Design notes.

The IR is what the Rust extractor hands to the Python rule engine, and it is the only thing rules ever see. It is not a copy of the Markdown tree. It is a flat list of prose regions, each carrying its kind, its structural owner, and the exact byte range it occupies in the file on disk.

That byte range is the whole contract. Diagnostics and fixes are expressed in original source offsets, so an edit can only ever land on text that was really there. Where markup was elided — emphasis, link syntax, a soft line break — a segment map records which slice of the region's text came from which source bytes, and marks the remainder synthetic so no fix can touch it.

Two more fields are first-class rather than conveniences. content_hash keys the extraction cache, so an unchanged file is never parsed twice. line_index turns a byte offset into a line and column without reparsing the source, which is what keeps diagnostic rendering cheap.

stilyagi dump-ir prints all of it as canonical JSON, and that is the debugging surface the whole architecture leans on: when a rule misfires, the IR tells you whether the extractor got the region wrong or the rule got the logic wrong.