usage-guard

1import type { Register, SessionRateLimit } from 'claude-code'
2
3// Temporary mod for the darkroom campaign (2026-10-09): the user asked for Fable subagents until
4// 2026-10-10 02:00 +08:00, then left model choice to the main session; this mod only steps Fable
5// subagents down to Opus 5.5 whenever usage gets tight.
6const TIGHT_PERCENT = 85                                   // any 5-hour or 7-day window at or past this is "tight"
7const WINDOWS = ['five_hour', 'seven_day']
8
9let limits: SessionRateLimit[] = []
10let warned = ''
11
12const label = (k: string) => (k === 'five_hour' ? '5h' : k === 'seven_day' ? '7d' : k)
13const tightOnes = () => limits.filter(l => WINDOWS.includes(l.kind) && l.percentUsed >= TIGHT_PERCENT)
14const summary = () => limits.filter(l => WINDOWS.includes(l.kind)).map(l => `${label(l.kind)} ${l.percentUsed}%`).join(' · ')
15
16const statusText = () => {
17  const s = summary()
18  return s ? `用量 ${s}${tightOnes().length ? '（緊繃：子代理改 Opus）' : ''}` : undefined
19}
20
21export const register: Register = on => {
22  on('session.start', async ($, e, next) => {
23    const r = await next(e)
24    try { limits = (await $.session.usage()).rateLimits } catch { /* no reading yet */ }
25    $.ui.status(statusText())
26    return r
27  })
28
29  on('session.measure', ($, e, next) => {
30    limits = e.rateLimits
31    $.ui.status(statusText())
32    return next(e)
33  })
34
35  on('tool.call', { tool: 'Agent' }, async ($, e, next) => {
36    if (e.model !== 'fable') return next(e)
37    const tight = tightOnes()
38    if (!tight.length) return next(e)
39    const why = `用量緊繃（${tight.map(l => `${label(l.kind)} ${l.percentUsed}%`).join('、')}）`
40    if (warned !== why) { warned = why; $.ui.toast(`usage-guard：${why}，子代理改用 Opus 5.5`) }
41    return next({ ...e, model: 'opus' })
42  }).catch(($, e, next) => next(e))   // never block a subagent because this mod failed
43}
44