surface_close · Wmux MCP: Risk & Policy

WHAT IT DOES

What surface_close does on Wmux

AI agents use surface_close to create or update resources in Wmux — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Wmux environment.

WHY IT NEEDS A POLICY

Why surface_close needs a policy

An AI agent can call surface_close faster than any human can review — one bad instruction and it creates or modifies resources in Wmux by the hundred, each call as confident as the last.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

surface_close Rate-limited

surface_close stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "surface_close": {
      "limits": [
        {
          "counter": "surface_close_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Wmux, so you can run agents against it safely.

FAQ

Questions about surface_close

What does the surface_close tool do? +

Close a surface and dispose its PTY. surfaceId is globally unique and resolved across all workspaces. It is categorised as a Write tool in the Wmux MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on surface_close? +

Register the Wmux MCP server in PolicyLayer and add a rule for surface_close: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Wmux. Nothing to install.

What risk level is surface_close? +

surface_close is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit surface_close? +

Yes. Add a rate_limit block to the surface_close rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block surface_close completely? +

Set action: deny in the PolicyLayer policy for surface_close. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides surface_close? +

surface_close is provided by the Wmux MCP server (openwong2kim/wmux). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

// THE FULL RECORD

surface_close is one line of Wmux's registry record.

The record carries the whole server: verified identity, auth posture, risk grade, every tool classified, recommended policy — re-checked continuously.

Teams ship this data inside their own products. See what a licence covers →