task: Node JSON Schema [PM-6402]

[m2ux]

Summary

Add a rpc.discover endpoint to the Midnight node that returns a complete, machine-readable OpenRPC document describing the entire JSON-RPC API — enabling automated client generation, API documentation, and compatibility testing.

🎫 Ticket 📐 Engineering

---

Motivation

The Midnight node exposes 16 custom JSON-RPC methods and ~42 standard Substrate methods, but there is no machine-readable specification of the API. Developers must read Rust source code to understand available methods, parameter types, return types, and error codes. This blocks automated client library generation, makes API documentation manual and error-prone, and prevents compatibility testing between node versions.

Adding a standards-compliant rpc.discover endpoint (following OpenRPC v1.4.x / EIP-1901) makes the node self-describing. The node builds the OpenRPC document once at startup using runtime introspection of registered methods, schemars-generated JSON Schema for Rust types, and manually maintained metadata for partner-chains types that use serde_json::Value.

---

Changes

Implementation (coming next):

• Add doc comments to MidnightApi trait (0% → 100% coverage)
• Add schemars = "0.8" dependency and derive JsonSchema on all RPC request/response types
• Create node/src/openrpc.rs — OpenRPC document builder with method metadata, type schemas, and error definitions
• Register rpc.discover endpoint in create_full() using module.method_names() for drift-free method enumeration
• Add CI validation comparing OpenRPC method inventory against actual registered methods
• Commit static openrpc.json for offline access

---

📌 Submission Checklist

• Changes are backward-compatible (or flagged if breaking)
• Pull request description explains why the change is needed
• Self-reviewed the diff
• I have included a change file, or skipped for this reason: [reason]
• If the changes introduce a new feature, I have bumped the node minor version
• Update documentation (if relevant)
• No new todos introduced

---

🔱 Fork Strategy

• Node Runtime Update
• Node Client Update
• Other
• N/A

---

🗹 TODO before merging

• Ready for review

[github-actions]

KICS version: v2.1.19

Category Results CRITICAL 0 HIGH 0 MEDIUM 47 LOW 3 INFO 59 TRACE 0 TOTAL 109	Metric Values Files scanned 26 Files parsed 26 Files failed to scan 0 Total executed queries 73 Queries failed to execute 0 Execution time 11