3c87527 added engine/paths.go:resolveCanonical, duplicating the
ancestor-walk + EvalSymlinks algorithm that already lived in
fs/guard.go:ResolveWrite. Two implementations of the same TOCTOU defense
is exactly the wrong shape for security code — a bug fix in one would
silently miss the other.
Extracts the shared algorithm to security.CanonicalizePath. Both call
sites become thin wrappers that pre-anchor relative paths against the
appropriate root (cwd for engine, workspace root for guard). The
"hit-root" defensive branch in engine's version (commented "highly
unlikely") is tightened to match guard's error behavior.
Adds focused unit tests for the helper covering existing path,
non-existent leaf, non-existent mid-component, symlinked ancestor, and
relative-path rejection.
vikingowl
9853a522e6