HeliosDB Nano v3.18.0 Release Notes

HeliosDB Nano v3.18.0 Release Notes

Release Date: 2026-04-24 Theme: MCP endpoint phase 4 MVP — native JSON-RPC for AI coding agents (opt-in, FR 5)

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Highlights

First landing for the native MCP endpoint. Ships a JSON-RPC 2.0 dispatcher on top of the existing src/mcp_extensions/ tool catalogue so an MCP-capable agent (Claude Code, Cursor, Continue, Codex, Aider) can drive HeliosDB Nano with no wrapper process.

cargo build --release --features mcp-endpoint

Additive — embedded-only callers compile without it.

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What’s New

src/mcp_http/ Module

• rpc.rs — handle_rpc(req) → resp, pure function over JSON-RPC.
  • initialize — server-info handshake.
  • tools/list — enumerate the mcp_extensions catalogue.
  • tools/call — dispatch one tool with arguments.
  • ping — keepalive.
  • Unknown methods return canonical -32601 Method not found.
• mod.rs — re-exports.

Tool Catalogue (Auto-Surfaced)

Every tool already registered in mcp_extensions::tools::list_tools() is surfaced automatically:

Tool	Purpose
heliosdb_bm25_index	Create BM25 indexes
heliosdb_hybrid_search	BM25 + HNSW with RRF / MMR fusion
heliosdb_graph_add_edge	Add graph edges
heliosdb_graph_traverse	Traverse from a node
heliosdb_graph_path	Find shortest path
heliosdb_embed_and_store	Vectorise text and INSERT in one call

Server-Info Handshake

{ "name": "heliosdb-nano", "version": "3.18.0" }

Reported in the response to MCP initialize.

Mounting Pattern

handle_rpc is a pure function — the MVP ships no Axum route wiring. Embedders mount it on whatever route / auth surface they want:

use heliosdb_nano::mcp_http::handle_rpc;
use axum::{routing::post, Json, Router};

let app = Router::new()
    .route("/mcp", post(|Json(req)| async { Json(handle_rpc(req)) }));

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Out of Scope (Tracked for Follow-Ups)

• WebSocket / SSE framing → v3.19 (streaming progress notifications)
• Repair of legacy src/mcp/ module — BLOCKER_mcp_legacy.md stays accurate; phase 4 deliberately does not touch it.
• Macro-driven auto-registration of lsp_* / graph_rag_* as MCP tools → v3.19

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Regression Coverage

• 4 unit tests (src/mcp_http/rpc.rs): initialize, tools/list, unknown method, tools/call without name.
• 4 integration tests (tests/mcp_endpoint_phase4.rs): canonical handshake, real tool call, unknown tool → isError=true, ping.

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Migration

Additive feature. Default builds compile without mcp-endpoint. To enable:

cargo build --release --features mcp-endpoint

See MCP_ENDPOINT_TUTORIAL for hands-on integration with Claude Code, Cursor, and Aider.

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Compatibility Matrix

Component	Version
PostgreSQL wire	14, 15, 16
MySQL wire	5.7, 8.0
MCP protocol	1.0
JSON-RPC	2.0