- Extracted chunk tree formatting logic into dedicated `format_selector_tree()` function for reuse across error handling.
- Refactored error messages to display chunk children as hierarchical tree structure with line numbers and signatures instead of comma-separated lists.
- Removed `format_chunk_ref()` helper and consolidated formatting logic into tree-based error hint generation.
- Updated test assertions to validate tree-formatted output with regex patterns matching branch symbols and structure.
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