Allow run_script to run on a remote runner

[titouanmathis]

Summary

Lets the MCP server delegate run_script execution to a separate runner so a script's memory/CPU (and any OOM) is isolated from the main server — important on small VMs (the hosted HTTP MCP runs on 256 MB, where a heavy in-process run could OOM-kill the whole server). Infrastructure-agnostic and load-balancer-ready.

How it works

• Front (PRODUCTIVE_MCP_RUN_RUNNER_URL set): handleRunScript forwards a stateless { code, args, flags, dry_run, credentials } POST to the runner and relays its ToolResult. The runner URL also enables run_script without the local PRODUCTIVE_MCP_ENABLE_RUN flag (the front can stay tiny + gated).
• Runner (HTTP transport, PRODUCTIVE_MCP_RUN_RUNNER_TOKEN set, PRODUCTIVE_MCP_ENABLE_RUN=true): a token-gated POST /run runs the script through the normal pipeline (its own limits + sandbox) and returns the ToolResult.
• No runner configured: runs locally exactly as before (graceful fallback). Agents see no difference either way.

Infra-agnostic / LB-ready

The /run contract is a single stateless HTTP POST, so any backend works (Fly machine pool, k8s, serverless, …) and you can put a load balancer in front of a runner pool. It is:

• stateless — everything is in the body, no session/affinity;
• token-authenticated — PRODUCTIVE_MCP_RUN_RUNNER_TOKEN (constant-time compare), so the hop is safe even on a shared private network;
• not to be proxy-retried — a non-dry_run script can mutate, so retries must be disabled at the LB/proxy.

Config

Front: PRODUCTIVE_MCP_RUN_RUNNER_URL, PRODUCTIVE_MCP_RUN_RUNNER_TOKEN, optional PRODUCTIVE_MCP_RUN_RUNNER_TIMEOUT_MS (30000).
Runner: PRODUCTIVE_MCP_RUN_RUNNER_TOKEN (activates /run), PRODUCTIVE_MCP_ENABLE_RUN=true, plus the existing PRODUCTIVE_MCP_RUN_* limits.

Testing

• Unit tests: remote.ts (config parsing, token compare, forwarding success/non-2xx/timeout/transport-error, header/body), /run core (run-endpoint.ts — token gating 404/401, body/credential validation, happy path), and the handleRunScript remote branch (forwards, doesn't run locally, still validates code).
• 926 MCP unit tests pass; npm run check clean; build OK. The thin H3 wiring in http.ts is covered by the executeRunRequest core tests.

Depends on a release before the runner deployment can pin it.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.27%. Comparing base (e00aa34) to head (e334000).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #182      +/-   ##
==========================================
+ Coverage   97.25%   97.27%   +0.02%     
==========================================
  Files         264      266       +2     
  Lines        8802     8867      +65     
  Branches     2783     2806      +23     
==========================================
+ Hits         8560     8625      +65     
  Misses        236      236              
  Partials        6        6              

Flag	Coverage Δ
unittests	97.27% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.