```json
{
"root_cause": "Two bugs: (1) Promise.all rejects immediately if any task rejects, instead of ignoring rejected tasks; (2) results.find(Boolean) incorrectly treats falsy fulfilled values (0, false, '') as failures, causing them to be skipped in favor of null.",
"replacement": "async function firstSuccessful(tasks) {\n const settled = await Promise.allSettled(tasks.map((task) => task()));\n const firstFulfilled = settled.find((r) => r.status === 'fulfilled');\n return firstFulfilled ? firstFulfilled.value : null;\n}",
"tests": [
"test('returns null for empty array', async () => { expect(await firstSuccessful([])).toBeNull(); });",
"test('returns null when all tasks reject', async () => { const tasks = [() => Promise.reject('err1'), () => Promise.reject('err2')]; expect(await firstSuccessful(tasks)).toBeNull(); });",
"test('returns first fulfilled value even if falsy (0)', async () => { const tasks = [() => Promise.resolve(0), () => Promise.resolve(42)]; expect(await firstSuccessful(tasks)).toBe(0); });",
"test('returns first fulfilled value even if false', async () => { const tasks = [() => Promise.resolve(false), () => Promise.resolve(true)]; expect(await firstSuccessful(tasks)).toBe(false); });",
"test('returns first fulfilled value even if empty string', async () => { const tasks = [() => Promise.resolve(''), () => Promise.resolve('nonempty')]; expect(await firstSuccessful(tasks)).toBe(''); });",
"test('ignores leading rejected tasks and returns first fulfilled in order', async () => { const tasks = [() => Promise.reject('err'), () => Promise.resolve('second'), () => Promise.resolve('third')]; expect(await firstSuccessful(tasks)).toBe('second'); });",
"test('preserves input order even if later task resolves faster', async () => { const tasks = [() => new Promise((res) => setTimeout(() => res('slow-first'), 50)), () => new Promise((res) => setTimeout(() => res('fast-second'), 5))]; expect(await firstSuccessful(tasks)).toBe('slow-first'); });"
],
"remaining_risk": "The fix assumes 'first fulfilled value in input order' means the first task by array index that fulfills, regardless of timing, which matches the contract wording but await Promise.allSettled waits for all tasks to complete (including slow ones) before returning, which may not be desired if early-exit performance is needed; also unhandled promise rejection warnings are avoided by allSettled, but if tasks throw synchronously instead of returning rejected promises, this is not explicitly tested here beyond the reject cases."
}
```
Claude Opus 5：フル出力
{
"root_cause": "Two defects. (1) `Promise.all` rejects as soon as any task rejects, so a single rejected task makes the whole function reject instead of ignoring it and returning a later fulfilled value. (2) `results.find(Boolean) || null` selects by truthiness rather than by fulfillment, so legitimate fulfilled values such as 0, false, '', NaN, null, or undefined are skipped and/or coerced to null. Using `Promise.allSettled` plus a status check on the settled records fixes both, and returning `record.value` directly preserves falsy results.",
"replacement": "async function firstSuccessful(tasks) {\n const results = await Promise.allSettled(tasks.map((task) => task()));\n const firstFulfilled = results.find((result) => result.status === 'fulfilled');\n return firstFulfilled ? firstFulfilled.value : null;\n}",
"tests": [
"firstSuccessful([]) resolves to null (empty input).",
"firstSuccessful([() => Promise.resolve('a'), () => Promise.resolve('b')]) resolves to 'a' (input order, not completion order).",
"firstSuccessful([() => new Promise((res) => setTimeout(() => res('slow-first'), 50)), () => Promise.resolve('fast-second')]) resolves to 'slow-first' (order is by index, not by who settles first).",
"firstSuccessful([() => Promise.reject(new Error('boom')), () => Promise.resolve('second')]) resolves to 'second' (rejection ignored, does not propagate).",
"firstSuccessful([() => Promise.reject(new Error('a')), () => Promise.reject(new Error('b'))]) resolves to null (all reject).",
"firstSuccessful([() => Promise.resolve(0)]) resolves to 0, not null (falsy number preserved).",
"firstSuccessful([() => Promise.resolve(false)]) resolves to false (falsy boolean preserved).",
"firstSuccessful([() => Promise.resolve('')]) resolves to '' (empty string preserved).",
"firstSuccessful([() => Promise.resolve(undefined), () => Promise.resolve('later')]) resolves to undefined (first fulfilled wins even if its value is undefined).",
"firstSuccessful([() => Promise.reject(new Error('x')), () => Promise.resolve(null), () => Promise.resolve('third')]) resolves to null because index 1 fulfilled with null — verifying null-as-value is not confused with the all-rejected sentinel by inspecting status.",
"firstSuccessful([() => Promise.resolve(NaN)]) resolves to NaN (Number.isNaN on the result is true)."
],
"remaining_risk": "The function still starts every task and awaits all of them, so there is no short-circuiting: a slow or never-settling later task delays or blocks the result, and side effects of later tasks always occur. A task that throws synchronously (rather than returning a rejected promise) will throw inside `tasks.map`, causing the returned promise to reject instead of being ignored; wrap the invocation in `Promise.resolve().then(task)` if that must also be tolerated. `null` is still returned both for all-rejected/empty input and when a task genuinely fulfills with `null`, so callers cannot distinguish those cases. Non-array or non-function inputs are not validated, and rejection reasons are discarded rather than aggregated (no AggregateError), which can hide diagnostics."
}
Claude Fable 5.1：フル出力
{"root_cause":"Two defects: (1) Promise.all rejects as soon as any task rejects, so rejected tasks are not ignored and the function throws instead of skipping them; (2) results.find(Boolean) skips legitimate falsy fulfilled values (0, false, '') and the trailing '|| null' also converts such values to null, violating the requirement to return the first fulfilled value even when it is falsy.","replacement":"async function firstSuccessful(tasks) {\n const results = await Promise.allSettled(tasks.map((task) => task()));\n const first = results.find((result) => result.status === 'fulfilled');\n return first ? first.value : null;\n}","tests":["firstSuccessful([]) resolves to null","firstSuccessful([() => Promise.resolve('a'), () => Promise.resolve('b')]) resolves to 'a'","firstSuccessful([() => Promise.reject(new Error('x')), () => Promise.resolve('b')]) resolves to 'b' and does not throw","firstSuccessful([() => Promise.reject(new Error('x')), () => Promise.reject(new Error('y'))]) resolves to null","firstSuccessful([() => Promise.resolve(0), () => Promise.resolve(5)]) resolves to 0","firstSuccessful([() => Promise.resolve(false), () => Promise.resolve(true)]) resolves to false","firstSuccessful([() => Promise.resolve(''), () => Promise.resolve('z')]) resolves to ''","firstSuccessful([() => Promise.reject(new Error('x')), () => Promise.resolve(null)]) resolves to null (fulfilled null is returned as-is)","firstSuccessful([() => new Promise(r => setTimeout(() => r('slow'), 50)), () => Promise.resolve('fast')]) resolves to 'slow' (input order wins over settlement order)"],"remaining_risk":"All tasks are started concurrently and the function waits for every task to settle before returning, so a slow task delays the result even when an earlier task has already fulfilled; a sequential or early-exit strategy would be needed if latency matters. A task that throws synchronously (rather than returning a rejected promise) will still cause the function to reject, since the contract assumes tasks return promises. Promise.allSettled requires ES2020 or a polyfill."}
