Documents the param?: Type pattern that esbuild mishandles in .svelte
files (strips the type but leaves ?, producing invalid JavaScript). Adds
the full write-up to REFERENCE__Common_Agent_Mistakes.md and a summary
entry #10 to BOOTSTRAP__AI_Agent_Quickstart.md §7.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>