calldiff does git diff for call stacks across 22 languages, built specifically because agents rewire call flow.

tanishqkancharla/calldiff hit 323 stars in four days. It reads both git trees via git show, loads bundled tree-sitter grammars, builds per-function callee lists, expands them into call trees, and diffs the trees. The stated motivation: "when an agent (or you) rewires call flow, plain line diffs bury the shape of the change." Ships JSON/YAML/Markdown output plus an MCP server. Explicitly syntactic, so dynamic calls won't resolve. I've wanted this exact tool for months without knowing how to describe it.