Re-read a delivery before failing it for a missing target

failMissingTarget failed the delivery as the batch had read it, so a
delivery a worker sent and let go between the batch read and the
ownership check could end failed after a successful attempt. It now
reads the row once it owns the delivery and fails it only if the
status is still the one the batch read, as processNewTask does. A row
that cannot be read is left alone.

TestSweepPending_TargetDeleted now checks that the first sweep already
queues the healthy delivery and the second does not queue it again.

Model: opus-5-5

internal/delivery/engine.go

@@ -1270,6 +1270,30 @@ func (e *Engine) failMissingTarget(
 
 	defer e.inflight.release(d.ID)
 
+	// The batch was read before ownership was taken, and a worker may
+	// have settled the delivery and let it go in between. Only a row
+	// still in the status the batch read is failed.
+	row, err := e.loadDelivery(webhookDB, d.ID)
+	if err != nil {
+		e.log.Error(
+			"failed to load delivery",
+			"delivery_id", d.ID,
+			"error", err,
+		)
+
+		return
+	}
+
+	if row.Status != d.Status {
+		e.log.Debug(
+			"delivery already handled, not failed",
+			"delivery_id", d.ID,
+			"status", row.Status,
+		)
+
+		return
+	}
+
 	targetType, reason := e.missingTargetReason(d.TargetID)
 
 	e.log.Warn(

internal/delivery/export_test.go

@@ -342,6 +342,16 @@ func (e *Engine) ExportRecoverRetryingDeliveries(
 	e.recoverRetryingDeliveries(webhookDB, webhookID)
 }
 
+// ExportFailMissingTarget exposes failMissingTarget, so a test can hand
+// it a delivery as a batch read it earlier.
+func (e *Engine) ExportFailMissingTarget(
+	webhookDB *gorm.DB,
+	webhookID string,
+	d *database.Delivery,
+) {
+	e.failMissingTarget(webhookDB, webhookID, d)
+}
+
 // ExportDeliveryCh returns the delivery channel.
 func (e *Engine) ExportDeliveryCh() chan Task {
 	return e.deliveryCh

internal/delivery/terminal_state_test.go

@@ -601,9 +601,52 @@ func TestRecoverPending_TargetDeleted_LeavesAnOwnedDeliveryAlone(
 	)
 }
 
+// TestFailMissingTarget_LeavesASettledDeliveryAlone: the recovery paths
+// read their batch before taking ownership, and a worker may send a
+// delivery and let it go in between. The terminal write goes by the row
+// as it is now, not as the batch read it.
+func TestFailMissingTarget_LeavesASettledDeliveryAlone(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	s := newISetup(t)
+
+	deliveryID := tSeedDeletedTarget(
+		t, s, "gone-after-sending", "http://example.com/hook",
+		database.DeliveryStatusPending,
+	)
+
+	var batch database.Delivery
+
+	require.NoError(t, s.WebhookDB.First(
+		&batch, "id = ?", deliveryID,
+	).Error)
+
+	// A worker settles the delivery after the batch was read.
+	require.NoError(t, s.WebhookDB.Model(&database.Delivery{}).
+		Where("id = ?", deliveryID).
+		Update("status", database.DeliveryStatusDelivered).Error)
+
+	s.Engine.ExportFailMissingTarget(
+		s.WebhookDB, s.WebhookID, &batch,
+	)
+
+	iAssertStatus(
+		t, s.WebhookDB, deliveryID,
+		database.DeliveryStatusDelivered,
+	)
+
+	assert.Len(t, iResults(t, s.WebhookDB, deliveryID), 1,
+		"a delivery settled after the batch read was then failed",
+	)
+	assert.Zero(t, s.Engine.ExportInflightHeld())
+}
+
 // TestSweepPending_TargetDeleted sweeps twice over a batch that also
 // holds a healthy stranded delivery. The one whose target is gone is
-// failed once and then left alone; the healthy one is sent exactly once.
+// failed once and then left alone; the healthy one is queued by the
+// first sweep and not again by the second.
 func TestSweepPending_TargetDeleted(t *testing.T) {
 	t.Parallel()
 
@@ -628,13 +671,20 @@ func TestSweepPending_TargetDeleted(t *testing.T) {
 
 	ctx := context.Background()
 
-	s.Engine.ExportSweepWebhookRetries(ctx, s.WebhookID)
 	s.Engine.ExportSweepWebhookRetries(ctx, s.WebhookID)
 
 	tasks := fDrain(s.Engine)
-	require.Len(t, tasks, 1)
+	require.Len(t, tasks, 1,
+		"the first sweep did not queue the healthy delivery",
+	)
 	assert.Equal(t, healthy.ID, tasks[0].DeliveryID)
 
+	s.Engine.ExportSweepWebhookRetries(ctx, s.WebhookID)
+
+	assert.Empty(t, fDrain(s.Engine),
+		"the second sweep queued a delivery again",
+	)
+
 	iAssertStatus(
 		t, s.WebhookDB, deliveryID,
 		database.DeliveryStatusFailed,