feat(evm): mine + claim test ETH via evm.faucet

[qu0b]

What

evm.faucet(network, address) mines the network's PoW faucet and claims test ETH, returning the claim tx hash (it used to return a browser URL — useless to an agent). Crucially, the faucet is reachable only through the panda proxy, which authenticates the caller — a client-side login check is meaningless if the endpoint is open.

from ethpandaops import evm
w = evm.wallet()
tx = evm.faucet("glamsterdam-devnet-6", w["address"])   # mines + claims, returns tx hash

How

• pkg/proxy /faucet/{network}/ passthrough (handlers/faucet.go) — mirrors the ethnode handler: the proxy's auth middleware authenticates the caller, then it forwards to the network's credential-gated faucet host with basic auth that only the proxy holds. No public faucet surface for panda users.
• pkg/faucet Transport — the Argon2id mining flow (x/crypto/argon2, zero external deps) runs either directly (tests/CLI) or through the proxy.
• evm.faucet op — routes via proxyRequest("/faucet/<network>/…"); the local panda auth check is only a fast pre-check now, the proxy is the real boundary.

Auth model

The proxy is the single authenticated gateway (same as every datasource). The faucet endpoint is credential-gated and only the proxy holds the credential, so there is no way to reach it except an authenticated request through the proxy. The full chain: panda auth login → OIDC issuer (GitHub OAuth behind it) → proxy verifies the bearer → proxy attaches the faucet basic-auth credential upstream. Every faucet surface (web UI, REST API, websocket) sits behind the ingress basic auth.

The credential is configurable: an optional faucet: block in the proxy config gives the faucet its own basic-auth pair (rotatable independently of node access); when omitted it falls back to the ethnode credential, since the faucet lives on the same credential-gated *.ethpandaops.io surface as the nodes.

Tests

• Unit: mining core vs a faithful mock (real argon2 + difficulty), non-standard-param rejection, difficulty mask; proxy FaucetHandler (host derivation, bearer→basic-auth rewrite, path validation); op auth gate (401) + resolution errors.
• e2e through a local panda-proxy against glamsterdam-devnet-6: pkg/faucet → proxy /faucet/… → faucet → mine → claim → funded 1 ETH in ~30 s (tx confirmed).

Deploy order — the faucet lockdown is LAST

1. Merge this PR → panda-proxy build has the faucet handler.
2. Deploy panda-proxy (with the handler) + panda-server.
3. Then make the faucet non-public (basic-auth ingress). Doing this earlier breaks both the direct and proxy paths.

Faucet-side notes (ACG #554 / glamsterdam)

• ipinfo disabled on the agent faucet: behind the proxy the faucet sees the proxy's IP, so IP-reputation checks fail — they don't apply to a proxy-gated faucet.
• Per-IP concurrency/recurring limits also collapse behind the proxy (all traffic shares the proxy IP). Addressed on both sides: the proxy rate-limits startSession per authenticated user (30/h rolling, in this PR), and the faucet scopes concurrency + recurring limits per target address via byAddrOnly (ethereum-helm-charts#485 chart 1.1.0, wired in ACG#554).

Requires a PoWFaucet build with the agent REST API at Argon2id/v19 (live: ghcr.io/qu0b/powfaucet:v2.5.0-agent.4).

[github-actions]

🐼 Smoke eval — 23efca6: ✅ 8/8 pass

📊 Interactive report — tokens p50 18,295 · tokens/solve 20,489.

Reference points: master@1f61a26 100% · v0.38.7 98% · qu0b/faucet-agent-command@cf93705 100%.

question	result	tokens	tools
forky_node_coverage	✅	16,193	7
tracoor_node_coverage	✅	17,486	7
mainnet_block_arrival_p50	✅	15,265	6
list_datasources	✅	13,020	2
block_count_24h	✅	25,239	12
missed_slots_24h	✅	19,424	15
chartkit_default_arrival_distribution	✅	38,184	20
storage_upload_session_scoped	✅	19,104	13

🔭 Langfuse traces (8 runs; ⚠️ = failed)

• forky_node_coverage
• tracoor_node_coverage
• mainnet_block_arrival_p50
• list_datasources
• block_count_24h
• missed_slots_24h
• chartkit_default_arrival_distribution
• storage_upload_session_scoped

_{The report walks this branch's commits against the master baseline and the most recent release. A self-contained copy is in the run's eval-smoke-* artifact.}