feat(json)!: bump MCP_JSON_FORMAT_VERSION to '2'

All 9 tools now emit structured McpErrorEnvelope for failures instead
of ad-hoc {error:string,...} shapes. The format version bump signals
the breaking contract change to clients.

Envelope shape:
  { error: { code, message, retryable, suggestedFix? } }

Migration path for v1 consumers:
  before: if (r.error === 'not_found') ...
  after:  if (r.error?.code === 'NOT_FOUND') ...

Docs + idempotency follow in the next commit.

Author: AlbinoGeek

src/server/json.test.ts

@@ -14,8 +14,8 @@ import {
 } from "./json.js";
 
 describe("MCP_JSON_FORMAT_VERSION", () => {
-  test("is '1'", () => {
-    expect(MCP_JSON_FORMAT_VERSION).toBe("1");
+  test("is '2'", () => {
+    expect(MCP_JSON_FORMAT_VERSION).toBe("2");
   });
 });
 

src/server/json.ts

@@ -2,7 +2,7 @@ import { readFileSync } from "node:fs";
 import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
 
-export const MCP_JSON_FORMAT_VERSION = "1" as const;
+export const MCP_JSON_FORMAT_VERSION = "2" as const;
 
 export function readPackageVersion(): string {
   const here = dirname(fileURLToPath(import.meta.url));