First rewrite

The three-step flow agents and humans both use.

1. Preview

recast 'OldName' 'NewName' src/

Output:

--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1 +1 @@
-fn OldName() {}
+fn NewName() {}
recast: 1 file(s) would change, 1 match(es) across 8 scanned.

No writes happen until you pass --apply.

2. Apply

recast --apply 'OldName' 'NewName' src/

Output:

recast: applying 1 file(s), 1 match(es).

Under the hood: every file is staged in a sibling .recast.tmp.N (written + fsync’d), then renamed into place via a per-file original → .recast.bak.N / temp → original swap. A failure at any step reverse-renames every committed file from its backup, leaving the tree bit-identical to the pre-image. See Safety guarantees.

3. Re-run is safe

recast --apply 'OldName' 'NewName' src/
# recast: already applied; no changes needed.

recast checks convergence (re-applying the pattern to its own output produces no further change) and reports “already applied” with exit 0, so retrying a rewrite in CI or from an LLM-agent retry loop is safe.

If the pattern is non-convergent (e.g. 'a' -> 'aa'), recast refuses with a non_convergent error before touching any file.