Claude Code (drop-in)

Overview

@solvela/dropin is a tiny localhost process that lets Claude Code pay for its own API calls with USDC — no API key, no account. Claude Code points at it via ANTHROPIC_BASE_URL; the sidecar holds a delegated channel session key, signs a spend-down channel voucher for each request, and relays the gateway's native Anthropic response — SSE bytes verbatim, so thinking-block signatures survive.

Claude Code can't sign anything per-request (it sends one static ANTHROPIC_AUTH_TOKEN). The sidecar is the bridge: the per-request client signature is the spend cap, the key never leaves your machine, and nobody else ever controls the funds.

Setup

Fund and open a channel (one-time; prompts before signing — verify the amount and recipient it prints)

npx solvela-dropin open \
  --gateway https://api.solvela.ai \
  --amount 5 \
  --wallet ~/.config/solana/id.json \
  --rpc-url https://api.mainnet-beta.solana.com

--wallet accepts a standard Solana id.json (64-byte JSON array) or a Solvela wallet.json ({"private_key": "<base58>"}, as written by the MCP server).

Point Claude Code at the sidecar

Paste the two env vars open prints into your Claude Code environment:

export ANTHROPIC_BASE_URL=http://127.0.0.1:8484
export ANTHROPIC_AUTH_TOKEN=<printed local token>

Run the sidecar

npx solvela-dropin serve

Claude Code now works normally — each request is paid from the channel.

Close when done

npx solvela-dropin close    # re-run to poll the refund status

The unspent balance is refunded on-chain to the funding wallet.

Warning

Verify what you sign. The deposit recipient and mint are discovered from the gateway's /v1/escrow/config — which is only as trustworthy as the --gateway URL you typed. The mint is pinned to canonical mainnet USDC and a mismatch is a hard reject (--expected-mint pins a non-mainnet mint deliberately, e.g. devnet); pass --expected-recipient <b58> to also pin the recipient independently. --yes only skips the interactive prompt — it never bypasses a mint or recipient mismatch.

How a request is paid

Claude Code POSTs /v1/messages to the sidecar with the local token.
The sidecar forwards it to the gateway unpaid; the gateway answers with an x402 402 quote (the fee-inclusive estimate for this request).
The sidecar signs a cumulative voucher for exactly that quote — it never computes fees or invents amounts — and retries with the byte-identical body plus a payment-signature header. The voucher's digest binds it to those bytes.
The gateway verifies the voucher off-chain (no per-call on-chain transaction), serves, and advances the channel ledger. The response is relayed to Claude Code untouched.

POST /v1/messages/count_tokens is free and forwarded verbatim — never signed, never charged.

Limitations

Draws are strictly serial per channel. Each voucher signs last + quote, so concurrent requests (e.g. parallel subagents) queue behind a single-flight gate — expect added latency under parallel load, not failures. One channel per sidecar instance.
expiry_slot is sourced from the gateway (GET /v1/escrow/config, cached ~30s) and fails closed: if the current Solana slot is unavailable, the sidecar refuses to sign rather than guess.

Local-only, by design

The sidecar binds 127.0.0.1 only, and a hosted sidecar is deliberately unsupported: a server signing vouchers on users' behalf would hold effective control over user funds — exactly the custodial problem the per-request client signature exists to remove. Do not put it behind a reverse proxy.

The local token (ANTHROPIC_AUTH_TOKEN) only authenticates Claude Code to the sidecar so a stray local process can't drive your channel; it is never forwarded upstream and is not a gateway credential.

State

~/.solvela/dropin.json (mode 0600) holds the gateway URL, channel ID, the session-key seed, and the local token. It controls the channel — keep it private, and delete it after close confirms the refund. The stored cumulative counter is a best-effort optimization: the gateway's ledger is ground truth and the sidecar resyncs from its structured 402 responses, so a stale value costs one extra round-trip, never money.