feat(autofix): Thread insert_index through explorer API for step retry (#112287)

Thread `insert_index` through the explorer autofix API so the frontend
can request
a retry-from-step that truncates all downstream blocks. When provided,
Seer does
`blocks = blocks[:insert_index]` before re-running the step, ensuring
downstream
sections (e.g. Code Changes after retrying Plan) are properly removed.

Changes:
- Add `insert_index` field to `ExplorerAutofixRequestSerializer`
- Pass it through `trigger_autofix_explorer()` → `client.continue_run()`

A follow-up frontend PR (#112290) adds retry buttons that use this
parameter.

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: isaacwang-sentry

src/sentry/seer/autofix/autofix_agent.py

@@ -230,6 +230,7 @@ def trigger_autofix_explorer(
     stopping_point: AutofixStoppingPoint | None = None,
     intelligence_level: Literal["low", "medium", "high"] = "low",
     user_context: str | None = None,
+    insert_index: int | None = None,
 ) -> int:
     """
     Start or continue an Explorer-based autofix run.
@@ -287,6 +288,7 @@ def trigger_autofix_explorer(
             prompt_metadata=prompt_metadata,
             artifact_key=artifact_key,
             artifact_schema=artifact_schema,
+            insert_index=insert_index,
         )
 
     payload = {

src/sentry/seer/endpoints/group_ai_autofix.py

@@ -129,6 +129,10 @@ class ExplorerAutofixRequestSerializer(CamelSnakeSerializer):
         required=False,
         help_text="Optional repository name for which to create the pull request. Do not pass a repository name to create pull requests in all relevant repositories.",
     )
+    insert_index = serializers.IntegerField(
+        required=False,
+        help_text="Block index to insert at. When provided, truncates blocks after this point for retry-from-step.",
+    )
 
     def validate(self, data: dict[str, Any]) -> dict[str, Any]:
         stopping_point = data.get("stopping_point", None)
@@ -289,6 +293,7 @@ def _post_explorer(self, request: Request, group: Group) -> Response:
                 run_id=run_id,
                 intelligence_level=data["intelligence_level"],
                 user_context=data.get("user_context"),
+                insert_index=data.get("insert_index"),
             )
             return Response({"run_id": run_id}, status=status.HTTP_202_ACCEPTED)
         except SeerPermissionError as e:

tests/sentry/seer/endpoints/test_group_ai_autofix.py

@@ -940,6 +940,35 @@ def test_stopping_point(self, mock_trigger_explorer):
                 run_id=None,
                 intelligence_level="low",
                 user_context=None,
+                insert_index=None,
+            )
+
+    @patch("sentry.seer.endpoints.group_ai_autofix.trigger_autofix_explorer")
+    def test_insert_index_passed_through(self, mock_trigger_explorer):
+        """POST passes insert_index to trigger_autofix_explorer for retry-from-step."""
+        for flag in EXPLORER_FLAGS:
+            mock_trigger_explorer.reset_mock()
+            group = self.create_group()
+            mock_trigger_explorer.return_value = 123
+
+            self.login_as(user=self.user)
+            with self.feature(flag):
+                response = self.client.post(
+                    self._get_url(group.id, mode="explorer"),
+                    data={"step": "solution", "run_id": 42, "insert_index": 3},
+                    format="json",
+                )
+
+            assert response.status_code == 202, f"Failed for {flag}: {response.data}"
+            mock_trigger_explorer.assert_called_once_with(
+                group=group,
+                step=AutofixStep.SOLUTION,
+                referrer=AutofixReferrer.GROUP_AUTOFIX_ENDPOINT,
+                stopping_point=None,
+                run_id=42,
+                intelligence_level="low",
+                user_context=None,
+                insert_index=3,
             )
 
     @patch("sentry.seer.autofix.autofix._call_autofix")