output-trimmer

1import { atom, update } from 'claude-code'
2import type { EngineInterface, Register } from 'claude-code'
3
4const MAX_LINES = 150
5const MAX_CHARS = 8000
6const HEAD = 30
7const TAIL = 60
8const MAX_SIGNALS = 40
9const LINE_CHARS = 300
10const DIR = 'claude-trimmed'
11// savings-meter reads this
12const trimmedAtom = atom({ plugin: 'output-trimmer', key: 'trimmed' } as const, 0)
13const SIGNAL = /error|fail|warn|exception|traceback|panic|assert|denied|not found|✗|✖/i
14// Claude asked for exactly this text (a file, a diff, a search), so trimming it would hide what it came for.
15const READS = /^\s*(cat|type|head|tail|sed|awk|less|more|grep|rg|jq|diff|git\s+(diff|show|log|blame))\b/
16
17// Keeps the first and last lines plus any line that looks like an error; undefined when it's short enough already.
18export const trim = (text: string): string | undefined => {
19  const lines = text.split('\n')
20  if (lines.length <= MAX_LINES && text.length <= MAX_CHARS) return undefined
21  const keep = lines.map((_, i) => i < HEAD || i >= lines.length - TAIL)
22  let signals = 0
23  lines.forEach((line, i) => {
24    if (!keep[i] && signals < MAX_SIGNALS && SIGNAL.test(line)) keep[i] = !!++signals
25  })
26  const out: string[] = []
27  let gap = 0
28  lines.forEach((line, i) => {
29    if (!keep[i]) return void gap++
30    if (gap) out.push(`... ${gap} lines trimmed ...`)
31    gap = 0
32    out.push(line.length > LINE_CHARS ? `${line.slice(0, LINE_CHARS)}...` : line)
33  })
34  if (gap) out.push(`... ${gap} lines trimmed ...`)
35  const trimmed = out.join('\n')
36  return trimmed.length < text.length ? trimmed : undefined
37}
38
39const save = async ($: EngineInterface, id: string, text: string, kept: number) => {
40  await update($, trimmedAtom, n => n + Math.round((text.length - kept) / 4))
41  const tmp = (await $.env.get('TEMP')) ?? (await $.env.get('TMPDIR')) ?? '/tmp'
42  const path = `${tmp.replace(/\\/g, '/')}/${DIR}/${id}.txt`
43  await $.fs.write(path, text)
44  return `[output-trimmer kept the start, the end and the error lines. Full output: ${path}]`
45}
46
47export const register: Register = on => {
48  on('tool.call', { tool: 'Bash' }, async ($, e, next) => {
49    const ran = await next(e)
50    if (ran.deny !== undefined || READS.test(e.command) || e.command.includes(DIR)) return ran
51    const id = e.tool_use_id ?? String(await $.clock.now())
52
53    // A failed command's output only reaches Claude as error text; a deny after the run delivers the trimmed text the same way.
54    if (ran.isError) {
55      const short = ran.text === undefined ? undefined : trim(ran.text)
56      return short === undefined || ran.text === undefined ? ran : { deny: `${await save($, id, ran.text, short.length)}\n${short}` }
57    }
58
59    const r = ran.result
60    if (r.isImage || r.backgroundTaskId || r.persistedOutputPath) return ran
61    const stdout = trim(r.stdout)
62    const stderr = trim(r.stderr)
63    if (stdout === undefined && stderr === undefined) return ran
64    const note = await save($, id, `${r.stdout}\n${r.stderr}`, (stdout ?? r.stdout).length + (stderr ?? r.stderr).length)
65    return { result: { ...r, stdout: `${note}\n${stdout ?? r.stdout}`, stderr: stderr ?? r.stderr }, context: ran.context }
66  }).catch(($, e, next) => next(e))
67}
68

1// tokens cut from Bash output this session, at about 4 characters a token
2declare module 'claude-code' {
3  interface PluginState {
4    'output-trimmer': { trimmed: number }
5  }
6}
7export type Contract = never
8