feat: clearer Arguments editor with typed-together detection and one-click fix

- Label now explains the model with an example: a flag and its value go
  on separate lines. Placeholder shows the common uv pattern.
- split_suspicious_args() flags lines that contain whitespace plus a
  dash-prefixed token ('--directory /path') — legit single args with
  spaces ('My Documents') are never touched. Quotes are respected.
- The editor shows a warning under the args box with a 'Fix: split onto
  separate lines' button; the fix goes through the undo stack.

bcc.py

@@ -360,14 +360,30 @@ class ServerEditor(QFrame):
         self.command.setPlaceholderText("npx, uvx, node, python3, or a full path")
         self.command.textChanged.connect(self._emit)
         v.addWidget(self.command)
-        v.addWidget(self._lbl("Arguments  (one per line)"))
-        self.args = ArgsEdit()
-        self.args.setPlaceholderText(
-            "-y\n@modelcontextprotocol/server-filesystem\n/Users/you/Documents"
+        args_lbl = self._lbl(
+            "Arguments — each line is one argument. A flag and its value go on "
+            "separate lines, e.g. “--directory” on line 1, “/path/to/server” on line 2."
         )
+        args_lbl.setWordWrap(True)
+        v.addWidget(args_lbl)
+        self.args = ArgsEdit()
+        self.args.setPlaceholderText("--directory\n/path/to/your/server\nrun\nmain.py")
         self.args.setMinimumHeight(70)
         self.args.textChanged.connect(self._emit)
         v.addWidget(self.args, 1)
+
+        # Shown when a line looks like several arguments typed together.
+        self.args_warn = QLabel("")
+        self.args_warn.setStyleSheet(f"color: {WARN};")
+        self.args_warn.setWordWrap(True)
+        self.args_warn.hide()
+        self.args_fix_btn = QPushButton("Fix: split onto separate lines")
+        self.args_fix_btn.clicked.connect(self._fix_args)
+        self.args_fix_btn.hide()
+        warn_row = QHBoxLayout()
+        warn_row.addWidget(self.args_warn, 1)
+        warn_row.addWidget(self.args_fix_btn)
+        v.addLayout(warn_row)
         v.addWidget(self._lbl("Environment variables"))
         self.env = KeyValueTable(
             "Variable", "Value", on_change=self._emit, before_change=self._before_change
@@ -411,6 +427,8 @@ class ServerEditor(QFrame):
             self.details_btn.setChecked(False)
             self.diag_text.clear()
             self._set_dep({"status": "unknown", "label": "—"})
+            self.args_warn.hide()
+            self.args_fix_btn.hide()
             self._loading = False
             return
         self.setEnabled(True)
@@ -440,6 +458,7 @@ class ServerEditor(QFrame):
             self.env.load(d.get("env", {}))
         self._loading = False
         self.refresh_dependency(auto_open=True)
+        self._check_args()
 
     def dump_data(self) -> dict:
         """Build the server dict from the form, preserving unknown fields."""
@@ -485,6 +504,32 @@ class ServerEditor(QFrame):
         if not self._loading and self._on_change:
             self._on_change()
             self.refresh_dependency(auto_open=False)
+            self._check_args()
+
+    # --- args sanity check ------------------------------------------------ #
+    def _current_arg_lines(self) -> list[str]:
+        return [ln for ln in self.args.toPlainText().splitlines() if ln.strip() != ""]
+
+    def _check_args(self):
+        """Warn (and offer a fix) when a line looks like several args in one."""
+        if self.type.currentIndex() != 0:  # stdio page only
+            self.args_warn.hide()
+            self.args_fix_btn.hide()
+            return
+        _, notes = core.split_suspicious_args(self._current_arg_lines())
+        if notes:
+            self.args_warn.setText("⚠  " + "\n".join(notes))
+            self.args_warn.show()
+            self.args_fix_btn.show()
+        else:
+            self.args_warn.hide()
+            self.args_fix_btn.hide()
+
+    def _fix_args(self):
+        if self._before_change:
+            self._before_change()
+        fixed, _ = core.split_suspicious_args(self._current_arg_lines())
+        self.args.setPlainText("\n".join(fixed))  # triggers _emit -> recheck
 
     # --- dependency ------------------------------------------------------ #
     def refresh_dependency(self, auto_open=False):