInput,
+  AdminAuditQueryInput,
   AuditEventInput,
   MfaRequiredInput,
   SignInActor,
@@ -141,6 +142,37 @@ export class AuditWriter {
     });
   }
 
+  /**
+   * Typed event: an admin queried the audit-log viewer. Recorded at
+   * **coarser granularity** per ADR-0020 §"Audit log captures every
+   * admin write action … Read actions (audit log viewing, user list
+   * browsing) are also captured … to deter fishing expeditions".
+   *
+   * The filter object the admin used is serialised into the payload
+   * so a reviewer can see what was searched (event type, time range,
+   * actor hash, etc.). `resultCount` is the number of rows the SPA
+   * received in this trip — paged calls each emit one event; an
+   * auditor spotting a sequence of `admin.audit.query` with growing
+   * offsets is the v1 detection signal for a sweep.
+   *
+   * `outcome=success` regardless of whether the query returned any
+   * rows: the event captures "the admin ran a query", not "the
+   * query matched something". An `outcome=failure` audit row from
+   * this surface is reserved for the day we add per-row authZ.
+   */
+  async adminAuditQuery(input: AdminAuditQueryInput): Promise<void> {
+    await this.recordEvent({
+      eventType: 'admin.audit.query',
+      audience: 'workforce',
+      outcome: 'success',
+      actorIdHash: this.hashUserId.hash(input.actor.oid),
+      payload: {
+        filters: input.filters,
+        resultCount: input.resultCount,
+      },
+    });
+  }
+
   /**
    * Typed event: `/api/admin/*` request rejected by `AdminRoleGuard`
    * because the session's `roles` claim does not include `admin`.

apps/portal-bff/src/audit/audit.types.ts

@@ -101,6 +101,23 @@ export interface AdminAccessDeniedInput {
   rolesHeld: readonly string[];
 }
 
+export interface AdminAuditQueryInput {
+  actor: { oid: string };
+  /**
+   * Filters the admin used on the audit-viewer query. Captured into
+   * the payload so a reviewer auditing audit-log reads can see what
+   * the admin was searching for — per ADR-0020 §"Read actions are
+   * also captured ... to deter fishing expeditions". Empty object
+   * is meaningful (the admin asked for everything).
+   */
+  filters: Record<string, unknown>;
+  /**
+   * Result-set size returned to the admin. Bounded by the DTO's
+   * `MAX_LIMIT`; persisted so an auditor can spot oversized scans.
+   */
+  resultCount: number;
+}
+
 /** Reason `RequireMfaGuard` rejected a request — fed into the audit payload. */
 export type MfaRequiredReason = 'no-mfa-in-amr' | 'no-mfa-verified-at' | 'mfa-stale';