feat(preprod): Add snapshot auto-approval for repeated PR builds (#112421)

Closes EME-976

Adds auto-approval logic for snapshot comparisons. When a snapshot build
on a PR is approved and a subsequent build is uploaded for the same PR
(e.g. after a rebase), the new build is automatically approved if its
"interesting" images (changed, added, removed, errored, renamed) match
the previously approved build — same image names, same categories, and
same content hashes.

This addresses a pain point where rebasing a PR would pull in new
unchanged images from main, causing the snapshot comparison to lose its
approval even though the PR's actual visual changes hadn't changed.
Users were forced to re-approve identical snapshots after every rebase.

The old Emerge implementation required an exact one-to-one match of ALL
images between builds, which broke on rebases. The new approach only
compares the non-unchanged subset, so new unchanged images from main
don't affect auto-approval. Content hashes are still verified to ensure
the PR's actual visual output hasn't changed.

The matching scopes to the same project, app_id, build_configuration, PR
number, and repo name to prevent cross-build false matches.

how the UI looks for an auto-approved snapshot
<img width="1726" height="1744" alt="CleanShot 2026-04-07 at 15 45
02@2x"
src="https://github.com/user-attachments/assets/e9a01fc0-5a0f-47ef-880d-a4c69f963be2"
/>

---------

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

Author: 2 people

src/sentry/preprod/api/endpoints/preprod_artifact_snapshot.py

@@ -394,9 +394,11 @@ def get(self, request: Request, organization: Organization, snapshot_id: str) ->
                             source="github",
                         )
                     )
+            is_auto_approved = any((a.extras or {}).get("auto_approval") is True for a in approved)
             approval_info = SnapshotApprovalInfo(
                 status="approved",
                 approvers=approver_list,
+                is_auto_approved=is_auto_approved,
             )
         elif all_approvals:
             # If records exist but none are APPROVED, they must be NEEDS_APPROVAL

src/sentry/preprod/api/models/snapshots/project_preprod_snapshot_models.py

@@ -59,6 +59,7 @@ class SnapshotApprover(BaseModel):
 class SnapshotApprovalInfo(BaseModel):
     status: Literal["approved", "requires_approval"]
     approvers: list[SnapshotApprover] = []
+    is_auto_approved: bool = False
 
 
 class SnapshotDetailsApiResponse(BaseModel):

src/sentry/preprod/snapshots/tasks.py

@@ -7,12 +7,13 @@
 import orjson
 from django.db import IntegrityError
 from django.utils import timezone
+from objectstore_client import Session
 from objectstore_client.client import RequestError
 from pydantic import ValidationError
 from taskbroker_client.retry import Retry
 
 from sentry.objectstore import get_preprod_session
-from sentry.preprod.models import PreprodArtifact
+from sentry.preprod.models import PreprodArtifact, PreprodComparisonApproval
 from sentry.preprod.snapshots.image_diff.compare import compare_images_batch
 from sentry.preprod.snapshots.image_diff.odiff import OdiffServer
 from sentry.preprod.snapshots.manifest import (
@@ -113,6 +114,128 @@ def _create_pixel_batches(
     return batches
 
 
+class ImageFingerprint(NamedTuple):
+    name: str
+    status: str
+    head_hash: str | None = None
+    previous_image_file_name: str | None = None
+
+
+def _build_comparison_fingerprints(manifest: ComparisonManifest) -> set[ImageFingerprint]:
+    fingerprints: set[ImageFingerprint] = set()
+    for name, image in manifest.images.items():
+        if image.status == "unchanged":
+            continue
+        if image.status in ("changed", "added"):
+            if not image.head_hash:
+                continue
+            fingerprints.add(ImageFingerprint(name, image.status, image.head_hash))
+        elif image.status == "renamed":
+            if not image.head_hash or not image.previous_image_file_name:
+                continue
+            fingerprints.add(
+                ImageFingerprint(name, "renamed", image.head_hash, image.previous_image_file_name)
+            )
+        else:
+            fingerprints.add(ImageFingerprint(name, image.status))
+    return fingerprints
+
+
+def _try_auto_approve_snapshot(
+    head_artifact: PreprodArtifact,
+    comparison_manifest: ComparisonManifest,
+    session: Session,
+) -> None:
+    cc = head_artifact.commit_comparison
+    if not cc or not cc.pr_number or not cc.head_repo_name:
+        return
+
+    head_fingerprints = _build_comparison_fingerprints(comparison_manifest)
+    if not head_fingerprints:
+        return
+
+    approved_sibling = (
+        PreprodArtifact.objects.filter(
+            project_id=head_artifact.project_id,
+            app_id=head_artifact.app_id,
+            build_configuration=head_artifact.build_configuration,
+            commit_comparison__pr_number=cc.pr_number,
+            commit_comparison__head_repo_name=cc.head_repo_name,
+            preprodcomparisonapproval__preprod_feature_type=PreprodComparisonApproval.FeatureType.SNAPSHOTS,
+            preprodcomparisonapproval__approval_status=PreprodComparisonApproval.ApprovalStatus.APPROVED,
+            preprodsnapshotmetrics__snapshot_comparisons_head_metrics__state=PreprodSnapshotComparison.State.SUCCESS,
+        )
+        .exclude(id=head_artifact.id)
+        .order_by("-date_added")
+        .first()
+    )
+
+    if not approved_sibling:
+        return
+
+    sibling_comparison = (
+        PreprodSnapshotComparison.objects.filter(
+            head_snapshot_metrics__preprod_artifact=approved_sibling,
+            state=PreprodSnapshotComparison.State.SUCCESS,
+        )
+        .order_by("-date_updated")
+        .first()
+    )
+
+    if not sibling_comparison:
+        return
+
+    sibling_comparison_key = (sibling_comparison.extras or {}).get("comparison_key")
+    if not sibling_comparison_key:
+        return
+
+    try:
+        sibling_manifest = ComparisonManifest(
+            **orjson.loads(session.get(sibling_comparison_key).payload.read())
+        )
+    except Exception:
+        logger.exception(
+            "auto_approve: failed to load sibling comparison manifest",
+            extra={
+                "head_artifact_id": head_artifact.id,
+                "sibling_artifact_id": approved_sibling.id,
+                "comparison_key": sibling_comparison_key,
+            },
+        )
+        return
+
+    sibling_fingerprints = _build_comparison_fingerprints(sibling_manifest)
+
+    if head_fingerprints != sibling_fingerprints:
+        logger.info(
+            "auto_approve: fingerprints do not match",
+            extra={
+                "head_artifact_id": head_artifact.id,
+                "sibling_artifact_id": approved_sibling.id,
+            },
+        )
+        return
+
+    PreprodComparisonApproval.objects.create(
+        preprod_artifact=head_artifact,
+        preprod_feature_type=PreprodComparisonApproval.FeatureType.SNAPSHOTS,
+        approval_status=PreprodComparisonApproval.ApprovalStatus.APPROVED,
+        approved_at=timezone.now(),
+        extras={
+            "auto_approval": True,
+            "prev_approved_artifact_id": approved_sibling.id,
+        },
+    )
+
+    logger.info(
+        "auto_approve: snapshot auto-approved",
+        extra={
+            "head_artifact_id": head_artifact.id,
+            "prev_approved_artifact_id": approved_sibling.id,
+        },
+    )
+
+
 @instrumented_task(
     name="sentry.preprod.tasks.compare_snapshots",
     namespace=preprod_tasks,
@@ -581,6 +704,14 @@ def _fetch_hash(h: str) -> None:
         ):
             metrics.incr("preprod.snapshots.diff.zero_changes", sample_rate=1.0, tags=metric_tags)
 
+        try:
+            _try_auto_approve_snapshot(head_artifact, comparison_manifest, session)
+        except Exception:
+            logger.exception(
+                "Auto-approve failed after successful comparison",
+                extra={"head_artifact_id": head_artifact_id},
+            )
+
         create_preprod_snapshot_status_check_task.apply_async(
             kwargs={
                 "preprod_artifact_id": head_artifact_id,

static/app/views/preprod/snapshots/header/snapshotHeaderActions.tsx

@@ -5,6 +5,7 @@ import {Tag} from '@sentry/scraps/badge';
 import {Button} from '@sentry/scraps/button';
 import {Flex} from '@sentry/scraps/layout';
 import {Text} from '@sentry/scraps/text';
+import {Tooltip} from '@sentry/scraps/tooltip';
 
 import {addErrorMessage, addSuccessMessage} from 'sentry/actionCreators/indicator';
 import {Client} from 'sentry/api';
@@ -15,6 +16,7 @@ import {
   IconCheckmark,
   IconDelete,
   IconEllipsis,
+  IconInfo,
   IconRefresh,
   IconThumb,
   IconTimer,
@@ -47,6 +49,7 @@ export function SnapshotHeaderActions({
   const [isDeleting, setIsDeleting] = useState(false);
 
   const isApproved = data.approval_info?.status === 'approved';
+  const isAutoApproved = data.approval_info?.is_auto_approved ?? false;
   const approvers: AvatarUser[] = (data.approval_info?.approvers ?? []).map((a, i) => ({
     id: a.id ?? `approver-${i}`,
     name: a.name ?? '',
@@ -148,9 +151,22 @@ export function SnapshotHeaderActions({
       {data.approval_info &&
         (isApproved ? (
           <Flex align="center" gap="xl">
-            <Tag variant="success" icon={<IconCheckmark />}>
-              {t('Approved')}
-            </Tag>
+            <Flex align="center" gap="xs">
+              <Tag variant="success" icon={<IconCheckmark />}>
+                {isAutoApproved ? t('Auto-approved') : t('Approved')}
+              </Tag>
+              {isAutoApproved && (
+                <Tooltip
+                  title={t(
+                    'Automatically approved because the changes match a previously approved build on this PR.'
+                  )}
+                >
+                  <Flex align="center">
+                    <IconInfo size="sm" />
+                  </Flex>
+                </Tooltip>
+              )}
+            </Flex>
             {approvers.length > 0 && (
               <AvatarList users={approvers} avatarSize={24} maxVisibleAvatars={2} />
             )}

static/app/views/preprod/types/snapshotTypes.ts

@@ -36,6 +36,7 @@ export interface SnapshotApprover {
 export interface SnapshotApprovalInfo {
   approvers: SnapshotApprover[];
   status: 'approved' | 'requires_approval';
+  is_auto_approved?: boolean;
 }
 
 export interface SnapshotDetailsApiResponse {