feat: numbered gutter in the Arguments editor

The one-arg-per-line model read as odd text wrapping — a path on its
own line looked like a wrapped continuation of the previous argument.
A line-number gutter makes each argument visibly its own item.
ArgsEdit also owns the NoWrap setting now.

bcc.py

@@ -13,8 +13,8 @@ from __future__ import annotations
 import sys
 from pathlib import Path
 
-from PySide6.QtCore import QSettings, Qt, QThread, QTimer, Signal
+from PySide6.QtCore import QRect, QSettings, QSize, Qt, QThread, QTimer, Signal
-from PySide6.QtGui import QAction, QColor, QGuiApplication
+from PySide6.QtGui import QAction, QColor, QGuiApplication, QPainter
 from PySide6.QtWidgets import (
     QAbstractItemView,
     QApplication,
@@ -361,14 +361,11 @@ class ServerEditor(QFrame):
         self.command.textChanged.connect(self._emit)
         v.addWidget(self.command)
         v.addWidget(self._lbl("Arguments  (one per line)"))
-        self.args = QPlainTextEdit()
+        self.args = ArgsEdit()
         self.args.setPlaceholderText(
             "-y\n@modelcontextprotocol/server-filesystem\n/Users/you/Documents"
         )
         self.args.setMinimumHeight(70)
-        # One argument per line means wrapping is actively misleading — a long
-        # path that soft-wraps looks like two separate args. Scroll instead.
-        self.args.setLineWrapMode(QPlainTextEdit.LineWrapMode.NoWrap)
         self.args.textChanged.connect(self._emit)
         v.addWidget(self.args, 1)
         v.addWidget(self._lbl("Environment variables"))
@@ -565,6 +562,76 @@ class ServerEditor(QFrame):
         self.dep_label.setStyleSheet(f"color: {color};")
 
 
+# --------------------------------------------------------------------------- #
+# Arguments editor: one line = one argument, with a numbered gutter so that
+# model is visible (a long path on its own line reads as "arg 2", not as a
+# wrapped continuation of arg 1).
+# --------------------------------------------------------------------------- #
+class _ArgsGutter(QWidget):
+    def __init__(self, editor: ArgsEdit):
+        super().__init__(editor)
+        self._editor = editor
+
+    def sizeHint(self):
+        return QSize(self._editor.gutter_width(), 0)
+
+    def paintEvent(self, event):
+        self._editor.gutter_paint(event)
+
+
+class ArgsEdit(QPlainTextEdit):
+    def __init__(self):
+        super().__init__()
+        self.setLineWrapMode(QPlainTextEdit.LineWrapMode.NoWrap)
+        self._gutter = _ArgsGutter(self)
+        self.blockCountChanged.connect(self._update_gutter_width)
+        self.updateRequest.connect(self._on_update_request)
+        self._update_gutter_width()
+
+    def gutter_width(self) -> int:
+        digits = max(1, len(str(self.blockCount())))
+        return 14 + self.fontMetrics().horizontalAdvance("9") * digits
+
+    def _update_gutter_width(self, *_):
+        self.setViewportMargins(self.gutter_width(), 0, 0, 0)
+
+    def _on_update_request(self, rect, dy):
+        if dy:
+            self._gutter.scroll(0, dy)
+        else:
+            self._gutter.update(0, rect.y(), self._gutter.width(), rect.height())
+        if rect.contains(self.viewport().rect()):
+            self._update_gutter_width()
+
+    def resizeEvent(self, e):
+        super().resizeEvent(e)
+        cr = self.contentsRect()
+        self._gutter.setGeometry(QRect(cr.left(), cr.top(), self.gutter_width(), cr.height()))
+
+    def gutter_paint(self, event):
+        painter = QPainter(self._gutter)
+        painter.setPen(QColor(MUTED))
+        fm = self.fontMetrics()
+        block = self.firstVisibleBlock()
+        n = block.blockNumber()
+        top = round(self.blockBoundingGeometry(block).translated(self.contentOffset()).top())
+        bottom = top + round(self.blockBoundingRect(block).height())
+        while block.isValid() and top <= event.rect().bottom():
+            if block.isVisible() and bottom >= event.rect().top():
+                painter.drawText(
+                    0,
+                    top,
+                    self._gutter.width() - 8,
+                    fm.height(),
+                    Qt.AlignmentFlag.AlignRight,
+                    str(n + 1),
+                )
+            block = block.next()
+            top = bottom
+            bottom = top + round(self.blockBoundingRect(block).height())
+            n += 1
+
+
 # --------------------------------------------------------------------------- #
 # Paste-JSON dialog
 # --------------------------------------------------------------------------- #