diff --git a/cms/djangoapps/contentstore/rest_api/v2/tests/__init__.py b/cms/djangoapps/contentstore/rest_api/v2/tests/__init__.py
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/cms/djangoapps/contentstore/rest_api/v2/tests/test_home.py b/cms/djangoapps/contentstore/rest_api/v2/tests/test_home.py
new file mode 100644
index 000000000000..1b3a034be8ad
--- /dev/null
+++ b/cms/djangoapps/contentstore/rest_api/v2/tests/test_home.py
@@ -0,0 +1,53 @@
+"""
+ADR 0029 – Standardized error-response tests for home views (v2).
+
+Both HomeCoursesViewSetV2 and HomePageCoursesViewV2 are free of
+DeveloperErrorViewMixin and inline error returns. These tests are regression
+tests verifying that the central exception handler produces the correct
+ADR 0029 envelope for auth errors.
+"""
+from django.urls import reverse
+from rest_framework import status
+from rest_framework.test import APIClient, APITestCase
+
+_REQUIRED_ERROR_FIELDS = ("type", "title", "status", "detail", "instance")
+
+
+class TestHomeCoursesViewSetV2ErrorShape(APITestCase):
+    """
+    ADR 0029 – error response shape regression tests for HomeCoursesViewSetV2.
+
+    Verifies that 401 responses on the list action conform to the standardized
+    JSON envelope.
+    """
+
+    def setUp(self):
+        super().setUp()
+        self.client = APIClient()
+        self.list_url = reverse("cms.djangoapps.contentstore:v2:home-courses-list")
+
+    def test_unauthenticated_returns_standardized_401(self):
+        """Unauthenticated GET must return 401 with the ADR 0029 envelope."""
+        response = self.client.get(self.list_url)
+        self.assertEqual(response.status_code, status.HTTP_401_UNAUTHORIZED)
+        for field in _REQUIRED_ERROR_FIELDS:
+            self.assertIn(field, response.data, f"ADR 0029: missing field '{field}'")
+
+    def test_unauthenticated_401_type_uri(self):
+        """The ``type`` field for 401 must be the ADR 0029 authn URI."""
+        response = self.client.get(self.list_url)
+        self.assertEqual(response.status_code, status.HTTP_401_UNAUTHORIZED)
+        self.assertEqual(response.data.get("type"), "https://docs.openedx.org/errors/authn")
+
+    def test_error_body_has_no_developer_message(self):
+        """Error responses must NOT contain old DeveloperErrorViewMixin fields."""
+        response = self.client.get(self.list_url)
+        self.assertEqual(response.status_code, status.HTTP_401_UNAUTHORIZED)
+        self.assertNotIn("developer_message", response.data)
+        self.assertNotIn("error_code", response.data)
+
+    def test_instance_field_is_request_path(self):
+        """The ``instance`` field must equal the request path."""
+        response = self.client.get(self.list_url)
+        self.assertEqual(response.status_code, status.HTTP_401_UNAUTHORIZED)
+        self.assertEqual(response.data.get("instance"), self.list_url)
diff --git a/openedx/core/lib/api/exceptions.py b/openedx/core/lib/api/exceptions.py
new file mode 100644
index 000000000000..ad394b66a790
--- /dev/null
+++ b/openedx/core/lib/api/exceptions.py
@@ -0,0 +1,81 @@
+"""ADR 0029 – Standardized error-response exception handler and helpers."""
+from rest_framework.exceptions import APIException, ValidationError
+from rest_framework.response import Response
+
+
+class Conflict(APIException):
+    """HTTP 409 Conflict — ADR 0029."""
+    status_code = 409
+    default_detail = "A conflict occurred."
+    default_code = "conflict"
+
+
+def standardized_error_exception_handler(exc, context):
+    """ADR 0029 – platform-level DRF exception handler."""
+    from openedx.core.lib.request_utils import ignored_error_exception_handler
+    response = ignored_error_exception_handler(exc, context)
+    if response is None:
+        return Response(
+            {"type": "https://docs.openedx.org/errors/internal",
+             "title": "Internal Server Error", "status": 500,
+             "detail": "An unexpected error occurred. Please try again later."},
+            status=500,
+        )
+    request = context.get("request")
+    body = {
+        "type": f"https://docs.openedx.org/errors/{_error_type(exc)}",
+        "title": _error_title(exc),
+        "status": response.status_code,
+        "detail": _flatten_detail(response.data),
+    }
+    if request:
+        body["instance"] = request.path
+    if hasattr(exc, "user_message") and exc.user_message:
+        body["user_message"] = exc.user_message
+    if isinstance(exc, ValidationError) and hasattr(exc, "detail"):
+        body["errors"] = _normalize_validation_errors(exc.detail)
+    response.data = body
+    response["Content-Type"] = "application/json"
+    return response
+
+
+def _error_type(exc):
+    from rest_framework.exceptions import (
+        AuthenticationFailed, NotAuthenticated, NotFound, PermissionDenied, Throttled, ValidationError,
+    )
+    if isinstance(exc, (NotAuthenticated, AuthenticationFailed)): return "authn"
+    if isinstance(exc, PermissionDenied): return "authz"
+    if isinstance(exc, NotFound): return "not-found"
+    if isinstance(exc, ValidationError): return "validation"
+    if isinstance(exc, Throttled): return "rate-limited"
+    if isinstance(exc, Conflict): return "conflict"
+    return "internal"
+
+
+def _error_title(exc):
+    from rest_framework.exceptions import (
+        AuthenticationFailed, NotAuthenticated, NotFound, PermissionDenied, Throttled, ValidationError,
+    )
+    return {
+        NotAuthenticated: "Authentication Required",
+        AuthenticationFailed: "Authentication Failed",
+        PermissionDenied: "Permission Denied",
+        NotFound: "Not Found",
+        ValidationError: "Validation Error",
+        Throttled: "Too Many Requests",
+        Conflict: "Conflict",
+    }.get(type(exc), "Internal Server Error")
+
+
+def _flatten_detail(data):
+    if isinstance(data, str): return data
+    if isinstance(data, dict) and "detail" in data: return str(data["detail"])
+    if isinstance(data, list) and data: return str(data[0])
+    return str(data)
+
+
+def _normalize_validation_errors(detail):
+    if isinstance(detail, dict):
+        return {f: [str(e) for e in (errs if isinstance(errs, list) else [errs])] for f, errs in detail.items()}
+    if isinstance(detail, list): return {"non_field_errors": [str(e) for e in detail]}
+    return {"non_field_errors": [str(detail)]}
diff --git a/openedx/envs/common.py b/openedx/envs/common.py
index 5d7c105025ed..1247116e397c 100644
--- a/openedx/envs/common.py
+++ b/openedx/envs/common.py
@@ -820,7 +820,7 @@ def add_optional_apps(optional_apps, installed_apps):
     'DEFAULT_RENDERER_CLASSES': (
         'rest_framework.renderers.JSONRenderer',
     ),
-    'EXCEPTION_HANDLER': 'openedx.core.lib.request_utils.ignored_error_exception_handler',
+    'EXCEPTION_HANDLER': 'openedx.core.lib.api.exceptions.standardized_error_exception_handler',  # ADR 0029
     'PAGE_SIZE': 10,
     'URL_FORMAT_OVERRIDE': None,
     'DEFAULT_THROTTLE_RATES': {