Introduces FileCache (OrderedDict LRU, st_mtime_ns validation) to avoid redundant disk reads and duplicate content in conversation context. Read tools return a short "[Cached]" message on cache hit instead of resending unchanged file content, saving tokens. Write/edit/delete tools invalidate affected paths; str_replace pre-warms the cache after edits. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>