[Firefly0619sec]

Problem

opcode-web binds to 0.0.0.0 by default and its HTTP/WebSocket API has no authentication:

• web_main.rs: #[arg(short = 'H', long, default_value = "0.0.0.0")], but host was never passed to the server — web_server.rs hard-coded SocketAddr::from(([0, 0, 0, 0], port));
• CORS is allow_origin(Any) with all methods/headers;
• endpoints include /api/sessions/execute, /api/sessions/continue, /ws/claude, which drive Claude Code — i.e. anyone on the LAN (or anyone reaching a forwarded port) can execute commands.

This is documented as a feature ("access from phone"), but the secure default should be loopback, with an explicit opt-in for LAN exposure.

Change

• opcode-web now defaults to 127.0.0.1;
• the --host argument is actually passed through to create_web_server (it was ignored before);
• printing a warning when --host 0.0.0.0 is used, because the API is still unauthenticated.

Notes

• --host 0.0.0.0 still works exactly as before for users who need phone access;
• I did not add authentication here (that is a larger change) — this PR only makes the dangerous mode opt-in;
• Happy to follow up with a token/basic-auth layer if you want one.