super-loop-mcp — Sling

A referee for self-improving AI agent loops. Sling mines your past agent sessions for the workflows that actually worked, tries to improve them, and refuses to call anything "better" or "done" without measured proof — and it never stops until you stop it.

local-first · zero dependencies · Node ≥18 · MCP over stdio

In one minute (no jargon)

When you put an AI agent on a repetitive improvement task — "make this prompt/workflow better, and keep going" — three things tend to go wrong:

• it says "done" when it isn't,
• it skips steps it was told to follow,
• it stops early because it "thought hard" and felt finished.

Sling is the supervisor that doesn't allow that. It sits between you and the AI and acts like a strict lab referee:

• It holds the improvement procedure (a "loop") and hands the agent one step at a time — the next step only unlocks once the current one has left real evidence on disk.
• It keeps a sealed scorecard. The agent can't grade its own work; Sling measures the result itself and re-checks it from the sealed record before accepting any "this is better."
• It never declares victory. The run keeps going until you say stop — and it says so, plainly, the whole time:

WARNING: You are the stop condition. This loop does not stop until you stop it.

Everything runs on your machine. Nothing is uploaded.

What it does for you

• Mines your history — reads back through your past agent sessions to surface the loops/workflows that genuinely worked (the Strip Miner).
• Improves a loop — takes a loop and tries to make it better, generation after generation (Loop-de-loop).
• Only promotes real wins — a change is "promoted" only if it is measurably better on a frozen test and re-verified from sealed bytes; otherwise it is blocked.
• Keeps your authorship — your loops never leave your machine, and it never overwrites your canonical loop without you.

Quickstart

cd super-loop-mcp
npm test       # full node:test suite (118 checks) — no install, zero deps
npm run demo   # spawns the real server and drives a whole campaign over stdio (38/38 checks)
npm run verify # prove the bundled loop hashes against the mandated contract

Then point your MCP host (e.g. Claude Code) at it:

{
  "mcpServers": {
    "super-loop": {
      "command": "node",
      "args": ["/path/to/super-loop-mcp/src/server.mjs"]
    }
  }
}

On start, the agent is told to engage its runtime's native continuous mode so the run is not stopped early — Claude Code → `/loop`, Codex → `/goal` (other runtimes → their equivalent). State lives under SUPER_LOOP_HOME (default <package>/.super-loop). Nothing leaves your machine.

For developers

Everything below is the engineering detail behind the one-minute summary.

Why this exists

Drop a 300+ line loop into a model's context and it may ingest the whole thing, skip the structure, and treat an unverified argument as a test. Sling fixes that with hard mechanics:

1. Ask-once — starts with a brief explanation plus a few short questions once:

• the goal;
• whether to start by mining a new loop or improving an existing one;
• how wide to mine — your whole session history, or stop after a set number of loops;
• what order to improve in — best loops first, or in the order found (asked with an up-front warning that a run can take hours, days, or weeks depending on the task and how deep it mines);
• what "better" means (this becomes the frozen benchmark);
• any task-specific limit;
• and a final deeper-explanation offer, honored in the same response.

It never asks you to choose the model, promotion mode, or benchmark policy — the supervisor decides those from the task — and afterward it does not ask again or mark the campaign complete by itself.

1. Phase-gated streaming — holds the loop inside the MCP and hands you the next section only after the current one has recorded evidence. No 1k-line dump.
2. Benchmark-first — the baseline is hash-locked and the scorecard is frozen before any challenger. Model self-reported metrics never count.
3. Frontier hypothesis engine — full tests need 3–5 hypotheses on frontier routes (haiku/mini/nano/lite/prior-gen rejected); one no-improvement run is never "perfect".
4. Promotion gate — promotion requires a tool-measured, deep-reverified result that moves the quality/cost frontier past threshold. Otherwise: BLOCKED.

Two surfaces share one engine: the reactive MCP (a host calls its tools — the in-conversation hook) and the autonomous driver (super-loop-run CLI / run_campaign tool) that drives the whole campaign itself and only stops on the operator stop-file. The whole point: a model cannot promote, upgrade, or call a loop "perfect" from reasoning alone — every decision is hooked through a tool that demands tool-measured artifacts on disk, and the operator is the only stop condition.

Built fresh, zero dependencies, runs on plain Node ≥18. The full private 345-line Strip Miner and the full private 75-line Loop-de-loop (Loop 2) live inside the supervisor, byte-identical to source and hash-locked, streamed one section at a time.

The bundled loops (hash-locked)

These are the local big sources — the operator's full private cross-agent Strip Miner (with the old pause/complete language patched into checkpoint/continue semantics), not the short public miner. The server refuses to start, and the test suite fails, if either file's hash or line count drifts — so the short public miner can never be silently substituted.

Add your own loops (local loop library)

Users add their own loops through a tool, not by hand-editing source:

loop_register { id:"my-loop", title:"My Loop", content:"<full loop text>" }   → hash-locked, sectionized, persisted locally
loop_library                                                                   → lists mandated (hash-locked) + your custom loops
loop_start  { loop:"my-loop" }                                                 → streams it phase-gated, exactly like the mandated loops

Custom loops are sha256 hash-locked (write-once per version; overwrite:true makes a new version), get a safe id (no path traversal), persist under SUPER_LOOP_HOME/custom-loops/, and cannot collide with or overwrite the mandated Strip Miner / Loop-de-loop. They stream through the same phase gate. Nothing leaves your machine.

Tools (25)

Block codes you will see

NOT_INITIALIZED · PHASE_SKIP · BASELINE_FIRST · BASELINE_LOCKED · BENCHMARK_FIRST · BENCHMARK_FROZEN · WEAK_BENCHMARK · BASELINE_BAR_FIRST · HYPOTHESIS_COUNT · BANNED_ROUTE · BUILDER_ROUTE · FULLTEST_AGENTS · MODEL_REPORTED · MEASUREMENT_AUTHORITY · QUALITY_UNVERIFIED · NO_SCORE_MATRIX · NOT_REVERIFIED · BELOW_THRESHOLD · BELOW_FLOOR · STAGED_TRADEOFF · OPERATOR_IS_STOP · DASHBOARD_ONLY · NO_ACTIVE_LANE · EXEC_DISABLED · EXEC_FAILED · LOOP_EXISTS · LOOP_SOURCE

Live execution + autonomous harness (opt-in)

By default the server never executes commands (audited posture). Set SUPER_LOOP_ALLOW_EXEC=1 to let Sling own benchmark execution end-to-end: execute_full_test launches the frontier workers itself (allowlisted claude/codex/glm/gemini only, via execFile with no shell, prompt passed on stdin so untrusted text never reaches argv), captures each output, parses real token usage when the CLI reports it, enforces a hard timeout, and feeds the tool-captured bytes through the same gate. This closes the last self-report hole — when the supervisor launches the worker, there is no model-supplied run-log to fabricate. A failed/timed-out/non-allowlisted launch is an invalid batch and does not count toward retirement.

The autonomous driver sits on top of that — the difference between "a supervisor you call" and "a harness that drives itself":

SUPER_LOOP_ALLOW_EXEC=1 node scripts/run-campaign.mjs --config campaign.json --stop-file ./STOP

It runs the whole loop unattended (intake → mine → improve targets → validate every worker → bank Stones → advance/retire → re-mine) and only stops when you create the stop-file. The same logic is the run_campaign MCP tool, bounded by maxBatches for the in-call version. An MCP alone is reactive (a host calls it); the supervisor is what makes Sling self-driving.

Workers run on the real CLIs via stdin (claude -p --output-format json, codex exec --json) — the prompt never touches argv (no injection), and the real answer text + token usage are extracted for benchmarking. Benchmark modes: oracle (deterministic → auto-promote on a measured win) and judge (an independent Opus/GLM judge scores baseline-vs-challenger real outputs under a rubric → subjective → queues to the dashboard, never auto-promotes; the challenger never scores itself).

A full campaign, in order

initialize_loop_run            → brief + ask-once (a few Qs) → answer → INITIALIZED
loop_start strip-miner         → section 0
  observation_record (phase 0) → request_next_phase → section 1 → … (gated)
artifact_record role=baseline  → hash-locked
benchmark_propose → benchmark_select        → scorecard frozen
artifact_record measurement → benchmark_run arm=baseline   → bar set (tool-measured)
register_hypotheses (3–5 frontier)
test_hypothesis (3–5 agents, tool-measured) → MOVED_FRONTIER | NO_IMPROVEMENT
reverify_run → promotion_request            → PROMOTE | BLOCKED
update_dashboard / report_export            → checkpoint; lanes keep running

Two distinct thresholds, neither of which stops the campaign:

• Risk advisory (10–15, configurable): after ~12 consecutive valid no-improvement full tests the supervisor raises an economic-exhaustion risk advisory and opens dashboard review — it only reports risk, it does not stop.
• Branch retirement (30 valid batches): a branch retires only after 30 valid full real test batches (3–5 frontier workers each) with no qualifying improvement, then the supervisor auto-pivots to the next lane. Invalid / fake-metric / early-stopped / summary-only batches are blocked upstream and never count.

If the Strip Miner saturates, the supervisor auto-transitions (Strip Miner → Loop-de-loop, or the next improvement lane) via report_saturation — never a pause/await/stop. Checkpoint/report/dashboard/refused-terminal/saturation/retirement events persist a machine-readable continuation obligation until a real progress tool runs. continue_run records the model's next-lane commitment but deliberately cannot clear the obligation by itself. Only the operator stops the campaign.

Design notes

• Zero dependencies on purpose. No SDK, nothing to npm install that can fail or time out, nothing phoning home. The MCP transport is ~90 lines of newline-delimited JSON-RPC in src/server.mjs. There is nothing to install.
• Tool-computed measurement authority. The MCP derives every metric from the recorded raw bytes — tokenCost always (a deterministic token estimate), quality via the frozen benchmark's deterministic oracle when one exists. A number the model types is caller-reported and is refused by the benchmark/test gates (MEASUREMENT_AUTHORITY). reverify_run re-derives from the sealed bytes, so a tampered number cannot survive. The honest boundary, stated plainly: the MCP cannot prove the recorded bytes came from a real frontier-agent run unless it launched the worker (the opt-in live executor), and it cannot judge subjective quality without an oracle. Subjective quality routes to the dashboard for a human and never auto-promotes (QUALITY_UNVERIFIED); deterministic, oracle-scored quality promotes autonomously. In short: deterministic → tool-measured, subjective → dashboard.
• Host capability preflight, no execution. host_capability_preflight resolves known frontier-agent CLI names against PATH with a filesystem stat — it never spawns a command, never probes a model-supplied binary, and is not SOTA/web research. Presence on PATH ≠ working auth, and it says so.
• Anti-tampering. Baseline and benchmark are write-once within a cycle; changing either needs an explicit new epoch + rationale.
• Path hardening. runId and artifact ids are validated before touching disk, and sourcePath reads are refused so a model cannot turn the MCP into a local-file reader. Submit artifact bytes through content.
• Dashboard-only human review, with a real apply path. The model can queue/list Approve/Sludge items (and may propose a loop adoption by queuing a review that carries the improved loop text), but human_review_request { action:"resolve" } returns DASHBOARD_ONLY — the model can never approve its own work. Click-and-done: the autonomous campaign serves the dashboard (or run node scripts/dashboard-server.mjs); open it and just click Approve/Sludge. The click POSTs to the local server (127.0.0.1 only, cross-origin refused), which queues it to the run inbox, and the running campaign adopts it on its next tick — no file, no command, model-independent, non-blocking. (Headless fallbacks: save the dashboard's Export to runs/<runId>/inbox-decisions.json for the supervisor to auto-apply, or node scripts/apply-decisions.mjs --file <export>.) Approving a loop-adoption review installs the improved loop as a new versioned custom loop (the prior version is archived for rollback via operator.rollbackLoop), which loop_start then streams next cycle. The mandated canonical loops are immutable and never touched. Applying is non-blocking — the campaign never pauses for it, and adoption is never a model-callable tool (it lives under api.operator, off the tools/call surface). This is how a proven improvement actually becomes the loop Sling runs.
• Continuation is a host obligation, stated honestly. An MCP cannot force the host agent loop to keep running — only the host can (which is why the agent is told its native continuous command, /loop / /goal, on start). What the MCP can do, and does: every report / dashboard / saturation / no-improvement / refused-terminal event persists a machine-readable continuation obligation with a concrete next tool+lane, and continue_run records intent without clearing it (only a real progress tool clears it). The MCP makes stopping early visibly incomplete; it does not pretend to be the host scheduler. The operator is the only stop condition.
• Never overwrites your canonical loop. Promotion records an internal champion; changing the canonical loop file is HUMAN-GATED and left to you.
• Standalone by design.

Layout

loops/            bundled hash-locked loop sources (+ MANIFEST in constants)
src/
  server.mjs      MCP stdio JSON-RPC transport + tool schemas
  engine.mjs      Sling core — every tool handler + gate
  loops.mjs       registry, hash-lock, sectionizer (mandated + custom loaders)
  measure.mjs     tool-computed measurement (derive cost/quality from bytes) + honest boundary
  executor.mjs    opt-in live worker execution (allowlist, execFile, stdin) — off by default
  supervisor.mjs  autonomous campaign driver (validate → accept/re-enter boundary)
  host.mjs        host capability preflight (PATH presence only, no execution)
  models.mjs      frontier-route policy (banlist/allowlist)
  scorecard.mjs   promotion frontier rule + score matrix
  store.mjs       local atomic JSON persistence (runs + custom-loops)
  dashboard.mjs   polished dashboard.html + markdown report
  constants/util  shared facts + helpers
scripts/          demo.mjs (live proof), run-campaign.mjs (autonomous CLI, serves the dashboard),
                  dashboard-server.mjs (zero-dep served dashboard: click Approve/Sludge → adopt),
                  apply-decisions.mjs (operator-only headless fallback), verify-sources.mjs
test/             node:test suites (sources, ask-once, phase gate, benchmark,
                  hypotheses, promotion, hook, dashboard, transport, security,
                  loop library, measurement authority, host preflight, executor,
                  supervisor, adoption, dashboard-server)