2 files changed, 30 insertions, 5 deletions
diff --git a/src/renderer/src/App.tsx b/src/renderer/src/App.tsx
index f3f9f79..0f48a3c 100644
--- a/src/renderer/src/App.tsx
+++ b/src/renderer/src/App.tsx
@@ -309,6 +309,17 @@ export default function App() {
       setStatusMessage('Overleaf session expired — please sign in again')
     })
 
+    // Main document changed (by us or a collaborator) — track it
+    const unsubRootDoc = window.api.onProjectRootDocUpdated?.((docId) => {
+      const store = useAppStore.getState()
+      store.setMainDocument(docId)
+      if (store.overleafProject) {
+        store.setOverleafProject({ ...store.overleafProject, rootDocId: docId })
+      }
+      const name = store.docPathMap[docId]?.split('/').pop()
+      if (name) setStatusMessage(`Main document: ${name}`)
+    })
+
     // Keep the file tree in sync with Overleaf project-entity socket events.
     const unsubEntityCreated = window.api.onSyncEntityCreated((data) => {
       applyEntityCreated(data)
@@ -427,6 +438,7 @@ export default function App() {
       unsubCursorDisconnected()
       unsubFileStatus?.()
       unsubAuthExpired?.()
+      unsubRootDoc?.()
       remoteCursors.clear()
       stopAutocompleteSync()
     }
diff --git a/src/renderer/src/components/FileTree.tsx b/src/renderer/src/components/FileTree.tsx
index 5486f20..f53ae2f 100644
--- a/src/renderer/src/components/FileTree.tsx
+++ b/src/renderer/src/components/FileTree.tsx
@@ -212,14 +212,27 @@ export default function FileTree() {
 
   // ── Project view actions (Overleaf entities) ──
 
-  const handleSetMainDoc = () => {
+  const handleSetMainDoc = async () => {
     if (!ctxMenu) return
     const node = ctxMenu.node
-    if (node.docId) {
-      useAppStore.getState().setMainDocument(node.docId)
-      useAppStore.getState().setStatusMessage(`Main document set to ${node.name}`)
-    }
     closeMenu()
+    if (!node.docId) return
+    const store = useAppStore.getState()
+    // Optimistic local update; the official settings endpoint persists it
+    // project-wide (and broadcasts rootDocUpdated to collaborators)
+    store.setMainDocument(node.docId)
+    const projectId = store.overleafProjectId
+    if (!projectId) return
+    const r = await window.api.overleafSetRootDoc(projectId, node.docId)
+    if (r.success) {
+      const st = useAppStore.getState()
+      if (st.overleafProject) {
+        st.setOverleafProject({ ...st.overleafProject, rootDocId: node.docId })
+      }
+      st.setStatusMessage(`Main document set to ${node.name}`)
+    } else {
+      useAppStore.getState().setStatusMessage(`Failed to set main document (${r.message || 'error'})`)
+    }
   }
 
   const handleCopyPath = () => {