AI agents use cmux_break_pane to create or update resources in Cmux Agent — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Cmux Agent environment.
This tool reorganizes/moves a pane into a new workspace, which is a reversible structural modification to the workspace layout. It creates a new workspace and moves an existing pane there, but does not delete data or execute arbitrary code. Classified as Write with medium severity since misuse could disrupt multi-agent session organization.
From the tool's definition Move a pane to its own new workspace
Documented attack patterns abuse exactly the kind of access cmux_break_pane gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Cmux Agent, and nothing reaches the server without passing your rules. This is the rule we recommend for cmux_break_pane:
{
"version": "1",
"default": "deny",
"tools": {
"cmux_break_pane": {
"limits": [
{
"counter": "cmux_break_pane_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}cmux_break_pane 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.
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Move a pane to its own new workspace. It is categorised as a Write tool in the Cmux Agent MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Cmux Agent MCP server in PolicyLayer and add a rule for cmux_break_pane: 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 Cmux Agent. Nothing to install.
cmux_break_pane is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the cmux_break_pane 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.
Set action: deny in the PolicyLayer policy for cmux_break_pane. 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.
cmux_break_pane is provided by the Cmux Agent MCP server (multiagentcognition/cmux-agent-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Cmux Agent, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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63 Cmux Agent tools catalogued and risk-classified — across an index of 43,000+ MCP servers.