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

Trust 80%Fully autonomoussuccess · first tryCompare

Estimated cost: $0.01
Wall time: 54s
Human step-ins: 0
Outcome: Pass

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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: 1.11. Claude Code's own reported cost for claude-haiku-5.5: $0.011845. 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: $0.01
Wall time: 54s
Human step-ins: 0
Turns: 7

Model usage
Model	Input tok	Output tok	Cost
AClaude Haiku 5.5anthropic/claude-haiku-5.5effort default (no --effort flag) · thinking on	185,533	12,146	$0.01

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Haiku 5.5 (anthropic/claude-haiku-5.5, effort default (no --effort flag) · thinking on) via Claude Code 2.1.299 (headless -p), cloud.
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.
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.

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Automated checks

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

Run date is not in the future : passed
Model is in the dated pricing table : passed
Cost recomputed from tokens matches : passed
Cached tokens are consistent : passed
Output throughput is plausible : passed
Autonomy matches step-ins : passed
Step-ins do not exceed turns : passed
Retries agree with first-try result : passed
Evidence log SHA-256 matches : passed
Evidence log is substantial : passed

Evidence log

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  "result": "I rewrote `breaker.js` to follow the spec and added `test/breaker.test.js`. All 11 tests pass with `node --test test/`.\n\nWhat changed:\n- **Closed:** failures are kept as timestamps and pruned to `t > now - windowMs` on each failure. Successes don't touch the history. Reaching `failureThreshold` opens the breaker with `openedAt = now()`.\n- **Open \u2192 half_open:** the `state` getter checks the cooldown and transitions lazily, so it reports `'half_open'` before any call and emits the `open -> half_open` event.\n- **Half-open:** `halfOpenMax` caps in-flight trials, and extra calls get `EOPEN` without invoking `fn`. A trial failure reopens the breaker. `successThreshold` consecutive successes close it and clear the failure history.\n- **Stale results:** every transition bumps an epoch, and a call only affects state if the epoch hasn't changed since it started. That covers in-flight trials after a reopen and closed-state calls that settle after a transition.\n- **Timeout:** `timeoutMs > 0` rejects with `ETIMEOUT` and counts as a failure. The timer is cleared on first settlement, and a late result is ignored.\n- `call` is now a plain method returning a promise instead of `async`. Behaviour is the same, and the constructor options and export are unchanged.\n\nJudgment calls where the spec was open:\n- A non-failure rejection (`isFailure` returns false) counts as a success during half-open, since the spec says \"treated like a success\". In closed it has no effect.\n- A timeout counts as a failure regardless of `isFailure`.\n\nThis isn't a git repository, so I didn't commit anything.",
  "ttft_ms": 1305,
  "type": "result",
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  "uuid": "[REDACTED]",
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  "time_to_request_ms": 255,
  "first_content_frame_ms": 1110,
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  "result_index": 0
 }
]