feat(architecture): generic "jsonrpc" passthrough architecture for non-EVM JSON-RPC nodes

[snowkide]

eRPC serves EVM and SVM chains, each with a chain model (chain-id or genesis detection, state poller, method hooks). Many other chains expose a plain JSON-RPC API (Bitcoin-family nodes, Stellar RPC and others) and only need eRPC's generic pipeline: upstream selection, failsafe policies, rate limiting, multiplexing, metrics and healthchecks.

This adds a third architecture, jsonrpc, that provides exactly that and nothing chain-specific, plus two wire-level changes such servers need.

Commits (reviewable separately):

1. fix(json-rpc): treat "error": null in upstream responses as success. JSON-RPC 1.0-style servers (Bitcoin Core and forks) always send "error": null; today every successful call to such a node is parsed as a server error and retried elsewhere.
2. feat(architecture): the jsonrpc architecture.
   • architecture/jsonrpc registers a no-op ArchitectureHandler; errors fall through to the default extractor.
   • Networks: architecture: jsonrpc with jsonRpc.id (defaults to the alias); network id jsonrpc:<id>; inferred from a jsonRpc block; lazily creatable from /<project>/jsonrpc/<id>.
   • Upstreams: type: jsonrpc with jsonRpc.networkId (type inferred when set). Bootstrap sends nothing to the node. HTTP and WebSocket clients are reused; gRPC endpoints are rejected.
   • Requests are validated as JSON-RPC and forwarded unchanged; finality is unknown unless set via methods.definitions; no cache (no block/slot model).
   • Healthcheck scoping and all:activeUpstreams understand jsonrpc networks. TypeScript config types regenerated with tygo.
3. feat(json-rpc): upstreams[].jsonRpc.omitEmptyParams. Leaves params out of outbound requests whose params are empty instead of sending "params":[]; params is optional in JSON-RPC 2.0 and some servers reject an empty array for methods without parameters. Defaults to true for type: jsonrpc upstreams and false otherwise, so the wire format of EVM and SVM upstreams does not change unless the setting is turned on. Cache keys are unchanged (hashed from parsed params).
4. docs: config/projects/networks and config/projects/upstreams.

networks:
  - architecture: jsonrpc
    alias: btc-mainnet
upstreams:
  - endpoint: https://btc-rpc.example.com
    jsonRpc:
      networkId: btc-mainnet

Verification

Based on erpc/erpc main @ 094b912.

• go build ./..., go vet ./... and gofmt -l on touched files are clean.
• make test-fast (what CI runs): passes, exit 0, no failing test.
• New tests for the setting: TestJsonRpcRequest_WireRequest, TestUpstreamConfig_SetDefaults_OmitEmptyParams (false for evm, true for jsonrpc, explicit opt-out respected), TestHttpJsonRpcClient_OmitEmptyParams (default, disabled, enabled). The passthrough end-to-end test checks that a jsonrpc upstream receives no params for an empty call.
• TypeScript config types regenerated with tygo generate.

AI assistance

• Model: anthropic/claude-opus-5.5
• Harness / skills: Claude Code
• Human-reviewed: no, pending

🤖 Generated with Claude Code