Mention speed/grep fallback in LSP lesson motivation section

Co-authored-by: calebwilson706 <71669491+calebwilson706@users.noreply.github.com>

Author: Copilot

tutorial/lessons/18-lsp-servers.md

@@ -14,7 +14,7 @@ Language servers power the "go to definition", "find all references", and inline
 
 ### Why does this matter for Copilot CLI?
 
-Without an LSP server, Copilot reads your code as text. It's smart enough to infer a lot — but it's still working from patterns in source files.
+Without an LSP server, Copilot reads your code as text. When it needs to find a symbol it falls back to grep-style text search across your files — slower, and prone to false matches (e.g. a variable named `task` appearing in comments, strings, and unrelated files). It's smart enough to infer a lot, but it's still working from patterns rather than facts.
 
 With an LSP server configured, Copilot can: