feat(preprod): Persist comparison records for sequential monitor evaluations

Wire _run_size_analysis_comparison into the sequential (n-1) monitor
path so that PreprodArtifactSizeComparison records are created and
file-level diffs are persisted, matching the git-based status check
path. Base metrics are now fetched once per unique base artifact and
cached, removing redundant per-detector DB queries.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mtopo27

src/sentry/preprod/size_analysis/tasks.py

@@ -632,16 +632,13 @@ def _maybe_emit_issues_from_diff_size_results(
                 base = None
             query_to_base[normalized_query] = base
 
-    for detector in detectors:
-        query = detector.config.get("query", "")
-        normalized_query = query.strip() if query else ""
-        base_artifact = query_to_base.get(normalized_query)
-        if base_artifact is None:
-            logger.info(
-                "preprod.size_analysis.diff_results.no_base",
-                extra={"detector_id": detector.id, "artifact_id": artifact.id},
-            )
+    # Run comparisons for unique sequential bases (persists file-level diffs)
+    base_artifact_to_metric: dict[int, PreprodArtifactSizeMetrics] = {}
+    seen_base_ids: set[int] = set()
+    for base_artifact in query_to_base.values():
+        if base_artifact is None or base_artifact.id in seen_base_ids:
             continue
+        seen_base_ids.add(base_artifact.id)
 
         base_metrics = list(
             PreprodArtifactSizeMetrics.objects.filter(
@@ -654,6 +651,31 @@ def _maybe_emit_issues_from_diff_size_results(
             continue
 
         base_metric = base_metrics[0]
+        base_artifact_to_metric[base_artifact.id] = base_metric
+
+        with transaction.atomic(router.db_for_write(PreprodArtifactSizeComparison)):
+            PreprodArtifactSizeComparison.objects.get_or_create(
+                head_size_analysis=head_metric,
+                base_size_analysis=base_metric,
+                organization_id=org_id,
+                defaults={"state": PreprodArtifactSizeComparison.State.PENDING},
+            )
+        _run_size_analysis_comparison(org_id, head_metric, base_metric)
+
+    for detector in detectors:
+        query = detector.config.get("query", "")
+        normalized_query = query.strip() if query else ""
+        base_artifact = query_to_base.get(normalized_query)
+        if base_artifact is None:
+            logger.info(
+                "preprod.size_analysis.diff_results.no_base",
+                extra={"detector_id": detector.id, "artifact_id": artifact.id},
+            )
+            continue
+
+        base_metric = base_artifact_to_metric.get(base_artifact.id)
+        if base_metric is None:
+            continue
 
         metadata: SizeAnalysisMetadata = {
             "platform": _get_platform(artifact),

tests/sentry/preprod/size_analysis/test_size_analysis_tasks.py

@@ -3,7 +3,11 @@
 
 from django.utils import timezone
 
-from sentry.preprod.models import PreprodArtifact, PreprodArtifactSizeMetrics
+from sentry.preprod.models import (
+    PreprodArtifact,
+    PreprodArtifactSizeComparison,
+    PreprodArtifactSizeMetrics,
+)
 from sentry.preprod.size_analysis.grouptype import (
     PreprodSizeAnalysisGroupType,
     _artifact_to_tags,
@@ -220,6 +224,25 @@ def test_batches_queries(self):
             # Should only be called once for the shared empty query
             assert mock_lookup.call_count == 1
 
+    def test_creates_comparison_record(self):
+        now = timezone.now()
+        self._create_artifact_with_metrics(
+            max_install_size=4000000,
+            date_added=now - timedelta(hours=2),
+        )
+        head = self._create_artifact_with_metrics(
+            max_install_size=5000000,
+            date_added=now - timedelta(hours=1),
+        )
+        self._create_diff_detector()
+
+        with self.feature("organizations:preprod-issues"):
+            maybe_emit_issues_from_diff_size_results(head, self.organization.id)
+
+        assert PreprodArtifactSizeComparison.objects.count() == 1
+        comparison = PreprodArtifactSizeComparison.objects.first()
+        assert comparison is not None
+
 
 class MaybeEmitIssuesFromSizeResultsTest(TestCase):
     """Tests for the maybe_emit_issues_from_absolute_size_results function."""