session_save · Ensemble MCP: Risk & Policy

WHAT IT DOES

What session_save does on Ensemble

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

WHY IT NEEDS A POLICY

Why session_save needs a policy

This tool creates or modifies checkpoint state data for AI agent pipelines. It is a Write operation because it persists data in a versioned manner, allowing recovery of prior states. It is not Destructive because versioning implies previous checkpoints are retained. Severity is medium because misuse could corrupt pipeline state or consume storage, but the reversible nature and local operation limit blast radius.

From the tool's definition Tool name 'session_save' combined with description 'Save pipeline checkpoint state with optimistic versioning' indicates creation/modification of checkpoint data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

session_save Rate-limited

session_save 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": {
    "session_save": {
      "limits": [
        {
          "counter": "session_save_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 Ensemble, so you can run agents against it safely.

FAQ

Questions about session_save

What does the session_save tool do? +

Save pipeline checkpoint state with optimistic versioning. It is categorised as a Write tool in the Ensemble MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on session_save? +

Register the Ensemble MCP server in PolicyLayer and add a rule for session_save: 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 Ensemble. Nothing to install.

What risk level is session_save? +

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

Can I rate-limit session_save? +

Yes. Add a rate_limit block to the session_save 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 session_save completely? +

Set action: deny in the PolicyLayer policy for session_save. 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 session_save? +

session_save is provided by the Ensemble MCP server (lynkbyte/ensemble). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.