Summary

Running two Unity projects with the plugin at the same time (each on its own port) results in mutual exclusion: connecting/recompiling one Editor drops the other's MCP connection. Reconnect that one and the first drops. Only one project stays connected at a time, even though their ports differ.

Environment

• Plugin: com.ivanmurzak.unity.mcp 0.81.0 (also present on main)
• OS: Windows 11; two separate Unity projects, ports 26645 and 26646
• connectionMode: Custom, keepServerRunning: true

Repro

1. Open project A (port 26645) -> its server starts, MCP connects.
2. Open project B (port 26646) -> its server starts, MCP connects.
3. Recompile / enter Play / reconnect in project A -> project B's MCP connection drops (connection-refused on B's port; B's gamedev-mcp-server is gone).
4. Symmetric: touching B second kills A.

Root cause

McpServerManager stores the running server PID under a fixed EditorPrefs key, "McpServerManager_ProcessId", that is not qualified by port/project. EditorPrefs are machine-global (shared across all projects of the same Editor version), so both Editors read/write one slot. After B overwrites the slot with B's PID, A's CheckExistingProcess() (on domain reload) reads B's PID, adopts B's server as its own _serverProcess, and StopServer() later terminates it. The per-project binary folder (Library/mcp-server) and KillOrphanedServerProcesses() are already port-scoped -- this PID key is the last piece of shared state.

Fix

Qualify the key by port. PR opened against this issue.