## What changed
- Discover synchronous `mcp_tool` hook handlers and invoke their configured MCP server and tool through a supplied executor.
- Expand nested hook-event placeholders in MCP tool inputs while preserving JSON types, and process tool output through the existing hook output contract.
- Represent hook details as handler-specific metadata in `hooks/list`, including MCP server and tool fields, and show those details in the TUI hooks browser.
- Skip unsupported `SessionEnd` MCP hooks and runtimes without MCP invocation support with startup warnings.
## Testing
- Cover argument expansion, missing placeholders, MCP invocation and hook decisions, discovery warnings, `hooks/list` metadata, and TUI rendering.
GitOrigin-RevId: 295b845471fe92bd7ad7cd272fbcd2c3713912e0
85fc4def35