feat(TRUEREF-0011): implement MCP server with stdio transport

Adds a Model Context Protocol server that exposes resolve-library-id
and query-docs tools via stdio, with tool schemas identical to context7
for drop-in compatibility with Claude Code, Cursor, and Zed.

- src/mcp/index.ts — server entry point (io.github.trueref/trueref)
- src/mcp/client.ts — HTTP client for TrueRef REST API (TRUEREF_API_URL)
- src/mcp/tools/resolve-library-id.ts — library search tool handler
- src/mcp/tools/query-docs.ts — documentation retrieval tool handler
- src/mcp/index.test.ts — integration tests spawning real server subprocess
- .claude/rules/trueref.md — Claude Code rule file for MCP usage
- package.json: mcp:start script using tsx

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/mcp/tools/query-docs.ts

@@ -0,0 +1,98 @@
+/**
+ * query-docs tool handler
+ *
+ * Fetches documentation and code examples from TrueRef for a specific library.
+ * Tool schema is identical to context7 for drop-in compatibility.
+ */
+
+import { z } from 'zod';
+import { fetchContext } from '../client.js';
+
+export const QueryDocsSchema = z.object({
+	libraryId: z
+		.string()
+		.describe('The TrueRef library ID obtained from resolve-library-id, e.g. /facebook/react'),
+	query: z
+		.string()
+		.describe('Specific question about the library to retrieve relevant documentation'),
+	tokens: z.number().optional().describe('Maximum token budget for the response (default: 10000)')
+});
+
+export type QueryDocsInput = z.infer<typeof QueryDocsSchema>;
+
+export const QUERY_DOCS_TOOL = {
+	name: 'query-docs',
+	description: [
+		'Fetches documentation and code examples from TrueRef for a specific library.',
+		'Requires a library ID obtained from resolve-library-id.',
+		'Returns relevant snippets formatted for LLM consumption.',
+		'Call at most 3 times per user question.'
+	].join(' '),
+	inputSchema: {
+		type: 'object' as const,
+		properties: {
+			libraryId: {
+				type: 'string',
+				description: 'TrueRef library ID, e.g. /facebook/react'
+			},
+			query: {
+				type: 'string',
+				description: 'Specific question about the library'
+			},
+			tokens: {
+				type: 'number',
+				description: 'Max token budget (default: 10000)'
+			}
+		},
+		required: ['libraryId', 'query']
+	}
+};
+
+export async function handleQueryDocs(args: unknown) {
+	const { libraryId, query, tokens } = QueryDocsSchema.parse(args);
+
+	const response = await fetchContext({ libraryId, query, tokens, type: 'txt' });
+
+	if (!response.ok) {
+		const status = response.status;
+
+		if (status === 404) {
+			return {
+				content: [
+					{
+						type: 'text' as const,
+						text: `Library "${libraryId}" not found. Please run resolve-library-id first.`
+					}
+				],
+				isError: true
+			};
+		}
+
+		if (status === 503) {
+			return {
+				content: [
+					{
+						type: 'text' as const,
+						text: `Library "${libraryId}" is currently being indexed. Please try again in a moment.`
+					}
+				],
+				isError: true
+			};
+		}
+
+		return {
+			content: [
+				{
+					type: 'text' as const,
+					text: `Error fetching documentation: ${response.status} ${response.statusText}`
+				}
+			],
+			isError: true
+		};
+	}
+
+	const text = await response.text();
+	return {
+		content: [{ type: 'text' as const, text }]
+	};
+}