Replace the comment preservation workaround (comment_map type,
separate_comments, reinterleave, strip_interior_comments,
extract_fragment_comments, inject_comments — ~170 lines) with
CST-based editing (~80 lines).
write_edit_cst: compares old AST vs new AST per node. Unchanged
nodes keep original source verbatim. Changed nodes are pretty-printed
with original leading trivia preserved. New nodes (insertions) get
minimal formatting.
parse_file_cst: returns (AST tree, CST file). AST goes to tree-tools,
CST is used for write-back.
extract_cst_comments / inject_cst_comments: read comment trivia from
CST nodes for summarise/read_tree display.
Net: -39 lines. 24/24 CST round-trip tests, 2583/2583 evaluator tests.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
af63d49451