fix: opt-in --debug flag and README security warning

README.md

@@ -62,6 +62,11 @@ python app.py --port 8080 --host 0.0.0.0
 python app.py --base-dir /path/to/claude/projects
 ```
 
+> **Security warning:** Do not use `--host 0.0.0.0` together with `--debug` on untrusted networks.
+> That combination exposes Werkzeug's interactive debugger, which allows arbitrary code execution
+> from any browser that can reach the server. For typical local browsing, keep the default
+> `--host 127.0.0.1` and omit `--debug`.
+
 ### CLI Export
 
 ```bash

app.py

@@ -41,6 +41,12 @@ def index():
     parser = argparse.ArgumentParser(description="Claude Code Chat Browser")
     parser.add_argument("--port", type=int, default=5000)
     parser.add_argument("--host", default="127.0.0.1")
+    parser.add_argument(
+        "--debug",
+        action="store_true",
+        default=False,
+        help="Enable Flask/Werkzeug debug mode (never use with --host 0.0.0.0 on untrusted networks).",
+    )
     parser.add_argument("--base-dir", default=None, help="Override Claude projects dir")
     parser.add_argument(
         "--exclude-rules", "-e",
@@ -56,6 +62,6 @@ def index():
     app.run(
         host=args.host,
         port=args.port,
-        debug=True,
+        debug=args.debug,
         use_reloader=(sys.platform != "win32"),
     )

tests/test_cli_args.py

@@ -9,6 +9,7 @@
     pytest tests/test_cli_args.py -v
 """
 
+import ast
 import sys
 import os
 import importlib
@@ -23,6 +24,43 @@
 from scripts.export import build_parser
 
 
+def _is_app_run_call(node: ast.AST) -> bool:
+    if not isinstance(node, ast.Call):
+        return False
+    func = node.func
+    return (
+        isinstance(func, ast.Attribute)
+        and func.attr == "run"
+        and isinstance(func.value, ast.Name)
+        and func.value.id == "app"
+    )
+
+
+def _call_passes_hardcoded_debug_true(call: ast.Call) -> bool:
+    """True if this Call passes literal True for debug (kwarg or positional)."""
+    for kw in call.keywords:
+        if kw.arg == "debug" and isinstance(kw.value, ast.Constant) and kw.value.value is True:
+            return True
+    for arg in call.args:
+        if isinstance(arg, ast.Constant) and arg.value is True:
+            return True
+    return False
+
+
+def _debug_kwarg_uses_args(call: ast.Call) -> bool:
+    for kw in call.keywords:
+        if kw.arg != "debug":
+            continue
+        val = kw.value
+        return (
+            isinstance(val, ast.Attribute)
+            and isinstance(val.value, ast.Name)
+            and val.value.id == "args"
+            and val.attr == "debug"
+        )
+    return False
+
+
 # ---------------------------------------------------------------------------
 # export.py argument tests
 # ---------------------------------------------------------------------------
@@ -221,6 +259,7 @@ def _build_parser(self) -> argparse.ArgumentParser:
         parser = argparse.ArgumentParser(description="Claude Code Chat Browser")
         parser.add_argument("--port", type=int, default=5000)
         parser.add_argument("--host", default="127.0.0.1")
+        parser.add_argument("--debug", action="store_true", default=False)
         parser.add_argument("--base-dir", default=None)
         parser.add_argument("--exclude-rules", "-e", default=None,
                             metavar="PATH", dest="exclude_rules")
@@ -237,6 +276,26 @@ def test_host_override(self):
         args = parser.parse_args(["--host", "127.0.0.1"])
         assert args.host == "127.0.0.1"
 
+    def test_debug_default_is_false(self):
+        parser = self._build_parser()
+        args = parser.parse_args([])
+        assert args.debug is False
+
+    def test_debug_explicit_true(self):
+        parser = self._build_parser()
+        args = parser.parse_args(["--debug"])
+        assert args.debug is True
+
+    def test_app_py_debug_not_hardcoded_true(self):
+        """app.run() must wire debug from args, not a literal True."""
+        app_path = os.path.join(REPO_ROOT, "app.py")
+        with open(app_path, encoding="utf-8") as f:
+            tree = ast.parse(f.read(), filename=app_path)
+        app_run_calls = [n for n in ast.walk(tree) if _is_app_run_call(n)]
+        assert app_run_calls, "expected at least one app.run() call in app.py"
+        assert not any(_call_passes_hardcoded_debug_true(c) for c in app_run_calls)
+        assert any(_debug_kwarg_uses_args(c) for c in app_run_calls)
+
     def test_port_default(self):
         parser = self._build_parser()
         args = parser.parse_args([])