AI agents call hg_stack to retrieve information from Mercurial without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves and displays the state of topic-based workflow information. It has no side effects, makes no modifications to the repository or any data, and poses minimal risk if invoked by an AI agent. It is a simple status/query operation consistent with the 'Read' category.
From the tool's definition Tool name 'hg_stack' and description 'Shows the current topic stack' indicate a read-only operation that displays information about the current Mercurial topic stack without modifying any data.
Attacks that exploit this kind of access
Shows the current topic stack. It is categorised as a Read tool in the Mercurial MCP Server, which means it retrieves data without modifying state.
Register the Mercurial MCP server in PolicyLayer and add a rule for hg_stack: 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 Mercurial. Nothing to install.
hg_stack is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the hg_stack 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 hg_stack. 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.
hg_stack is provided by the Mercurial MCP server (metal-shark-sharktech/mcp-server-mercurial). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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