Preserve legacy version fallback in offline replay

composer.json

@@ -79,7 +79,7 @@
             "dev-main": "2.0.x-dev"
         },
         "durable-workflow": {
-            "product-train": "2.5.0",
+            "product-train": "2.5.1",
             "laravel-embedded-upgrade-contract": "resources/laravel-embedded-upgrade-contract.json",
             "laravel-dependency-security-policy": "resources/laravel-dependency-security-policy.json"
         },

scripts/ci/validate-regression-corpus.py

@@ -161,6 +161,7 @@
         "tests/Fixtures/V2/TestParallelChildReplayWorkflow.php",
         "tests/Fixtures/V2/TestSequentialChildReplayWorkflow.php",
         "tests/Fixtures/V2/TestServiceResponseReplayWorkflow.php",
+        "tests/Fixtures/V2/TestLegacyPatchReplayWorkflow.php",
         "tests/Fixtures/V2/TestServiceGroupedConditionReopenWorkflow.php",
         "tests/Fixtures/V2/TestSignalResumedParallelWorkflow.php",
         "tests/Fixtures/V2/TestCancellationContextWorkflow.php",

src/V2/Support/QueryStateReplayer.php

@@ -326,13 +326,17 @@ public function replayState(WorkflowRun $run): ReplayState
                 $historySequence = $this->historySequenceForReplayPosition($historySequencesByPosition, $sequence);
 
                 $this->applyRecordedUpdates($run, $workflow, $historySequence);
-                WorkflowStepHistory::assertCompatible($run, $historySequence, WorkflowStepHistory::VERSION_MARKER, [
-                    'change_id' => $current->changeId,
-                ]);
-
                 $versionEvent = $this->versionMarkerEvent($run, $historySequence);
                 $resolution = VersionResolver::resolve($run, $versionEvent, $current, $historySequence);
 
+                // A legacy default occupies no history slot. The next durable
+                // step can already be recorded at this position.
+                if ($resolution->advancesSequence) {
+                    WorkflowStepHistory::assertCompatible($run, $historySequence, WorkflowStepHistory::VERSION_MARKER, [
+                        'change_id' => $current->changeId,
+                    ]);
+                }
+
                 $this->syncWorkflowCursor($workflow, $sequence + ($resolution->advancesSequence ? 1 : 0));
                 $current = $workflowExecution->send(
                     $current->resolveValue($resolution->version),

tests/Feature/V2/V2EmbeddedReplayRegressionCorpusTest.php

@@ -8,6 +8,7 @@
 use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Facades\Queue;
 use Symfony\Component\Uid\Ulid;
+use Tests\Fixtures\V2\TestQueryReplayGuardActivity;
 use Tests\TestCase;
 use Throwable;
 use Workflow\Serializers\Serializer;
@@ -39,6 +40,7 @@
 use Workflow\V2\Support\EmbeddedV2HistoryImport;
 use Workflow\V2\Support\HistoryExport;
 use Workflow\V2\Support\QueryStateReplayer;
+use Workflow\V2\Support\ReplayDiff;
 use Workflow\V2\Support\RunActivityView;
 use Workflow\V2\Support\RunTimelineProjector;
 use Workflow\V2\Support\WorkflowFiberRunner;
@@ -121,6 +123,12 @@ public function testFixturesExecuteThroughDeclaredReplayConsumers(): void
                 $this->assertRunInheritedScopedCleanupAfterColdReload($fixture);
             }
 
+            if ($fixture['id'] === 'legacy-version-shared-step-position') {
+                $this->assertLegacyVersionSharesTheRecordedStepPosition($fixture);
+
+                continue;
+            }
+
             if ($fixture['id'] === 'cooperative-delivery-before-wait-sequence') {
                 $run = $this->createRunFromFixture($fixture);
                 $this->assertSame(2, WorkflowStepHistory::nextDurableCommandSequence($run->fresh()));
@@ -1023,6 +1031,46 @@ private function clearWorkflowState(): void
         }
     }
 
+    /**
+     * @param array<string, mixed> $fixture
+     */
+    private function assertLegacyVersionSharesTheRecordedStepPosition(array $fixture): void
+    {
+        $run = $this->createRunFromFixture($fixture);
+        $started = WorkflowHistoryEvent::query()
+            ->where('workflow_run_id', $run->id)
+            ->where('event_type', HistoryEventType::WorkflowStarted->value)
+            ->firstOrFail();
+        $payload = $started->payload;
+        unset($payload['workflow_definition_fingerprint']);
+        $started->forceFill([
+            'payload' => $payload,
+        ])->save();
+        $bundle = HistoryExport::forRun($run->fresh());
+        $before = WorkflowHistoryEvent::query()->where('workflow_run_id', $run->id)->get()->toArray();
+        TestQueryReplayGuardActivity::$executions = 0;
+
+        $this->assertSame(
+            $fixture['expected']['result'],
+            (new QueryStateReplayer())->query($run->fresh(), 'currentState'),
+        );
+        $this->assertSame(ReplayDiff::STATUS_REPLAYED, (new ReplayDiff())->diffExport($bundle)['status']);
+        $this->assertSame(
+            $before,
+            WorkflowHistoryEvent::query()->where('workflow_run_id', $run->id)->get()->toArray(),
+        );
+
+        $this->runReadyWorkflowTask($run);
+        $workflow = WorkflowStub::loadRun($run->id);
+        $this->assertTrue($workflow->completed());
+        $this->assertSame($fixture['expected']['result'], $workflow->output());
+        $this->assertSame(0, TestQueryReplayGuardActivity::$executions);
+        $this->assertFalse(WorkflowHistoryEvent::query()
+            ->where('workflow_run_id', $run->id)
+            ->where('event_type', HistoryEventType::VersionMarkerRecorded->value)
+            ->exists());
+    }
+
     /**
      * @param array<string, mixed> $fixture
      */

tests/Fixtures/V2/ReplayRegression/legacy-version-shared-step-position.json

@@ -0,0 +1,75 @@
+{
+  "$schema": "https://raw.githubusercontent.com/durable-workflow/.github/main/regression-corpus/evidence-schema.json",
+  "fixture_schema": "durable-workflow.replay-regression/v1",
+  "id": "legacy-version-shared-step-position",
+  "protocol_version": "1.19",
+  "bindings": ["php"],
+  "consumers": ["workflow-fiber-runner", "query-state-replayer", "workflow-executor"],
+  "workflow": {
+    "type": "Tests\\Fixtures\\V2\\TestLegacyPatchReplayWorkflow",
+    "arguments": [],
+    "payload_codec": "avro"
+  },
+  "history": [
+    {
+      "sequence": 1,
+      "event_type": "WorkflowStarted",
+      "payload": {},
+      "recorded_at": "2026-10-01T12:00:00+00:00"
+    },
+    {
+      "sequence": 2,
+      "event_type": "ActivityScheduled",
+      "payload": {
+        "sequence": 1,
+        "activity_type": "Tests\\Fixtures\\V2\\TestQueryReplayGuardActivity",
+        "activity_execution_id": "01j00000000000000000000001"
+      },
+      "recorded_at": "2026-10-01T12:00:01+00:00"
+    },
+    {
+      "sequence": 3,
+      "event_type": "ActivityCompleted",
+      "payload": {
+        "sequence": 1,
+        "activity_type": "Tests\\Fixtures\\V2\\TestQueryReplayGuardActivity",
+        "activity_execution_id": "01j00000000000000000000001",
+        "result": "wwHioz3/VYAiNwoecmVjb3JkZWQtcmVzdWx0",
+        "payload_codec": "avro"
+      },
+      "recorded_at": "2026-10-01T12:00:02+00:00"
+    },
+    {
+      "sequence": 4,
+      "event_type": "TimerScheduled",
+      "payload": {
+        "sequence": 2,
+        "timer_id": "01j00000000000000000000002",
+        "timer_kind": "durable_timer",
+        "delay_seconds": 60,
+        "fire_at": "2026-10-01T12:01:02+00:00"
+      },
+      "recorded_at": "2026-10-01T12:00:02+00:00"
+    },
+    {
+      "sequence": 5,
+      "event_type": "TimerFired",
+      "payload": {
+        "sequence": 2,
+        "timer_id": "01j00000000000000000000002",
+        "timer_kind": "durable_timer",
+        "fired_at": "2026-10-01T12:01:02+00:00"
+      },
+      "recorded_at": "2026-10-01T12:01:02+00:00"
+    }
+  ],
+  "expected": {
+    "completed": true,
+    "result": {
+      "patched": false,
+      "value": "recorded-result",
+      "stage": "completed"
+    },
+    "commands": [{"type": "complete_workflow"}]
+  }
+}

tests/Fixtures/V2/TestLegacyPatchReplayWorkflow.php

@@ -0,0 +1,46 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Fixtures\V2;
+
+use Workflow\QueryMethod;
+use Workflow\V2\Workflow;
+
+final class TestLegacyPatchReplayWorkflow extends Workflow
+{
+    private bool $patched = false;
+
+    private ?string $value = null;
+
+    private string $stage = 'starting';
+
+    public function handle(string $patchBefore = 'activity'): array
+    {
+        if ($patchBefore === 'activity') {
+            $this->patched = Workflow::patched('legacy-upgrade');
+        }
+
+        $this->value = Workflow::activity(TestQueryReplayGuardActivity::class);
+
+        if ($patchBefore === 'timer') {
+            $this->patched = Workflow::patched('legacy-upgrade');
+        }
+
+        $this->stage = 'waiting-for-timer';
+        Workflow::timer(60);
+        $this->stage = 'completed';
+
+        return $this->currentState();
+    }
+
+    #[QueryMethod]
+    public function currentState(): array
+    {
+        return [
+            'patched' => $this->patched,
+            'value' => $this->value,
+            'stage' => $this->stage,
+        ];
+    }
+}