perf(git-sync): depth=1 fetch and skip fetch when remote is unchanged

--depth=1 limits fetch to only the latest commit's tree objects instead
of the full history, dramatically reducing fetch time on repos with
many commits. A git ls-remote check before fetching skips the fetch
entirely when local HEAD already matches remote HEAD, which is the
common case after a push with no external changes.

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

services/web/app/src/Features/GitSync/GitSyncHandler.mjs

@@ -169,13 +169,25 @@ async function pushToRemote(
   // objects are sent — git handles the diff automatically.
   const repoDir = await ensureRepo(projectId, remoteUrl, branch)
 
-  // Fetch remote state (trees only, no blobs) to preserve files outside the managed area.
-  // read-tree updates the index without checking out any files, so no blobs are downloaded.
+  // Fetch remote state (trees only, latest commit only) to preserve files outside the managed area.
+  // Skipped when remote HEAD already matches local HEAD (common case: re-push without external changes).
   try {
-    await spawnGit(['fetch', '--filter=blob:none', 'origin', branch], repoDir)
-    // --mixed: moves HEAD to FETCH_HEAD + updates index, no working tree change.
-    // This makes FETCH_HEAD the parent of our next commit so the diff only shows subPath changes.
-    await spawnGit(['reset', '--mixed', 'FETCH_HEAD'], repoDir)
+    let needsFetch = true
+    try {
+      const remoteRef = await spawnGitOutput(['ls-remote', 'origin', branch], repoDir)
+      const remoteHead = remoteRef.split(/\s/)[0].trim()
+      const localHead = await spawnGitOutput(['rev-parse', 'HEAD'], repoDir)
+      needsFetch = remoteHead !== localHead
+    } catch {
+      // Can't compare — proceed with fetch
+    }
+    if (needsFetch) {
+      // --depth=1 --filter=blob:none: only the latest commit's tree objects, no blobs
+      await spawnGit(['fetch', '--filter=blob:none', '--depth=1', 'origin', branch], repoDir)
+      // --mixed: moves HEAD to FETCH_HEAD + updates index, no working tree change.
+      // This makes FETCH_HEAD the parent of our next commit so the diff only shows subPath changes.
+      await spawnGit(['reset', '--mixed', 'FETCH_HEAD'], repoDir)
+    }
   } catch {
     // Empty remote or first push — proceed with empty index
   }
@@ -256,8 +268,8 @@ async function pullFromRemote(projectId, remoteUrl, subPath, branch, userId) {
   logger.debug({ projectId, subPath }, 'git sync: fetching remote for pull')
 
   const repoDir = await ensureRepo(projectId, remoteUrl, branch)
-  // Fetch with blob filter — only trees/commits downloaded upfront
-  await spawnGit(['fetch', '--filter=blob:none', 'origin', branch], repoDir)
+  // depth=1 + blob filter: only the latest commit's tree objects, no blobs upfront
+  await spawnGit(['fetch', '--filter=blob:none', '--depth=1', 'origin', branch], repoDir)
 
   if (subPath) {
     // Checkout only the subPath directory — triggers lazy blob fetch for those files only