Check committed Go formatting

docs/internal/validation.md

@@ -18,9 +18,13 @@ executing a target binary. Test, vet, and package-compilation failures retain
 their `go-test`, `go-vet`, and `package-compile` identities, selected target
 where applicable, and underlying causes. Its
 request carries the captured repository directory and commit, output writer,
-and internal settings. `Request.ReadCandidateTree` lets a
-selected file check request candidate contents; the Go-only path does not
-enumerate the tree.
+and internal settings. When selected, the Go-format check loads the candidate
+tree once, reads regular Go blobs from the captured commit, and compares them
+with go/format output. It includes vendor and nested-module files, skips
+symlink blobs, reports all unformatted paths, and stops with a contextual cause
+on parse or inspection errors. It runs before product checks and build callbacks.
+`Request.ReadCandidateTree` lets selected file checks request candidate
+contents; the Go-only path does not enumerate the tree.
 `CandidateTree` gets metadata and bytes from Git objects, reads blob bytes
 lazily, and resolves destinations without consulting the worktree or
 neighboring files.