Posit mcp-repl Code Runner — mcp_repl

Creates a dsprrr code runner backed by Posit's mcp-repl MCP server. mcp-repl keeps a long-lived R session and enforces its sandbox with operating-system primitives. This makes it suitable for code proposed by an optimizer or language model.

Usage

mcp_repl_runner(
  repl = NULL,
  command = "mcp-repl",
  interpreter = "r",
  sandbox = "workspace-write",
  timeout = 30,
  max_output_chars = 100000L,
  oversized_output = "files",
  extra_args = character()
)

Arguments

repl: Optional function implementing the mcp-repl repl tool.
command: Path or command name for the mcp-repl executable.
interpreter: Interpreter passed to mcp-repl. Currently only "r" is supported by this runner.
sandbox: mcp-repl sandbox policy. Defaults to "workspace-write". "inherit-codex" may be used only when the MCP client propagates Codex sandbox metadata; mcptools::mcp_tools() does not currently do so.
timeout: Maximum execution time in seconds.
max_output_chars: Maximum number of output characters returned to the optimizer.
oversized_output: mcp-repl oversized-output mode.
extra_args: Additional command-line arguments passed to mcp-repl.

Value

An McpReplRunner implementing the dsprrr code-runner protocol.

Details

By default, mcp_repl_runner() starts mcp-repl through mcptools::mcp_tools() with:

the R interpreter;
the workspace-write sandbox;
network access disabled by the sandbox; and
oversized output written to sandbox-visible files.

The sandbox is deliberately on by default. Setting sandbox = "off" is rejected because this runner advertises itself as safe for untrusted code. Use r_code_runner() explicitly for trusted-input-only subprocess isolation.

Supplying repl is useful for an already-managed MCP connection and for deterministic tests. It must be a function with the mcp-repl tool contract: repl(input, timeout_ms).

Examples

if (FALSE) { # \dontrun{
runner <- mcp_repl_runner()
runner$execute("mean(1:10)")
runner$reset()
} # }