feature: add human-in-the-loop approval rail for Colang v2 output rails

[MuneezaAzmat]

Did you check the docs?

• I have read all the NeMo-Guardrails docs

Is your feature request related to a problem? Please describe.

NeMo Guardrails has strong automated input/output rails, but there is no built-in library rail for human-in-the-loop (HITL) approval when bot output matches sensitive patterns (e.g. destructive SQL, shell commands). Teams building agentic or tool-using apps often need a reviewer to approve or reject specific bot responses before they are released to the user.

Describe the solution you'd like

Add a new library rail under nemoguardrails/library/human_approval/ for Colang v2 output rails:

• Configurable regex patterns that trigger approval when matched in bot output
• Configurable approval_keywords (e.g. approve, yes)
• Customizable approval_message / rejection_message
• Colang flow human approval on bot output $output_text that:
  - Checks output against patterns
  - Prompts the human if matched
  - Releases original output on approval, or aborts with rejection message on deny
• HumanApprovalConfig on RailsConfigData
• Example config at examples/configs/human_approval_v2/
• Unit tests + Colang v2 integration tests

summary

Add a Colang v2 output rail library module with regex pattern matching on bot output, an interactive approve/reject flow using configured keywords, and HumanApprovalConfig on RailsConfigData. Wire via standard output rails (import guardrails + flow output rails).

Describe alternatives you've considered

• Tool output rails: Custom tool output rails are not wired in the v2 passthrough/dialog path (guardrails.co only hooks input/output text rails). This proposal uses output rails to gate bot text before release.

Additional context

I have a working branch (feat/human-approval-rail) on my fork with:

• HumanApprovalCheckAction / HumanApprovalMatchesKeywordsAction
• 17 unit tests + 2 v2 integration tests (approve / reject paths)
• Example wiring via import guardrails + custom flow output rails

[MuneezaAzmat]

cc @Pouyanpi @tgasser-nv; if you think this is a good proposal, please assign me to it :)