From 07db3f6b68422ac5577e26685270c0ab44a34c12 Mon Sep 17 00:00:00 2001
From: Carl Schwan <carl@carlschwan.eu>
Date: Fri, 4 Sep 2026 10:57:13 +0200
Subject: [PATCH] fix(preview): Be a bit more verbose when failing to migrate
 previews

Signed-off-by: Carl Schwan <carl@carlschwan.eu>
Assisted-by: ClaudeCode:claude-sonnet-5
---
 core/BackgroundJobs/PreviewMigrationJob.php     |  8 +++++++-
 lib/private/Preview/PreviewMigrationService.php | 12 ++++++++++--
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/core/BackgroundJobs/PreviewMigrationJob.php b/core/BackgroundJobs/PreviewMigrationJob.php
index e5bd2b4a49450..45f71e561244f 100644
--- a/core/BackgroundJobs/PreviewMigrationJob.php
+++ b/core/BackgroundJobs/PreviewMigrationJob.php
@@ -45,6 +45,7 @@ protected function run(mixed $argument): void {
 
 		$storage = $this->rootFolder->getMountPoint()->getStorage();
 		if ($storage === null) {
+			$this->logger->warning('Preview migration skipped: the root mount point has no storage.');
 			$this->appConfig->setValueBool('core', 'previewMovedDone', true);
 			return;
 		}
@@ -52,7 +53,12 @@ protected function run(mixed $argument): void {
 		$cache = $storage->getCache();
 		$previewRootId = $cache->getId(rtrim($this->previewRootPath, '/'));
 		if ($previewRootId === -1) {
-			// No previews have ever been generated on this instance.
+			// No previews were ever generated, or the storage config no longer
+			// matches the one the filecache data was recorded under.
+			$this->logger->warning('Preview migration skipped: no preview root found at "{path}" on storage "{storageId}".', [
+				'path' => $this->previewRootPath,
+				'storageId' => $storage->getId(),
+			]);
 			$this->appConfig->setValueBool('core', 'previewMovedDone', true);
 			return;
 		}
diff --git a/lib/private/Preview/PreviewMigrationService.php b/lib/private/Preview/PreviewMigrationService.php
index 377950da84952..31529cbe2f02b 100644
--- a/lib/private/Preview/PreviewMigrationService.php
+++ b/lib/private/Preview/PreviewMigrationService.php
@@ -135,17 +135,25 @@ public function migrateFileId(int $fileId, bool $flatPath, ?array $entries = nul
 			}
 		} else {
 			// No matching fileId, delete the orphaned preview files themselves.
+			$transactionStarted = false;
 			try {
 				$folder = $this->appData->getFolder($internalPath);
 				$this->connection->beginTransaction();
+				$transactionStarted = true;
 				foreach ($folder->getDirectoryListing() as $file) {
 					$file->delete();
 				}
 				$this->connection->commit();
 			} catch (NotFoundException) {
 				// Folder already gone, nothing to clean up.
-			} catch (Exception) {
-				$this->connection->rollback();
+			} catch (\Throwable $e) {
+				// Also catches non-DB failures from $file->delete(), e.g. an unreachable objectstore.
+				if ($transactionStarted) {
+					$this->connection->rollback();
+				}
+				$this->logger->error('Unable to delete orphaned preview at ' . $internalPath, [
+					'exception' => $e,
+				]);
 			}
 		}