diff --git a/artifacts/views.py b/artifacts/views.py
index 9765b9a..0db2e82 100644
--- a/artifacts/views.py
+++ b/artifacts/views.py
@@ -237,6 +237,9 @@ class ArtifactDetailView(APIView):
         length_error = validate_field_lengths(data, ["title", "source_name", "source_id"])
         if length_error:
             return length_error
+        string_error = validate_string_fields(data, ["source_name", "source_id", "source_prompt"])
+        if string_error:
+            return string_error
         if "title" in data:
             if not data["title"]:
                 return Response({"detail": "title cannot be blank"}, status=400)
@@ -860,6 +863,19 @@ def validate_field_lengths(data, fields):
     return None
 
 
+def validate_string_fields(data, fields):
+    """Rejects non-string JSON types (object/array/number) instead of letting
+    them reach save(), where Django's CharField/TextField silently coerce via
+    str() - which for a dict/list produces Python repr() syntax, not JSON,
+    and is irreversible.
+    """
+    for field in fields:
+        value = data.get(field)
+        if value is not None and not isinstance(value, str):
+            return Response({"detail": f"{field} must be a string"}, status=400)
+    return None
+
+
 def validate_content_shape(kind, content):
     lower = (content or "").lower()
     if kind == Artifact.DECK and "<section" not in lower:
@@ -889,6 +905,9 @@ def validate_source_fields(data):
     length_error = validate_field_lengths(data, ["source", "title", "source_name", "source_id", "theme"])
     if length_error:
         return length_error
+    string_error = validate_string_fields(data, ["source_name", "source_id", "source_prompt"])
+    if string_error:
+        return string_error
     if source_type := data.get("source_type"):
         if source_type not in {choice[0] for choice in Artifact.SOURCE_TYPE_CHOICES}:
             return Response({"detail": "source_type must be agent, person, or system"}, status=400)
diff --git a/issues/008-source-fields-untyped-and-mangled.md b/issues/008-source-fields-untyped-and-mangled.md
new file mode 100644
index 0000000..e7cbee7
--- /dev/null
+++ b/issues/008-source-fields-untyped-and-mangled.md
@@ -0,0 +1,70 @@
+# 008 — `source_name`/`source_id`/`source_prompt` accept any JSON type and get silently mangled into `repr()` strings
+
+**Status:** Fixed
+
+Follow-up to the #007 handover, which specifically asked to probe other
+wrong-typed `PATCH` fields beyond `tags` now that #005 is fixed.
+
+## Description
+
+Unlike `tags`, `metadata`, and `tag_colors` (all now type-checked, `tags`
+since #005), `source_name`, `source_id`, and `source_prompt` accept any
+JSON type — object, array, number — on both `POST` (`source_fields()` in
+`views.py`) and `PATCH` (`ArtifactDetailView.patch`). Nothing validates
+they're strings before assignment.
+
+`source_name`/`source_id` are `CharField`, `source_prompt` is `TextField`.
+Django's `Field.get_prep_value()` silently coerces non-string input via
+plain `str(value)` at save time — which for a `dict`/`list` produces
+**Python `repr()` syntax, not JSON**: `{"a": 1}` becomes the *string*
+`"{'a': 1}"` (single quotes, unparseable as JSON). This is lossy and
+irreversible — there's no way to recover the original structured value.
+
+**Worse: the API response is internally inconsistent.** Immediately after
+a `POST`/`PATCH` with a non-string value, the response echoes back the
+*raw, pre-save Python object* (still a real JSON object/array in the
+response body) — but a subsequent `GET` of the same artifact returns the
+mangled `repr()` string instead. Same request, two different apparent
+types for the same field depending only on *when* you read it.
+
+Reproduced:
+
+```bash
+# PATCH source_name with an int, source_id with a list, source_prompt with a dict
+curl -X PATCH .../api/artifacts/a74de286 -d '{"source_name": 12345}' ...
+# -> 200, response shows "source_name": 12345 (int)
+
+curl .../api/artifacts/a74de286   # fresh GET, session auth
+# -> "source_name": "12345" (string)
+
+# Actual DB values (confirmed via shell):
+# source_name = '12345'
+# source_id   = "['a', 'b']"          <- repr() of the list, not JSON
+# source_prompt = "{'nested': 'object'}"  <- repr() of the dict, not JSON
+```
+
+Also reproduced identically on `POST` (create), not just `PATCH` — a
+freshly created artifact's immediate response shows
+`"source_name": {"a": 1}` (real object) even though what's stored (and
+what any later `GET` returns) is the mangled string form.
+
+## Suggested Fix
+
+Add a type check for `source_name`, `source_id`, and `source_prompt`
+(must be `str` or absent/null) alongside the existing `tags`/`metadata`/
+`tag_colors` checks in `validate_source_fields` (create path) and
+`ArtifactDetailView.patch` (update path) — return `400` naming the field,
+consistent with #005's approach for `tags`. This also removes the
+response/DB inconsistency, since invalid types would never reach `save()`
+in the first place.
+
+## Resolution
+
+Added `validate_string_fields(data, fields)` in `artifacts/views.py`,
+rejecting any non-`None`, non-`str` value with `400`. Called from
+`validate_source_fields` (covers `POST`, both text and binary paths) and
+directly in `ArtifactDetailView.patch` for `source_name`, `source_id`,
+`source_prompt` — matching #005's approach for `tags`. Invalid values never
+reach `save()`, so the response/DB inconsistency the issue described can no
+longer occur. Verified live against the running dev instance and with new
+tests in `tests/api/test_artifacts.py`.
diff --git a/tests/api/test_artifacts.py b/tests/api/test_artifacts.py
index e889e06..bbd634e 100644
--- a/tests/api/test_artifacts.py
+++ b/tests/api/test_artifacts.py
@@ -427,3 +427,31 @@ class ArtifactAPITestCase(APITestCase):
     def test_create_csv_artifact_with_header_only(self):
         response = self.create_artifact(kind="csv", content="name,score")
         self.assertEqual(response.status_code, 201)
+
+    # -- source_name/source_id/source_prompt type checks (issue #008) -------
+
+    def test_create_rejects_non_string_source_name(self):
+        response = self.create_artifact(source_name=12345)
+        self.assertEqual(response.status_code, 400)
+        self.assertIn("source_name", response.data["detail"])
+
+    def test_create_rejects_non_string_source_id(self):
+        response = self.create_artifact(source_id=["a", "b"])
+        self.assertEqual(response.status_code, 400)
+
+    def test_create_rejects_non_string_source_prompt(self):
+        response = self.create_artifact(source_prompt={"nested": "object"})
+        self.assertEqual(response.status_code, 400)
+
+    def test_patch_rejects_non_string_source_name(self):
+        artifact_id = self.create_artifact().data["id"]
+        response = self.client.patch(
+            reverse("artifact-detail-api", args=[artifact_id]),
+            {"source_name": 12345},
+            format="json",
+            **self.auth_headers(self.token),
+        )
+        self.assertEqual(response.status_code, 400)
+
+        artifact = Artifact.objects.get(pk=artifact_id)
+        self.assertEqual(artifact.source_name, "test-agent")  # unchanged, not mangled