Keep only the comments the code cannot make itself

The validator arrived over-annotated: paragraphs justifying why a helper
was not shared with another package, prose re-listing rules the schema
already states, doc blocks on four-line functions. Cut to the things a
reader cannot reconstruct — that refusing to coerce a JSON string is
deliberate, that per-op required fields have nowhere to live in one
shared object schema, and that these limits must track tools.ts.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>