Release 2.0.0: migrate MCP Unity to Unity CLI and Pipeline

[CoderGamester]

Summary

MCP Unity 2.0 replaces the custom WebSocket bridge with Unity CLI and com.unity.pipeline@0.3.1-exp.1.

• Raises the minimum Editor version to Unity 6000.0 and supports Unity 6.0, 6.3, and 6.5.
• Installs Pipeline automatically as an exact UPM dependency while keeping machine-level Unity CLI installation user- or CI-initiated.
• Replaces the legacy Server Window with Window > MCP Unity > Setup for Pipeline status, CLI detection, official install guidance, and configuration copying.
• Adds five bounded Pipeline extensions: inspect_gameobject, duplicate_gameobject, unload_scene, editor_step, and assign_material.
• Keeps Server~ as a private, self-contained optional Node 20 companion for the Unity dashboard, six read-oriented resources, and two prompts.
• Removes the WebSocket server/client, port 8090, legacy settings, command queues, retries, bundled DLL, npm installation controls, automatic client mutation, and duplicated tools now supplied by Pipeline.
• Adds the complete 1.4.0 release changelog and migration table.

Why

Unity CLI and Pipeline now provide the maintained command and MCP transport layers. Building on those official surfaces removes duplicated infrastructure, reduces lifecycle and networking complexity, and gives future Unity versions a cleaner compatibility path.

Breaking changes

• Unity 2022.3 support ends with release 1.4.0; 2.0 requires Unity 6000.0 or newer within the tested 6.0/6.3/6.5 lines.
• Unity CLI 1.0.0-beta.2 or newer must be installed separately on each developer or CI machine.
• The former custom tool aliases, Server Window, WebSocket endpoint, port and timeout settings, remote-host mode, and ProjectSettings/McpUnitySettings.json are removed.
• Existing clients should migrate old tool names to official Pipeline commands or the five documented MCP Unity extensions.

Validation

• Unity EditMode: 63/63 tests passed on Unity 6000.0, 6000.3, and 6000.5.
• Node companion: 112/112 tests passed with open-handle detection.
• Production bundle and deterministic build:check passed.
• Clean copied-package Node 20 smoke passed, including nested MCP and dashboard reads.
• Live unity mcp discovery exposed all five extensions alongside official Pipeline commands.
• Verified exact UPM dependency pins, no legacy settings or bridge artifacts, and no listener on port 8090.
• Independent final review reported no Critical, Important, or Minor findings.

Known dependency note

The pinned MCP SDK currently inherits two moderate npm advisories through an unused Hono HTTP adapter. The companion is stdio-only; changing the mandated SDK pin is intentionally deferred to a compatibility upgrade.