diff --git a/server/src/common/types/fastify-cookie.d.ts b/server/src/common/types/fastify-cookie.d.ts
new file mode 100644
index 000000000..16bfda76c
--- /dev/null
+++ b/server/src/common/types/fastify-cookie.d.ts
@@ -0,0 +1,14 @@
+import type fastifyCookie from '@fastify/cookie';
+
+// TypeScript 6 does not merge the plugin's package-level augmentation into Fastify's source interfaces.
+declare module 'fastify/types/request' {
+  interface FastifyRequest {
+    cookies: Record<string, string | undefined>;
+  }
+}
+
+declare module 'fastify/types/reply' {
+  interface FastifyReply {
+    setCookie(name: string, value: string, options?: fastifyCookie.CookieSerializeOptions): this;
+  }
+}
diff --git a/server/src/common/utils/bootstrap.utils.test.ts b/server/src/common/utils/bootstrap.utils.test.ts
index 37d71c45b..391d4fb38 100644
--- a/server/src/common/utils/bootstrap.utils.test.ts
+++ b/server/src/common/utils/bootstrap.utils.test.ts
@@ -98,35 +98,22 @@ describe('parseTrustProxy', () => {
     expect(parseTrustProxy('   ')).toBe('loopback,linklocal,uniquelocal');
   });
 
-  it.each(['false', '0', 'no', 'off'])('returns false for falsy string %s', (val) => {
+  it.each(['false', 'no', 'off'])('returns false for falsy string %s', (val) => {
     expect(parseTrustProxy(val)).toBe(false);
   });
 
-  it.each(['true', '1', 'yes', 'on'])('returns true for truthy string %s', (val) => {
+  it.each(['true', 'yes', 'on'])('returns true for truthy string %s', (val) => {
     expect(parseTrustProxy(val)).toBe(true);
   });
 
-  it('parses non-negative integer hop counts', () => {
-    expect(parseTrustProxy('0')).toBe(false); // '0' is a falsy string, handled before hop-count check
-    expect(parseTrustProxy('1')).toBe(true); // '1' is a truthy string
-    expect(parseTrustProxy('2')).toBe(2);
-    expect(parseTrustProxy('10')).toBe(10);
-  });
-
   it('returns the raw string for arbitrary proxy values', () => {
     expect(parseTrustProxy('127.0.0.1')).toBe('127.0.0.1');
     expect(parseTrustProxy('10.0.0.0/8')).toBe('10.0.0.0/8');
     expect(parseTrustProxy('loopback')).toBe('loopback');
   });
 
-  it('returns the raw string for decimal numbers (not valid integers)', () => {
-    expect(parseTrustProxy('1.5')).toBe('1.5');
-    expect(parseTrustProxy('2.9')).toBe('2.9');
-  });
-
-  it('returns the raw string for negative integers', () => {
-    expect(parseTrustProxy('-1')).toBe('-1');
-    expect(parseTrustProxy('-5')).toBe('-5');
+  it.each(['0', '1', '2', '10', '1.5', '2.9', '-1', '-5', '1e2'])('rejects numeric hop-count value %s', (value) => {
+    expect(() => parseTrustProxy(value)).toThrow('Numeric TRUST_PROXY hop counts are not supported; configure trusted proxy IP or CIDR ranges');
   });
 
   it('trims surrounding whitespace before evaluating', () => {
diff --git a/server/src/common/utils/bootstrap.utils.ts b/server/src/common/utils/bootstrap.utils.ts
index aba5c6c2f..f2d58c4a9 100644
--- a/server/src/common/utils/bootstrap.utils.ts
+++ b/server/src/common/utils/bootstrap.utils.ts
@@ -10,16 +10,17 @@ const BODY_METHODS = new Set(['DELETE', 'PATCH', 'POST', 'PUT']);
 const HSTS_MAX_AGE_SECONDS = 365 * 24 * 60 * 60;
 const HSTS_HEADER_VALUE = `max-age=${HSTS_MAX_AGE_SECONDS}; includeSubDomains`;
 
-export function parseTrustProxy(value: string | undefined): string | boolean | number {
+export function parseTrustProxy(value: string | undefined): string | boolean {
   const raw = value?.trim();
   if (!raw) return DEFAULT_TRUST_PROXY;
 
   const normalized = raw.toLowerCase();
-  if (['false', '0', 'no', 'off'].includes(normalized)) return false;
-  if (['true', '1', 'yes', 'on'].includes(normalized)) return true;
+  if (['false', 'no', 'off'].includes(normalized)) return false;
+  if (['true', 'yes', 'on'].includes(normalized)) return true;
 
-  const hopCount = Number(raw);
-  if (Number.isInteger(hopCount) && hopCount >= 0) return hopCount;
+  if (!Number.isNaN(Number(raw))) {
+    throw new Error('Numeric TRUST_PROXY hop counts are not supported; configure trusted proxy IP or CIDR ranges');
+  }
 
   return raw;
 }
diff --git a/server/src/config/env.validation.test.ts b/server/src/config/env.validation.test.ts
index da2e7d90f..b06259e01 100644
--- a/server/src/config/env.validation.test.ts
+++ b/server/src/config/env.validation.test.ts
@@ -99,6 +99,18 @@ describe('validateEnv', () => {
     ).toThrow('SWAGGER_ENABLED must be one of true/false/1/0/yes/no/on/off');
   });
 
+  it('accepts explicit trusted proxy addresses and boolean values', () => {
+    for (const TRUST_PROXY of ['', 'true', 'false', 'yes', 'no', 'on', 'off', 'loopback,linklocal,uniquelocal', '127.0.0.1', '10.0.0.0/8']) {
+      expect(() => validateEnv({ ...BASE_ENV, TRUST_PROXY })).not.toThrow();
+    }
+  });
+
+  it.each(['0', '1', '2', '10', '1.5', '-1', '1e2'])('rejects numeric TRUST_PROXY hop count %s', (TRUST_PROXY) => {
+    expect(() => validateEnv({ ...BASE_ENV, TRUST_PROXY })).toThrow(
+      'TRUST_PROXY must be a boolean value or trusted proxy IP/CIDR; numeric hop counts are not supported',
+    );
+  });
+
   it('accepts a custom Book Dock container path', () => {
     expect(() =>
       validateEnv({
diff --git a/server/src/config/env.validation.ts b/server/src/config/env.validation.ts
index d62db42a9..dd8323060 100644
--- a/server/src/config/env.validation.ts
+++ b/server/src/config/env.validation.ts
@@ -3,6 +3,7 @@ import { isAbsolute } from 'node:path';
 import { z } from 'zod';
 
 const BOOLEAN_ENV_VALUES = ['true', 'false', '1', '0', 'yes', 'no', 'on', 'off'];
+const TRUST_PROXY_BOOLEAN_VALUES = ['true', 'false', 'yes', 'no', 'on', 'off'];
 
 function isValidPostgresConnectionString(value: string): boolean {
   if (!value.trim()) {
@@ -32,6 +33,16 @@ function booleanEnvFlag(name: string) {
     .optional();
 }
 
+function trustProxyEnv() {
+  return z
+    .string()
+    .trim()
+    .refine((value) => value === '' || TRUST_PROXY_BOOLEAN_VALUES.includes(value.toLowerCase()) || Number.isNaN(Number(value)), {
+      message: 'TRUST_PROXY must be a boolean value or trusted proxy IP/CIDR; numeric hop counts are not supported',
+    })
+    .optional();
+}
+
 const envSchema = z.object({
   NODE_ENV: z.enum(['development', 'production', 'test']).default('development'),
   DATABASE_URL: z.string().refine(isValidPostgresConnectionString, 'DATABASE_URL must be a valid PostgreSQL connection string').optional(),
@@ -58,7 +69,7 @@ const envSchema = z.object({
   FILE_WRITE_MAX_CONCURRENT_WRITES: z.coerce.number().int().positive().optional(),
   CLIENT_URL: z.string().url().optional(),
   APP_URL: z.string().url().default('http://localhost:5173'),
-  TRUST_PROXY: z.string().optional(),
+  TRUST_PROXY: trustProxyEnv(),
   EMAIL_ENCRYPTION_KEY: z.string().optional(),
   MIGRATION_ENCRYPTION_KEY: z.string().optional(),
   MIGRATION_IMPORT_ROOT: z
diff --git a/server/src/main.ts b/server/src/main.ts
index f3c6fa78c..2d5ca3be3 100644
--- a/server/src/main.ts
+++ b/server/src/main.ts
@@ -12,6 +12,7 @@ import fastifyMultipart from '@fastify/multipart';
 import fastifyStatic from '@fastify/static';
 import fastifyHelmet from '@fastify/helmet';
 import fastifyCompress from '@fastify/compress';
+import type { FastifyInstance } from 'fastify';
 import { appConfig } from './config/config';
 import { setupSwaggerDocs } from './swagger';
 import {
@@ -35,6 +36,8 @@ async function bootstrap() {
   app.useLogger(app.get(Logger));
 
   const fastify = adapter.getInstance();
+  // Nest adds originalUrl to the raw request, but these helpers only use standard Fastify APIs.
+  const standardFastify = fastify as unknown as FastifyInstance;
 
   // Fastify's default JSON parser rejects empty bodies, so we inject '{}' before parsing.
   fastify.addHook('preParsing', (request, _reply, payload, done) => {
@@ -45,7 +48,7 @@ async function bootstrap() {
     done(null, payload);
   });
   // Reverse proxies can forward empty mutating requests with chunked transfer or an unsupported content type.
-  registerEmptyBodyContentTypeParser(fastify);
+  registerEmptyBodyContentTypeParser(standardFastify);
 
   // Echo pino-http's request ID so clients can correlate errors with server logs.
   fastify.addHook('onSend', (_request, reply, _payload, done) => {
@@ -78,7 +81,7 @@ async function bootstrap() {
   }
 
   await app.register(fastifyHelmet as never, buildHelmetOptions({ allowCloudflareInsights }));
-  registerConditionalHsts(fastify);
+  registerConditionalHsts(standardFastify);
 
   await app.register(fastifyCompress as never, { encodings: ['gzip', 'br'] });