New lsp.rs: LspRegistry manages persistent LSP server connections.
Spawns child processes, speaks LSP protocol (Content-Length framed
JSON-RPC over stdio). Server indexes the project once; queries are
cheap.
Tools: lsp_definition, lsp_references, lsp_hover, lsp_symbols,
lsp_callers. Each takes file/line/character, queries the running
language server.
LspRegistry lives on Agent as Option<Arc>, shared across forks.
Still needs: config-driven server startup (like MCP).
Co-Authored-By: Proof of Concept <poc@bcachefs.org>
