feat: backup restore UI (#3)

Add list_backups / backup_label / backup_diff / restore_backup to bcc_core,
RestoreDialog to bcc.py, and a "Restore…" button in the profile top bar.

Restore is selective: only mcpServers and _disabledMcpServers are replaced;
all other keys in the config (history, project state) are preserved verbatim.
Goes through write_config() so a pre-restore backup is always created first.

Closes #3

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

bcc.py

@@ -28,6 +28,8 @@ from PySide6.QtWidgets import (
     QHeaderView,
     QLabel,
     QLineEdit,
+    QListWidget,
+    QListWidgetItem,
     QMainWindow,
     QMenu,
     QMessageBox,
@@ -833,6 +835,97 @@ class RepairDialog(QDialog):
         v.addWidget(btns)
 
 
+# --------------------------------------------------------------------------- #
+# Backup restore dialog: lists available backups, shows a diff of what will
+# change, and confirms before writing.  Only servers are restored — all other
+# keys in the current config are preserved verbatim.
+# --------------------------------------------------------------------------- #
+class RestoreDialog(QDialog):
+    def __init__(self, parent, profile: core.Profile, full_config: dict):
+        super().__init__(parent)
+        self.setWindowTitle(f"Restore from backup — {profile.label}")
+        self.resize(700, 480)
+        self._profile = profile
+        self._full_config = full_config
+
+        v = QVBoxLayout(self)
+        v.setSpacing(8)
+
+        intro = QLabel(
+            "Select a backup to preview the change. Only <b>mcpServers</b> and "
+            "<b>_disabledMcpServers</b> are restored — all other keys in your config are preserved."
+        )
+        intro.setWordWrap(True)
+        v.addWidget(intro)
+
+        splitter = QSplitter(Qt.Orientation.Horizontal)
+
+        # --- left: backup list ---
+        left = QWidget()
+        lv = QVBoxLayout(left)
+        lv.setContentsMargins(0, 0, 0, 0)
+        lv.addWidget(QLabel("Backups (newest first):"))
+        self.backup_list = QListWidget()
+        self.backup_list.currentItemChanged.connect(self._on_backup_selected)
+        lv.addWidget(self.backup_list, 1)
+        splitter.addWidget(left)
+
+        # --- right: diff preview ---
+        right = QWidget()
+        rv = QVBoxLayout(right)
+        rv.setContentsMargins(0, 0, 0, 0)
+        rv.addWidget(QLabel("Preview (what will change):"))
+        self.diff_view = QPlainTextEdit()
+        self.diff_view.setObjectName("diag")
+        self.diff_view.setReadOnly(True)
+        self.diff_view.setPlaceholderText("Select a backup on the left to see the diff.")
+        rv.addWidget(self.diff_view, 1)
+        splitter.addWidget(right)
+
+        splitter.setSizes([220, 460])
+        v.addWidget(splitter, 1)
+
+        self.btns = QDialogButtonBox()
+        self.restore_btn = self.btns.addButton("Restore", QDialogButtonBox.ButtonRole.AcceptRole)
+        self.restore_btn.setObjectName("primary")
+        self.restore_btn.setEnabled(False)
+        self.btns.addButton(QDialogButtonBox.StandardButton.Cancel)
+        self.btns.accepted.connect(self.accept)
+        self.btns.rejected.connect(self.reject)
+        v.addWidget(self.btns)
+
+        self._populate()
+
+    def _populate(self):
+        backups = core.list_backups(self._profile.path)
+        if not backups:
+            self.backup_list.addItem("(no backups found)")
+            return
+        for bp in backups:
+            item = QListWidgetItem(core.backup_label(bp))
+            item.setData(Qt.ItemDataRole.UserRole, str(bp))
+            self.backup_list.addItem(item)
+
+    def _on_backup_selected(self, current: QListWidgetItem | None, _prev):
+        if current is None or current.data(Qt.ItemDataRole.UserRole) is None:
+            self.diff_view.setPlainText("")
+            self.restore_btn.setEnabled(False)
+            return
+        bp = current.data(Qt.ItemDataRole.UserRole)
+        try:
+            diff = core.backup_diff(self._profile.path, bp, self._full_config)
+        except Exception as e:
+            diff = f"(error generating diff: {e})"
+        self.diff_view.setPlainText(diff)
+        self.restore_btn.setEnabled(True)
+
+    def selected_backup(self) -> str | None:
+        item = self.backup_list.currentItem()
+        if item is None:
+            return None
+        return item.data(Qt.ItemDataRole.UserRole)
+
+
 # --------------------------------------------------------------------------- #
 # Paste-JSON dialog
 # --------------------------------------------------------------------------- #
@@ -992,6 +1085,10 @@ class MainWindow(QMainWindow):
         reload_btn = QPushButton("Reload")
         reload_btn.clicked.connect(lambda: self.load_profile(self.current_profile, confirm=True))
         bar.addWidget(reload_btn)
+        self.restore_btn = QPushButton("Restore…")
+        self.restore_btn.setToolTip("Restore servers from a previous backup")
+        self.restore_btn.clicked.connect(self._restore_from_backup)
+        bar.addWidget(self.restore_btn)
         bar.addStretch()
         self.save_btn = QPushButton("Save")
         self.save_btn.setObjectName("primary")
@@ -1544,6 +1641,28 @@ class MainWindow(QMainWindow):
             f"Saved {self.current_profile.path}{bnote}  ·  Restart {self.current_profile.label} to apply."
         )
 
+    def _restore_from_backup(self):
+        if not self.current_profile:
+            return
+        if self.dirty and not self._confirm_discard():
+            return
+        dlg = RestoreDialog(self, self.current_profile, self.full_config)
+        if not dlg.exec():
+            return
+        bp = dlg.selected_backup()
+        if not bp:
+            return
+        try:
+            core.restore_backup(self.current_profile.path, bp, current_cfg=self.full_config)
+        except Exception as e:
+            QMessageBox.critical(self, "Restore failed", str(e))
+            return
+        # Reload from disk so the UI reflects the restored state
+        self.load_profile(self.current_profile, confirm=False)
+        self.status.setText(
+            f"Restored from {Path(bp).name}  ·  Restart {self.current_profile.label} to apply."
+        )
+
     # --- dirty / status -------------------------------------------------- #
     def _mark_dirty(self):
         self.dirty = True