diff --git a/src/common/errors/api-exception.filter.ts b/src/common/errors/api-exception.filter.ts
new file mode 100644
index 0000000..ee55cf6
--- /dev/null
+++ b/src/common/errors/api-exception.filter.ts
@@ -0,0 +1,51 @@
+import { ArgumentsHost, Catch, ExceptionFilter, Logger } from '@nestjs/common';
+import { randomUUID, createHash } from 'node:crypto';
+import type { Request, Response } from 'express';
+import { classifyError } from './classify-error';
+import { ERRORS } from './error-catalog';
+
+@Catch()
+export class ApiExceptionFilter implements ExceptionFilter {
+  private readonly logger = new Logger('ApiException');
+  catch(error: unknown, host: ArgumentsHost): void {
+    const http = host.switchToHttp();
+    const request = http.getRequest<Request>();
+    const response = http.getResponse<Response>();
+    const failure = classifyError(error);
+    const requestId =
+      (response.locals.requestId as string | undefined) ?? randomUUID();
+    const record = {
+      event: failure.code,
+      message: ERRORS[failure.code][2],
+      diagnostic: failure.diagnostic,
+      requestId,
+      method: request.method,
+      route: request.route?.path ?? 'unmatched',
+      // Fingerprints distinguish unexpected faults without logging raw errors, queries or secrets.
+      faultId:
+        failure.code === 'INTERNAL_FAILURE' && error instanceof Error
+          ? createHash('sha256')
+              .update(error.stack ?? error.name)
+              .digest('hex')
+              .slice(0, 16)
+          : undefined,
+    };
+    if (failure.getStatus() >= 500) this.logger.error(JSON.stringify(record));
+    else this.logger.warn(JSON.stringify(record));
+    if (response.headersSent) return;
+    response.setHeader('X-Request-Id', requestId);
+    response.setHeader('Cache-Control', 'no-store');
+    if (failure.getStatus() === 429)
+      response.setHeader(
+        'Retry-After',
+        String(failure.retryAfterSeconds ?? 60),
+      );
+    response.status(failure.getStatus()).json({
+      statusCode: failure.getStatus(),
+      code: failure.code,
+      message: failure.message,
+      requestId,
+      ...(failure.fields ? { fields: failure.fields } : {}),
+    });
+  }
+}
diff --git a/src/common/errors/app-error.ts b/src/common/errors/app-error.ts
new file mode 100644
index 0000000..02df76c
--- /dev/null
+++ b/src/common/errors/app-error.ts
@@ -0,0 +1,16 @@
+import { HttpException } from '@nestjs/common';
+import { ERRORS, type ErrorCode } from './error-catalog';
+
+export class AppError extends HttpException {
+  constructor(
+    readonly code: ErrorCode,
+    readonly diagnostic?: string,
+    readonly fields?: string[],
+    readonly retryAfterSeconds?: number,
+  ) {
+    super(
+      { code, message: ERRORS[code][1], ...(fields ? { fields } : {}) },
+      ERRORS[code][0],
+    );
+  }
+}
diff --git a/src/common/errors/classify-error.ts b/src/common/errors/classify-error.ts
new file mode 100644
index 0000000..4ef3d84
--- /dev/null
+++ b/src/common/errors/classify-error.ts
@@ -0,0 +1,42 @@
+import { HttpException } from '@nestjs/common';
+import { Prisma } from '../../generated/prisma/client';
+import { AppError } from './app-error';
+import type { ErrorCode } from './error-catalog';
+
+export function classifyError(error: unknown): AppError {
+  if (error instanceof AppError) return error;
+  if (error instanceof Prisma.PrismaClientKnownRequestError) {
+    const codes: Record<string, ErrorCode> = {
+      P2002: 'RECORD_CONFLICT',
+      P2003: 'REFERENCE_INVALID',
+      P2004: 'DATA_CONSTRAINT',
+      P2025: 'RECORD_NOT_FOUND',
+      P2024: 'DATABASE_BUSY',
+      P2028: 'DATABASE_BUSY',
+      P2034: 'TRANSACTION_CONFLICT',
+    };
+    return new AppError(codes[error.code] ?? 'INTERNAL_FAILURE', error.code);
+  }
+  if (error instanceof Prisma.PrismaClientInitializationError)
+    return new AppError('DATABASE_BUSY');
+  if (error instanceof HttpException) {
+    const codes: Record<number, ErrorCode> = {
+      400: 'REQUEST_MALFORMED',
+      401: 'AUTH_REQUIRED',
+      403: 'ACCESS_DENIED',
+      404: 'ROUTE_NOT_FOUND',
+      413: 'REQUEST_TOO_LARGE',
+      429: 'RATE_LIMITED',
+      503: 'DATABASE_BUSY',
+    };
+    return new AppError(codes[error.getStatus()] ?? 'INTERNAL_FAILURE');
+  }
+  // Express parser errors are not Nest HttpExceptions.
+  if (typeof error === 'object' && error !== null && 'type' in error) {
+    if (error.type === 'entity.too.large')
+      return new AppError('REQUEST_TOO_LARGE');
+    if (error.type === 'entity.parse.failed')
+      return new AppError('REQUEST_MALFORMED');
+  }
+  return new AppError('INTERNAL_FAILURE');
+}
diff --git a/src/common/errors/commerce-errors.ts b/src/common/errors/commerce-errors.ts
new file mode 100644
index 0000000..0143f92
--- /dev/null
+++ b/src/common/errors/commerce-errors.ts
@@ -0,0 +1,84 @@
+export const COMMERCE_ERRORS = {
+  PRODUCT_NOT_FOUND: [404, 'Product not found', 'Scoped product lookup failed'],
+  PRODUCT_NOT_PUBLISHABLE: [
+    409,
+    'Add an active priced variant before publishing',
+    'Product publish eligibility failed',
+  ],
+  PRODUCT_ARCHIVED: [
+    409,
+    'Archived products cannot be edited',
+    'Archived product mutation rejected',
+  ],
+  VARIANT_NOT_FOUND: [
+    404,
+    'Product variant not found',
+    'Scoped product variant lookup failed',
+  ],
+  VARIANT_LIMIT: [
+    409,
+    'Product variant limit reached',
+    'Variant resource quota exceeded',
+  ],
+  VARIANT_REQUIRED: [
+    409,
+    'A published product needs an active variant',
+    'Last sellable variant deactivation rejected',
+  ],
+  GROUP_NOT_FOUND: [
+    404,
+    'Catalogue group not found',
+    'Scoped catalogue group lookup failed',
+  ],
+  ADDRESS_NOT_FOUND: [
+    404,
+    'Address not found',
+    'Private address lookup failed',
+  ],
+  ADDRESS_LIMIT: [
+    409,
+    'Address limit reached',
+    'Account address quota exceeded',
+  ],
+  WAREHOUSE_NOT_FOUND: [
+    404,
+    'Warehouse not found',
+    'Scoped warehouse lookup failed',
+  ],
+  STOCK_NOT_FOUND: [404, 'Stock item not found', 'Scoped stock lookup failed'],
+  STOCK_INSUFFICIENT: [
+    409,
+    'Insufficient available stock',
+    'Inventory availability check rejected operation',
+  ],
+  STOCK_CAPACITY: [
+    409,
+    'Stock balance limit would be exceeded',
+    'Inventory integer bound rejected operation',
+  ],
+  IDEMPOTENCY_CONFLICT: [
+    409,
+    'Idempotency key was used for a different request',
+    'Idempotency payload mismatch',
+  ],
+  RESERVATION_NOT_FOUND: [
+    404,
+    'Stock reservation not found',
+    'Scoped reservation lookup failed',
+  ],
+  RESERVATION_EXPIRED: [
+    409,
+    'Stock reservation has expired',
+    'Expired reservation commit rejected',
+  ],
+  RESERVATION_CLOSED: [
+    409,
+    'Stock reservation is already closed',
+    'Invalid reservation state transition',
+  ],
+  PRODUCT_UNAVAILABLE: [
+    409,
+    'Product variant is not available for reservation',
+    'Non-sellable variant reservation rejected',
+  ],
+} as const;
diff --git a/src/common/errors/error-catalog.ts b/src/common/errors/error-catalog.ts
new file mode 100644
index 0000000..d8d1774
--- /dev/null
+++ b/src/common/errors/error-catalog.ts
@@ -0,0 +1,4 @@
+import { PLATFORM_ERRORS } from './platform-errors';
+import { COMMERCE_ERRORS } from './commerce-errors';
+export const ERRORS = { ...PLATFORM_ERRORS, ...COMMERCE_ERRORS } as const;
+export type ErrorCode = keyof typeof ERRORS;
diff --git a/src/common/errors/platform-errors.ts b/src/common/errors/platform-errors.ts
new file mode 100644
index 0000000..21da11a
--- /dev/null
+++ b/src/common/errors/platform-errors.ts
@@ -0,0 +1,122 @@
+export const PLATFORM_ERRORS = {
+  REQUEST_INVALID: [400, 'Invalid request', 'Request schema validation failed'],
+  REQUEST_MALFORMED: [
+    400,
+    'Malformed request syntax',
+    'HTTP request parser rejected input',
+  ],
+  REQUEST_TOO_LARGE: [
+    413,
+    'Request body exceeds the allowed size',
+    'HTTP payload limit exceeded',
+  ],
+  ROUTE_NOT_FOUND: [404, 'API route not found', 'Unmatched HTTP route'],
+  AUTH_REQUIRED: [
+    401,
+    'Authentication is required',
+    'Bearer credential missing or malformed',
+  ],
+  AUTH_INVALID_CREDENTIALS: [
+    401,
+    'Invalid credentials',
+    'Login credential verification failed',
+  ],
+  SESSION_INVALID: [
+    401,
+    'Session is invalid or expired',
+    'Session authentication rejected',
+  ],
+  ACCESS_DENIED: [
+    403,
+    'You do not have permission for this action',
+    'Permission check rejected operation',
+  ],
+  SCOPE_DENIED: [
+    403,
+    'Account scope is not authorized',
+    'Transaction principal or organization mismatch',
+  ],
+  RECORD_CONFLICT: [
+    409,
+    'A record with these details already exists',
+    'Database uniqueness conflict',
+  ],
+  REFERENCE_INVALID: [
+    409,
+    'A related record is unavailable',
+    'Database foreign-key constraint rejected operation',
+  ],
+  DATA_CONSTRAINT: [
+    409,
+    'Operation violates a data integrity rule',
+    'Database check constraint rejected operation',
+  ],
+  RECORD_NOT_FOUND: [
+    404,
+    'Requested record is unavailable',
+    'Database record lookup failed',
+  ],
+  DATABASE_BUSY: [
+    503,
+    'Database is temporarily busy; retry later',
+    'Database timeout or connection unavailable',
+  ],
+  TRANSACTION_CONFLICT: [
+    409,
+    'Concurrent update detected; retry this operation',
+    'Database transaction conflict',
+  ],
+  INTERNAL_FAILURE: [
+    500,
+    'An unexpected error occurred',
+    'Unhandled application failure',
+  ],
+  USER_NOT_FOUND: [404, 'User not found', 'Scoped user lookup failed'],
+  ROLE_NOT_FOUND: [404, 'Role not found', 'Scoped role lookup failed'],
+  ROLE_GRANT_DENIED: [
+    403,
+    'Cannot grant permissions you do not hold',
+    'Role grant would exceed actor permissions',
+  ],
+  ROLE_IMMUTABLE: [
+    403,
+    'System role is immutable',
+    'Attempt to modify protected system role',
+  ],
+  ROLE_ASSIGNMENT_DENIED: [
+    403,
+    'Cannot change these role assignments',
+    'Protected or self role assignment rejected',
+  ],
+  ROLE_SYSTEM_DENIED: [
+    403,
+    'System role cannot be assigned',
+    'Attempt to assign owner role',
+  ],
+  USER_STATUS_DENIED: [
+    403,
+    'Cannot change this account status',
+    'Protected or self approval change rejected',
+  ],
+  OWNER_EXISTS: [
+    409,
+    'Owner already exists',
+    'Installation bootstrap repeated',
+  ],
+  RECOVERY_INVALID: [
+    400,
+    'Invalid or expired recovery token',
+    'Recovery token consumption rejected',
+  ],
+  RECOVERY_UNAVAILABLE: [
+    503,
+    'Password recovery is not configured',
+    'SMTP recovery configuration missing',
+  ],
+  RATE_LIMITED: [429, 'Too many requests', 'Durable request quota exceeded'],
+  DATABASE_NOT_READY: [
+    503,
+    'Service is not ready',
+    'Database readiness probe failed',
+  ],
+} as const;
diff --git a/src/common/input.ts b/src/common/input.ts
new file mode 100644
index 0000000..b5b8868
--- /dev/null
+++ b/src/common/input.ts
@@ -0,0 +1,12 @@
+import { z } from 'zod';
+export const text = (max: number, min = 1) =>
+  z
+    .string()
+    .trim()
+    .min(min)
+    .max(max)
+    .regex(/^[^<>\u0000-\u001F\u007F]*$/, 'Plain text only');
+export const ids = z
+  .array(z.uuid())
+  .max(20)
+  .refine((values) => new Set(values).size === values.length);
diff --git a/src/common/validation.pipe.ts b/src/common/validation.pipe.ts
index 17f19fa..5c0a2b2 100644
--- a/src/common/validation.pipe.ts
+++ b/src/common/validation.pipe.ts
@@ -1,17 +1,15 @@
-import { BadRequestException, PipeTransform } from '@nestjs/common';
+import type { PipeTransform } from '@nestjs/common';
 import { z } from 'zod';
+import { AppError } from './errors/app-error';
 
 export class SchemaPipe<T> implements PipeTransform<unknown, T> {
   constructor(private readonly schema: z.ZodType<T>) {}
   transform(value: unknown): T {
     const result = this.schema.safeParse(value);
     if (!result.success) {
-      throw new BadRequestException({
-        message: 'Invalid request',
-        fields: [
-          ...new Set(result.error.issues.map((issue) => issue.path.join('.'))),
-        ],
-      });
+      throw new AppError('REQUEST_INVALID', 'SCHEMA_REJECTED', [
+        ...new Set(result.error.issues.map((issue) => issue.path.join('.'))),
+      ]);
     }
     return result.data;
   }
diff --git a/src/config/environment.ts b/src/config/environment.ts
index ac46ee8..f127e39 100644
--- a/src/config/environment.ts
+++ b/src/config/environment.ts
@@ -8,6 +8,7 @@ const schema = z
       .enum(['development', 'test', 'production'])
       .default('development'),
     PORT: z.coerce.number().int().min(1).max(65535).default(3000),
+    DATABASE_POOL_SIZE: z.coerce.number().int().min(1).max(50).default(10),
     DATABASE_URL: z.url().refine((value) => /^postgres(ql)?:/.test(value)),
     CORS_ORIGINS: z
       .string()
diff --git a/src/configure-app.ts b/src/configure-app.ts
index 11c5b33..df83db1 100644
--- a/src/configure-app.ts
+++ b/src/configure-app.ts
@@ -1,6 +1,10 @@
 import type { INestApplication } from '@nestjs/common';
+import type { NestExpressApplication } from '@nestjs/platform-express';
 import helmet from 'helmet';
+import { randomUUID } from 'node:crypto';
+import type { Request, Response, NextFunction } from 'express';
 import type { Environment } from './config/environment';
+import { ApiExceptionFilter } from './common/errors/api-exception.filter';
 
 export function configureApp(
   app: INestApplication,
@@ -8,6 +12,19 @@ export function configureApp(
 ): void {
   app.setGlobalPrefix('api/v1');
   app.use(helmet());
+  app.use((_request: Request, response: Response, next: NextFunction) => {
+    response.locals.requestId = randomUUID();
+    response.setHeader('X-Request-Id', response.locals.requestId);
+    response.setHeader('Cache-Control', 'no-store');
+    next();
+  });
+  (app as NestExpressApplication).useBodyParser('json', { limit: '32kb' });
+  (app as NestExpressApplication).useBodyParser('urlencoded', {
+    limit: '32kb',
+    extended: false,
+    parameterLimit: 100,
+  });
+  app.useGlobalFilters(new ApiExceptionFilter());
   app.enableCors({ origin: environment.CORS_ORIGINS, credentials: true });
   app.enableShutdownHooks();
 }
diff --git a/src/database/database.service.ts b/src/database/database.service.ts
index 00fb00f..0cf9fad 100644
--- a/src/database/database.service.ts
+++ b/src/database/database.service.ts
@@ -20,7 +20,7 @@ export class DatabaseService
         connectionString: environment.DATABASE_URL,
         connectionTimeoutMillis: 3000,
         query_timeout: 3000,
-        max: 10,
+        max: environment.DATABASE_POOL_SIZE,
       }),
     });
   }
diff --git a/src/health/health.service.ts b/src/health/health.service.ts
index 372dfb8..897094f 100644
--- a/src/health/health.service.ts
+++ b/src/health/health.service.ts
@@ -1,4 +1,5 @@
-import { Injectable, ServiceUnavailableException } from '@nestjs/common';
+import { AppError } from '../common/errors/app-error';
+import { Injectable } from '@nestjs/common';
 import { DatabaseService } from '../database/database.service';
 
 @Injectable()
@@ -13,7 +14,7 @@ export class HealthService {
     try {
       await this.database.ping();
     } catch {
-      throw new ServiceUnavailableException('Service is not ready');
+      throw new AppError('DATABASE_NOT_READY');
     }
     return { status: 'ok' };
   }
diff --git a/src/identity/access.guard.ts b/src/identity/access.guard.ts
index 922bb06..bd562a4 100644
--- a/src/identity/access.guard.ts
+++ b/src/identity/access.guard.ts
@@ -1,10 +1,6 @@
-import {
-  CanActivate,
-  ExecutionContext,
-  ForbiddenException,
-  Injectable,
-  UnauthorizedException,
-} from '@nestjs/common';
+import { RateLimitService } from './rate-limit.service';
+import { AppError } from '../common/errors/app-error';
+import { CanActivate, ExecutionContext, Injectable } from '@nestjs/common';
 import { Reflector } from '@nestjs/core';
 import { SessionStore } from './session.store';
 import { PUBLIC_ROUTE, REQUIRED_PERMISSION } from './access.decorator';
@@ -15,6 +11,7 @@ export class AccessGuard implements CanActivate {
   constructor(
     private readonly reflector: Reflector,
     private readonly sessions: SessionStore,
+    private readonly limits: RateLimitService,
   ) {}
   async canActivate(context: ExecutionContext): Promise<boolean> {
     const targets = [context.getHandler(), context.getClass()];
@@ -24,14 +21,20 @@ export class AccessGuard implements CanActivate {
     const match = /^Bearer ([A-Za-z0-9_-]{43})$/.exec(
       request.headers.authorization ?? '',
     );
-    if (!match) throw new UnauthorizedException();
+    if (!match) throw new AppError('AUTH_REQUIRED');
+    await this.limits.consume(`protected-ip:${request.ip}`, 300, 60);
     request.principal = await this.sessions.authenticate(match[1]);
+    await this.limits.consume(
+      `protected-user:${request.principal.userId}`,
+      180,
+      60,
+    );
     const permission = this.reflector.getAllAndOverride<string>(
       REQUIRED_PERMISSION,
       targets,
     );
     if (permission && !request.principal.permissions.includes(permission))
-      throw new ForbiddenException();
+      throw new AppError('ACCESS_DENIED');
     return true;
   }
 }
diff --git a/src/identity/access.store.ts b/src/identity/access.store.ts
index a221e0b..4f63011 100644
--- a/src/identity/access.store.ts
+++ b/src/identity/access.store.ts
@@ -1,11 +1,8 @@
-import {
-  ConflictException,
-  ForbiddenException,
-  Injectable,
-} from '@nestjs/common';
+import { Injectable } from '@nestjs/common';
 import { DatabaseService } from '../database/database.service';
 import { Prisma } from '../generated/prisma/client';
 import { readPrincipal } from './session.store';
+import { AppError } from '../common/errors/app-error';
 import type { Principal } from './identity.types';
 import type { Permission } from './permissions';
 
@@ -14,20 +11,24 @@ export class AccessStore {
   constructor(private readonly db: DatabaseService) {}
   async mutate<T>(
     actor: Principal,
-    permission: Permission,
+    permission: Permission | null,
     work: (tx: Prisma.TransactionClient, current: Principal) => Promise<T>,
+    lockOrganization = true,
   ): Promise<T> {
     try {
       return await this.db.$transaction(async (tx) => {
-        // Serialize administration within an organization and recheck permissions after locking.
-        await tx.$queryRaw`SELECT id FROM organizations WHERE id = ${actor.organizationId}::uuid FOR UPDATE`;
+        if (lockOrganization) {
+          await tx.$queryRaw`SELECT id FROM organizations WHERE id = ${actor.organizationId}::uuid FOR UPDATE`;
+        }
         const current = await readPrincipal(tx, actor.sessionId);
         if (
           current.organizationId !== actor.organizationId ||
-          !current.permissions.includes(permission)
+          current.userId !== actor.userId
         ) {
-          throw new ForbiddenException();
+          throw new AppError('SCOPE_DENIED');
         }
+        if (permission && !current.permissions.includes(permission))
+          throw new AppError('ACCESS_DENIED');
         return work(tx, current);
       });
     } catch (error) {
@@ -35,9 +36,7 @@ export class AccessStore {
         error instanceof Prisma.PrismaClientKnownRequestError &&
         error.code === 'P2002'
       ) {
-        throw new ConflictException(
-          'A record with these details already exists',
-        );
+        throw new AppError('RECORD_CONFLICT');
       }
       throw error;
     }
diff --git a/src/identity/auth.service.ts b/src/identity/auth.service.ts
index f48eedb..fff59c7 100644
--- a/src/identity/auth.service.ts
+++ b/src/identity/auth.service.ts
@@ -1,6 +1,7 @@
-import { Inject, Injectable, UnauthorizedException } from '@nestjs/common';
+import { Inject, Injectable } from '@nestjs/common';
 import { ENVIRONMENT } from '../config/environment.module';
 import type { Environment } from '../config/environment';
+import { AppError } from '../common/errors/app-error';
 import { AuthStore } from './auth.store';
 import { PasswordService } from './password.service';
 import { RateLimitService } from './rate-limit.service';
@@ -22,12 +23,18 @@ export class AuthService {
       900,
     );
     const user = await this.store.findUser(input.organizationId, input.email);
-    const valid = user
-      ? await this.passwords.verify(input.password, user.passwordHash)
-      : (await this.passwords.dummyVerify(input.password), false);
+    let valid = false;
+    if (user)
+      valid = await this.passwords.verify(input.password, user.passwordHash);
+    else await this.passwords.dummyVerify(input.password);
     if (!valid || !user || user.status !== 'ACTIVE') {
       if (user) await this.store.failedLogin(user.organizationId, user.id);
-      throw new UnauthorizedException('Invalid credentials');
+      const reason = !user
+        ? 'ACCOUNT_UNKNOWN'
+        : !valid
+          ? 'PASSWORD_MISMATCH'
+          : 'ACCOUNT_INACTIVE';
+      throw new AppError('AUTH_INVALID_CREDENTIALS', reason);
     }
     const { token, tokenHash } = issueToken();
     const expiresAt = new Date(
diff --git a/src/identity/auth.store.ts b/src/identity/auth.store.ts
index 4683605..f39b18c 100644
--- a/src/identity/auth.store.ts
+++ b/src/identity/auth.store.ts
@@ -1,4 +1,5 @@
-import { Injectable, UnauthorizedException } from '@nestjs/common';
+import { AppError } from '../common/errors/app-error';
+import { Injectable } from '@nestjs/common';
 import { DatabaseService } from '../database/database.service';
 import { recordAudit } from './audit';
 import type { Principal } from './identity.types';
@@ -21,7 +22,7 @@ export class AuthStore {
       await tx.$queryRaw`SELECT id FROM users WHERE id = ${userId}::uuid FOR UPDATE`;
       const user = await tx.user.findUniqueOrThrow({ where: { id: userId } });
       if (user.status !== 'ACTIVE' || user.passwordHash !== expectedHash)
-        throw new UnauthorizedException();
+        throw new AppError('SESSION_INVALID', 'LOGIN_SNAPSHOT_CHANGED');
       await tx.session.create({ data: { userId, tokenHash, expiresAt } });
       await recordAudit(
         tx,
diff --git a/src/identity/bootstrap.service.ts b/src/identity/bootstrap.service.ts
index 63d9172..d8592a1 100644
--- a/src/identity/bootstrap.service.ts
+++ b/src/identity/bootstrap.service.ts
@@ -1,4 +1,5 @@
-import { ConflictException, Injectable } from '@nestjs/common';
+import { AppError } from '../common/errors/app-error';
+import { Injectable } from '@nestjs/common';
 import { DatabaseService } from '../database/database.service';
 import { PasswordService } from './password.service';
 import { PERMISSIONS } from './permissions';
@@ -17,7 +18,7 @@ export class BootstrapService {
       // One-time installation bootstrap, serialized across processes.
       await tx.$queryRaw`SELECT pg_advisory_xact_lock(74192001)::text`;
       if (await tx.user.count({ where: { isOwner: true } }))
-        throw new ConflictException('Owner already exists');
+        throw new AppError('OWNER_EXISTS');
       const organization = await tx.organization.create({
         data: { name: organizationName },
       });
diff --git a/src/identity/identity.module.ts b/src/identity/identity.module.ts
index 8ee3afe..904e7de 100644
--- a/src/identity/identity.module.ts
+++ b/src/identity/identity.module.ts
@@ -46,6 +46,6 @@ import { UsersController } from './users.controller';
     UserStore,
     { provide: APP_GUARD, useClass: AccessGuard },
   ],
-  exports: [BootstrapService],
+  exports: [BootstrapService, AccessStore, RateLimitService],
 })
 export class IdentityModule {}
diff --git a/src/identity/permissions.ts b/src/identity/permissions.ts
index b6392ae..e52b281 100644
--- a/src/identity/permissions.ts
+++ b/src/identity/permissions.ts
@@ -6,5 +6,13 @@ export const PERMISSIONS = [
   'roles.read',
   'roles.manage',
   'audit.read',
+  'catalog.read',
+  'catalog.manage',
+  'catalog.publish',
+  'inventory.read',
+  'inventory.manage',
+  'inventory.adjust',
+  'inventory.reserve',
+  'inventory.commit',
 ] as const;
 export type Permission = (typeof PERMISSIONS)[number];
diff --git a/src/identity/rate-limit.service.ts b/src/identity/rate-limit.service.ts
index 3bed16c..0c090a4 100644
--- a/src/identity/rate-limit.service.ts
+++ b/src/identity/rate-limit.service.ts
@@ -1,4 +1,5 @@
-import { HttpException, HttpStatus, Injectable } from '@nestjs/common';
+import { AppError } from '../common/errors/app-error';
+import { Injectable } from '@nestjs/common';
 import { DatabaseService } from '../database/database.service';
 import { hashToken } from './tokens';
 
@@ -7,19 +8,23 @@ export class RateLimitService {
   constructor(private readonly db: DatabaseService) {}
   async consume(key: string, limit: number, seconds: number): Promise<void> {
     const digest = hashToken(key);
-    const [row] = await this.db.$queryRaw<Array<{ hits: number }>>`
+    const [row] = await this.db.$queryRaw<
+      Array<{ hits: number; expiresAt: Date }>
+    >`
       INSERT INTO rate_limits (key, hits, expires_at)
       VALUES (${digest}, 1, NOW() + ${seconds} * INTERVAL '1 second')
       ON CONFLICT (key) DO UPDATE SET
         hits = CASE WHEN rate_limits.expires_at <= NOW() THEN 1 ELSE rate_limits.hits + 1 END,
         expires_at = CASE WHEN rate_limits.expires_at <= NOW()
           THEN NOW() + ${seconds} * INTERVAL '1 second' ELSE rate_limits.expires_at END
-      RETURNING hits
+      RETURNING hits, expires_at AS "expiresAt"
     `;
     if (row.hits > limit)
-      throw new HttpException(
-        'Too many requests',
-        HttpStatus.TOO_MANY_REQUESTS,
+      throw new AppError(
+        'RATE_LIMITED',
+        key.split(':')[0],
+        undefined,
+        Math.max(1, Math.ceil((row.expiresAt.getTime() - Date.now()) / 1000)),
       );
   }
 }
diff --git a/src/identity/recovery-mailer.ts b/src/identity/recovery-mailer.ts
index 7cbead6..916b6a3 100644
--- a/src/identity/recovery-mailer.ts
+++ b/src/identity/recovery-mailer.ts
@@ -1,8 +1,5 @@
-import {
-  Inject,
-  Injectable,
-  ServiceUnavailableException,
-} from '@nestjs/common';
+import { AppError } from '../common/errors/app-error';
+import { Inject, Injectable } from '@nestjs/common';
 import { createTransport } from 'nodemailer';
 import { ENVIRONMENT } from '../config/environment.module';
 import type { Environment } from '../config/environment';
@@ -11,10 +8,7 @@ import type { Environment } from '../config/environment';
 export class RecoveryMailer {
   constructor(@Inject(ENVIRONMENT) private readonly env: Environment) {}
   assertConfigured(): void {
-    if (!this.env.SMTP_HOST)
-      throw new ServiceUnavailableException(
-        'Password recovery is not configured',
-      );
+    if (!this.env.SMTP_HOST) throw new AppError('RECOVERY_UNAVAILABLE');
   }
   async send(email: string, token: string): Promise<void> {
     this.assertConfigured();
diff --git a/src/identity/recovery.service.ts b/src/identity/recovery.service.ts
index ac29f74..7c26f64 100644
--- a/src/identity/recovery.service.ts
+++ b/src/identity/recovery.service.ts
@@ -41,7 +41,12 @@ export class RecoveryService {
     } catch {
       await this.store.discard(tokenHash);
       // SMTP errors may contain credentials and addresses; do not log the raw error.
-      this.logger.error('Password recovery delivery failed');
+      this.logger.error(
+        JSON.stringify({
+          event: 'RECOVERY_DELIVERY_FAILED',
+          message: 'Password recovery delivery failed',
+        }),
+      );
     }
   }
   async reset(token: string, password: string): Promise<void> {
diff --git a/src/identity/recovery.store.ts b/src/identity/recovery.store.ts
index a20bb97..e0f01a6 100644
--- a/src/identity/recovery.store.ts
+++ b/src/identity/recovery.store.ts
@@ -1,4 +1,5 @@
-import { BadRequestException, Injectable } from '@nestjs/common';
+import { AppError } from '../common/errors/app-error';
+import { Injectable } from '@nestjs/common';
 import { DatabaseService } from '../database/database.service';
 import { recordAudit } from './audit';
 
@@ -32,8 +33,7 @@ export class RecoveryStore {
   async reset(tokenHash: string, passwordHash: string) {
     await this.db.$transaction(async (tx) => {
       const token = await tx.recoveryToken.findUnique({ where: { tokenHash } });
-      if (!token)
-        throw new BadRequestException('Invalid or expired recovery token');
+      if (!token) throw new AppError('RECOVERY_INVALID');
       await tx.$queryRaw`SELECT id FROM users WHERE id = ${token.userId}::uuid FOR UPDATE`;
       const user = await tx.user.findUniqueOrThrow({
         where: { id: token.userId },
@@ -42,7 +42,7 @@ export class RecoveryStore {
         where: { id: token.id, expiresAt: { gt: new Date() } },
       });
       if (consumed.count !== 1 || user.status !== 'ACTIVE') {
-        throw new BadRequestException('Invalid or expired recovery token');
+        throw new AppError('RECOVERY_INVALID');
       }
       await tx.user.update({ where: { id: user.id }, data: { passwordHash } });
       await tx.recoveryToken.deleteMany({ where: { userId: user.id } });
diff --git a/src/identity/role.store.ts b/src/identity/role.store.ts
index 5191123..fcaf08b 100644
--- a/src/identity/role.store.ts
+++ b/src/identity/role.store.ts
@@ -1,8 +1,5 @@
-import {
-  ForbiddenException,
-  Injectable,
-  NotFoundException,
-} from '@nestjs/common';
+import { AppError } from '../common/errors/app-error';
+import { Injectable } from '@nestjs/common';
 import { DatabaseService } from '../database/database.service';
 import { AccessStore } from './access.store';
 import { recordAudit } from './audit';
@@ -13,7 +10,7 @@ function ensureGrantable(actor: Principal, permissions: string[]) {
   if (
     permissions.some((permission) => !actor.permissions.includes(permission))
   ) {
-    throw new ForbiddenException('Cannot grant permissions you do not hold');
+    throw new AppError('ROLE_GRANT_DENIED');
   }
 }
 @Injectable()
@@ -37,9 +34,8 @@ export class RoleStore {
         const role = await tx.role.findFirst({
           where: { id, organizationId: actor.organizationId },
         });
-        if (!role) throw new NotFoundException();
-        if (role.isSystem)
-          throw new ForbiddenException('System role is immutable');
+        if (!role) throw new AppError('ROLE_NOT_FOUND');
+        if (role.isSystem) throw new AppError('ROLE_IMMUTABLE');
         ensureGrantable(current, role.permissions);
       }
       const role = id
@@ -66,9 +62,9 @@ export class RoleStore {
           where: { id: userId, organizationId: actor.organizationId },
           include: { roles: { include: { role: true } } },
         });
-        if (!user) throw new NotFoundException();
+        if (!user) throw new AppError('USER_NOT_FOUND');
         if (user.isOwner || user.id === current.userId)
-          throw new ForbiddenException('Cannot change these role assignments');
+          throw new AppError('ROLE_ASSIGNMENT_DENIED');
         ensureGrantable(
           current,
           user.roles.flatMap((assignment) => assignment.role.permissions),
@@ -76,9 +72,10 @@ export class RoleStore {
         const roles = await tx.role.findMany({
           where: { id: { in: roleIds }, organizationId: actor.organizationId },
         });
-        if (roles.length !== roleIds.length) throw new NotFoundException();
+        if (roles.length !== roleIds.length)
+          throw new AppError('ROLE_NOT_FOUND');
         if (roles.some((role) => role.isSystem))
-          throw new ForbiddenException('System role cannot be assigned');
+          throw new AppError('ROLE_SYSTEM_DENIED');
         ensureGrantable(
           current,
           roles.flatMap((role) => role.permissions),
diff --git a/src/identity/session.store.ts b/src/identity/session.store.ts
index c6ef6bc..68d2206 100644
--- a/src/identity/session.store.ts
+++ b/src/identity/session.store.ts
@@ -1,4 +1,5 @@
-import { Injectable, UnauthorizedException } from '@nestjs/common';
+import { AppError } from '../common/errors/app-error';
+import { Injectable } from '@nestjs/common';
 import { DatabaseService } from '../database/database.service';
 import type { Prisma } from '../generated/prisma/client';
 import { hashToken } from './tokens';
@@ -18,7 +19,7 @@ export async function readPrincipal(
     session.expiresAt <= new Date() ||
     session.user.status !== 'ACTIVE'
   ) {
-    throw new UnauthorizedException();
+    throw new AppError('SESSION_INVALID');
   }
   return {
     userId: session.userId,
@@ -36,7 +37,7 @@ export class SessionStore {
     const session = await this.db.session.findUnique({
       where: { tokenHash: hashToken(token) },
     });
-    if (!session) throw new UnauthorizedException();
+    if (!session) throw new AppError('SESSION_INVALID');
     return readPrincipal(this.db, session.id);
   }
 }
diff --git a/src/identity/user.store.ts b/src/identity/user.store.ts
index 9f1de3c..f656264 100644
--- a/src/identity/user.store.ts
+++ b/src/identity/user.store.ts
@@ -1,8 +1,5 @@
-import {
-  ForbiddenException,
-  Injectable,
-  NotFoundException,
-} from '@nestjs/common';
+import { AppError } from '../common/errors/app-error';
+import { Injectable } from '@nestjs/common';
 import { DatabaseService } from '../database/database.service';
 import { AccessStore } from './access.store';
 import { PasswordService } from './password.service';
@@ -66,9 +63,9 @@ export class UserStore {
       const user = await tx.user.findFirst({
         where: { id, organizationId: actor.organizationId },
       });
-      if (!user) throw new NotFoundException();
+      if (!user) throw new AppError('USER_NOT_FOUND');
       if (user.isOwner || user.id === actor.userId)
-        throw new ForbiddenException('Cannot change this account status');
+        throw new AppError('USER_STATUS_DENIED');
       const updated = await tx.user.update({
         where: { id },
         data: { status },
diff --git a/test/admin-policy.spec.ts b/test/admin-policy.spec.ts
index 5f49657..621bc1c 100644
--- a/test/admin-policy.spec.ts
+++ b/test/admin-policy.spec.ts
@@ -77,7 +77,7 @@ describe('administration use-case policy', () => {
   it('hides users outside the organization scope', async () => {
     tx.user.findFirst.mockResolvedValue(null);
     await expect(users.setStatus(actor, 'foreign', 'ACTIVE')).rejects.toThrow(
-      'Not Found',
+      /not found/i,
     );
     expect(tx.user.update).not.toHaveBeenCalled();
   });
@@ -105,7 +105,7 @@ describe('administration use-case policy', () => {
     tx.role.findFirst.mockResolvedValue(null);
     await expect(
       roles.save(actor, { name: 'Changed', permissions: [] }, 'foreign'),
-    ).rejects.toThrow('Not Found');
+    ).rejects.toThrow(/not found/i);
   });
   it('does not remove a target user permissions the actor cannot grant', async () => {
     tx.user.findFirst.mockResolvedValue({
@@ -121,7 +121,7 @@ describe('administration use-case policy', () => {
   it('hides missing assignment targets', async () => {
     tx.user.findFirst.mockResolvedValue(null);
     await expect(roles.assign(actor, 'foreign', [])).rejects.toThrow(
-      'Not Found',
+      /not found/i,
     );
   });
 });
diff --git a/test/error-handling.spec.ts b/test/error-handling.spec.ts
new file mode 100644
index 0000000..2bd0d7f
--- /dev/null
+++ b/test/error-handling.spec.ts
@@ -0,0 +1,109 @@
+import { ArgumentsHost, HttpException, Logger } from '@nestjs/common';
+import { ApiExceptionFilter } from '../src/common/errors/api-exception.filter';
+import { AppError } from '../src/common/errors/app-error';
+import { ERRORS } from '../src/common/errors/error-catalog';
+import { classifyError } from '../src/common/errors/classify-error';
+import { Prisma } from '../src/generated/prisma/client';
+
+describe('safe error responses and logs', () => {
+  beforeEach(() => {
+    jest.spyOn(Logger.prototype, 'warn').mockImplementation();
+    jest.spyOn(Logger.prototype, 'error').mockImplementation();
+  });
+  afterEach(() => jest.restoreAllMocks());
+  function dispatch(error: unknown, headersSent = false) {
+    const response = {
+      locals: { requestId: 'server-generated-id' },
+      headersSent,
+      setHeader: jest.fn(),
+      status: jest.fn().mockReturnThis(),
+      json: jest.fn(),
+    };
+    const host = {
+      switchToHttp: () => ({
+        getRequest: () => ({
+          method: 'POST',
+          route: { path: '/products/:id' },
+          body: { password: 'SECRET' },
+          headers: { authorization: 'Bearer SECRET' },
+          originalUrl: '/products?token=SECRET',
+        }),
+        getResponse: () => response,
+      }),
+    } as unknown as ArgumentsHost;
+    new ApiExceptionFilter().catch(error, host);
+    return response;
+  }
+  it('returns stable codes and correlation IDs without leaking raw faults', () => {
+    const response = dispatch(new Error('SQL password=SECRET token=SECRET'));
+    expect(response.json).toHaveBeenCalledWith(
+      expect.objectContaining({
+        code: 'INTERNAL_FAILURE',
+        requestId: 'server-generated-id',
+        statusCode: 500,
+      }),
+    );
+    const output = JSON.stringify([
+      response.json.mock.calls,
+      jest.mocked(Logger.prototype.error).mock.calls,
+    ]);
+    expect(output).not.toContain('SECRET');
+    expect(output).not.toContain('password=');
+    expect(output).toContain('faultId');
+  });
+  it('keeps validation field names and unique business error messages', () => {
+    const response = dispatch(
+      new AppError('REQUEST_INVALID', 'SCHEMA_REJECTED', ['price']),
+    );
+    expect(response.json).toHaveBeenCalledWith(
+      expect.objectContaining({ fields: ['price'], code: 'REQUEST_INVALID' }),
+    );
+    const messages = Object.values(ERRORS).map((value) => value[1]);
+    expect(new Set(messages).size).toBe(messages.length);
+  });
+  it('does not try to write a second response', () => {
+    expect(
+      dispatch(new AppError('STOCK_INSUFFICIENT'), true).json,
+    ).not.toHaveBeenCalled();
+  });
+  it('adds retry guidance for throttling', () => {
+    expect(
+      dispatch(new AppError('RATE_LIMITED')).setHeader,
+    ).toHaveBeenCalledWith('Retry-After', '60');
+  });
+  it.each([
+    ['P2002', 'RECORD_CONFLICT'],
+    ['P2003', 'REFERENCE_INVALID'],
+    ['P2004', 'DATA_CONSTRAINT'],
+    ['P2025', 'RECORD_NOT_FOUND'],
+    ['P2028', 'DATABASE_BUSY'],
+    ['P2034', 'TRANSACTION_CONFLICT'],
+    ['P9999', 'INTERNAL_FAILURE'],
+  ])('classifies database error %s as %s', (databaseCode, code) => {
+    const error = new Prisma.PrismaClientKnownRequestError('SECRET', {
+      code: databaseCode,
+      clientVersion: 'test',
+    });
+    expect(classifyError(error).code).toBe(code);
+  });
+  it('classifies parser, transport and connection failures', () => {
+    expect(classifyError({ type: 'entity.too.large' }).code).toBe(
+      'REQUEST_TOO_LARGE',
+    );
+    expect(classifyError({ type: 'entity.parse.failed' }).code).toBe(
+      'REQUEST_MALFORMED',
+    );
+    expect(classifyError(new HttpException('SECRET', 404)).code).toBe(
+      'ROUTE_NOT_FOUND',
+    );
+    expect(classifyError(new HttpException('SECRET', 502)).code).toBe(
+      'INTERNAL_FAILURE',
+    );
+    expect(
+      classifyError(
+        new Prisma.PrismaClientInitializationError('SECRET', 'test'),
+      ).code,
+    ).toBe('DATABASE_BUSY');
+    expect(classifyError(null).code).toBe('INTERNAL_FAILURE');
+  });
+});
diff --git a/test/helpers/identity-app.ts b/test/helpers/identity-app.ts
index 2383cc4..de1b80b 100644
--- a/test/helpers/identity-app.ts
+++ b/test/helpers/identity-app.ts
@@ -16,6 +16,7 @@ export async function identityApp() {
   const env = parseEnvironment({
     DATABASE_URL: database.connectionUrl,
     NODE_ENV: 'test',
+    DATABASE_POOL_SIZE: process.env.TEST_DATABASE_URL ? '10' : '1',
   });
   const mailer = {
     assertConfigured: jest.fn(),
@@ -28,6 +29,7 @@ export async function identityApp() {
     .useValue(mailer)
     .compile();
   const app = module.createNestApplication();
+  app.useLogger(false);
   configureApp(app, env);
   await app.init();
   const db = app.get(DatabaseService);
@@ -51,6 +53,7 @@ export async function identityApp() {
     app,
     db,
 
+    executeSql: database.execute,
     owner,
     token,
     api,
diff --git a/test/identity-auth.spec.ts b/test/identity-auth.spec.ts
index 1522cf8..82fcce2 100644
--- a/test/identity-auth.spec.ts
+++ b/test/identity-auth.spec.ts
@@ -58,7 +58,8 @@ describe('authentication with migrated PostgreSQL engine', () => {
     const missing = await ctx.login('missing@example.com');
     const wrong = await ctx.login('owner@example.com', 'wrong password');
     expect(missing.status).toBe(401);
-    expect(wrong.body).toEqual(missing.body);
+    expect(wrong.body.code).toBe(missing.body.code);
+    expect(wrong.body.message).toBe(missing.body.message);
   });
   it('validates payloads without echoing secrets and rejects mass assignment', async () => {
     const response = await ctx
diff --git a/test/security-http.spec.ts b/test/security-http.spec.ts
new file mode 100644
index 0000000..31cfe8d
--- /dev/null
+++ b/test/security-http.spec.ts
@@ -0,0 +1,71 @@
+import { Logger } from '@nestjs/common';
+import { identityApp, type IdentityApp } from './helpers/identity-app';
+import { randomUUID } from 'node:crypto';
+
+describe('HTTP security boundaries', () => {
+  let ctx: IdentityApp;
+  beforeAll(async () => {
+    ctx = await identityApp();
+  }, 60000);
+  afterAll(async () => {
+    await ctx?.close();
+  });
+  afterEach(() => jest.restoreAllMocks());
+  it('bounds bodies and rejects malformed JSON with distinct codes', async () => {
+    const large = await ctx
+      .api()
+      .post('/api/v1/products')
+      .auth(ctx.token, { type: 'bearer' })
+      .send({ name: 'A', slug: 'a', description: 'x'.repeat(40000) })
+      .expect(413);
+    expect(large.body.code).toBe('REQUEST_TOO_LARGE');
+    const invalid = await ctx
+      .api()
+      .post('/api/v1/products')
+      .set('Content-Type', 'application/json')
+      .send('{"invalid":')
+      .expect(400);
+    expect(invalid.body.code).toBe('REQUEST_MALFORMED');
+  });
+  it('generates its own request IDs and ignores cookie credentials', async () => {
+    const response = await ctx
+      .api()
+      .get('/api/v1/addresses')
+      .set('X-Request-Id', 'attacker-controlled')
+      .set('Cookie', 'accessToken=' + ctx.token)
+      .expect(401);
+    expect(response.body.requestId).toMatch(/^[a-f0-9-]{36}$/);
+    expect(response.headers['x-request-id']).toBe(response.body.requestId);
+    expect(response.headers['cache-control']).toBe('no-store');
+  });
+  it('treats SQL-looking input as data and prevents field injection', async () => {
+    const name = "Robert'); DROP TABLE users;--";
+    await ctx
+      .api()
+      .post('/api/v1/products')
+      .auth(ctx.token, { type: 'bearer' })
+      .send({ name, slug: randomUUID() })
+      .expect(201);
+    expect(await ctx.db.user.count()).toBeGreaterThan(0);
+    await ctx
+      .api()
+      .get('/api/v1/products?limit=999999')
+      .auth(ctx.token, { type: 'bearer' })
+      .expect(400);
+  });
+  it('logs an unexpected database failure without exposing sensitive text', async () => {
+    const logger = jest.spyOn(Logger.prototype, 'error').mockImplementation();
+    jest
+      .spyOn(ctx.db.product, 'findMany')
+      .mockRejectedValueOnce(new Error('SELECT secret password=SECRET'));
+    const response = await ctx
+      .api()
+      .get('/api/v1/products')
+      .auth(ctx.token, { type: 'bearer' })
+      .expect(500);
+    expect(response.body.code).toBe('INTERNAL_FAILURE');
+    expect(JSON.stringify([response.body, logger.mock.calls])).not.toContain(
+      'SECRET',
+    );
+  });
+});