AnyRewriter

Fastify rewriter/proxy for Claude-compatible requests through AnyRouter, plus the read-only operations dashboard source that was paired with it in production.

The 2026-08-20 source snapshot was taken before the retired deployment was removed. It intentionally excludes .env, credentials, databases, control state, request dumps, event streams, access logs, generated state, backups, and container/runtime evidence.

What it does

• Proxies Claude API paths (/v1/*, /anthropic/*) to an upstream gateway.
• Rewrites unsupported model names to a configured target model.
• Preserves supported Claude model families, including haiku, opus, and fable.
• Adds required anthropic-beta flags when clients omit them.
• Repairs malformed historical tool_result blocks caused by cross-protocol history pollution.
• Removes empty-signature thinking blocks that can trigger upstream validation failures.
• Keeps historical-thinking pruning available as an emergency option, but defaults it off.
• Learns 524 / slow-520 stuck-body fingerprints and strips message-level thinking only on the client's retry.
• Uses deterministic hash-daily / hash-hourly session IDs to recover from session-level bans.
• Passes through rate-limit and pool-level failures instead of wasting retries.
• Aborts upstream work when the downstream client disconnects mid-stream.

Requirements

• Node.js 22+
• npm packages:
  • fastify
  • undici

The committed package.json and package-lock.json reproduce the rewriter dependencies.

Run

npm ci
UPSTREAM_URL=https://anyrouter.top \
TARGET_MODEL=claude-opus-4-8 \
PORT=8787 \
node rewriter.js

dashboard/server.js and dashboard/public/index.html preserve the dashboard source. The dashboard expects explicitly supplied, local read-only data paths; no production data is included in this repository.

Environment

Variable	Default	Purpose
UPSTREAM_URL	http://new-api:3000	Upstream API base URL.
TARGET_MODEL	claude-opus-4-8	Fallback model for unsupported model names.
PORT	8787	Listen port.
AUTO_PRUNE_HISTORY_THINKING	false	Optional emergency historical-thinking pruning.
THINKING_RESCUE_AFTER_524	true	Enable learn-first 524/slow-520 thinking rescue.
UPSTREAM_HEADERS_TIMEOUT_MS	320000	Header wait timeout before aborting a stuck upstream fetch.

Notes

rewriter.js is designed as an operational compatibility shim. It should avoid changing user semantic settings such as output_config.effort; it only changes request structure when needed for upstream compatibility or recovery.