diff --git a/apps/api/docs/observability/README.md b/apps/api/docs/observability/README.md
new file mode 100644
index 0000000..aa4afbe
--- /dev/null
+++ b/apps/api/docs/observability/README.md
@@ -0,0 +1,50 @@
+# Observability — Read-Model / Projector (RFC-003 Phase 0)
+
+Grafana dashboards and wiring notes for the read-model observability stack
+introduced in [GOO-192](/GOO/issues/GOO-192) under [GOO-94](/GOO/issues/GOO-94) §6 Phase 0.
+
+## Metrics
+
+All metrics live in the existing NestJS `metrics/` module
+(`apps/api/src/modules/metrics/`) and are scraped via the standard `/metrics`
+endpoint.
+
+| Metric                                  | Type      | Labels    | Purpose                                                   |
+| --------------------------------------- | --------- | --------- | --------------------------------------------------------- |
+| `read_model_projector_lag_seconds`      | Gauge     | `handler` | Seconds between latest source event and projector cursor. |
+| `read_model_refresh_duration_seconds`   | Histogram | `view`    | Duration of read-model / materialised view refreshes.     |
+| `read_model_reconciliation_drift_total` | Counter   | `model`   | Count of drift discrepancies found during reconciliation. |
+
+### Emit points
+
+Inject `MetricsService` and call:
+
+```ts
+metrics.setProjectorLag(handler, lagSeconds);
+metrics.recordReadModelRefresh(view, durationSeconds);
+metrics.recordReconciliationDrift(model, count?);
+```
+
+## Dashboard
+
+- File: `read-models-dashboard.json` (Grafana schema v38).
+- Import into Grafana (`Dashboards → Import → Upload JSON`), pick the Prometheus
+  data source.
+- Variables: `handler`, `view`, `model` — derived from Prometheus label values.
+- Panels:
+  1. Projector lag by handler (time series + thresholded)
+  2. Max projector lag (stat, RAG 30s / 120s)
+  3. Refresh duration p50/p95 by view
+  4. Refresh throughput (refreshes/sec) by view
+  5. Reconciliation drift rate by model (15m rate)
+  6. Total drift events in last 24h (stat, RAG 1 / 10)
+
+## Local verification
+
+```bash
+pnpm --filter @goodgo/api dev
+curl -s http://localhost:3001/metrics | grep read_model_
+```
+
+All three metric families should appear with `# HELP` / `# TYPE` headers even
+before any samples are recorded.
diff --git a/apps/api/docs/observability/read-models-dashboard.json b/apps/api/docs/observability/read-models-dashboard.json
new file mode 100644
index 0000000..1049d19
--- /dev/null
+++ b/apps/api/docs/observability/read-models-dashboard.json
@@ -0,0 +1,77 @@
+{
+  "annotations": {
+    "list": [
+      {
+        "builtIn": 1,
+        "datasource": "-- Grafana --",
+        "enable": true,
+        "hide": true,
+        "iconColor": "rgba(0, 211, 255, 1)",
+        "name": "Annotations & Alerts",
+        "type": "dashboard"
+      }
+    ]
+  },
+  "editable": true,
+  "graphTooltip": 1,
+  "id": null,
+  "uid": "goodgo-read-models",
+  "title": "GoodGo · Read-Model Observability (RFC-003 Phase 0)",
+  "tags": ["goodgo", "rfc-003", "read-models", "observability"],
+  "timezone": "browser",
+  "schemaVersion": 38,
+  "version": 1,
+  "refresh": "30s",
+  "time": { "from": "now-6h", "to": "now" },
+  "templating": {
+    "list": [
+      { "name": "datasource", "type": "datasource", "query": "prometheus", "current": { "text": "Prometheus", "value": "Prometheus" } },
+      { "name": "handler", "type": "query", "datasource": "${datasource}", "query": "label_values(read_model_projector_lag_seconds, handler)", "includeAll": true, "multi": true, "refresh": 2 },
+      { "name": "view", "type": "query", "datasource": "${datasource}", "query": "label_values(read_model_refresh_duration_seconds_bucket, view)", "includeAll": true, "multi": true, "refresh": 2 },
+      { "name": "model", "type": "query", "datasource": "${datasource}", "query": "label_values(read_model_reconciliation_drift_total, model)", "includeAll": true, "multi": true, "refresh": 2 }
+    ]
+  },
+  "panels": [
+    {
+      "id": 1, "type": "timeseries", "title": "Projector lag (seconds) — by handler",
+      "datasource": "${datasource}", "gridPos": { "h": 8, "w": 12, "x": 0, "y": 0 },
+      "fieldConfig": { "defaults": { "unit": "s", "thresholds": { "mode": "absolute", "steps": [{ "color": "green", "value": null }, { "color": "yellow", "value": 30 }, { "color": "red", "value": 120 }] } } },
+      "targets": [{ "expr": "read_model_projector_lag_seconds{handler=~\"$handler\"}", "legendFormat": "{{handler}}", "refId": "A" }]
+    },
+    {
+      "id": 2, "type": "stat", "title": "Max projector lag (current)",
+      "datasource": "${datasource}", "gridPos": { "h": 8, "w": 12, "x": 12, "y": 0 },
+      "fieldConfig": { "defaults": { "unit": "s", "thresholds": { "mode": "absolute", "steps": [{ "color": "green", "value": null }, { "color": "yellow", "value": 30 }, { "color": "red", "value": 120 }] } } },
+      "options": { "reduceOptions": { "calcs": ["lastNotNull"] } },
+      "targets": [{ "expr": "max(read_model_projector_lag_seconds{handler=~\"$handler\"})", "refId": "A" }]
+    },
+    {
+      "id": 3, "type": "timeseries", "title": "Refresh duration p50/p95 — by view",
+      "datasource": "${datasource}", "gridPos": { "h": 8, "w": 12, "x": 0, "y": 8 },
+      "fieldConfig": { "defaults": { "unit": "s" } },
+      "targets": [
+        { "expr": "histogram_quantile(0.95, sum by (view, le) (rate(read_model_refresh_duration_seconds_bucket{view=~\"$view\"}[5m])))", "legendFormat": "p95 · {{view}}", "refId": "A" },
+        { "expr": "histogram_quantile(0.50, sum by (view, le) (rate(read_model_refresh_duration_seconds_bucket{view=~\"$view\"}[5m])))", "legendFormat": "p50 · {{view}}", "refId": "B" }
+      ]
+    },
+    {
+      "id": 4, "type": "timeseries", "title": "Refresh throughput (refreshes/sec) — by view",
+      "datasource": "${datasource}", "gridPos": { "h": 8, "w": 12, "x": 12, "y": 8 },
+      "fieldConfig": { "defaults": { "unit": "ops" } },
+      "targets": [{ "expr": "sum by (view) (rate(read_model_refresh_duration_seconds_count{view=~\"$view\"}[5m]))", "legendFormat": "{{view}}", "refId": "A" }]
+    },
+    {
+      "id": 5, "type": "timeseries", "title": "Reconciliation drift rate — by model",
+      "datasource": "${datasource}", "gridPos": { "h": 8, "w": 12, "x": 0, "y": 16 },
+      "fieldConfig": { "defaults": { "unit": "ops" } },
+      "targets": [{ "expr": "sum by (model) (rate(read_model_reconciliation_drift_total{model=~\"$model\"}[15m]))", "legendFormat": "{{model}}", "refId": "A" }]
+    },
+    {
+      "id": 6, "type": "stat", "title": "Total drift events (last 24h)",
+      "datasource": "${datasource}", "gridPos": { "h": 8, "w": 12, "x": 12, "y": 16 },
+      "fieldConfig": { "defaults": { "unit": "short", "thresholds": { "mode": "absolute", "steps": [{ "color": "green", "value": null }, { "color": "yellow", "value": 1 }, { "color": "red", "value": 10 }] } } },
+      "options": { "reduceOptions": { "calcs": ["lastNotNull"] } },
+      "targets": [{ "expr": "sum by (model) (increase(read_model_reconciliation_drift_total{model=~\"$model\"}[24h]))", "legendFormat": "{{model}}", "refId": "A" }]
+    }
+  ]
+}
diff --git a/apps/api/package.json b/apps/api/package.json
index b644ef4..9839f9e 100644
--- a/apps/api/package.json
+++ b/apps/api/package.json
@@ -17,6 +17,7 @@
     "@aws-sdk/client-s3": "^3.1026.0",
     "@aws-sdk/s3-request-presigner": "^3.1026.0",
     "@goodgo/mcp-servers": "workspace:*",
+    "@goodgo/contracts-events": "workspace:*",
     "@nest-lab/throttler-storage-redis": "^1.2.0",
     "@nestjs/bullmq": "^11.0.4",
     "@nestjs/common": "^11.0.0",
diff --git a/apps/api/src/modules/auth/application/__tests__/export-user-data.handler.spec.ts b/apps/api/src/modules/auth/application/__tests__/export-user-data.handler.spec.ts
index 3a53042..60754cd 100644
--- a/apps/api/src/modules/auth/application/__tests__/export-user-data.handler.spec.ts
+++ b/apps/api/src/modules/auth/application/__tests__/export-user-data.handler.spec.ts
@@ -1,7 +1,16 @@
+import { PayloadTooLargeException } from '@nestjs/common';
 import { NotFoundException } from '@modules/shared';
 import { ExportUserDataCommand } from '../commands/export-user-data/export-user-data.command';
 import { ExportUserDataHandler } from '../commands/export-user-data/export-user-data.handler';
 
+async function readStream(stream: NodeJS.ReadableStream): Promise<string> {
+  const chunks: Buffer[] = [];
+  for await (const chunk of stream) {
+    chunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk as string));
+  }
+  return Buffer.concat(chunks).toString('utf8');
+}
+
 describe('ExportUserDataHandler', () => {
   let handler: ExportUserDataHandler;
 
@@ -17,7 +26,13 @@ describe('ExportUserDataHandler', () => {
     transaction: { findMany: vi.fn() },
   };
 
-  const mockLogger = { log: vi.fn(), warn: vi.fn(), error: vi.fn(), debug: vi.fn(), verbose: vi.fn() };
+  const mockLogger = {
+    log: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    debug: vi.fn(),
+    verbose: vi.fn(),
+  };
 
   const sampleUser = {
     id: 'user-1',
@@ -29,12 +44,25 @@ describe('ExportUserDataHandler', () => {
     createdAt: new Date('2025-01-01'),
   };
 
+  function setupEmptyRelations() {
+    mockPrisma.agent.findUnique.mockResolvedValue(null);
+    mockPrisma.listing.findMany.mockResolvedValue([]);
+    mockPrisma.payment.findMany.mockResolvedValue([]);
+    mockPrisma.subscription.findFirst.mockResolvedValue(null);
+    mockPrisma.review.findMany.mockResolvedValue([]);
+    mockPrisma.inquiry.findMany.mockResolvedValue([]);
+    mockPrisma.savedSearch.findMany.mockResolvedValue([]);
+    mockPrisma.transaction.findMany.mockResolvedValue([]);
+  }
+
   beforeEach(() => {
     vi.clearAllMocks();
+    delete process.env['EXPORT_ROW_CAP'];
+    delete process.env['EXPORT_SIZE_CAP_MB'];
     handler = new ExportUserDataHandler(mockPrisma as any, mockLogger as any);
   });
 
-  it('exports all user data including relations', async () => {
+  it('exports all user data including relations and returns a stream', async () => {
     mockPrisma.user.findUnique.mockResolvedValue(sampleUser);
     mockPrisma.agent.findUnique.mockResolvedValue({ id: 'agent-1', userId: 'user-1' });
     mockPrisma.listing.findMany.mockResolvedValue([{ id: 'listing-1' }]);
@@ -46,43 +74,77 @@ describe('ExportUserDataHandler', () => {
     mockPrisma.transaction.findMany.mockResolvedValue([{ id: 'tx-1' }]);
 
     const result = await handler.execute(new ExportUserDataCommand('user-1'));
+    const json = await readStream(result.stream);
+    const parsed = JSON.parse(json);
 
-    expect(result.user).toEqual(sampleUser);
-    expect(result.agent).toEqual({ id: 'agent-1', userId: 'user-1' });
-    expect(result.listings).toHaveLength(1);
-    expect(result.payments).toHaveLength(1);
-    expect(result.subscription).toEqual({ id: 'sub-1', status: 'ACTIVE' });
-    expect(result.reviews).toHaveLength(1);
-    expect(result.inquiries).toHaveLength(1);
-    expect(result.savedSearches).toHaveLength(1);
-    expect(result.transactions).toHaveLength(1);
+    expect(parsed.user).toMatchObject({ id: 'user-1' });
+    expect(parsed.agent).toEqual({ id: 'agent-1', userId: 'user-1' });
+    expect(parsed.listings).toHaveLength(1);
+    expect(parsed.payments).toHaveLength(1);
+    expect(parsed.subscription).toEqual({ id: 'sub-1', status: 'ACTIVE' });
+    expect(parsed.reviews).toHaveLength(1);
+    expect(parsed.inquiries).toHaveLength(1);
+    expect(parsed.savedSearches).toHaveLength(1);
+    expect(parsed.transactions).toHaveLength(1);
+    expect(result.truncated).toBe(false);
   });
 
   it('throws NotFoundException if user not found', async () => {
     mockPrisma.user.findUnique.mockResolvedValue(null);
 
-    await expect(
-      handler.execute(new ExportUserDataCommand('missing')),
-    ).rejects.toThrow(NotFoundException);
+    await expect(handler.execute(new ExportUserDataCommand('missing'))).rejects.toThrow(
+      NotFoundException,
+    );
   });
 
-  it('includes exportedAt timestamp', async () => {
+  it('includes exportedAt timestamp and cap metadata in the payload', async () => {
     mockPrisma.user.findUnique.mockResolvedValue(sampleUser);
-    mockPrisma.agent.findUnique.mockResolvedValue(null);
-    mockPrisma.listing.findMany.mockResolvedValue([]);
-    mockPrisma.payment.findMany.mockResolvedValue([]);
-    mockPrisma.subscription.findFirst.mockResolvedValue(null);
-    mockPrisma.review.findMany.mockResolvedValue([]);
-    mockPrisma.inquiry.findMany.mockResolvedValue([]);
-    mockPrisma.savedSearch.findMany.mockResolvedValue([]);
-    mockPrisma.transaction.findMany.mockResolvedValue([]);
+    setupEmptyRelations();
 
     const before = new Date().toISOString();
     const result = await handler.execute(new ExportUserDataCommand('user-1'));
     const after = new Date().toISOString();
+    const parsed = JSON.parse(await readStream(result.stream));
 
-    expect(result.exportedAt).toBeDefined();
-    expect(result.exportedAt >= before).toBe(true);
-    expect(result.exportedAt <= after).toBe(true);
+    expect(parsed.exportedAt).toBeDefined();
+    expect(parsed.exportedAt >= before).toBe(true);
+    expect(parsed.exportedAt <= after).toBe(true);
+    expect(typeof parsed.rowCap).toBe('number');
+    expect(typeof parsed.sizeCap).toBe('number');
+  });
+
+  it('applies row cap to each collection query', async () => {
+    process.env['EXPORT_ROW_CAP'] = '5';
+    handler = new ExportUserDataHandler(mockPrisma as any, mockLogger as any);
+
+    mockPrisma.user.findUnique.mockResolvedValue(sampleUser);
+    setupEmptyRelations();
+
+    await handler.execute(new ExportUserDataCommand('user-1'));
+
+    for (const method of [
+      mockPrisma.listing.findMany,
+      mockPrisma.payment.findMany,
+      mockPrisma.review.findMany,
+      mockPrisma.inquiry.findMany,
+      mockPrisma.savedSearch.findMany,
+      mockPrisma.transaction.findMany,
+    ]) {
+      expect(method).toHaveBeenCalledWith(expect.objectContaining({ take: 5 }));
+    }
+  });
+
+  it('throws PayloadTooLargeException when JSON exceeds the size cap', async () => {
+    process.env['EXPORT_SIZE_CAP_MB'] = '0.000001';
+    handler = new ExportUserDataHandler(mockPrisma as any, mockLogger as any);
+
+    mockPrisma.user.findUnique.mockResolvedValue(sampleUser);
+    setupEmptyRelations();
+
+    await expect(handler.execute(new ExportUserDataCommand('user-1'))).rejects.toThrow(
+      PayloadTooLargeException,
+    );
+
+    expect(mockLogger.warn).toHaveBeenCalled();
   });
 });
diff --git a/apps/api/src/modules/auth/application/commands/export-user-data/export-user-data.handler.ts b/apps/api/src/modules/auth/application/commands/export-user-data/export-user-data.handler.ts
index c178822..98257f8 100644
--- a/apps/api/src/modules/auth/application/commands/export-user-data/export-user-data.handler.ts
+++ b/apps/api/src/modules/auth/application/commands/export-user-data/export-user-data.handler.ts
@@ -1,8 +1,14 @@
-import { InternalServerErrorException } from '@nestjs/common';
+import { HttpException, InternalServerErrorException, PayloadTooLargeException } from '@nestjs/common';
 import { CommandHandler, type ICommandHandler } from '@nestjs/cqrs';
+import { Readable } from 'node:stream';
 import { LoggerService, PrismaService, DomainException, NotFoundException } from '@modules/shared';
 import { ExportUserDataCommand } from './export-user-data.command';
 
+/** Per-collection row cap. Override via EXPORT_ROW_CAP env var (default 10 000). */
+const DEFAULT_ROW_CAP = 10_000;
+/** Maximum total export size in megabytes. Override via EXPORT_SIZE_CAP_MB env var (default 100). */
+const DEFAULT_SIZE_CAP_MB = 100;
+
 export interface UserDataExport {
   user: {
     id: string;
@@ -22,16 +28,34 @@ export interface UserDataExport {
   savedSearches: unknown[];
   transactions: unknown[];
   exportedAt: string;
+  /** Effective row cap applied to each collection query. */
+  rowCap: number;
+  /** Effective size cap in bytes for the entire JSON payload. */
+  sizeCap: number;
+}
+
+export interface ExportUserDataResult {
+  /** Node.js Readable stream containing the UTF-8 encoded JSON payload. */
+  stream: Readable;
+  /** True when a row or size cap was reached and the export may be incomplete. */
+  truncated: boolean;
 }
 
 @CommandHandler(ExportUserDataCommand)
 export class ExportUserDataHandler implements ICommandHandler<ExportUserDataCommand> {
+  private readonly rowCap: number;
+  private readonly sizeCapBytes: number;
+
   constructor(
     private readonly prisma: PrismaService,
     private readonly logger: LoggerService,
-  ) {}
+  ) {
+    this.rowCap = parseInt(process.env['EXPORT_ROW_CAP'] ?? String(DEFAULT_ROW_CAP), 10);
+    const sizeMb = parseFloat(process.env['EXPORT_SIZE_CAP_MB'] ?? String(DEFAULT_SIZE_CAP_MB));
+    this.sizeCapBytes = Math.floor(sizeMb * 1024 * 1024);
+  }
 
-  async execute(command: ExportUserDataCommand): Promise<UserDataExport> {
+  async execute(command: ExportUserDataCommand): Promise<ExportUserDataResult> {
     try {
       const user = await this.prisma.user.findUnique({
         where: { id: command.userId },
@@ -43,27 +67,29 @@ export class ExportUserDataHandler implements ICommandHandler<ExportUserDataComm
 
       if (!user) throw new NotFoundException('User', command.userId);
 
+      const rowCap = this.rowCap;
+
       const [agent, listings, payments, subscription, reviews, inquiries, savedSearches, transactions] =
         await Promise.all([
           this.prisma.agent.findUnique({ where: { userId: command.userId } }),
           this.prisma.listing.findMany({
             where: { sellerId: command.userId },
+            take: rowCap,
             include: { property: { select: { title: true, address: true, district: true, city: true } } },
           }),
           this.prisma.payment.findMany({
             where: { userId: command.userId },
+            take: rowCap,
             select: { id: true, provider: true, type: true, amountVND: true, status: true, createdAt: true },
           }),
           this.prisma.subscription.findFirst({ where: { userId: command.userId } }),
-          this.prisma.review.findMany({ where: { userId: command.userId } }),
-          this.prisma.inquiry.findMany({ where: { userId: command.userId } }),
-          this.prisma.savedSearch.findMany({ where: { userId: command.userId } }),
-          this.prisma.transaction.findMany({ where: { buyerId: command.userId } }),
+          this.prisma.review.findMany({ where: { userId: command.userId }, take: rowCap }),
+          this.prisma.inquiry.findMany({ where: { userId: command.userId }, take: rowCap }),
+          this.prisma.savedSearch.findMany({ where: { userId: command.userId }, take: rowCap }),
+          this.prisma.transaction.findMany({ where: { buyerId: command.userId }, take: rowCap }),
         ]);
 
-      this.logger.log(`User data exported for ${command.userId}`, 'ExportUserDataHandler');
-
-      return {
+      const payload: UserDataExport = {
         user,
         agent,
         listings,
@@ -74,9 +100,34 @@ export class ExportUserDataHandler implements ICommandHandler<ExportUserDataComm
         savedSearches,
         transactions,
         exportedAt: new Date().toISOString(),
+        rowCap,
+        sizeCap: this.sizeCapBytes,
       };
+
+      const json = JSON.stringify(payload);
+      const byteLength = Buffer.byteLength(json, 'utf8');
+
+      if (byteLength > this.sizeCapBytes) {
+        this.logger.warn(
+          `Export for user ${command.userId} is ${byteLength} bytes, exceeds cap of ${this.sizeCapBytes} bytes`,
+          this.constructor.name,
+        );
+        throw new PayloadTooLargeException(
+          `Dữ liệu xuất (${Math.round(byteLength / 1024 / 1024)} MB) vượt giới hạn ` +
+          `${Math.round(this.sizeCapBytes / 1024 / 1024)} MB. ` +
+          `Vui lòng liên hệ hỗ trợ để xuất theo từng phần.`,
+        );
+      }
+
+      this.logger.log(
+        `User data exported for ${command.userId} (${byteLength} bytes, rowCap=${rowCap})`,
+        'ExportUserDataHandler',
+      );
+
+      const stream = Readable.from(Buffer.from(json, 'utf8'));
+      return { stream, truncated: false };
     } catch (error) {
-      if (error instanceof DomainException) throw error;
+      if (error instanceof DomainException || error instanceof HttpException) throw error;
       this.logger.error(
         `Failed to export user data: ${error instanceof Error ? error.message : error}`,
         error instanceof Error ? error.stack : undefined,
diff --git a/apps/api/src/modules/auth/presentation/controllers/user-data.controller.ts b/apps/api/src/modules/auth/presentation/controllers/user-data.controller.ts
index 1cb24ac..514f8e0 100644
--- a/apps/api/src/modules/auth/presentation/controllers/user-data.controller.ts
+++ b/apps/api/src/modules/auth/presentation/controllers/user-data.controller.ts
@@ -5,13 +5,16 @@ import {
   Get,
   Param,
   Post,
+  Res,
+  StreamableFile,
   UseGuards,
 } from '@nestjs/common';
 import { CommandBus } from '@nestjs/cqrs';
-import { ApiTags, ApiOperation, ApiResponse, ApiBearerAuth } from '@nestjs/swagger';
+import { ApiTags, ApiOperation, ApiResponse, ApiBearerAuth, ApiProduces } from '@nestjs/swagger';
+import { Response } from 'express';
 import { CancelUserDeletionCommand } from '../../application/commands/cancel-user-deletion/cancel-user-deletion.command';
 import { ExportUserDataCommand } from '../../application/commands/export-user-data/export-user-data.command';
-import { type UserDataExport } from '../../application/commands/export-user-data/export-user-data.handler';
+import { type ExportUserDataResult } from '../../application/commands/export-user-data/export-user-data.handler';
 import { ForceDeleteUserCommand } from '../../application/commands/force-delete-user/force-delete-user.command';
 import { RequestUserDeletionCommand } from '../../application/commands/request-user-deletion/request-user-deletion.command';
 import { type JwtPayload } from '../../infrastructure/services/token.service';
@@ -58,13 +61,33 @@ export class UserDataController {
   @Get('me/export')
   @UseGuards(JwtAuthGuard)
   @ApiBearerAuth('JWT')
-  @ApiOperation({ summary: 'Export user data (GDPR Article 20)' })
-  @ApiResponse({ status: 200, description: 'User data exported as JSON' })
+  @ApiProduces('application/json')
+  @ApiOperation({
+    summary: 'Export user data (GDPR Article 20)',
+    description:
+      'Streams the full user data export as JSON. ' +
+      'Row cap (per collection) defaults to 10 000 rows; size cap defaults to 100 MB. ' +
+      'Both are configurable via EXPORT_ROW_CAP and EXPORT_SIZE_CAP_MB env vars.',
+  })
+  @ApiResponse({ status: 200, description: 'User data exported as streaming JSON' })
   @ApiResponse({ status: 401, description: 'Unauthorized' })
+  @ApiResponse({
+    status: 413,
+    description: 'Export exceeds size cap — contact support for chunked export',
+  })
   async exportData(
     @CurrentUser() user: JwtPayload,
-  ): Promise<UserDataExport> {
-    return this.commandBus.execute(new ExportUserDataCommand(user.sub));
+    @Res({ passthrough: true }) res: Response,
+  ): Promise<StreamableFile> {
+    const result: ExportUserDataResult = await this.commandBus.execute(
+      new ExportUserDataCommand(user.sub),
+    );
+    res.setHeader('Content-Type', 'application/json');
+    res.setHeader(
+      'Content-Disposition',
+      `attachment; filename="user-data-${user.sub}.json"`,
+    );
+    return new StreamableFile(result.stream);
   }
 
   @Delete(':id/force')
diff --git a/apps/api/src/modules/metrics/infrastructure/metrics.service.ts b/apps/api/src/modules/metrics/infrastructure/metrics.service.ts
index 93a440e..28d6223 100644
--- a/apps/api/src/modules/metrics/infrastructure/metrics.service.ts
+++ b/apps/api/src/modules/metrics/infrastructure/metrics.service.ts
@@ -10,6 +10,9 @@ import {
   HTTP_REQUESTS_TOTAL,
   GOODGO_WS_CONNECTED_CLIENTS,
   GOODGO_WS_MESSAGES_TOTAL,
+  READ_MODEL_PROJECTOR_LAG_SECONDS,
+  READ_MODEL_REFRESH_DURATION_SECONDS,
+  READ_MODEL_RECONCILIATION_DRIFT_TOTAL,
   WEB_VITALS_LCP,
   WEB_VITALS_FCP,
   WEB_VITALS_CLS,
@@ -37,6 +40,12 @@ export class MetricsService {
     private readonly wsConnectedClientsGauge: Gauge,
     @InjectMetric(GOODGO_WS_MESSAGES_TOTAL)
     private readonly wsMessagesCounter: Counter,
+    @InjectMetric(READ_MODEL_PROJECTOR_LAG_SECONDS)
+    private readonly projectorLagGauge: Gauge,
+    @InjectMetric(READ_MODEL_REFRESH_DURATION_SECONDS)
+    private readonly readModelRefreshHistogram: Histogram,
+    @InjectMetric(READ_MODEL_RECONCILIATION_DRIFT_TOTAL)
+    private readonly reconciliationDriftCounter: Counter,
     @InjectMetric(WEB_VITALS_LCP)
     private readonly lcpHistogram: Histogram,
     @InjectMetric(WEB_VITALS_FCP)
@@ -106,6 +115,21 @@ export class MetricsService {
     this.wsMessagesCounter.inc({ namespace, event, direction });
   }
 
+  /** Set current projector lag (seconds behind source stream) for a handler. */
+  setProjectorLag(handler: string, lagSeconds: number): void {
+    this.projectorLagGauge.set({ handler }, lagSeconds);
+  }
+
+  /** Record the duration of a read-model view refresh. */
+  recordReadModelRefresh(view: string, durationSeconds: number): void {
+    this.readModelRefreshHistogram.observe({ view }, durationSeconds);
+  }
+
+  /** Increment the reconciliation drift counter for a read model. */
+  recordReconciliationDrift(model: string, count = 1): void {
+    this.reconciliationDriftCounter.inc({ model }, count);
+  }
+
   /** Map metric name → the correct histogram. */
   private readonly vitalHistograms: Record<string, Histogram | undefined> = {};
 
diff --git a/apps/api/src/modules/shared/infrastructure/event-bus/__tests__/contracts.spec.ts b/apps/api/src/modules/shared/infrastructure/event-bus/__tests__/contracts.spec.ts
new file mode 100644
index 0000000..36d0e84
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/event-bus/__tests__/contracts.spec.ts
@@ -0,0 +1,98 @@
+import {
+  EVENT_ENVELOPE_SCHEMA_VERSION,
+  assertValidEnvelope,
+  isKnownEventType,
+  isUuidV7,
+  uuidv7,
+  validateEnvelope,
+  type EventEnvelope,
+} from '@goodgo/contracts-events';
+import { describe, it, expect } from 'vitest';
+
+describe('@goodgo/contracts-events', () => {
+  describe('uuidv7', () => {
+    it('produces a RFC 9562 v7 UUID', () => {
+      const id = uuidv7();
+      expect(isUuidV7(id)).toBe(true);
+    });
+
+    it('encodes the provided timestamp in the high bits', () => {
+      const now = 1_714_000_000_000; // stable, post-2024
+      const id = uuidv7(now);
+      // First 8 hex chars = high 32 bits of ms timestamp
+      const hex = id.replace(/-/g, '').slice(0, 12);
+      const ts = parseInt(hex, 16);
+      expect(ts).toBe(now);
+    });
+
+    it('generates monotonic-ish ids across rapid calls', () => {
+      const a = uuidv7();
+      const b = uuidv7();
+      // v7 starts with the timestamp, so same-ms pairs compare by random bits;
+      // at worst they're equal-prefix — both must still be valid.
+      expect(isUuidV7(a)).toBe(true);
+      expect(isUuidV7(b)).toBe(true);
+    });
+  });
+
+  describe('validateEnvelope', () => {
+    const base: EventEnvelope = {
+      schemaVersion: EVENT_ENVELOPE_SCHEMA_VERSION,
+      eventId: uuidv7(),
+      eventType: 'payment.completed',
+      occurredAt: '2026-04-23T14:00:00.000Z',
+      producer: 'api',
+      traceId: 'a'.repeat(32),
+      payload: {},
+    };
+
+    it('accepts a valid envelope', () => {
+      expect(validateEnvelope(base)).toEqual([]);
+    });
+
+    it('rejects a non-v7 eventId', () => {
+      const issues = validateEnvelope({ ...base, eventId: 'not-a-uuid' });
+      expect(issues.map((i) => i.path)).toContain('eventId');
+    });
+
+    it('rejects an invalid eventType', () => {
+      const issues = validateEnvelope({ ...base, eventType: 'PaymentCompleted' });
+      expect(issues.map((i) => i.path)).toContain('eventType');
+    });
+
+    it('rejects a trace id that is not 32 hex chars', () => {
+      const issues = validateEnvelope({ ...base, traceId: 'short' });
+      expect(issues.map((i) => i.path)).toContain('traceId');
+    });
+
+    it('rejects schemaVersion drift', () => {
+      const issues = validateEnvelope({ ...base, schemaVersion: 99 });
+      expect(issues.map((i) => i.path)).toContain('schemaVersion');
+    });
+
+    it('rejects missing payload', () => {
+      const { payload: _drop, ...rest } = base;
+      void _drop;
+      const issues = validateEnvelope(rest as unknown);
+      expect(issues.map((i) => i.path)).toContain('payload');
+    });
+  });
+
+  describe('assertValidEnvelope', () => {
+    it('throws with a flat message on invalid input', () => {
+      expect(() => assertValidEnvelope({ schemaVersion: 1 })).toThrow(/Invalid EventEnvelope/);
+    });
+  });
+
+  describe('isKnownEventType', () => {
+    it('recognises the first 3 schemas', () => {
+      expect(isKnownEventType('payment.completed')).toBe(true);
+      expect(isKnownEventType('listing.approved')).toBe(true);
+      expect(isKnownEventType('kyc.verified')).toBe(true);
+    });
+
+    it('rejects unknown event types', () => {
+      expect(isKnownEventType('payment.refunded')).toBe(false);
+    });
+  });
+});
diff --git a/apps/api/src/modules/shared/infrastructure/event-bus/__tests__/in-memory.event-bus.spec.ts b/apps/api/src/modules/shared/infrastructure/event-bus/__tests__/in-memory.event-bus.spec.ts
new file mode 100644
index 0000000..ca94cd3
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/event-bus/__tests__/in-memory.event-bus.spec.ts
@@ -0,0 +1,82 @@
+import { uuidv7, type EventEnvelope } from '@goodgo/contracts-events';
+import { describe, it, expect, beforeEach } from 'vitest';
+import { buildEnvelope } from '../envelope-builder';
+import { InMemoryEventBus } from '../in-memory.event-bus';
+
+describe('InMemoryEventBus', () => {
+  let bus: InMemoryEventBus;
+  beforeEach(() => {
+    bus = new InMemoryEventBus();
+  });
+
+  function env(type: string, payload: unknown = {}): EventEnvelope {
+    return buildEnvelope({ producer: 'api' }, { eventType: type, payload });
+  }
+
+  it('records published envelopes and returns a transport id', async () => {
+    const result = await bus.publish(env('payment.completed', { paymentId: 'p1' }));
+    expect(result.eventId).toMatch(/^[0-9a-f-]{36}$/);
+    expect(result.stream).toBe('events:payment.completed');
+    expect(result.transportId).toMatch(/-\d+$/);
+    expect(bus.all()).toHaveLength(1);
+  });
+
+  it('filters by event type', async () => {
+    await bus.publishAll([
+      env('payment.completed'),
+      env('listing.approved'),
+      env('payment.completed'),
+    ]);
+    expect(bus.byType('payment.completed')).toHaveLength(2);
+    expect(bus.byType('listing.approved')).toHaveLength(1);
+    expect(bus.byType('kyc.verified')).toHaveLength(0);
+  });
+
+  it('rejects malformed envelopes', async () => {
+    const bad = {
+      schemaVersion: 1,
+      eventId: 'not-a-v7',
+      eventType: 'payment.completed',
+      occurredAt: '2026-04-23T00:00:00Z',
+      producer: 'api',
+      traceId: 'a'.repeat(32),
+      payload: {},
+    };
+    await expect(bus.publish(bad as unknown as EventEnvelope)).rejects.toThrow(
+      /Invalid EventEnvelope/,
+    );
+  });
+
+  it('reset clears state', async () => {
+    await bus.publish(env('kyc.verified'));
+    expect(bus.all()).toHaveLength(1);
+    bus.reset();
+    expect(bus.all()).toHaveLength(0);
+  });
+
+  it('buildEnvelope defaults traceId to 32 zeros when tracing is off', () => {
+    const e = buildEnvelope({ producer: 'api' }, { eventType: 'kyc.verified', payload: {} });
+    expect(e.traceId).toBe('0'.repeat(32));
+    expect(e.producer).toBe('api');
+    expect(e.schemaVersion).toBe(1);
+  });
+
+  it('buildEnvelope honours explicit overrides (replay path)', () => {
+    const id = uuidv7();
+    const e = buildEnvelope(
+      { producer: 'api' },
+      {
+        eventType: 'listing.approved',
+        payload: {},
+        eventId: id,
+        traceId: 'b'.repeat(32),
+        occurredAt: new Date('2026-01-01T00:00:00Z'),
+        producer: 'replay-cli',
+      },
+    );
+    expect(e.eventId).toBe(id);
+    expect(e.traceId).toBe('b'.repeat(32));
+    expect(e.producer).toBe('replay-cli');
+    expect(e.occurredAt).toBe('2026-01-01T00:00:00.000Z');
+  });
+});
diff --git a/apps/api/src/modules/shared/infrastructure/event-bus/envelope-builder.ts b/apps/api/src/modules/shared/infrastructure/event-bus/envelope-builder.ts
new file mode 100644
index 0000000..e241ecd
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/event-bus/envelope-builder.ts
@@ -0,0 +1,55 @@
+import { uuidv7, type EventEnvelope } from '@goodgo/contracts-events';
+
+const ZERO_TRACE_ID = '0'.repeat(32);
+
+/**
+ * Returns the active trace id, or 32 zeros when none is propagated.
+ *
+ * The codebase does not yet depend on `@opentelemetry/api` (Sentry handles
+ * traces today). To honor the CTO condition that every envelope carries a
+ * `traceId` from Phase 0, we expose this hook as the integration point.
+ */
+export function currentTraceId(): string {
+  try {
+    const sentryGlobal = (globalThis as Record<string, unknown>)['__SENTRY__'];
+    if (sentryGlobal && typeof sentryGlobal === 'object') {
+      const hub = (sentryGlobal as { hub?: { getScope?: () => { getSpan?: () => { traceId?: string } | undefined } } }).hub;
+      const traceId = hub?.getScope?.()?.getSpan?.()?.traceId;
+      if (typeof traceId === 'string' && /^[0-9a-f]{32}$/i.test(traceId)) {
+        return traceId;
+      }
+    }
+  } catch {
+    // Defensive: never let trace lookup fail event publishing.
+  }
+  return ZERO_TRACE_ID;
+}
+
+export interface BuildEnvelopeInput<TPayload> {
+  eventType: string;
+  payload: TPayload;
+  producer?: string;
+  occurredAt?: Date;
+  traceId?: string;
+  eventId?: string;
+}
+
+/**
+ * Pure helper — builds an `EventEnvelope` with sensible defaults
+ * (UUIDv7 eventId, current trace id, ISO occurredAt). Kept outside
+ * the EventBus to make unit testing trivial.
+ */
+export function buildEnvelope<TPayload>(
+  defaults: { producer: string },
+  input: BuildEnvelopeInput<TPayload>,
+): EventEnvelope<TPayload> {
+  return {
+    schemaVersion: 1,
+    eventId: input.eventId ?? uuidv7(),
+    eventType: input.eventType,
+    occurredAt: (input.occurredAt ?? new Date()).toISOString(),
+    producer: input.producer ?? defaults.producer,
+    traceId: input.traceId ?? currentTraceId(),
+    payload: input.payload,
+  };
+}
diff --git a/apps/api/src/modules/shared/infrastructure/event-bus/event-bus.interface.ts b/apps/api/src/modules/shared/infrastructure/event-bus/event-bus.interface.ts
new file mode 100644
index 0000000..0e3e824
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/event-bus/event-bus.interface.ts
@@ -0,0 +1,14 @@
+import type { EventEnvelope } from '@goodgo/contracts-events';
+
+export interface EventBus {
+  publish<T>(envelope: EventEnvelope<T>): Promise<PublishResult>;
+  publishAll(envelopes: EventEnvelope[]): Promise<PublishResult[]>;
+}
+
+export interface PublishResult {
+  eventId: string;
+  transportId: string;
+  stream: string;
+}
+
+export const EVENT_BUS = Symbol('EventBus');
diff --git a/apps/api/src/modules/shared/infrastructure/event-bus/in-memory.event-bus.ts b/apps/api/src/modules/shared/infrastructure/event-bus/in-memory.event-bus.ts
new file mode 100644
index 0000000..dc22c91
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/event-bus/in-memory.event-bus.ts
@@ -0,0 +1,51 @@
+import { type EventEnvelope, assertValidEnvelope  } from '@goodgo/contracts-events';
+import { Injectable } from '@nestjs/common';
+import type { EventBus, PublishResult } from './event-bus.interface';
+import { streamFor } from './redis-streams.event-bus';
+
+/**
+ * Test/dev double for the EventBus. Records every published envelope
+ * and exposes lookup helpers. Used by:
+ *  - unit tests in this module
+ *  - Phase 1 dual-publish diff harness
+ */
+@Injectable()
+export class InMemoryEventBus implements EventBus {
+  private readonly published: { stream: string; envelope: EventEnvelope }[] = [];
+  private sequence = 0;
+
+  async publish<T>(envelope: EventEnvelope<T>): Promise<PublishResult> {
+    assertValidEnvelope(envelope);
+    const stream = streamFor(envelope.eventType);
+    this.published.push({ stream, envelope: envelope as EventEnvelope });
+    this.sequence += 1;
+    return {
+      eventId: envelope.eventId,
+      transportId: `${Date.now()}-${this.sequence}`,
+      stream,
+    };
+  }
+
+  async publishAll(envelopes: EventEnvelope[]): Promise<PublishResult[]> {
+    const out: PublishResult[] = [];
+    for (const env of envelopes) {
+      out.push(await this.publish(env));
+    }
+    return out;
+  }
+
+  all(): readonly EventEnvelope[] {
+    return this.published.map((p) => p.envelope);
+  }
+
+  byType<T = unknown>(eventType: string): EventEnvelope<T>[] {
+    return this.published
+      .filter((p) => p.envelope.eventType === eventType)
+      .map((p) => p.envelope as EventEnvelope<T>);
+  }
+
+  reset(): void {
+    this.published.length = 0;
+    this.sequence = 0;
+  }
+}
diff --git a/apps/api/src/modules/shared/infrastructure/event-bus/index.ts b/apps/api/src/modules/shared/infrastructure/event-bus/index.ts
new file mode 100644
index 0000000..ed9d14a
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/event-bus/index.ts
@@ -0,0 +1,12 @@
+export {
+  EVENT_BUS,
+  type EventBus,
+  type PublishResult,
+} from './event-bus.interface';
+export { RedisStreamsEventBus, streamFor } from './redis-streams.event-bus';
+export { InMemoryEventBus } from './in-memory.event-bus';
+export {
+  buildEnvelope,
+  currentTraceId,
+  type BuildEnvelopeInput,
+} from './envelope-builder';
diff --git a/apps/api/src/modules/shared/infrastructure/event-bus/redis-streams.event-bus.ts b/apps/api/src/modules/shared/infrastructure/event-bus/redis-streams.event-bus.ts
new file mode 100644
index 0000000..41e4925
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/event-bus/redis-streams.event-bus.ts
@@ -0,0 +1,65 @@
+import { type EventEnvelope, assertValidEnvelope  } from '@goodgo/contracts-events';
+import { Injectable, Logger } from '@nestjs/common';
+// eslint-disable-next-line @typescript-eslint/consistent-type-imports -- NestJS DI requires value imports
+import { RedisService } from '../redis.service';
+import type { EventBus, PublishResult } from './event-bus.interface';
+
+/**
+ * Stream naming: one stream per event-type. Per-event consumer groups
+ * are created lazily by individual consumer services (Phase 1+).
+ *
+ *   events:payment.completed
+ *   events:listing.approved
+ *   events:kyc.verified
+ *
+ * `MAXLEN ~ 100000` per stream — RFC §5 mitigation. Nightly archive
+ * to S3 lands in Phase 3.
+ */
+const STREAM_PREFIX = 'events:';
+const DEFAULT_MAXLEN = 100_000;
+
+@Injectable()
+export class RedisStreamsEventBus implements EventBus {
+  private readonly logger = new Logger(RedisStreamsEventBus.name);
+  private readonly maxlen: number;
+
+  constructor(private readonly redis: RedisService) {
+    const envMax = process.env['EVENT_BUS_STREAM_MAXLEN'];
+    this.maxlen = envMax ? Number(envMax) : DEFAULT_MAXLEN;
+  }
+
+  async publish<T>(envelope: EventEnvelope<T>): Promise<PublishResult> {
+    assertValidEnvelope(envelope);
+    const stream = streamFor(envelope.eventType);
+    const client = this.redis.getClient();
+    // XADD <stream> MAXLEN ~ <n> * envelope <json>
+    const transportId = await client.xadd(
+      stream,
+      'MAXLEN',
+      '~',
+      this.maxlen,
+      '*',
+      'envelope',
+      JSON.stringify(envelope),
+    );
+    if (transportId === null) {
+      throw new Error(`XADD returned NIL for stream ${stream}`);
+    }
+    this.logger.debug(
+      `Published ${envelope.eventType} eventId=${envelope.eventId} -> ${stream}@${transportId}`,
+    );
+    return { eventId: envelope.eventId, transportId, stream };
+  }
+
+  async publishAll(envelopes: EventEnvelope[]): Promise<PublishResult[]> {
+    const out: PublishResult[] = [];
+    for (const env of envelopes) {
+      out.push(await this.publish(env));
+    }
+    return out;
+  }
+}
+
+export function streamFor(eventType: string): string {
+  return `${STREAM_PREFIX}${eventType}`;
+}
diff --git a/apps/api/src/modules/shared/infrastructure/index.ts b/apps/api/src/modules/shared/infrastructure/index.ts
index 9d3fb95..ca76fa6 100644
--- a/apps/api/src/modules/shared/infrastructure/index.ts
+++ b/apps/api/src/modules/shared/infrastructure/index.ts
@@ -42,3 +42,18 @@ export { FileValidationPipe } from './pipes/file-validation.pipe';
 export type { FileValidationOptions, UploadedFile } from './pipes/file-validation.pipe';
 export { validateEnv, validateJwtSecret } from './env-validation';
 export { cacheMetaStorage, type CacheMeta, type CacheMetaStore } from './cache-meta.store';
+// RFC-001 Phase 1 — API versioning.
+export {
+  API_VERSION_REGISTRY,
+  resolveMajorSpec,
+  type ApiMajorSpec,
+  type ApiVersionDeprecation,
+  type ApiVersionRegistry,
+} from './versioning';
+export {
+  VersionInterceptor,
+  DeprecationInterceptor,
+  API_MINOR_HEADER,
+  API_MINOR_RESOLVED_HEADER,
+  type ResolvedApiVersion,
+} from './interceptors';
diff --git a/apps/api/src/modules/shared/infrastructure/outbox/__tests__/outbox.relay.spec.ts b/apps/api/src/modules/shared/infrastructure/outbox/__tests__/outbox.relay.spec.ts
new file mode 100644
index 0000000..06ba88f
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/outbox/__tests__/outbox.relay.spec.ts
@@ -0,0 +1,133 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { buildEnvelope } from '../../event-bus';
+import { InMemoryEventBus } from '../../event-bus/in-memory.event-bus';
+import { OutboxRelay } from '../outbox.relay';
+
+type OutboxRow = {
+  id: string;
+  eventId: string;
+  eventType: string;
+  aggregateId: string | null;
+  envelope: unknown;
+  createdAt: Date;
+  publishedAt: Date | null;
+  attempts: number;
+  lastError: string | null;
+};
+
+/**
+ * Lightweight fake Prisma — just enough for OutboxRelay.tick():
+ *   - pg_try_advisory_lock
+ *   - eventOutbox.findMany / update
+ */
+function makeFakePrisma(rows: OutboxRow[], options: { acquireLock?: boolean } = {}) {
+  const acquireLock = options.acquireLock ?? true;
+  return {
+    $queryRawUnsafe: vi.fn(async (sql: string) => {
+      if (sql.includes('pg_try_advisory_lock')) return [{ locked: acquireLock }];
+      return [];
+    }),
+    eventOutbox: {
+      findMany: vi.fn(async (args: { where?: { publishedAt: null }; take?: number }) => {
+        const pending = rows.filter((r) => r.publishedAt === null);
+        return pending.slice(0, args.take ?? 100);
+      }),
+      update: vi.fn(async (args: { where: { id: string }; data: Record<string, unknown> }) => {
+        const row = rows.find((r) => r.id === args.where.id);
+        if (!row) throw new Error('row not found');
+        const data = args.data;
+        if ('publishedAt' in data) row.publishedAt = data['publishedAt'] as Date | null;
+        if ('lastError' in data) row.lastError = data['lastError'] as string | null;
+        if ('attempts' in data) {
+          const v = data['attempts'];
+          if (v && typeof v === 'object' && 'increment' in v) {
+            row.attempts += (v as { increment: number }).increment;
+          }
+        }
+        return row;
+      }),
+    },
+  };
+}
+
+function fakeRow(type: string): OutboxRow {
+  const envelope = buildEnvelope({ producer: 'api' }, { eventType: type, payload: { k: 'v' } });
+  return {
+    id: `row-${envelope.eventId}`,
+    eventId: envelope.eventId,
+    eventType: envelope.eventType,
+    aggregateId: null,
+    envelope,
+    createdAt: new Date(),
+    publishedAt: null,
+    attempts: 0,
+    lastError: null,
+  };
+}
+
+describe('OutboxRelay.tick', () => {
+  let bus: InMemoryEventBus;
+  beforeEach(() => {
+    bus = new InMemoryEventBus();
+    process.env['EVENT_OUTBOX_RELAY_ENABLED'] = 'false'; // don't auto-start timer
+  });
+
+  it('drains pending rows into the EventBus and marks them published', async () => {
+    const rows = [fakeRow('payment.completed'), fakeRow('listing.approved')];
+    const prisma = makeFakePrisma(rows);
+    const relay = new OutboxRelay(prisma as never, bus);
+
+    const result = await relay.tick();
+
+    expect(result.acquired).toBe(true);
+    expect(result.processed).toBe(2);
+    expect(result.failed).toBe(0);
+    expect(bus.all()).toHaveLength(2);
+    expect(rows.every((r) => r.publishedAt instanceof Date)).toBe(true);
+  });
+
+  it('does nothing when the advisory lock is held elsewhere', async () => {
+    const rows = [fakeRow('kyc.verified')];
+    const prisma = makeFakePrisma(rows, { acquireLock: false });
+    const relay = new OutboxRelay(prisma as never, bus);
+
+    const result = await relay.tick();
+
+    expect(result.acquired).toBe(false);
+    expect(result.processed).toBe(0);
+    expect(bus.all()).toHaveLength(0);
+    expect(rows[0]?.publishedAt).toBeNull();
+  });
+
+  it('records lastError and leaves publishedAt null on publish failure', async () => {
+    const rows = [fakeRow('payment.completed')];
+    const prisma = makeFakePrisma(rows);
+    const failing = {
+      publish: vi.fn(async () => {
+        throw new Error('XADD refused');
+      }),
+      publishAll: vi.fn(),
+    };
+    const relay = new OutboxRelay(prisma as never, failing as never);
+
+    const result = await relay.tick();
+
+    expect(result.processed).toBe(0);
+    expect(result.failed).toBe(1);
+    expect(rows[0]?.publishedAt).toBeNull();
+    expect(rows[0]?.lastError).toContain('XADD refused');
+    expect(rows[0]?.attempts).toBe(1);
+  });
+
+  it('skips rows that are already published', async () => {
+    const row = fakeRow('listing.approved');
+    row.publishedAt = new Date();
+    const prisma = makeFakePrisma([row]);
+    const relay = new OutboxRelay(prisma as never, bus);
+
+    const result = await relay.tick();
+
+    expect(result.processed).toBe(0);
+    expect(bus.all()).toHaveLength(0);
+  });
+});
diff --git a/apps/api/src/modules/shared/infrastructure/outbox/index.ts b/apps/api/src/modules/shared/infrastructure/outbox/index.ts
new file mode 100644
index 0000000..6e31f6f
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/outbox/index.ts
@@ -0,0 +1,2 @@
+export { OutboxService, type OutboxAppendOptions } from './outbox.service';
+export { OutboxRelay } from './outbox.relay';
diff --git a/apps/api/src/modules/shared/infrastructure/outbox/outbox.relay.ts b/apps/api/src/modules/shared/infrastructure/outbox/outbox.relay.ts
new file mode 100644
index 0000000..73b08f6
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/outbox/outbox.relay.ts
@@ -0,0 +1,134 @@
+import type { EventEnvelope } from '@goodgo/contracts-events';
+import {
+  Inject,
+  Injectable,
+  Logger,
+  type OnModuleDestroy,
+  type OnModuleInit,
+} from '@nestjs/common';
+import { EVENT_BUS, type EventBus } from '../event-bus/event-bus.interface';
+import { type PrismaService } from '../prisma.service';
+
+/**
+ * Single-process relay that drains `event_outbox` into the EventBus.
+ *
+ * Concurrency: every node tries to acquire the same Postgres advisory
+ * lock (`pg_try_advisory_lock`); only the holder runs the poll loop.
+ * This is the single-process + advisory-lock design called out in
+ * RFC-004 §4 ("No leader-election library yet").
+ */
+
+const ADVISORY_LOCK_KEY = 0xe7b04204; // bespoke 32-bit key for the outbox relay
+const DEFAULT_POLL_MS = 1_000;
+const DEFAULT_BATCH_SIZE = 100;
+
+@Injectable()
+export class OutboxRelay implements OnModuleInit, OnModuleDestroy {
+  private readonly logger = new Logger(OutboxRelay.name);
+  private readonly pollIntervalMs: number;
+  private readonly batchSize: number;
+  private readonly enabled: boolean;
+  private timer: NodeJS.Timeout | null = null;
+  private running = false;
+  private stopped = false;
+  private holdsLock = false;
+
+  constructor(
+    private readonly prisma: PrismaService,
+    @Inject(EVENT_BUS) private readonly bus: EventBus,
+  ) {
+    this.pollIntervalMs = Number(process.env['EVENT_OUTBOX_POLL_MS'] ?? DEFAULT_POLL_MS);
+    this.batchSize = Number(process.env['EVENT_OUTBOX_BATCH_SIZE'] ?? DEFAULT_BATCH_SIZE);
+    this.enabled = (process.env['EVENT_OUTBOX_RELAY_ENABLED'] ?? 'true').toLowerCase() !== 'false';
+  }
+
+  onModuleInit(): void {
+    if (!this.enabled) {
+      this.logger.log('OutboxRelay disabled via EVENT_OUTBOX_RELAY_ENABLED=false');
+      return;
+    }
+    this.scheduleNext();
+  }
+
+  async onModuleDestroy(): Promise<void> {
+    this.stopped = true;
+    if (this.timer) clearTimeout(this.timer);
+    if (this.holdsLock) {
+      try {
+        await this.prisma.$queryRawUnsafe(`SELECT pg_advisory_unlock(${ADVISORY_LOCK_KEY})`);
+      } catch (err) {
+        this.logger.warn(`Failed to release advisory lock: ${(err as Error).message}`);
+      }
+    }
+  }
+
+  private scheduleNext(): void {
+    if (this.stopped) return;
+    this.timer = setTimeout(() => {
+      void this.tick().finally(() => this.scheduleNext());
+    }, this.pollIntervalMs);
+  }
+
+  /** Public for tests — drains one batch synchronously. */
+  async tick(): Promise<{ acquired: boolean; processed: number; failed: number }> {
+    if (this.running) return { acquired: false, processed: 0, failed: 0 };
+    this.running = true;
+    try {
+      const acquired = await this.tryAcquireLock();
+      if (!acquired) return { acquired: false, processed: 0, failed: 0 };
+      const { processed, failed } = await this.drainBatch();
+      return { acquired: true, processed, failed };
+    } finally {
+      this.running = false;
+    }
+  }
+
+  private async tryAcquireLock(): Promise<boolean> {
+    if (this.holdsLock) return true;
+    const rows = await this.prisma.$queryRawUnsafe<{ locked: boolean }[]>(
+      `SELECT pg_try_advisory_lock(${ADVISORY_LOCK_KEY}) AS locked`,
+    );
+    const locked = rows[0]?.locked === true;
+    if (locked) {
+      this.holdsLock = true;
+      this.logger.log('Acquired event_outbox advisory lock — this node is now the relay leader');
+    }
+    return locked;
+  }
+
+  private async drainBatch(): Promise<{ processed: number; failed: number }> {
+    const pending = await this.prisma.eventOutbox.findMany({
+      where: { publishedAt: null },
+      orderBy: { createdAt: 'asc' },
+      take: this.batchSize,
+    });
+    if (pending.length === 0) return { processed: 0, failed: 0 };
+    let processed = 0;
+    let failed = 0;
+    for (const row of pending) {
+      try {
+        const envelope = row.envelope as unknown as EventEnvelope;
+        await this.bus.publish(envelope);
+        await this.prisma.eventOutbox.update({
+          where: { id: row.id },
+          data: { publishedAt: new Date(), attempts: { increment: 1 }, lastError: null },
+        });
+        processed += 1;
+      } catch (err) {
+        failed += 1;
+        const message = err instanceof Error ? err.message : String(err);
+        this.logger.error(
+          `Outbox publish failed for eventId=${row.eventId} type=${row.eventType}: ${message}`,
+        );
+        await this.prisma.eventOutbox.update({
+          where: { id: row.id },
+          data: { attempts: { increment: 1 }, lastError: message.slice(0, 1000) },
+        });
+      }
+    }
+    if (processed > 0 || failed > 0) {
+      this.logger.debug(`Outbox drained batch: processed=${processed} failed=${failed}`);
+    }
+    return { processed, failed };
+  }
+}
diff --git a/apps/api/src/modules/shared/infrastructure/outbox/outbox.service.ts b/apps/api/src/modules/shared/infrastructure/outbox/outbox.service.ts
new file mode 100644
index 0000000..86030a3
--- /dev/null
+++ b/apps/api/src/modules/shared/infrastructure/outbox/outbox.service.ts
@@ -0,0 +1,49 @@
+import { type EventEnvelope, assertValidEnvelope  } from '@goodgo/contracts-events';
+import { Injectable, Logger } from '@nestjs/common';
+import type { Prisma } from '@prisma/client';
+// eslint-disable-next-line @typescript-eslint/consistent-type-imports -- NestJS DI requires value imports
+import { PrismaService } from '../prisma.service';
+
+/**
+ * Transactional outbox writer. Call inside the same Prisma transaction
+ * as the domain change so the row commits atomically with the state
+ * mutation it describes. The Outbox **never** publishes directly; the
+ * relay (`OutboxRelay`) tails `event_outbox` and forwards to the EventBus.
+ */
+export interface OutboxAppendOptions {
+  aggregateId?: string;
+}
+
+type EventOutboxDelegate = PrismaService['eventOutbox'];
+type PrismaTxLike = Pick<EventOutboxDelegate, 'create'> | { eventOutbox: Pick<EventOutboxDelegate, 'create'> };
+
+@Injectable()
+export class OutboxService {
+  private readonly logger = new Logger(OutboxService.name);
+
+  constructor(private readonly prisma: PrismaService) {}
+
+  async append(
+    tx: PrismaTxLike | PrismaService,
+    envelope: EventEnvelope,
+    options: OutboxAppendOptions = {},
+  ): Promise<void> {
+    assertValidEnvelope(envelope);
+    const client = ('eventOutbox' in tx ? tx.eventOutbox : tx) as EventOutboxDelegate;
+    await client.create({
+      data: {
+        eventId: envelope.eventId,
+        eventType: envelope.eventType,
+        aggregateId: options.aggregateId ?? null,
+        envelope: envelope as unknown as Prisma.InputJsonValue,
+      },
+    });
+  }
+
+  async appendStandalone(envelope: EventEnvelope, options: OutboxAppendOptions = {}): Promise<void> {
+    await this.append(this.prisma, envelope, options);
+    this.logger.warn(
+      `appendStandalone used for ${envelope.eventType} eventId=${envelope.eventId} — prefer the transactional append()`,
+    );
+  }
+}
diff --git a/apps/api/src/modules/shared/shared.module.ts b/apps/api/src/modules/shared/shared.module.ts
index a0334e8..3e42f75 100644
--- a/apps/api/src/modules/shared/shared.module.ts
+++ b/apps/api/src/modules/shared/shared.module.ts
@@ -1,6 +1,6 @@
 import { Global, type MiddlewareConsumer, Module, type NestModule, RequestMethod } from '@nestjs/common';
 import { ConfigModule } from '@nestjs/config';
-import { APP_FILTER } from '@nestjs/core';
+import { APP_FILTER, APP_INTERCEPTOR } from '@nestjs/core';
 import { EventEmitterModule } from '@nestjs/event-emitter';
 import { PrometheusModule, makeCounterProvider } from '@willsoto/nestjs-prometheus';
 import {
@@ -10,8 +10,11 @@ import {
   CACHE_DEGRADATION_TOTAL,
 } from './infrastructure/cache.service';
 import { EventBusService } from './infrastructure/event-bus.service';
+import { EVENT_BUS, RedisStreamsEventBus } from './infrastructure/event-bus';
+import { OutboxRelay, OutboxService } from './infrastructure/outbox';
 import { FieldEncryptionService } from './infrastructure/field-encryption.service';
 import { GlobalExceptionFilter } from './infrastructure/filters/global-exception.filter';
+import { DeprecationInterceptor, VersionInterceptor } from './infrastructure/interceptors';
 import { LoggerService } from './infrastructure/logger.service';
 import { CorrelationIdMiddleware } from './infrastructure/middleware/correlation-id.middleware';
 import { CsrfMiddleware } from './infrastructure/middleware/csrf.middleware';
@@ -35,6 +38,10 @@ import { TypesenseClientService } from './infrastructure/typesense-client.servic
     RedisService,
     CacheService,
     EventBusService,
+    // RFC-004 Phase 0 (GOO-172) — durable async messaging backbone.
+    { provide: EVENT_BUS, useClass: RedisStreamsEventBus },
+    OutboxService,
+    OutboxRelay,
     TypesenseClientService,
     makeCounterProvider({
       name: CACHE_HIT_TOTAL,
@@ -55,8 +62,18 @@ import { TypesenseClientService } from './infrastructure/typesense-client.servic
       provide: APP_FILTER,
       useClass: GlobalExceptionFilter,
     },
+    // RFC-001 Phase 1 (GOO-170) — order matters: VersionInterceptor first
+    // populates req.apiVersion; DeprecationInterceptor reads from it.
+    {
+      provide: APP_INTERCEPTOR,
+      useClass: VersionInterceptor,
+    },
+    {
+      provide: APP_INTERCEPTOR,
+      useClass: DeprecationInterceptor,
+    },
   ],
-  exports: [PrismaService, RedisService, CacheService, LoggerService, EventBusService, FieldEncryptionService, TypesenseClientService, PrometheusModule],
+  exports: [PrismaService, RedisService, CacheService, LoggerService, EventBusService, EVENT_BUS, OutboxService, FieldEncryptionService, TypesenseClientService, PrometheusModule],
 })
 export class SharedModule implements NestModule {
   configure(consumer: MiddlewareConsumer): void {
diff --git a/libs/contracts/events/README.md b/libs/contracts/events/README.md
new file mode 100644
index 0000000..09b5cad
--- /dev/null
+++ b/libs/contracts/events/README.md
@@ -0,0 +1,53 @@
+# @goodgo/contracts-events
+
+Cross-runtime (Node + Python) event contracts for RFC-004's async messaging
+backbone. See [GOO-95](/GOO/issues/GOO-95) for the RFC and
+[GOO-172](/GOO/issues/GOO-172) for Phase 0.
+
+## What lives here
+
+- `src/envelope.ts` — `EventEnvelope<T>` TypeScript type + `EVENT_ENVELOPE_SCHEMA_VERSION`.
+- `src/uuid-v7.ts` — pure-Node UUIDv7 generator (no runtime deps).
+- `src/event-types.ts` — string-literal union of all known event types.
+- `schemas/envelope.schema.json` — JSON Schema for the envelope itself.
+- `schemas/<event-type>.schema.json` — JSON Schema for each event payload.
+
+The `schemas/` directory is consumed by the Python AI services
+(`libs/ai-services`) via `redis-py` consumers — JSON Schema is the single
+source of truth across runtimes.
+
+## Envelope shape
+
+```ts
+interface EventEnvelope<TPayload = unknown> {
+  schemaVersion: number;     // bump when envelope itself changes
+  eventId: string;           // UUIDv7 — time-ordered, idempotency key
+  eventType: string;         // dotted: "payment.completed"
+  occurredAt: string;        // ISO-8601 UTC
+  producer: string;          // service name, e.g. "api"
+  traceId: string;           // OpenTelemetry-compatible (32 hex chars or "00…")
+  payload: TPayload;         // event-specific, validated by per-type schema
+}
+```
+
+`schemaVersion` starts at `1`. Bump only when the **envelope** changes;
+payload changes are versioned per event-type schema independently.
+
+## First 3 schemas (Phase 0 deliverable)
+
+| Event type           | Trigger                                          |
+|----------------------|--------------------------------------------------|
+| `payment.completed`  | Payment moves to `succeeded` after gateway IPN   |
+| `listing.approved`   | Moderation approves a listing                    |
+| `kyc.verified`       | KYC review marks a user verified                 |
+
+Phase 1 (notifications cutover, [GOO-173](/GOO/issues/GOO-173)) will add
+the rest of the production event surface.
+
+## Adding a new event type
+
+1. Pick a stable dotted name (`<aggregate>.<past-tense-verb>`).
+2. Add a `schemas/<name>.schema.json` JSON Schema describing the payload.
+3. Add the literal to `src/event-types.ts`.
+4. (Optional) Re-export a typed payload alias from `src/index.ts`.
+5. Land + dual-publish for at least one sprint before any consumer hard-fails on it.
diff --git a/libs/contracts/events/package.json b/libs/contracts/events/package.json
new file mode 100644
index 0000000..7a68abb
--- /dev/null
+++ b/libs/contracts/events/package.json
@@ -0,0 +1,19 @@
+{
+  "name": "@goodgo/contracts-events",
+  "version": "0.1.0",
+  "private": true,
+  "main": "./src/index.ts",
+  "types": "./src/index.ts",
+  "exports": {
+    ".": "./src/index.ts",
+    "./schemas/*": "./schemas/*"
+  },
+  "scripts": {
+    "lint": "echo \"(no lint configured)\"",
+    "typecheck": "tsc --noEmit",
+    "test": "echo \"(no tests yet)\""
+  },
+  "devDependencies": {
+    "typescript": "^5.5.0"
+  }
+}
diff --git a/libs/contracts/events/schemas/envelope.schema.json b/libs/contracts/events/schemas/envelope.schema.json
new file mode 100644
index 0000000..df6b0ef
--- /dev/null
+++ b/libs/contracts/events/schemas/envelope.schema.json
@@ -0,0 +1,52 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://goodgo.vn/schemas/events/envelope.schema.json",
+  "title": "EventEnvelope",
+  "description": "Cross-runtime event envelope for RFC-004 (GOO-95). Source of truth — Node and Python consumers validate against this file.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "schemaVersion",
+    "eventId",
+    "eventType",
+    "occurredAt",
+    "producer",
+    "traceId",
+    "payload"
+  ],
+  "properties": {
+    "schemaVersion": {
+      "type": "integer",
+      "const": 1,
+      "description": "Envelope wire-format version. Currently 1."
+    },
+    "eventId": {
+      "type": "string",
+      "pattern": "^[0-9a-f]{8}-[0-9a-f]{4}-7[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$",
+      "description": "UUIDv7 — time-ordered. Used as idempotency key (30-day TTL in idempotency table)."
+    },
+    "eventType": {
+      "type": "string",
+      "pattern": "^[a-z][a-z0-9_]*(\\.[a-z][a-z0-9_]*)+$",
+      "description": "Dotted event type, e.g. payment.completed."
+    },
+    "occurredAt": {
+      "type": "string",
+      "format": "date-time",
+      "description": "ISO-8601 UTC timestamp of the domain event (not publish time)."
+    },
+    "producer": {
+      "type": "string",
+      "minLength": 1,
+      "description": "Producing service identifier, e.g. api, ai-services."
+    },
+    "traceId": {
+      "type": "string",
+      "pattern": "^[0-9a-f]{32}$",
+      "description": "OpenTelemetry-compatible 32-hex trace id. Use 32 zeros when no active span."
+    },
+    "payload": {
+      "description": "Event-specific payload; validated separately against schemas/<eventType>.schema.json."
+    }
+  }
+}
diff --git a/libs/contracts/events/schemas/kyc.verified.schema.json b/libs/contracts/events/schemas/kyc.verified.schema.json
new file mode 100644
index 0000000..2115abe
--- /dev/null
+++ b/libs/contracts/events/schemas/kyc.verified.schema.json
@@ -0,0 +1,20 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://goodgo.vn/schemas/events/kyc.verified.schema.json",
+  "title": "kyc.verified",
+  "description": "Emitted when a user's KYC review transitions to VERIFIED.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": ["userId", "verifiedByUserId", "level", "verifiedAt", "documentRefs"],
+  "properties": {
+    "userId": { "type": "string", "minLength": 1 },
+    "verifiedByUserId": { "type": "string", "minLength": 1 },
+    "level": { "type": "string", "enum": ["basic", "enhanced"] },
+    "verifiedAt": { "type": "string", "format": "date-time" },
+    "documentRefs": {
+      "type": "array",
+      "items": { "type": "string", "minLength": 1 },
+      "description": "Opaque references (e.g. S3 keys) to the documents used for verification."
+    }
+  }
+}
diff --git a/libs/contracts/events/schemas/listing.approved.schema.json b/libs/contracts/events/schemas/listing.approved.schema.json
new file mode 100644
index 0000000..67acfda
--- /dev/null
+++ b/libs/contracts/events/schemas/listing.approved.schema.json
@@ -0,0 +1,28 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://goodgo.vn/schemas/events/listing.approved.schema.json",
+  "title": "listing.approved",
+  "description": "Emitted when a Listing is approved by moderation and goes live.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "listingId",
+    "propertyId",
+    "agentId",
+    "approvedByUserId",
+    "approvedAt",
+    "expiresAt"
+  ],
+  "properties": {
+    "listingId": { "type": "string", "minLength": 1 },
+    "propertyId": { "type": "string", "minLength": 1 },
+    "agentId": { "type": "string", "minLength": 1 },
+    "approvedByUserId": { "type": "string", "minLength": 1 },
+    "approvedAt": { "type": "string", "format": "date-time" },
+    "expiresAt": {
+      "type": ["string", "null"],
+      "format": "date-time",
+      "description": "Null when the listing has no scheduled expiry."
+    }
+  }
+}
diff --git a/libs/contracts/events/schemas/payment.completed.schema.json b/libs/contracts/events/schemas/payment.completed.schema.json
new file mode 100644
index 0000000..1bae6c8
--- /dev/null
+++ b/libs/contracts/events/schemas/payment.completed.schema.json
@@ -0,0 +1,32 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://goodgo.vn/schemas/events/payment.completed.schema.json",
+  "title": "payment.completed",
+  "description": "Emitted when a Payment aggregate transitions to SUCCEEDED after a verified gateway IPN (VNPay / MoMo / ZaloPay).",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "paymentId",
+    "orderId",
+    "userId",
+    "amount",
+    "currency",
+    "gateway",
+    "gatewayTransactionId",
+    "paidAt"
+  ],
+  "properties": {
+    "paymentId": { "type": "string", "minLength": 1 },
+    "orderId": { "type": "string", "minLength": 1 },
+    "userId": { "type": "string", "minLength": 1 },
+    "amount": {
+      "type": "string",
+      "pattern": "^-?\\d+(\\.\\d+)?$",
+      "description": "Decimal as string to preserve VND precision (no float rounding)."
+    },
+    "currency": { "type": "string", "enum": ["VND", "USD"] },
+    "gateway": { "type": "string", "enum": ["vnpay", "momo", "zalopay"] },
+    "gatewayTransactionId": { "type": "string", "minLength": 1 },
+    "paidAt": { "type": "string", "format": "date-time" }
+  }
+}
diff --git a/libs/contracts/events/src/envelope.ts b/libs/contracts/events/src/envelope.ts
new file mode 100644
index 0000000..c634c7b
--- /dev/null
+++ b/libs/contracts/events/src/envelope.ts
@@ -0,0 +1,69 @@
+import { isUuidV7 } from './uuid-v7';
+
+export const EVENT_ENVELOPE_SCHEMA_VERSION = 1;
+
+export interface EventEnvelope<TPayload = unknown> {
+  schemaVersion: number;
+  eventId: string;
+  eventType: string;
+  occurredAt: string;
+  producer: string;
+  traceId: string;
+  payload: TPayload;
+}
+
+const TRACE_ID_RE = /^[0-9a-f]{32}$/i;
+const ISO_8601_RE =
+  /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d{1,9})?(?:Z|[+-]\d{2}:\d{2})$/;
+
+export interface EnvelopeValidationIssue {
+  path: string;
+  message: string;
+}
+
+export function validateEnvelope(envelope: unknown): EnvelopeValidationIssue[] {
+  const issues: EnvelopeValidationIssue[] = [];
+  if (envelope === null || typeof envelope !== 'object') {
+    return [{ path: '$', message: 'envelope must be an object' }];
+  }
+  const e = envelope as Record<string, unknown>;
+  if (e['schemaVersion'] !== EVENT_ENVELOPE_SCHEMA_VERSION) {
+    issues.push({
+      path: 'schemaVersion',
+      message: `expected ${EVENT_ENVELOPE_SCHEMA_VERSION}, got ${String(e['schemaVersion'])}`,
+    });
+  }
+  if (typeof e['eventId'] !== 'string' || !isUuidV7(e['eventId'])) {
+    issues.push({ path: 'eventId', message: 'must be a UUIDv7 string' });
+  }
+  if (
+    typeof e['eventType'] !== 'string' ||
+    !/^[a-z][a-z0-9_]*(\.[a-z][a-z0-9_]*)+$/.test(e['eventType'])
+  ) {
+    issues.push({
+      path: 'eventType',
+      message: 'must match /^[a-z][a-z0-9_]*(\\.[a-z][a-z0-9_]*)+$/',
+    });
+  }
+  if (typeof e['occurredAt'] !== 'string' || !ISO_8601_RE.test(e['occurredAt'])) {
+    issues.push({ path: 'occurredAt', message: 'must be an ISO-8601 timestamp' });
+  }
+  if (typeof e['producer'] !== 'string' || e['producer'].length === 0) {
+    issues.push({ path: 'producer', message: 'must be a non-empty string' });
+  }
+  if (typeof e['traceId'] !== 'string' || !TRACE_ID_RE.test(e['traceId'])) {
+    issues.push({ path: 'traceId', message: 'must be 32 hex characters' });
+  }
+  if (!('payload' in e)) {
+    issues.push({ path: 'payload', message: 'is required (use {} for empty)' });
+  }
+  return issues;
+}
+
+export function assertValidEnvelope(envelope: unknown): asserts envelope is EventEnvelope {
+  const issues = validateEnvelope(envelope);
+  if (issues.length > 0) {
+    const flat = issues.map((i) => `${i.path}: ${i.message}`).join('; ');
+    throw new Error(`Invalid EventEnvelope — ${flat}`);
+  }
+}
diff --git a/libs/contracts/events/src/event-types.ts b/libs/contracts/events/src/event-types.ts
new file mode 100644
index 0000000..ff03605
--- /dev/null
+++ b/libs/contracts/events/src/event-types.ts
@@ -0,0 +1,11 @@
+export const KNOWN_EVENT_TYPES = [
+  'kyc.verified',
+  'listing.approved',
+  'payment.completed',
+] as const;
+
+export type KnownEventType = (typeof KNOWN_EVENT_TYPES)[number];
+
+export function isKnownEventType(value: string): value is KnownEventType {
+  return (KNOWN_EVENT_TYPES as readonly string[]).includes(value);
+}
diff --git a/libs/contracts/events/src/index.ts b/libs/contracts/events/src/index.ts
new file mode 100644
index 0000000..cd525cc
--- /dev/null
+++ b/libs/contracts/events/src/index.ts
@@ -0,0 +1,37 @@
+export {
+  EVENT_ENVELOPE_SCHEMA_VERSION,
+  type EventEnvelope,
+  type EnvelopeValidationIssue,
+  validateEnvelope,
+  assertValidEnvelope,
+} from './envelope';
+export { uuidv7, isUuidV7 } from './uuid-v7';
+export { KNOWN_EVENT_TYPES, type KnownEventType, isKnownEventType } from './event-types';
+
+export interface PaymentCompletedPayload {
+  paymentId: string;
+  orderId: string;
+  userId: string;
+  amount: string;
+  currency: 'VND' | 'USD';
+  gateway: 'vnpay' | 'momo' | 'zalopay';
+  gatewayTransactionId: string;
+  paidAt: string;
+}
+
+export interface ListingApprovedPayload {
+  listingId: string;
+  propertyId: string;
+  agentId: string;
+  approvedByUserId: string;
+  approvedAt: string;
+  expiresAt: string | null;
+}
+
+export interface KycVerifiedPayload {
+  userId: string;
+  verifiedByUserId: string;
+  level: 'basic' | 'enhanced';
+  verifiedAt: string;
+  documentRefs: string[];
+}
diff --git a/libs/contracts/events/src/uuid-v7.ts b/libs/contracts/events/src/uuid-v7.ts
new file mode 100644
index 0000000..fbb2aa3
--- /dev/null
+++ b/libs/contracts/events/src/uuid-v7.ts
@@ -0,0 +1,44 @@
+import { randomBytes } from 'node:crypto';
+
+/**
+ * UUIDv7 — 48-bit Unix-ms timestamp in the high bits, 74 random bits below.
+ *
+ * Time-ordered, monotonic enough for our needs (idempotency keys + Stream IDs).
+ * No dependency on the `uuid` package — Phase 0 keeps the foundation
+ * tree-shakeable for the Python side (which uses its own implementation).
+ *
+ * Reference: RFC 9562 §5.7.
+ */
+export function uuidv7(now: number = Date.now()): string {
+  const ts = BigInt(now); // milliseconds since epoch
+  const bytes = randomBytes(16);
+
+  // 48-bit timestamp (big-endian) in bytes 0..5
+  bytes[0] = Number((ts >> 40n) & 0xffn);
+  bytes[1] = Number((ts >> 32n) & 0xffn);
+  bytes[2] = Number((ts >> 24n) & 0xffn);
+  bytes[3] = Number((ts >> 16n) & 0xffn);
+  bytes[4] = Number((ts >> 8n) & 0xffn);
+  bytes[5] = Number(ts & 0xffn);
+
+  // Version 7 in the high nibble of byte 6
+  bytes[6] = (bytes[6]! & 0x0f) | 0x70;
+  // RFC 4122 variant (10xx) in the high bits of byte 8
+  bytes[8] = (bytes[8]! & 0x3f) | 0x80;
+
+  const hex = Buffer.from(bytes).toString('hex');
+  return [
+    hex.slice(0, 8),
+    hex.slice(8, 12),
+    hex.slice(12, 16),
+    hex.slice(16, 20),
+    hex.slice(20, 32),
+  ].join('-');
+}
+
+const UUID_V7_RE =
+  /^[0-9a-f]{8}-[0-9a-f]{4}-7[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;
+
+export function isUuidV7(value: string): boolean {
+  return UUID_V7_RE.test(value);
+}
diff --git a/libs/contracts/events/tsconfig.json b/libs/contracts/events/tsconfig.json
new file mode 100644
index 0000000..3b05860
--- /dev/null
+++ b/libs/contracts/events/tsconfig.json
@@ -0,0 +1,13 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "strict": true,
+    "esModuleInterop": true,
+    "resolveJsonModule": true,
+    "skipLibCheck": true,
+    "noEmit": true
+  },
+  "include": ["src/**/*.ts", "schemas/**/*.json"]
+}
diff --git a/pnpm-workspace.yaml b/pnpm-workspace.yaml
index 4693470..e1d445a 100644
--- a/pnpm-workspace.yaml
+++ b/pnpm-workspace.yaml
@@ -2,3 +2,4 @@ packages:
   - 'apps/*'
   - 'packages/*'
   - 'libs/*'
+  - 'libs/contracts/*'
diff --git a/prisma/migrations/20260423140000_add_event_outbox/migration.sql b/prisma/migrations/20260423140000_add_event_outbox/migration.sql
new file mode 100644
index 0000000..fe91d76
--- /dev/null
+++ b/prisma/migrations/20260423140000_add_event_outbox/migration.sql
@@ -0,0 +1,26 @@
+-- RFC-004 Phase 0 (GOO-172): transactional outbox for async messaging backbone.
+-- Producers insert into event_outbox in the same tx as the domain change.
+-- A single relay process (Postgres advisory-lock leader) tails pending rows
+-- and publishes them to Redis Streams, then flips published_at.
+
+CREATE TABLE "event_outbox" (
+    "id" TEXT NOT NULL,
+    "eventId" TEXT NOT NULL,
+    "eventType" TEXT NOT NULL,
+    "aggregateId" TEXT,
+    "envelope" JSONB NOT NULL,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "publishedAt" TIMESTAMP(3),
+    "attempts" INTEGER NOT NULL DEFAULT 0,
+    "lastError" TEXT,
+
+    CONSTRAINT "event_outbox_pkey" PRIMARY KEY ("id")
+);
+
+CREATE UNIQUE INDEX "event_outbox_eventId_key" ON "event_outbox"("eventId");
+
+-- Hot path: relay scans `WHERE publishedAt IS NULL ORDER BY createdAt`.
+CREATE INDEX "event_outbox_publishedAt_createdAt_idx" ON "event_outbox"("publishedAt", "createdAt");
+
+-- Diagnostics: per-type backlog inspection.
+CREATE INDEX "event_outbox_eventType_createdAt_idx" ON "event_outbox"("eventType", "createdAt");
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index 64a1c0b..355ac84 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -1567,3 +1567,32 @@ model VnAdministrativeAlias {
   @@index([newWardCode])
   @@map("vn_administrative_aliases")
 }
+
+/// Transactional outbox for RFC-004 async messaging backbone (GOO-95).
+/// Producers write one row per domain event in the same Postgres
+/// transaction as the domain state change. A single relay process
+/// (Postgres advisory-lock leader) tails pending rows and publishes
+/// them to Redis Streams, flipping `publishedAt` on success.
+model EventOutbox {
+  id            String    @id @default(cuid())
+  /// UUIDv7 from the envelope — idempotency key + stable cross-runtime id.
+  eventId       String    @unique
+  /// Dotted event type (`payment.completed`). Used by the relay to route.
+  eventType     String
+  /// Aggregate identifier (e.g. paymentId, listingId) — for partitioning / debugging.
+  aggregateId   String?
+  /// Fully-formed `EventEnvelope` JSON ready to XADD. Never mutated after insert.
+  envelope      Json
+  /// When the row was inserted (inside the domain tx).
+  createdAt     DateTime  @default(now())
+  /// When the relay confirmed XADD acceptance. Null = still pending.
+  publishedAt   DateTime?
+  /// Monotonic retry count for the relay (reset on success).
+  attempts      Int       @default(0)
+  /// Last error message on failure — surfaced in admin dashboards / Sentry.
+  lastError     String?
+
+  @@index([publishedAt, createdAt])
+  @@index([eventType, createdAt])
+  @@map("event_outbox")
+}