refactor mcp and add instructions prefix

mcp/shared.ts

@@ -1,7 +1,28 @@
+import { cached } from "@ark/util";
+import { Octokit } from "@octokit/rest";
 import type { StandardSchemaV1 } from "@standard-schema/spec";
 import type { FastMCP, Tool } from "fastmcp";
+import { parseRepoContext, type RepoContext } from "../utils/github.ts";
 
-export const tool = <const params>(tool: Tool<{}, StandardSchemaV1<params>>) => tool;
+export const getMcpContext = cached((): McpContext => {
+  const githubInstallationToken = process.env.GITHUB_INSTALLATION_TOKEN;
+  if (!githubInstallationToken) {
+    throw new Error("GITHUB_INSTALLATION_TOKEN environment variable is required");
+  }
+
+  return {
+    ...parseRepoContext(),
+    octokit: new Octokit({
+      auth: githubInstallationToken,
+    }),
+  };
+});
+
+export interface McpContext extends RepoContext {
+  octokit: Octokit;
+}
+
+export const tool = <const params>(tool: Tool<any, StandardSchemaV1<params>>) => tool;
 
 export const addTools = (server: FastMCP, tools: Tool<any, any>[]) => {
   for (const tool of tools) {