agent-eval-gate

An MCP (Model Context Protocol) server, over stdio, that exposes one proven OFAC control as a single callable tool. A real MCP client calls authorize_funds_transfer and gets the governed gate's structured verdict: a transfer is permitted only if a version-pinned OFAC SDN screen returned CLEAR and COMPLETED before the transfer executed. Every unsafe ordering is denied.

This is a go-to-market wrapper around an already-proven control (agent-funds-gate, vendored under vendor/). It is not a new control and not a generic agent framework. We attacked our own gate and it holds.

The one command

Serve the tool over stdio:

./serve.sh

See the defeat-first acceptance demo (self-checking; exit 0 only if the race is denied and the safe case is permitted):

./demo.sh

Both are PYTHONPATH-setting wrappers around python3 -m .... No install, no network, no make. They read only the in-tree src and vendor files.

Related MCP server: trust-check-mcp

What it ADDS vs what it REUSES

REUSES (verbatim, vendored, unchanged): the FundsGate ordering enforcement and its naive_mode defeat; ScreenResult, ScreenStatus, GateDecision, the OFAC_CITE string, and the screen_completion_precedes_execution assertion. The server writes zero gate logic and imports the real public surface. See vendor/VENDOR.md for the pinned commit and per-file digests.

ADDS: an MCP / JSON-RPC 2.0 stdio transport (stdlib only) so a real MCP client can call the control; two server-level fail-closed promises the bare control lacks, each with a strippable polarity proof:

1. a non-extendable deadline. A caller may request a tighter budget; it can never request more than 90 seconds. If the evaluation runs longer than the budget, its result is discarded and the call denies. (If the machine sleeps mid-call, the monotonic clock advances past the budget on resume, so the call denies.)

2. error to DENY. Any exception inside the evaluation becomes a DENY; it never raises out and never permits.

It also adds a startup and per-call vendor-integrity refusal, and one-command, zero-install, no-network packaging.

The split: agent-funds-gate proves the control; agent-eval-gate makes it callable as a governed MCP tool with a deadline-bounded, fail-closed wrapper.

The defeat-first story

The scenario the demo runs: a $250,000 transfer fires at sequence 10. Its OFAC SDN screen for the same party is CLEAR but does not complete until sequence 15 -- after the money already moved. An under-governed agent (ordering check stripped) would permit this race; the governed gate denies it, naming the OFAC reg cite and the failing assertion screen_completion_precedes_execution, both read out of the real gate decision and never re-typed. This is a synthetic scenario run through our own control, not a real incident.

DENY vs error

A well-typed but unsafe scenario (the race, an SDN hit, a pending screen, a missing screen, a subject mismatch, a version mismatch) is a SUCCESSFUL tool result with structuredContent.decision = "DENY" and isError = false. A DENY is not a JSON-RPC error.

A protocol or argument fault (a missing required argument, a wrong JSON type, an unknown status enum, an unknown tool name, a malformed envelope, an unknown method, an unparseable line) is a JSON-RPC error object. A missing or null screen is not a fault; it is a safe DENY (screen_present).

A deadline_s greater than 90 is not an error. The guard silently caps the effective budget at 90; the SLA is not caller-extendable.

Exit-code contract

Server process (serve.sh):

JSON-RPC error codes inside the protocol: -32700 parse error, -32600 invalid request, -32601 method not found, -32602 invalid params. A tool DENY is a successful result, never an error object.

Demo process (demo.sh): 0 only if its own assertions hold (the race denied and the safe case permitted); non-zero if they do not. The demo is a self-checking acceptance gate, not just a print.

Injection posture

Tool-call arguments arrive from an MCP client that may be an under-governed agent. Every argument is treated as data. An argument only populates the subject, transfer_seq, required_sdn_version, and screen values handed to the gate. An argument can never select a code path, name a module to import, evaluate a string, trigger a file write, a network call, or a spend. A subject of "__import__('os').system('rm -rf /')" is an inert string the gate decides on by its ordering invariant alone. This is asserted by test (S16).

Scope limits

All scope limits of the vendored control stand and are linked, not restated, from CONTROL_INDEX.md. No new control, no second tool, no name or fuzzy matching, no 50%-rule, no license logic, no signed-screen verification. No external MCP SDK, no jsonschema lib, no network, no install step, no make, no Docker, no LLM calls, no agent runtime, no dashboard, and no publish, send, or spend step. stdio only. The server terminates at an MCP client reading a structured verdict.

How it stays honest

The server writes zero gate logic. Static tests assert that src/ defines no class FundsGate, no def authorize, no completed_seq comparison, no naive_mode=True, and no hand-written allow literal. The only permit reaching output is read out of a real GateDecision. The vendored control is pinned by per-file SHA-256; silent drift turns the suite red and makes the server refuse to serve. Run the full suite with python3 -m pytest -q.

License

MIT for the server's own wrapper code (see LICENSE). The vendored control is reused upstream IP under MIT; see vendor/VENDOR.md.