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):

bcc_core.py

@@ -580,6 +580,42 @@ def parse_pasted_json(text: str) -> dict[str, dict]:
     return servers
 
 
+def split_suspicious_args(args: list[str]) -> tuple[list[str], list[str]]:
+    """
+    Detect the classic argument-entry mistake: several argv tokens typed on one
+    line ("--directory /path/to/server"). An entry is only flagged when it
+    contains whitespace AND at least one whitespace-separated token starts with
+    "-" — so legitimate single arguments with spaces ("My Project Notes",
+    "/Users/me/My Documents") are never touched.
+
+    Returns (fixed_args, notes). notes is empty when nothing was suspicious;
+    otherwise it describes each split so a UI can show the proposed fix.
+    Quotes are respected when splitting ('--name "My Server"' becomes
+    ['--name', 'My Server']).
+    """
+    import shlex
+
+    out: list[str] = []
+    notes: list[str] = []
+    for a in args:
+        if isinstance(a, str) and _looks_like_multiple_args(a):
+            try:
+                parts = shlex.split(a)
+            except ValueError:  # unbalanced quotes — fall back to plain split
+                parts = a.split()
+            if len(parts) > 1:
+                out.extend(parts)
+                notes.append(f"“{a}” looks like {len(parts)} arguments — split onto separate lines")
+                continue
+        out.append(a)
+    return out, notes
+
+
+def _looks_like_multiple_args(a: str) -> bool:
+    toks = a.split()
+    return len(toks) > 1 and any(t.startswith("-") for t in toks)
+
+
 # --------------------------------------------------------------------------- #
 # Validation
 # --------------------------------------------------------------------------- #

tests/test_json_repair.py

@@ -172,6 +172,40 @@ def test_kitchen_sink():
     assert len(notes) >= 4
 
 
+# --------------------------------------------------------------------------- #
+# Suspicious-args detection (several argv tokens typed on one line)
+# --------------------------------------------------------------------------- #
+def test_split_flag_and_value_on_one_line():
+    fixed, notes = c.split_suspicious_args(["--directory /path/to/server", "run", "main.py"])
+    assert fixed == ["--directory", "/path/to/server", "run", "main.py"]
+    assert len(notes) == 1
+
+
+def test_split_full_option_string():
+    fixed, notes = c.split_suspicious_args(["-y @pkg/server --port 8080"])
+    assert fixed == ["-y", "@pkg/server", "--port", "8080"]
+    assert notes
+
+
+def test_split_respects_quotes():
+    fixed, _ = c.split_suspicious_args(['--name "My Server"'])
+    assert fixed == ["--name", "My Server"]
+
+
+def test_split_leaves_legit_spaces_alone():
+    args = ["/Users/me/My Documents", "hello world", "run"]
+    fixed, notes = c.split_suspicious_args(args)
+    assert fixed == args
+    assert notes == []
+
+
+def test_split_leaves_clean_args_alone():
+    args = ["--directory", "/path/to/server", "run", "main.py"]
+    fixed, notes = c.split_suspicious_args(args)
+    assert fixed == args
+    assert notes == []
+
+
 # --------------------------------------------------------------------------- #
 # Config-file repair (load-time)
 # --------------------------------------------------------------------------- #