Terminally fail retrying deliveries with a non-retry target type (closes #82)

Restart recovery and the 60s retry sweep both looked an orphaned
`retrying` delivery's target up in the registry and silently returned
when it did not implement `rescheduler`. If a target's type was edited
from a retry type (`http`/`slack`) to a fire-and-forget type
(`database`/`log`) or an unknown one while a delivery was still
retrying, that delivery stayed `retrying` forever.

Both sites now hand the delivery to one shared helper,
`failUnretryableRetry`, which records a `DeliveryResult` naming the
current target type as the reason and marks the delivery `failed`. It
logs at warn, not error: this is operator-caused state, not a system
fault.

Re-dispatching under the new type was rejected as it would perform a
delivery the operator never asked for; the event itself stays in the
per-webhook event database, so manual redelivery can recover it
deliberately.

Fire-and-forget targets never set status `retrying` under normal
operation, so this path stays unreachable for them in practice.

internal/delivery/engine_integration_test.go

@@ -748,6 +748,193 @@ func TestRecoverWebhookDeliveries_RetryingDeliveries(
 	case <-time.After(5 * time.Second):
 		t.Fatal("expected retry task from recovery")
 	}
+
+	// Regression guard: a target that still supports retries
+	// must be rescheduled, never terminally failed, and must
+	// not gain a synthetic result row.
+	iAssertStatus(
+		t, s.WebhookDB, d.ID,
+		database.DeliveryStatusRetrying,
+	)
+
+	assert.Len(t, iResults(t, s.WebhookDB, d.ID), 1)
+}
+
+// --- Retrying deliveries whose target type changed ---
+
+// iSeedRetryingWithType seeds a retrying delivery with one
+// recorded failed attempt against a target of the given type,
+// standing in for a target whose type was edited in the main
+// database while the delivery was still retrying.
+func iSeedRetryingWithType(
+	t *testing.T,
+	s iSetup,
+	targetType database.TargetType,
+) string {
+	t.Helper()
+
+	targetID := uuid.New().String()
+
+	iCreateTarget(t, s.MainDB, targetID,
+		s.WebhookID, "mutated-target", targetType,
+		iHTTPConfig("http://example.com/hook"), 5,
+	)
+
+	event := iSeedEvent(
+		t, s.WebhookDB, s.WebhookID,
+		`{"orphaned":"retry"}`,
+	)
+
+	d := iSeedDelivery(
+		t, s.WebhookDB, event.ID, targetID,
+		database.DeliveryStatusRetrying,
+	)
+
+	iSeedFailedResult(t, s.WebhookDB, d.ID)
+
+	return d.ID
+}
+
+// iResults loads a delivery's results in attempt order.
+func iResults(
+	t *testing.T, db *gorm.DB, deliveryID string,
+) []database.DeliveryResult {
+	t.Helper()
+
+	var results []database.DeliveryResult
+
+	require.NoError(t, db.
+		Where("delivery_id = ?", deliveryID).
+		Order("attempt_num").
+		Find(&results).Error)
+
+	return results
+}
+
+// iAssertTerminallyFailed asserts the delivery ended failed
+// with a result row recording why, and was not rescheduled.
+func iAssertTerminallyFailed(
+	t *testing.T,
+	s iSetup,
+	deliveryID string,
+	targetType database.TargetType,
+) {
+	t.Helper()
+
+	iAssertStatus(
+		t, s.WebhookDB, deliveryID,
+		database.DeliveryStatusFailed,
+	)
+
+	results := iResults(t, s.WebhookDB, deliveryID)
+	require.Len(t, results, 2)
+
+	last := results[1]
+
+	assert.False(t, last.Success)
+	assert.Equal(t, 2, last.AttemptNum)
+
+	assert.Contains(
+		t, last.Error, string(targetType),
+	)
+
+	assert.Contains(
+		t, last.Error, "does not support retries",
+	)
+
+	assert.Empty(t, s.Engine.ExportRetryCh())
+}
+
+func TestRecoverSingleRetry_TypeNoLongerRetries(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	s := newISetup(t)
+
+	iCreateWebhook(
+		t, s.MainDB, s.WebhookID, "mutated-type",
+	)
+
+	deliveryID := iSeedRetryingWithType(
+		t, s, database.TargetTypeLog,
+	)
+
+	s.Engine.ExportRecoverWebhookDeliveries(
+		context.Background(), s.WebhookID,
+	)
+
+	iAssertTerminallyFailed(
+		t, s, deliveryID, database.TargetTypeLog,
+	)
+}
+
+func TestSweepSingleRetry_TypeNoLongerRetries(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	s := newISetup(t)
+
+	iCreateWebhook(
+		t, s.MainDB, s.WebhookID, "mutated-type-sweep",
+	)
+
+	deliveryID := iSeedRetryingWithType(
+		t, s, database.TargetTypeDatabase,
+	)
+
+	s.Engine.ExportSweepWebhookRetries(
+		context.Background(), s.WebhookID,
+	)
+
+	iAssertTerminallyFailed(
+		t, s, deliveryID, database.TargetTypeDatabase,
+	)
+}
+
+func TestRecoverSingleRetry_UnknownTargetType(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	s := newISetup(t)
+
+	iCreateWebhook(
+		t, s.MainDB, s.WebhookID, "unknown-type",
+	)
+
+	unknown := database.TargetType("not-a-target-type")
+
+	deliveryID := iSeedRetryingWithType(t, s, unknown)
+
+	s.Engine.ExportRecoverWebhookDeliveries(
+		context.Background(), s.WebhookID,
+	)
+
+	iAssertTerminallyFailed(t, s, deliveryID, unknown)
+}
+
+func TestSweepSingleRetry_UnknownTargetType(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	s := newISetup(t)
+
+	iCreateWebhook(
+		t, s.MainDB, s.WebhookID, "unknown-type-sweep",
+	)
+
+	unknown := database.TargetType("not-a-target-type")
+
+	deliveryID := iSeedRetryingWithType(t, s, unknown)
+
+	s.Engine.ExportSweepWebhookRetries(
+		context.Background(), s.WebhookID,
+	)
+
+	iAssertTerminallyFailed(t, s, deliveryID, unknown)
 }
 
 // iSeedFailedResult creates a failed delivery result.