SessionStart hooks with mcp_tool type fire before MCP servers connect

Description

Plugin SessionStart hooks that use type: "mcp_tool" always fail because they fire before the MCP server has connected. The hooks execute synchronously during startup, and MCP connection begins ~290ms later. Every mcp_tool hook gets skipped with "MCP server not connected."

Steps to Reproduce

1. Create a plugin with hooks/hooks.json containing SessionStart hooks that call MCP tools:

{
  "hooks": {
    "SessionStart": [
      {
        "matcher": "startup",
        "hooks": [
          {
            "type": "mcp_tool",
            "server": "concurai-ememory",
            "tool": "e_property",
            "input": { "action": "list" },
            "timeout": 30
          }
        ]
      }
    ]
  }
}

1. Plugin has .mcp.json configuring an HTTP MCP server
2. Launch Claude Code with --plugin-dir

Expected Behavior

SessionStart hooks with type: "mcp_tool" should execute after the MCP server they reference has connected, or Claude Code should provide an McpReady hook event that fires after MCP connections are established.

Actual Behavior

All mcp_tool hooks are skipped with warning: Hooks: mcp_tool hook skipped — MCP server 'concurai-ememory' not connected

Debug log shows the timing gap clearly:

2026-05-11T01:45:08.907Z [WARN] Hooks: mcp_tool hook skipped — MCP server 'concurai-ememory' not connected
2026-05-11T01:45:08.907Z [WARN] Hooks: mcp_tool hook skipped — MCP server 'concurai-ememory' not connected
2026-05-11T01:45:08.907Z [WARN] Hooks: mcp_tool hook skipped — MCP server 'concurai-ememory' not connected
2026-05-11T01:45:08.907Z [WARN] Hooks: mcp_tool hook skipped — MCP server 'concurai-ememory' not connected
2026-05-11T01:45:08.921Z [DEBUG] MCP server "plugin:concurai-ememory:concurai-ememory": Starting connection...
2026-05-11T01:45:09.197Z [DEBUG] MCP server "plugin:concurai-ememory:concurai-ememory": Successfully connected (transport: http) in 280ms

Hooks fire at .907, MCP connection starts at .921 and completes at .197 — hooks never had a chance.

Use Case

Session memory continuity. Our plugin uses SessionStart hooks to restore context from a knowledge store on startup (orient), on context compaction (restore session state), and on resume (cross-session context). These are the primary use cases for mcp_tool hooks — they're useless if they can't call the MCP server they depend on.

Suggested Fix

Either:

1. Wait for MCP connections before firing SessionStart hooks that reference MCP tools
2. Add an McpReady hook event that fires after all MCP servers have connected
3. Retry mcp_tool hooks that fail due to server not connected (with backoff)

Environment

• Claude Code v2.1.138
• macOS (Darwin 25.3.0)
• MCP transport: HTTP (Streamable HTTP)
• Plugin loaded via --plugin-dir