feat: rpg-build crate + design_rpg MCP tool (v0.9.0) (#85)

New crate `rpg-build` produces an RPGraph from a natural-language project
specification, inverse of rpg-encoder which extracts a graph from existing
source code. Inspired by the ZeroRepo paper (Luo et al., 2026,
arXiv:2509.16198), limited to the design phases — code generation is
left to the connected coding agent.

Architecture:
- `rpg-build::design_rpg(spec, config)` returns `(RPGraph, DesignReport)`
- Reuses rpg-lift's LlmProvider abstraction (Anthropic / OpenAI /
  OpenRouter / Gemini)
- LLM produces a strict JSON schema (3-level hierarchy, entities with
  features, calls, imports)
- Parser extracts the JSON from fenced code blocks or balanced braces,
  validates types, drops dangling dependency references silently
- Output graph has full hierarchy + edges + features but no source code,
  no line ranges (line_start/end = 0)

New MCP tool `design_rpg`:
- Same provider/api_key/api_key_env pattern as auto_lift
- Returns the design rendered as a semantic_snapshot
- Optional `save=true` writes to .rpg/graph.json (clears auto-sync
  markers because the new graph has no committed correspondence yet)
- Feature-gated behind `rpg-build` (default ON, --no-default-features
  builds without it)

8 unit tests for the design parser + graph builder. All 660 workspace
tests pass.

Bumps to v0.9.0 (minor: new public crate added to the workspace).

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: userFRM

.gemini/extensions/rpg/gemini-extension.json

@@ -1,6 +1,6 @@
 {
   "name": "rpg-encoder",
-  "version": "0.8.1",
+  "version": "0.9.0",
   "description": "Build and query semantic code graphs (Repository Planning Graphs) for AI-assisted code understanding. Provides entity search, dependency exploration, and autonomous LLM-driven semantic lifting.",
   "mcpServers": {
     "rpg-encoder": {

CHANGELOG.md

@@ -5,6 +5,23 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/),
 and this project adheres to [Semantic Versioning](https://semver.org/).
 
+## [0.9.0] - 2026-04-14
+
+### Added
+
+- **`rpg-build` crate** — designs an `RPGraph` from a natural-language project
+  specification. Inverse of `rpg-encoder`: where the encoder extracts a graph
+  from existing source code, `rpg-build` produces a graph for code that doesn't
+  exist yet (hierarchy, entities, dependencies, verb-object features — but no
+  source code). Inspired by the ZeroRepo paper (Luo et al., 2026,
+  arXiv:2509.16198), limited to the design phases.
+- **`design_rpg` MCP tool** — exposes `rpg-build` over MCP. Takes a spec, returns
+  a proposed graph rendered as a `semantic_snapshot`. Pass `save=true` to write
+  the design to `.rpg/graph.json` (overwrites any existing graph). Same provider
+  surface as `auto_lift`: Anthropic, OpenAI, OpenRouter, Gemini, with
+  `api_key_env` for safe key handling.
+- MCP tool count: 27 → 28.
+
 ## [0.8.1] - 2026-04-14
 
 ### Fixed

Cargo.lock

@@ -8,10 +8,11 @@ members = [
     "crates/rpg-cli",
     "crates/rpg-mcp",
     "crates/rpg-lift",
+    "crates/rpg-build",
 ]
 
 [workspace.package]
-version = "0.8.1"
+version = "0.9.0"
 edition = "2024"
 license = "MIT"
 authors = ["userFRM"]
@@ -161,3 +162,4 @@ rpg-parser = { path = "crates/rpg-parser" }
 rpg-encoder = { path = "crates/rpg-encoder" }
 rpg-nav = { path = "crates/rpg-nav" }
 rpg-lift = { path = "crates/rpg-lift" }
+rpg-build = { path = "crates/rpg-build" }

Cargo.toml

@@ -96,7 +96,7 @@ Whenever your working tree changes — committed, staged, or unstaged — the MC
   <img src="diagrams/architecture.webp" alt="Your codebase (15 languages) → RPG Engine (5 Rust crates: parser, encoder, nav, lift, mcp) → Clients (Claude Code, Cursor, opencode) via MCP Protocol" width="95%" />
 </p>
 
-Seven Rust crates, one MCP server binary, one CLI binary:
+Eight Rust crates, one MCP server binary, one CLI binary:
 
 | Crate | Role |
 |-------|------|
@@ -105,19 +105,21 @@ Seven Rust crates, one MCP server binary, one CLI binary:
 | `rpg-encoder` | Encoding pipeline, lifting utilities, incremental evolution |
 | `rpg-nav` | Search, fetch, explore, snapshot, TOON serialization |
 | `rpg-lift` | Autonomous LLM lifting (Anthropic, OpenAI, OpenRouter, Gemini) |
+| `rpg-build` | Design RPG blueprints from natural-language specs (inverse of encoder) |
 | `rpg-cli` | CLI binary (`rpg-encoder`) |
-| `rpg-mcp` | MCP server binary (`rpg-mcp-server`) with 27 tools |
+| `rpg-mcp` | MCP server binary (`rpg-mcp-server`) with 28 tools |
 
 ---
 
-## MCP Tools (27)
+## MCP Tools (28)
 
 <details>
 <summary><strong>Build & Maintain</strong> (4 tools)</summary>
 
 | Tool | Description |
 |------|-------------|
 | `build_rpg` | Index the codebase (run once, instant) |
+| `design_rpg` | Design an RPG blueprint from a natural-language spec (inverse of build) |
 | `update_rpg` | Incremental update from git changes |
 | `reload_rpg` | Reload graph from disk after external changes |
 | `rpg_info` | Graph statistics, hierarchy overview, per-area lifting coverage |

README.md

@@ -0,0 +1,22 @@
+[package]
+name = "rpg-build"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+repository.workspace = true
+description = "Design Repository Planning Graphs from natural-language specifications (inverse of rpg-encoder)"
+
+[dependencies]
+rpg-core = { workspace = true }
+rpg-lift = { workspace = true }
+serde = { workspace = true }
+serde_json = { workspace = true }
+thiserror = { workspace = true }
+chrono = { workspace = true }
+
+[dev-dependencies]
+tempfile = { workspace = true }
+
+[lints]
+workspace = true