Fix per-key commit caching in DefaultGitSyncService

The lastCommit field was shared across all repository keys, causing
MissingObjectException when multiple repositories were registered.
When onUpdate fired for repo A it overwrote lastCommit, and subsequent
listFiles/getFileContent calls for repo B used repo A's commit whose
tree objects don't exist in repo B's object database.

Changed to a per-key Map<String, RevCommit> so each repository's
resolved commit is stored and retrieved independently.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

application/src/main/java/org/thingsboard/server/service/sync/DefaultGitSyncService.java

@@ -48,7 +48,7 @@ public class DefaultGitSyncService implements GitSyncService {
     private final Map<String, GitRepository> repositories = new ConcurrentHashMap<>();
     private final Map<String, Runnable> updateListeners = new ConcurrentHashMap<>();
 
-    private RevCommit lastCommit;
+    private final Map<String, RevCommit> lastCommits = new ConcurrentHashMap<>();
 
     @Override
     public void registerSync(String key, String repoUri, String branch, long fetchFrequencyMs, Runnable onUpdate) {
@@ -87,7 +87,7 @@ public class DefaultGitSyncService implements GitSyncService {
     @Override
     public List<RepoFile> listFiles(String key, String path, int depth, FileType type) {
         GitRepository repository = getRepository(key);
-        return repository.listFilesAtCommit(lastCommit, path, depth).stream()
+        return repository.listFilesAtCommit(getLastCommit(key), path, depth).stream()
                 .filter(file -> type == null || file.type() == type)
                 .toList();
     }
@@ -96,7 +96,7 @@ public class DefaultGitSyncService implements GitSyncService {
     @Override
     public byte[] getFileContent(String key, String path) {
         GitRepository repository = getRepository(key);
-        return repository.getFileContentAtCommit(path, lastCommit);
+        return repository.getFileContentAtCommit(path, getLastCommit(key));
     }
 
     @Override
@@ -143,7 +143,7 @@ public class DefaultGitSyncService implements GitSyncService {
         GitRepository repository = getRepository(key);
         String branchRef = getBranchRef(repository);
         try {
-            lastCommit = repository.resolveCommit(branchRef);
+            lastCommits.put(key, repository.resolveCommit(branchRef));
         } catch (Throwable e) {
             log.error("[{}] Failed to resolve commit for ref {}", key, branchRef, e);
             return;
@@ -166,6 +166,14 @@ public class DefaultGitSyncService implements GitSyncService {
         return Path.of(repositoriesFolder, name);
     }
 
+    private RevCommit getLastCommit(String key) {
+        RevCommit commit = lastCommits.get(key);
+        if (commit == null) {
+            throw new IllegalStateException(key + " repository has no resolved commit");
+        }
+        return commit;
+    }
+
     private String getBranchRef(GitRepository repository) {
         return "refs/remotes/origin/" + repository.getSettings().getDefaultBranch();
     }