[Draft] Generic x402 payment proxy: pre-paid HTTP budgets + in-cluster sidecar route

Status: draft / sketch. Open for refinement before scoping into work items. Not committing to the exact API surface below.

Background

Two halves of "agent-side x402 spending" already exist:

• Stateless single-shot — buy.py pay <url> (skill buy-x402, merged in 6eb9a8b) signs one EIP-3009 / Permit2 auth, attaches X-PAYMENT, sends any HTTP method, and returns the response. Works against any type:http x402 endpoint. Max loss = 1 request.
• Persistent inference budgets — buy.py buy <name> pre-signs N auths, stores them in a PurchaseRequest CR, and the x402-buyer sidecar in the litellm pod spends them transparently as the agent hits paid/<remote-model> through LiteLLM. Max loss = N × price; runtime path holds zero signer access.
• Seller side — obol sell http and obol sell demo {hello,blocks,oracle} let anyone gate any in-cluster HTTP service behind x402 ForwardAuth.

Gap

The persistent / sidecar-mediated path is inference-shaped, OpenAI-Chat-only. There's no equivalent for non-LLM HTTP services, and the only LLM wire format covered is OpenAI Chat. Specifically:

A. No pre-paid budgets for HTTP services

An agent that wants to call demo-blocks 200 times to monitor a wallet, or hit a paid OCR / RAG / indexer / market-data endpoint repeatedly, has to re-sign on every call via pay. That burns local-signer round-trips and adds latency to every request. The signing/retry/settlement state machine in internal/x402/buyer/ already handles the persistent case for inference — it just isn't exposed for arbitrary HTTP.

B. No in-cluster proxy endpoint for non-Python consumers

buy.py is a Python skill. Anything else in the cluster — Node.js MCP servers, Go indexers, Rust services in another pod, browser webapps behind the tunnel, other agent runtimes — cannot easily shell out to a Python script. They need an HTTP endpoint they can call to get paid responses back.

C. No transparent tool-call shape for agents

Even from a Python skill, pay is an explicit subprocess call. For an LLM tool call, "pay this URL" should look like a normal HTTP request the model issues, with the sidecar transparently handling 402 retries — same UX as paid/<model> for inference.

D. No Anthropic-native wire format

Claude Code, Cline, Aider, and most "Claude-class" agent tools speak the Anthropic Messages API (POST /v1/messages), not OpenAI Chat. They can't be pointed at the existing paid/* route without an adapter. Today the only path for those tools is to hold an ANTHROPIC_API_KEY and pay Anthropic directly — bypassing the cluster, the marketplace, and any seller's monetized models.

Proposal sketch

Reframe the sidecar as a single payment + retry + settle engine fronted by multiple wire-format adapters, not a single LLM-shaped proxy:

                       ┌──────────────────────────┐
   /v1/chat/completions │ OpenAI Chat adapter      │ ← shipped (paid/* via LiteLLM)
   ───────────────────► │                          │
                       │                          │
   /v1/messages         │ Anthropic Messages       │ ← new — Claude Code / Cline / Aider
   ───────────────────► │ adapter                  │
                       │                          │
   /proxy/<host>/<path> │ Generic HTTP adapter     │ ← new — arbitrary x402 services
   ───────────────────► │                          │
                       └────────────┬─────────────┘
                                    │
                       ┌────────────▼─────────────┐
                       │ Auth pool lookup         │
                       │ (host- or model-keyed)   │
                       │ X-PAYMENT attach         │
                       │ 402 retry                │
                       │ Settle on <400 success   │
                       └──────────────────────────┘

New endpoints on the existing x402-buyer sidecar:

POST /proxy/<host>/<path...>
  - per-host auth pool lookup
  - one auth attached as X-PAYMENT
  - upstream call forwarded verbatim
  - 402 retry with next auth
  - settle on <400 success
  - upstream response returned to caller

POST /v1/messages
  - Anthropic Messages API surface
  - translate request → OpenAI Chat → upstream (or pass-through if upstream is anthropic-native)
  - reuse the same paid/<model> auth pool the sidecar already drives
  - translate response back to Anthropic Messages format

POST /admin/budget
  - extension of the buy.py / PurchaseRequest path for type:http
  - pre-sign N auths against a (host, path-glob) tuple
  - store in a host-keyed pool alongside today's model-keyed pools

Plus controller / skill plumbing:

• Relax the PurchaseRequest inference-shape assumption: a type:http purchase should NOT publish a paid/<model> LiteLLM route. It should write a buyer-config entry keyed by (host, path-glob) instead of (upstream, model).
• Extend buy.py buy to accept --type http --path-glob <glob> and produce the right CR shape.
• Pricing-aware Anthropic adapter: respect the Anthropic-style cache_control markers we now inject by default for Anthropic models, so prompt caching cost savings carry through the paid path.

What this unlocks (concrete examples)

Demo services already in tree

• demo-blocks polling — 200-call wallet monitor: pre-buy budget once, hit /proxy/obol.stack:8080/services/demo-blocks/... from any pod. Today: 200 separate sign/send round-trips.
• demo-oracle from a Node dashboard — frontend (or any non-Python service in the cluster) does fetch("http://x402-buyer:8402/proxy/...") and gets paid responses, zero crypto code on the dashboard.

Real monetizable services

• Self-hosted OCR / transcription / embedding endpoints behind obol sell http, consumed as transparent agent tools.
• Private RAG corpus charged per-query, used inside a research session with bounded total cost.
• Custom indexers / Dune-style analytical queries monetized per call.
• Validator / DV monitoring feeds subscribed to with a daily auth budget.
• Image / video / voice generation endpoints — bulk batch with one budget instead of N signs.
• Third-party market data / weather / search — same agent, same code, regardless of upstream.

Cross-runtime

• MCP servers in the cluster expose tools whose backends are paid x402 endpoints. The MCP server just speaks HTTP to the sidecar — no key handling, no signing, no budget bookkeeping. Every MCP server in the ecosystem becomes spend-aware without code changes.

Adoption: Anthropic-native tools (new with the /v1/messages adapter)

The Anthropic Messages adapter turns every existing Claude-class tool into a potential obol buyer with one env var:

export ANTHROPIC_BASE_URL=http://x402-buyer.llm.svc.cluster.local:8402/anthropic
# or, from the host:
export ANTHROPIC_BASE_URL=http://127.0.0.1:18402/anthropic   # via kubectl port-forward
unset ANTHROPIC_API_KEY
claude   # or cline / aider / any anthropic-native client

From that point on:

• Claude Code's autonomous loop, tool calls, and subagents work unchanged.
• Every model call is paid per request from the agent's wallet against whatever upstream the cluster routes to (could be a marketplace seller's hosted Claude-compatible endpoint, a self-hosted GPU box, or a remote Anthropic-fork).
• No ANTHROPIC_API_KEY required.
• Live model switching reuses the existing LiteLLM model-routing layer.
• Spending caps, auto-refill, and audit trail come for free from the existing budget machinery.

The same env-var pattern works for any tool that respects ANTHROPIC_BASE_URL (Claude Code, Cline, Aider, claude-dev, custom integrations). It also gives sellers a much larger addressable audience — anyone with claude installed becomes a potential customer of any model exposed via obol sell http or obol sell inference.

Risk surface

• Auth pools are already per-upstream-keyed today — a malicious host can only spend auths the user pre-signed for it. Property carries over.
• SSRF guard required: /proxy/<host> must refuse <host> resolving to internal cluster addresses unless explicitly allowlisted. Same discipline that keeps frontend and erpc HTTPRoutes hostname-restricted in traefik / obol-frontend / erpc namespaces today.
• The Anthropic adapter must not silently drop fields it can't translate (vision, parallel tool use, MCP-shaped messages). Errors should be 400 with a clear body, not a "successful" payment for a degraded response. Document the supported subset up front.
• The sidecar is distroless — the new mux routes add no new dependencies.

Suggested split

• Sidecar route: POST /proxy/<host>/<path...> with per-host pool lookup, retry, settle (internal/x402/buyer/proxy.go).
• Sidecar route: POST /v1/messages Anthropic Messages adapter — translate request to OpenAI Chat, reuse the existing paid pool, translate response back. Document the supported subset (parity with what LiteLLM's anthropic-passthrough already covers, minus what's intentionally out of scope).
• Sidecar reload: extend /admin/reload to pick up host-keyed pools alongside model-keyed pools.
• SSRF allowlist in the sidecar config — reject internal cluster targets by default.
• Controller: relax PurchaseRequest to handle type:http without publishing a paid/<model> LiteLLM route (internal/serviceoffercontroller/).
• buy.py buy --type http --path-glob flag in internal/embed/skills/buy-x402/scripts/buy.py.
• Hermes / OpenClaw skill that exposes the proxy as a tool-call-shaped HTTP target so an LLM tool call looks like a normal fetch.
• Docs: "Use Claude Code with obol" walkthrough showing the ANTHROPIC_BASE_URL env-var setup, including the port-forward path for host-side use.
• Integration test extending the existing flow-08-buy.sh / monetize integration test to cover an HTTP budget against demo-blocks.
• Integration test: Anthropic Messages adapter end-to-end — claude (or a curl shaped like Anthropic Messages) → sidecar /v1/messages → upstream → settled response.

Out of scope for this issue

• Changing the verifier path (x402-verifier stays verify-only on the cluster-routed paid flow).
• Adding new chains / tokens — orthogonal to this proxy work.
• A dedicated CLI surface (obol agent pay …) — can come later as ergonomics on top of the sidecar route.
• Vision / image input on the Anthropic adapter — explicitly deferred to a follow-up; not all sellers' upstreams support it and the translation layer adds risk.

Start by reading internal/x402/buyer/proxy.go, internal/serviceoffercontroller/, and internal/embed/skills/buy-x402/scripts/buy.py, then inspect flow-08-buy.sh and the monetize integration test. The proposed work spans proxy routes, Anthropic translation, host-keyed budgets, SSRF configuration, controller and skill changes, and documentation. Done requires scoped decisions plus passing HTTP-budget and Anthropic end-to-end integration tests.