diff --git a/Data/Engine/builders/device_enrollment.py b/Data/Engine/builders/device_enrollment.py
index 26f64da..92f1217 100644
--- a/Data/Engine/builders/device_enrollment.py
+++ b/Data/Engine/builders/device_enrollment.py
@@ -7,9 +7,11 @@ from dataclasses import dataclass
 from typing import Optional
 
 from Data.Engine.domain.device_auth import DeviceFingerprint, sanitize_service_context
-from Data.Engine.domain.device_enrollment import ProofChallenge
+from Data.Engine.domain.device_enrollment import (
+    EnrollmentValidationError,
+    ProofChallenge,
+)
 from Data.Engine.integrations.crypto import keys as crypto_keys
-from Data.Engine.services.enrollment.errors import EnrollmentValidationError
 
 __all__ = [
     "EnrollmentRequestBuilder",
diff --git a/Data/Engine/domain/device_enrollment.py b/Data/Engine/domain/device_enrollment.py
index 375e463..85b680f 100644
--- a/Data/Engine/domain/device_enrollment.py
+++ b/Data/Engine/domain/device_enrollment.py
@@ -15,6 +15,7 @@ __all__ = [
     "EnrollmentApprovalStatus",
     "EnrollmentApproval",
     "EnrollmentRequest",
+    "EnrollmentValidationError",
     "ProofChallenge",
 ]
 
@@ -41,6 +42,24 @@ def _require(value: Optional[str], field: str) -> str:
     return text
 
 
+@dataclass(frozen=True, slots=True)
+class EnrollmentValidationError(Exception):
+    """Raised when enrollment input fails validation."""
+
+    code: str
+    http_status: int = 400
+    retry_after: Optional[float] = None
+
+    def to_response(self) -> dict[str, object]:
+        payload: dict[str, object] = {"error": self.code}
+        if self.retry_after is not None:
+            payload["retry_after"] = self.retry_after
+        return payload
+
+    def __str__(self) -> str:  # pragma: no cover - debug helper
+        return f"{self.code} (status={self.http_status})"
+
+
 @dataclass(frozen=True, slots=True)
 class EnrollmentCode:
     """Installer code metadata loaded from the persistence layer."""
diff --git a/Data/Engine/services/__init__.py b/Data/Engine/services/__init__.py
index ec0d241..5a2d092 100644
--- a/Data/Engine/services/__init__.py
+++ b/Data/Engine/services/__init__.py
@@ -15,9 +15,9 @@ from .enrollment import (
     EnrollmentService,
     EnrollmentStatus,
     EnrollmentTokenBundle,
-    EnrollmentValidationError,
     PollingResult,
 )
+from Data.Engine.domain.device_enrollment import EnrollmentValidationError
 from .jobs.scheduler_service import SchedulerService
 from .github import GitHubService, GitHubTokenPayload
 from .realtime import AgentRealtimeService, AgentRecord
diff --git a/Data/Engine/services/enrollment/__init__.py b/Data/Engine/services/enrollment/__init__.py
index 129d32c..063cd7b 100644
--- a/Data/Engine/services/enrollment/__init__.py
+++ b/Data/Engine/services/enrollment/__init__.py
@@ -7,9 +7,9 @@ from .enrollment_service import (
     EnrollmentService,
     EnrollmentStatus,
     EnrollmentTokenBundle,
-    EnrollmentValidationError,
     PollingResult,
 )
+from Data.Engine.domain.device_enrollment import EnrollmentValidationError
 
 __all__ = [
     "EnrollmentRequestResult",
diff --git a/Data/Engine/services/enrollment/enrollment_service.py b/Data/Engine/services/enrollment/enrollment_service.py
index ae960e7..e921eb2 100644
--- a/Data/Engine/services/enrollment/enrollment_service.py
+++ b/Data/Engine/services/enrollment/enrollment_service.py
@@ -23,10 +23,10 @@ from Data.Engine.domain.device_enrollment import (
     EnrollmentApproval,
     EnrollmentApprovalStatus,
     EnrollmentCode,
+    EnrollmentValidationError,
 )
 from Data.Engine.services.auth.device_auth_service import DeviceRecord
 from Data.Engine.services.auth.token_service import JWTIssuer
-from Data.Engine.services.enrollment.errors import EnrollmentValidationError
 from Data.Engine.services.enrollment.nonce_cache import NonceCache
 from Data.Engine.services.rate_limit import SlidingWindowRateLimiter
 
diff --git a/Data/Engine/services/enrollment/errors.py b/Data/Engine/services/enrollment/errors.py
deleted file mode 100644
index a77df2d..0000000
--- a/Data/Engine/services/enrollment/errors.py
+++ /dev/null
@@ -1,26 +0,0 @@
-"""Error types shared across enrollment components."""
-
-from __future__ import annotations
-
-from dataclasses import dataclass
-from typing import Optional
-
-__all__ = ["EnrollmentValidationError"]
-
-
-@dataclass(frozen=True, slots=True)
-class EnrollmentValidationError(Exception):
-    """Raised when enrollment input fails validation."""
-
-    code: str
-    http_status: int = 400
-    retry_after: Optional[float] = None
-
-    def to_response(self) -> dict[str, object]:
-        payload: dict[str, object] = {"error": self.code}
-        if self.retry_after is not None:
-            payload["retry_after"] = self.retry_after
-        return payload
-
-    def __str__(self) -> str:  # pragma: no cover - debug helper
-        return f"{self.code} (status={self.http_status})"