Fix bounded timeline projection rebuild

Bounded Waterline timeline reads now repair missing run timeline projection rows before returning a limited window, preserving the projected fast path when rows already exist.

Issue: zorporation/durable-workflow#539

Loop-ID: build-03

Author: durable-workflow-ops

src/V2/Support/RunTimelineProjector.php

@@ -151,6 +151,21 @@ private static function projectedWindow(WorkflowRun $run, int $limit): array
         $total = (int) (clone $baseQuery)->count();
 
         if ($total === 0) {
+            $canonicalTimeline = HistoryTimeline::fromHistory($run);
+
+            if ($canonicalTimeline !== []) {
+                $reprojected = self::project($run, $canonicalTimeline);
+
+                return self::boundedTimelinePayload(
+                    collect($reprojected)
+                        ->map(static fn (WorkflowTimelineEntry $entry): array => $entry->toTimelinePayload())
+                        ->values()
+                        ->all(),
+                    $limit,
+                    'workflow_run_timeline_entries_rebuilt_window',
+                );
+            }
+
             return [
                 'source' => 'workflow_run_timeline_entries_window',
                 'timeline' => [],
@@ -176,6 +191,19 @@ private static function projectedWindow(WorkflowRun $run, int $limit): array
         ];
     }
 
+    /**
+     * @param list<array<string, mixed>> $timeline
+     * @return array{source: string, timeline: list<array<string, mixed>>, total_count: int}
+     */
+    private static function boundedTimelinePayload(array $timeline, int $limit, string $source): array
+    {
+        return [
+            'source' => $source,
+            'timeline' => array_values(array_slice($timeline, -$limit)),
+            'total_count' => count($timeline),
+        ];
+    }
+
     /**
      * @return class-string<WorkflowTimelineEntry>
      */

tests/Feature/V2/V2HistoryTimelineTest.php

@@ -721,6 +721,44 @@ public function testTimelineProjectorCanReadBoundedProjectedWindowWithoutHistory
         );
     }
 
+    public function testBoundedTimelineRebuildsMissingProjectionRowsBeforeReturningWindow(): void
+    {
+        Queue::fake();
+
+        $workflow = WorkflowStub::make(TestGreetingWorkflow::class, 'timeline-projection-window-rebuild');
+        $workflow->start('Taylor');
+        $runId = $workflow->runId();
+
+        $this->assertNotNull($runId);
+
+        $this->drainReadyTasks();
+        $this->assertTrue($workflow->refresh()->completed());
+
+        /** @var WorkflowRun $run */
+        $run = WorkflowRun::query()->findOrFail($runId);
+        $historyCount = $run->historyEvents()
+            ->count();
+
+        $this->assertGreaterThan(2, $historyCount);
+
+        WorkflowTimelineEntry::query()
+            ->where('workflow_run_id', $runId)
+            ->delete();
+
+        $snapshot = RunTimelineProjector::snapshotForRun($run->fresh(), 2);
+
+        $this->assertSame('workflow_run_timeline_entries_rebuilt_window', $snapshot['source']);
+        $this->assertSame($historyCount, $snapshot['total_count']);
+        $this->assertCount(2, $snapshot['timeline']);
+        $this->assertSame(['ActivityCompleted', 'WorkflowCompleted'], array_column($snapshot['timeline'], 'type'));
+        $this->assertSame(
+            $historyCount,
+            WorkflowTimelineEntry::query()
+                ->where('workflow_run_id', $runId)
+                ->count(),
+        );
+    }
+
     public function testTimelineKeepsTimerSnapshotsWhenTimerRowDrifts(): void
     {
         Queue::fake();