feat: offer guided repair when loading a broken config file

If a config file on disk fails strict JSON parsing, BCC now runs it
through the same repair pipeline as pasted snippets and shows a dialog
listing the parse error, each fix it would apply, and a preview of the
resulting file. The user chooses: Repair & load (marks the profile
dirty; the file is only rewritten on Save, after the broken original
is backed up) or Cancel. Unsalvageable files keep the old error path.

repair_config_file() in bcc_core never writes to disk itself.

bcc.py

@@ -632,6 +632,56 @@ class ArgsEdit(QPlainTextEdit):
             n += 1
 
 
+# --------------------------------------------------------------------------- #
+# Config-repair dialog: shown when a config file on disk fails strict JSON
+# parsing but the repair pipeline can salvage it. Lists what's wrong, what
+# would change, and lets the user decide. Nothing touches disk until Save.
+# --------------------------------------------------------------------------- #
+class RepairDialog(QDialog):
+    def __init__(self, parent, path, error: str, notes: list[str], preview: str):
+        super().__init__(parent)
+        self.setWindowTitle("Config file needs repair")
+        self.resize(620, 520)
+        v = QVBoxLayout(self)
+        v.setSpacing(10)
+
+        intro = QLabel(f"<b>{path}</b><br>isn't valid JSON: {error}")
+        intro.setWordWrap(True)
+        v.addWidget(intro)
+
+        fixes_hdr = QLabel("BCC can repair it automatically. Fixes to apply:")
+        v.addWidget(fixes_hdr)
+        fixes = QLabel("\n".join(f"  •  {n}" for n in notes) or "  •  reformat as valid JSON")
+        fixes.setObjectName("muted")
+        fixes.setWordWrap(True)
+        v.addWidget(fixes)
+
+        prev_hdr = QLabel("The file would become:")
+        v.addWidget(prev_hdr)
+        box = QPlainTextEdit()
+        box.setObjectName("diag")
+        box.setReadOnly(True)
+        box.setPlainText(preview)
+        v.addWidget(box, 1)
+
+        note = QLabel(
+            "Nothing is written yet — choosing Repair loads the fixed config into the "
+            "editor. The file is only rewritten when you press Save, and the broken "
+            "original is backed up first."
+        )
+        note.setObjectName("muted")
+        note.setWordWrap(True)
+        v.addWidget(note)
+
+        btns = QDialogButtonBox()
+        ok = btns.addButton("Repair && load", QDialogButtonBox.ButtonRole.AcceptRole)
+        ok.setObjectName("primary")
+        btns.addButton(QDialogButtonBox.StandardButton.Cancel)
+        btns.accepted.connect(self.accept)
+        btns.rejected.connect(self.reject)
+        v.addWidget(btns)
+
+
 # --------------------------------------------------------------------------- #
 # Paste-JSON dialog
 # --------------------------------------------------------------------------- #
@@ -972,15 +1022,27 @@ class MainWindow(QMainWindow):
             return
         if confirm and self.dirty and not self._confirm_discard():
             return
+        repaired = False
         try:
             self.full_config = core.load_config(profile.path)
         except Exception as e:
-            QMessageBox.critical(
+            # Strict parse failed — see if the repair pipeline can salvage it,
-                self,
+            # and let the user decide with full visibility of the changes.
-                "Could not read config",
+            try:
-                f"{profile.path}\n\n{e}\n\nFix the file by hand or pick another install.",
+                cfg, notes, preview = core.repair_config_file(profile.path)
-            )
+            except Exception:
-            return
+                QMessageBox.critical(
+                    self,
+                    "Could not read config",
+                    f"{profile.path}\n\n{e}\n\nThe file couldn't be repaired automatically. "
+                    f"Fix it by hand or pick another install.",
+                )
+                return
+            dlg = RepairDialog(self, profile.path, str(e), notes, preview)
+            if not dlg.exec():
+                return
+            self.full_config = cfg
+            repaired = True
         self.current_profile = profile
         self.servers = core.extract_servers(self.full_config)
         self.dirty = False
@@ -988,6 +1050,12 @@ class MainWindow(QMainWindow):
         self.undo_btn.setEnabled(False)
         self._refresh_tables(select_index=0 if self.servers else -1)
         self._update_status(saved=False)
+        if repaired:
+            self._mark_dirty()
+            self.status.setText(
+                f"{profile.path}  ·  repaired config loaded — press Save to write the "
+                f"fix (the original file will be backed up)"
+            )
 
     # --- table rendering ------------------------------------------------- #
     def _add_row(self, table, master_idx, s):

bcc_core.py

@@ -132,6 +132,33 @@ def load_config(path: str | os.PathLike) -> dict:
     return obj
 
 
+def repair_config_file(path: str | os.PathLike) -> tuple[dict, list[str], str]:
+    """
+    Attempt to repair a config file that failed strict parsing, WITHOUT writing
+    anything to disk. The caller decides what to do with the result (BCC shows
+    the user the issues and asks before saving).
+
+    Returns (cfg, notes, repaired_text):
+      cfg           - the parsed dict from the repaired JSON
+      notes         - human-readable list of fixes that were applied
+      repaired_text - pretty-printed JSON the config would become
+
+    Raises ValueError if the file can't be salvaged automatically.
+    """
+    text = Path(path).read_text(encoding="utf-8")
+    candidate, notes = repair_json_text(text)
+    try:
+        obj = json.loads(candidate)
+    except json.JSONDecodeError as e:
+        raise ValueError(
+            f"Couldn't repair the file automatically (line {e.lineno}, column {e.colno}: {e.msg})."
+        ) from e
+    if not isinstance(obj, dict):
+        raise ValueError("Even after repair, the top level isn't a JSON object.")
+    pretty = json.dumps(obj, indent=2, ensure_ascii=False) + "\n"
+    return obj, notes, pretty
+
+
 def extract_servers(cfg: dict) -> list[ServerEntry]:
     """Pull enabled (`mcpServers`) and disabled (`_disabledMcpServers`) servers."""
     out: list[ServerEntry] = []

tests/test_json_repair.py

@@ -2,6 +2,8 @@
 parse_pasted_json_verbose). Every case here is a shape people actually paste
 from MCP docs, blog posts, and chat windows."""
 
+import json
+
 import pytest
 
 import bcc_core as c
@@ -170,6 +172,35 @@ def test_kitchen_sink():
     assert len(notes) >= 4
 
 
+# --------------------------------------------------------------------------- #
+# Config-file repair (load-time)
+# --------------------------------------------------------------------------- #
+def test_repair_config_file_fixes_and_reports(tmp_path):
+    p = tmp_path / "claude_desktop_config.json"
+    p.write_text(
+        '{\n  "globalShortcut": "Cmd+Space",\n'
+        "  // my servers\n"
+        '  "mcpServers": {\n'
+        '    "brave": {"command": "npx", "args": ["-y"],},\n'
+        "  },\n}"
+    )
+    cfg, notes, preview = c.repair_config_file(p)
+    assert cfg["mcpServers"]["brave"]["command"] == "npx"
+    assert cfg["globalShortcut"] == "Cmd+Space"  # unrelated keys survive
+    assert any("comment" in n for n in notes)
+    assert any("trailing" in n for n in notes)
+    assert json.loads(preview) == cfg
+    # nothing was written to disk
+    assert "//" in p.read_text()
+
+
+def test_repair_config_file_hopeless_raises(tmp_path):
+    p = tmp_path / "claude_desktop_config.json"
+    p.write_text("total nonsense, no braces at all")
+    with pytest.raises(ValueError):
+        c.repair_config_file(p)
+
+
 # --------------------------------------------------------------------------- #
 # Still fails cleanly on hopeless input
 # --------------------------------------------------------------------------- #