That's a really sharp parallel. "Did behavior change" is exactly the question in both cases, and the surface-level representation lies to you in both. We normalize ASTs before hashing so reformatting or renaming a local variable doesn't register as a change. Curious what normalization looks like on the agent observability side, feels like a harder problem when the output is natural language instead of code.

Great, did you opensource it?

Pretty much, yeah. sem graph builds a cross-file entity dependency graph and sem impact does transitive traversal on it. So you can ask "if I change this function, what breaks?" and get a deterministic answer without sending anything to an LLM.

difftastic is solid. The difference is roughly: syntax-aware (difftastic) knows what changed in the tree, sem knows which entity changed and whether it actually matters. difftastic will show you that a node in the AST moved. sem will tell you "the function processOrder was modified, and 3 other functions across 2 files depend on it." difftastic is a better diff. sem is trying to be a different layer on top of git entirely.