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](https://werkzeug.palletsprojects.com/en/stable/debug/),
+> 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

@@ -35,12 +35,19 @@ def index():
     return app
 
 
-if __name__ == "__main__":
+def build_cli_parser():
+    """CLI argument parser for ``python app.py`` (stdlib only; safe to import in tests)."""
     import argparse
 
     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",
@@ -49,13 +56,18 @@ def index():
         help="Path to exclusion rules file (sensitive sessions are omitted). "
              "If omitted, uses ~/.claude-code-chat-browser/exclusion-rules.txt if present.",
     )
-    args = parser.parse_args()
+    return parser
+
+
+if __name__ == "__main__":
+    args = build_cli_parser().parse_args()
 
     app = create_app(base_dir=args.base_dir, exclusion_rules_path=args.exclude_rules)
     print(f"Claude Code Chat Browser running at http://{args.host}:{args.port}")
+    # Reloader follows --debug on Unix only (Werkzeug file watcher, not the interactive debugger).
     app.run(
         host=args.host,
         port=args.port,
-        debug=True,
-        use_reloader=(sys.platform != "win32"),
+        debug=args.debug,
+        use_reloader=args.debug and (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
@@ -20,9 +21,66 @@
 REPO_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 sys.path.insert(0, REPO_ROOT)
 
+from app import build_cli_parser
 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
+
+
+def _ast_mentions_args_debug(node: ast.AST) -> bool:
+    for child in ast.walk(node):
+        if (
+            isinstance(child, ast.Attribute)
+            and child.attr == "debug"
+            and isinstance(child.value, ast.Name)
+            and child.value.id == "args"
+        ):
+            return True
+    return False
+
+
+def _use_reloader_kwarg_tied_to_debug(call: ast.Call) -> bool:
+    for kw in call.keywords:
+        if kw.arg == "use_reloader":
+            return _ast_mentions_args_debug(kw.value)
+    return False
+
+
 # ---------------------------------------------------------------------------
 # export.py argument tests
 # ---------------------------------------------------------------------------
@@ -214,62 +272,72 @@ def test_help_exits_zero(self):
 # ---------------------------------------------------------------------------
 
 class TestAppArgparse:
-    """app.py __main__ block must expose the same flags as cursor's app.py."""
-
-    def _build_parser(self) -> argparse.ArgumentParser:
-        """Re-create the argparse parser from app.py without importing Flask."""
-        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("--base-dir", default=None)
-        parser.add_argument("--exclude-rules", "-e", default=None,
-                            metavar="PATH", dest="exclude_rules")
-        return parser
+    """app.py CLI must expose the same flags as cursor's app.py."""
 
     def test_host_default_is_localhost(self):
         """Default host must be 127.0.0.1 to match cursor which binds to localhost only."""
-        parser = self._build_parser()
+        parser = build_cli_parser()
         args = parser.parse_args([])
         assert args.host == "127.0.0.1"
 
     def test_host_override(self):
-        parser = self._build_parser()
+        parser = build_cli_parser()
         args = parser.parse_args(["--host", "127.0.0.1"])
         assert args.host == "127.0.0.1"
 
+    def test_debug_default_is_false(self):
+        parser = build_cli_parser()
+        args = parser.parse_args([])
+        assert args.debug is False
+
+    def test_debug_explicit_true(self):
+        parser = build_cli_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()
+        parser = build_cli_parser()
         args = parser.parse_args([])
         assert args.port == 5000
 
     def test_port_override(self):
-        parser = self._build_parser()
+        parser = build_cli_parser()
         args = parser.parse_args(["--port", "8080"])
         assert args.port == 8080
 
     def test_base_dir_default_none(self):
-        parser = self._build_parser()
+        parser = build_cli_parser()
         args = parser.parse_args([])
         assert args.base_dir is None
 
     def test_base_dir_override(self):
-        parser = self._build_parser()
+        parser = build_cli_parser()
         args = parser.parse_args(["--base-dir", "/tmp/projects"])
         assert args.base_dir == "/tmp/projects"
 
     def test_exclude_rules_default_none(self):
-        parser = self._build_parser()
+        parser = build_cli_parser()
         args = parser.parse_args([])
         assert args.exclude_rules is None
 
     def test_exclude_rules_long_form(self):
-        parser = self._build_parser()
+        parser = build_cli_parser()
         args = parser.parse_args(["--exclude-rules", "/tmp/rules.txt"])
         assert args.exclude_rules == "/tmp/rules.txt"
 
     def test_exclude_rules_short_form(self):
         """Cursor's app.py uses -e as the short form; claude must too."""
-        parser = self._build_parser()
+        parser = build_cli_parser()
         args = parser.parse_args(["-e", "/tmp/rules.txt"])
         assert args.exclude_rules == "/tmp/rules.txt"
 
@@ -294,11 +362,15 @@ def test_app_py_host_default_is_localhost(self):
         assert '"127.0.0.1"' in src
 
     def test_app_py_use_reloader_is_platform_aware(self):
-        """use_reloader must depend on sys.platform, not be hardcoded False."""
+        """use_reloader must be opt-in via --debug and gated on non-Windows platforms."""
         app_path = os.path.join(REPO_ROOT, "app.py")
-        with open(app_path, "r", encoding="utf-8") as f:
+        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
+        assert all(_use_reloader_kwarg_tied_to_debug(c) for c in app_run_calls)
+        with open(app_path, encoding="utf-8") as f:
             src = f.read()
         assert "sys.platform" in src
         assert "win32" in src
-        # Must NOT have unconditional use_reloader=False
         assert "use_reloader=False" not in src