diff --git a/sdk/src/query-gsd-tools-runtime.ts b/sdk/src/query-gsd-tools-runtime.ts
index 22a00f4fb..4099c4de1 100644
--- a/sdk/src/query-gsd-tools-runtime.ts
+++ b/sdk/src/query-gsd-tools-runtime.ts
@@ -7,8 +7,7 @@ import { QuerySubprocessAdapter } from './query-subprocess-adapter.js';
 import { QueryNativeDirectAdapter } from './query-native-direct-adapter.js';
 import { QueryNativeHotpathAdapter } from './query-native-hotpath-adapter.js';
 import { formatQueryRawOutput } from './query-raw-output-projection.js';
-import { failureToolsError, timeoutToolsError } from './query-tools-error-factory.js';
-import type { QueryNativeErrorFactory, QueryToolsErrorFactory } from './query-tools-error-seam.js';
+import { createQueryNativeErrorFactory, createQueryToolsErrorFactory } from './query-tools-error-factory.js';
 
 export interface GSDToolsRuntime {
   registry: ReturnType<typeof createRegistry>;
@@ -29,12 +28,7 @@ export function createGSDToolsRuntime(opts: {
 }): GSDToolsRuntime {
   const registry = createRegistry(opts.eventStream, opts.sessionId);
 
-  const queryToolsErrorFactory: QueryToolsErrorFactory = {
-    createTimeoutError: (message, command, args, stderr, timeoutMs) =>
-      timeoutToolsError(message, command, args, stderr, timeoutMs),
-    createFailureError: (message, command, args, exitCode, stderr) =>
-      failureToolsError(message, command, args, exitCode, stderr),
-  };
+  const queryToolsErrorFactory = createQueryToolsErrorFactory();
 
   const subprocessAdapter = new QuerySubprocessAdapter({
     projectDir: opts.projectDir,
@@ -44,12 +38,7 @@ export function createGSDToolsRuntime(opts: {
     ...queryToolsErrorFactory,
   });
 
-  const nativeErrorFactory: QueryNativeErrorFactory = {
-    createNativeTimeoutError: (message, command, args) =>
-      timeoutToolsError(message, command, args, '', opts.timeoutMs),
-    createNativeFailureError: (message, command, args, cause) =>
-      failureToolsError(message, command, args, 1, '', cause),
-  };
+  const nativeErrorFactory = createQueryNativeErrorFactory(opts.timeoutMs);
 
   const nativeDirectAdapter = new QueryNativeDirectAdapter({
     timeoutMs: opts.timeoutMs,
diff --git a/sdk/src/query-tools-error-factory.test.ts b/sdk/src/query-tools-error-factory.test.ts
index dad1075e6..84f63a058 100644
--- a/sdk/src/query-tools-error-factory.test.ts
+++ b/sdk/src/query-tools-error-factory.test.ts
@@ -1,6 +1,8 @@
 import { describe, expect, it } from 'vitest';
 import { ErrorClassification, GSDError } from './errors.js';
 import {
+  createQueryNativeErrorFactory,
+  createQueryToolsErrorFactory,
   failureToolsError,
   timeoutToolsError,
   toToolsErrorFromUnknown,
@@ -22,4 +24,14 @@ describe('query tools error factory', () => {
     const err = toToolsErrorFromUnknown('state', ['load'], new Error('gsd-tools timed out after 50ms: state load'));
     expect(err.classification).toEqual({ kind: 'timeout', timeoutMs: 50 });
   });
+
+  it('builds subprocess/native error factories', () => {
+    const toolsFactory = createQueryToolsErrorFactory();
+    const nativeFactory = createQueryNativeErrorFactory(777);
+
+    expect(toolsFactory.createFailureError('x', 'state', ['load'], 1, '').classification).toEqual({ kind: 'failure' });
+    expect(toolsFactory.createTimeoutError('x', 'state', ['load'], '', 123).classification).toEqual({ kind: 'timeout', timeoutMs: 123 });
+    expect(nativeFactory.createNativeTimeoutError('x', 'state', ['load']).classification).toEqual({ kind: 'timeout', timeoutMs: 777 });
+    expect(nativeFactory.createNativeFailureError('x', 'state', ['load'], new Error('boom')).classification).toEqual({ kind: 'failure' });
+  });
 });
diff --git a/sdk/src/query-tools-error-factory.ts b/sdk/src/query-tools-error-factory.ts
index 838f51381..620a9fe85 100644
--- a/sdk/src/query-tools-error-factory.ts
+++ b/sdk/src/query-tools-error-factory.ts
@@ -1,6 +1,7 @@
 import { GSDError, exitCodeFor } from './errors.js';
 import { GSDToolsError } from './gsd-tools-error.js';
 import { errorMessage, toFailureSignal } from './query-failure-classification.js';
+import type { QueryNativeErrorFactory, QueryToolsErrorFactory } from './query-tools-error-seam.js';
 
 export function timeoutToolsError(message: string, command: string, args: string[], stderr = '', timeoutMs?: number): GSDToolsError {
   return GSDToolsError.timeout(message, command, args, stderr, timeoutMs);
@@ -29,3 +30,21 @@ export function toToolsErrorFromUnknown(command: string, args: string[], err: un
   }
   return failureToolsError(msg, command, args, 1, '', err instanceof Error ? err : undefined);
 }
+
+export function createQueryToolsErrorFactory(): QueryToolsErrorFactory {
+  return {
+    createTimeoutError: (message, command, args, stderr, timeoutMs) =>
+      timeoutToolsError(message, command, args, stderr, timeoutMs),
+    createFailureError: (message, command, args, exitCode, stderr) =>
+      failureToolsError(message, command, args, exitCode, stderr),
+  };
+}
+
+export function createQueryNativeErrorFactory(defaultTimeoutMs: number): QueryNativeErrorFactory {
+  return {
+    createNativeTimeoutError: (message, command, args) =>
+      timeoutToolsError(message, command, args, '', defaultTimeoutMs),
+    createNativeFailureError: (message, command, args, cause) =>
+      failureToolsError(message, command, args, 1, '', cause),
+  };
+}