- CleanupRenderer wraps jinja2.sandbox.SandboxedEnvironment with
StrictUndefined (no autoescape — shell context, not HTML).
- Custom filter regex_extract(text, pattern, group=1, default='') uses
google-re2 for linear-time matching (ReDoS-safe) and falls back to
re with a 1 MB input cap when re2 is absent.
- StepOutputs exposes {{ outputs.text }} and {{ outputs.blob('name') }}.
blob() decodes UTF-8 with latin-1 fallback, hard-capped at 10 MB
(consistent with F8 evidence limit, D-005).
- render_cleanup() is the module-level convenience wrapper.
