offscale/sidecar/claude-proxy.ts

import { existsSync, readFileSync } from 'node:fs';
import { join } from 'node:path';
import { DATA_PATH } from '@@/data-path';
import { ANTHROPIC_PROXY_URL } from '@@/officer-url.mjs';

// One-shot model calls, for sidecar features that need a sentence of reasoning rather than an agent.
//
// The target is `officer-anthropic-proxy` on loopback — the same process Claude Code itself talks to. It
// holds the owner's OAuth credential and refreshes it; callers hold nothing. Its `x-api-key` is a locally
// generated secret it writes to its own state file, so authenticating is a file read, not a credential this
// sidecar is given. That file is written by the proxy and read by everyone else; see claude/state.ts
// (`readProxySecretFromDisk`), which does the same thing for the agent.
//
// Not imported from claude/state.ts on purpose: that module initialises paths and a lock for a sidecar this
// one is not. Twenty lines of file read is a better dependency than another sidecar's lifecycle.
//
// This is a REQUEST-SCOPED call with a timeout, not a session. Anything conversational belongs in the chat
// surface, which already exists and already persists.

const DEFAULT_TIMEOUT_MS = 120_000;

/** The proxy is not running, has no token, or refused us. Distinct from the model declining to answer. */
export class ProxyUnavailable extends Error {}

/**
 * The proxy's own generated secret. Empty means "not on disk yet" — it persists on a debounce, so a
 * freshly installed machine has a window where the file exists without it.
 */
function readProxySecret(): string {
  try {
    const file = join(DATA_PATH, 'sidecar', 'claude-state.json');
    if (!existsSync(file)) return '';
    const parsed = JSON.parse(readFileSync(file, 'utf-8')) as { proxySecret?: unknown };
    return typeof parsed.proxySecret === 'string' ? parsed.proxySecret : '';
  } catch {
    return '';
  }
}

type AskParams = { model: string; system: string; prompt: string; maxTokens: number; timeoutMs?: number };

type MessagesResponse = { content?: { type?: string; text?: string }[]; error?: { message?: string } };

/**
 * One user turn, one reply, as plain text.
 *
 * The system prompt is sent as two blocks with Claude Code's own identity first. The proxy authenticates
 * with a Claude Pro/Max OAuth token, and that credential is issued to the CLI — asking it to be something
 * else is a request the upstream is entitled to refuse. (Measured 2026-08-06: a plain assistant prompt is
 * currently accepted too. Keeping the block costs ~14 tokens and removes the question.)
 */
export async function askClaude({ model, system, prompt, maxTokens, timeoutMs }: AskParams): Promise<string> {
  const secret = readProxySecret();
  if (!secret) throw new ProxyUnavailable('the Claude proxy has not started yet — try again in a moment');

  let res: Response;
  try {
    res = await fetch(`${ANTHROPIC_PROXY_URL}/v1/messages`, {
      method: 'POST',
      headers: { 'x-api-key': secret, 'anthropic-version': '2023-06-01', 'content-type': 'application/json' },
      body: JSON.stringify({
        model,
        max_tokens: maxTokens,
        system: [
          { type: 'text', text: "You are Claude Code, Anthropic's official CLI for Claude." },
          { type: 'text', text: system },
        ],
        messages: [{ role: 'user', content: prompt }],
      }),
      signal: AbortSignal.timeout(timeoutMs ?? DEFAULT_TIMEOUT_MS),
    });
  } catch (err) {
    if (err instanceof Error && err.name === 'TimeoutError') throw new ProxyUnavailable('the model took too long');
    throw new ProxyUnavailable('the Claude proxy is not reachable');
  }

  const body = (await res.json().catch(() => null)) as MessagesResponse | null;

  if (!res.ok) {
    const detail = body?.error?.message;
    // 401/429 are the proxy's own credential problems and read as "unavailable"; anything else is upstream
    // saying something specific about this request, which is worth passing through.
    if (res.status === 401 || res.status === 429) {
      throw new ProxyUnavailable(detail ?? `the Claude proxy returned ${res.status}`);
    }
    throw new Error(detail ?? `the model returned ${res.status}`);
  }

  const text = (body?.content ?? [])
    .filter((block) => block.type === 'text' && typeof block.text === 'string')
    .map((block) => block.text)
    .join('')
    .trim();

  if (!text) throw new Error('the model returned an empty reply');
  return text;
}