Plugin loader resolves HookSpec.Exec as a relative path joined to the
plugin directory, and manifest.checkSafePath rejects absolute paths and
'..' traversal — Exec was always meant to be an executable path.
The hook executor was wrapping it in 'sh -c', adding a redundant shell
interpretation step that turned any space, quote, or metacharacter in
the path into command-injection surface. Switch to exec.Command(path)
with no shell wrapping.
Closes audit finding C3. Adds a regression test that fails under the
old 'sh -c' code path: a canary file created via shell sequencing
remains absent when the executor treats Exec as a literal filename.
Hook command tests now write small /bin/sh scripts to t.TempDir and
point Exec at those — matching production semantics (resolved binary
path) rather than inline shell strings.
vikingowl