Skip to content

Claude Sonnet 5.5 (effort default (no --effort flag) · thinking on) on Fix a Node.js circuit breaker state machine (rolling window, half-open concurrency, timeouts, exact transition events)

AClaude Sonnet 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-17 · by @bobsiopener

Trust 80%Fully autonomoussuccess · first try
Estimated cost
$0.07
Wall time
22s
Human step-ins
0
Outcome
Pass

Compare with other models on this task →

Summary

Exact prompt

# Task: fix the circuit breaker state machine `breaker.js` (Node 20, CommonJS, no dependencies) wraps calls to a flaky service. Make `CircuitBreaker` implement exactly this state machine (keep the constructor options and export): - **closed**: `call(...args)` invokes `fn(...args)` and resolves/rejects with its result. A synchronous throw from `fn` behaves like a rejection. A failure is a rejection for which `isFailure(err)` returns true (others are passed through to the caller but otherwise treated like a success: not counted). Failures are counted in a **rolling window**: only failures whose time (`now()` when the call settled) is within the last `windowMs` (i.e. `t > now - windowMs`) count; successes do **not** reset the count. When the count reaches `failureThreshold`, the breaker goes **open** (`openedAt = now()`). - **open**: every call rejects immediately with an `Error` whose `code` is `'EOPEN'`, without invoking `fn`, until `now() - openedAt >= cooldownMs`; at that point the breaker is **half_open** (the `state` getter must already report `'half_open'` then, even before a call). - **half_open**: at most `halfOpenMax` trial calls may be in flight at once; extra calls reject with `EOPEN` without invoking `fn`. Any trial failure -> **open** again (new `openedAt`), and the in-flight results don't change state further. After `successThreshold` successful trials in a row -> **closed** with failure history cleared. - `timeoutMs` > 0: a call not settled within `timeoutMs` real milliseconds rejects with an `Error` with `code` `'ETIMEOUT'`, and counts as a failure (a later settlement of that call is ignored). The timer must be cleared when the call settles first. - `on('stateChange', cb)` calls `cb(from, to)` exactly once per actual transition (including open -> half_open), in order; `on` returns `this`. Add tests under `test/` if you want (`node --test test/`). No network, no npm.

Injected clock makes every boundary exact: rolling-window expiry, >= cooldown, lazy half_open in the getter, half-open in-flight cap, stale trial results after reopening, timeout-as-failure with cleared timers, and one event per real transition. Original benchmark task written for usecaserank.com (not based on a specific public post). Headless, offline run on a reproducible fixture. Each run's notes say how its cost was measured (estimates are marked).

Success criteria: 1. hidden_tests_pass: all 11 hidden node:test tests pass (node 20, 60 s cap). 2. own_tests_pass_or_absent: if the agent added tests under test/, `node --test test/` exits 0.

Setup notes: Use Case Scout batch 6 case f11-js-circuit-breaker (offline fixture). Prepared with batch6/prepare.sh; hidden key/tests kept outside the agent's work dir. Prompt = TASK.md verbatim. Scored with the scout's scorer: `python score.py WORKDIR KEYDIR`. Tools: Read/Write/Edit/Glob/Grep/Bash, web disabled. Single run, no retries. 1-min load average at scoring: 1.15. Claude Code's own reported cost for claude-sonnet-5.5: $0.07473. Score: 11/11. Cost is an ESTIMATE: measured tokens x pricing.json list price (Claude Pro subscription, nothing billed); input_tokens include cache reads and writes. Single run.

Estimated cost List-price estimate; not actually billed.

Metrics

Estimated cost
$0.07
Wall time
22s
Human step-ins
0
Turns
5
Model usage
ModelInput tokOutput tokCost
AClaude Sonnet 5.5anthropic/claude-sonnet-5.5effort default (no --effort flag) · thinking on60,1553,108$0.07

Reproduce this run

  1. Use the use case prompt on the use case page.
  2. Same setup: Claude Sonnet 5.5 (anthropic/claude-sonnet-5.5, effort default (no --effort flag) · thinking on) via Claude Code 2.1.299 (headless -p), cloud.
  3. It counts as a success only if it meets every success criterion: 1. hidden_tests_pass: all 11 hidden node:test tests pass (node 20, 60 s cap). 2. own_tests_pass_or_absent: if the agent added tests under test/, `node --test test/` exits 0.
  4. Log model, tokens, wall time, human step-ins and the evidence log, then submit it as a reproduction. A different model? Submit a head-to-head rerun.

How runs are scored: Methodology.

Was this useful?

⇄ Rerun on another model

Automated checks

Trust 80% comes from these checks (how Trust % works).

Evidence log
[
 {
  "duration_api_ms": 21323,
  "stop_reason": "end_turn",
  "session_id": "[REDACTED]",
  "total_cost_usd": 0.0747302,
  "usage": {
   "input_tokens": 6,
   "cache_creation_input_tokens": 9647,
   "cache_read_input_tokens": 50502,
   "output_tokens": 3108,
   "output_tokens_details": {
    "thinking_tokens": 577
   },
   "server_tool_use": {
    "web_search_requests": 0,
    "web_fetch_requests": 0
   },
   "service_tier": "standard",
   "cache_creation": {
    "ephemeral_1h_input_tokens": 9647,
    "ephemeral_5m_input_tokens": 0
   },
   "inference_geo": "global",
   "iterations": [
    {
     "input_tokens": 2,
     "output_tokens": 392,
     "cache_read_input_tokens": 19425,
     "cache_creation_input_tokens": 2761,
     "cache_creation": {
      "ephemeral_5m_input_tokens": 0,
      "ephemeral_1h_input_tokens": 2761
     },
     "type": "message"
    }
   ],
   "speed": "standard",
   "fallback_credit": null
  },
  "modelUsage": {
   "claude-sonnet-5-5": {
    "inputTokens": 6,
    "outputTokens": 3108,
    "cacheReadInputTokens": 50502,
    "cacheCreationInputTokens": 9647,
    "webSearchRequests": 0,
    "costUSD": 0.0747302,
    "contextWindow": 1000000,
    "maxOutputTokens": 128000,
    "thinkingTokens": 577,
    "canonicalModel": "claude-sonnet-5-5",
    "provider": "firstParty",
    "costBasis": "list"
   }
  },
  "permission_denials": [],
  "terminal_reason": "completed",
  "fast_mode_state": "off",
  "fast_mode_disabled_reason": "sdk_opt_in_required",
  "subagent_stats": {
   "spawned": 0,
   "requested": {
    "background": 0,
    "foreground": 0,
    "unset": 0
   },
   "started_in_background": 0,
   "max_depth": 0,
   "spawned_by_subagents": 0,
   "completed": 0,
   "failed": 0,
   "killed": {
    "parent": 0,
    "user": 0,
    "system": 0
   },
   "refused": {
    "depth_limit": 0,
    "concurrency_limit": 0,
    "budget": 0
   },
   "by_type": {}
  },
  "safety_stops": 0,
  "is_error": false,
  "num_turns": 5,
  "subtype": "success",
  "api_error_status": null,
  "result": "I rewrote `breaker.js` to follow the state machine you described, keeping the constructor options and the export. I added `test/breaker.test.js` with two tests, and both pass. The tests cover:\n- the closed \u2192 open \u2192 half_open \u2192 closed cycle, including the `EOPEN` rejection and the order of `stateChange` events;\n- the `ETIMEOUT` path.\n\nThe other rules (rolling window, `halfOpenMax`, `isFailure`, stale results) are implemented but have no tests yet.\n\nBehaviours to be aware of:\n- **Stale results:** each state transition bumps a generation counter. A call that settles after the breaker has changed state doesn't affect the new state. This is how in-flight results are ignored once a trial failure re-opens the breaker.\n- **Timeouts:** an `ETIMEOUT` always counts as a failure, whatever `isFailure` says. The timer is cleared when the call settles first, and a later settlement is ignored.\n- **`isFailure` throwing:** if `isFailure` itself throws, I treat the error as a failure.\n- **Half-open non-failures:** a rejection that `isFailure` rejects counts as a successful trial in half_open.",
  "ttft_ms": 2020,
  "type": "result",
  "duration_ms": 21914,
  "uuid": "[REDACTED]",
  "ttft_stream_ms": 1654,
  "time_to_request_ms": 243,
  "first_content_frame_ms": 1654,
  "queued_turn_count": 0,
  "result_index": 0
 }
]

Get new runs and ranking changes weekly