Function symbol_diff_range 

pub fn symbol_diff_range(
    repo_root: &Path,
    base_sha: &str,
    tip_sha: &str,
) -> RangeSymbolPacket

Build a deterministic packet for base_sha..tip_sha without reading the worktree.

An unreadable Git range produces an empty packet rather than a partial packet. The caller can distinguish that case from an unchanged valid range by resolving the requested revisions before calling this low-level, infallible engine entry point.