Support custom Handlebars helpers in comment templates

[nmoa]

Summary

I would like to propose support for repository-defined custom Handlebars helpers in validator comment templates.

Problem

issue-ops/validator already supports custom validation scripts, but comment templates are still limited to built-in helpers. Because of that, it is hard to format structured values in repository-specific ways.

For example, if an issue form contains a multiline textarea such as a list of team names, it may be more useful to render that value as a Markdown table in the success comment. That kind of formatting is difficult to do cleanly with only built-in helpers.

Proposal

Allow repositories to define custom Handlebars helpers in .github/validator/config.yml, alongside custom validators.

Example:

validators:
  - field: github_username
    script: username.js
helpers:
  - name: linesToMarkdownTable
    script: lines-to-markdown-table.js

The helper scripts would live in .github/validator/ and be loaded when rendering success.mustache and failure.mustache.

Example Use Case

There is a sample of the expected behavior in nmoa/issueops#8.

In that example, a multiline Teams to Add field is rendered as a Markdown table in the validator comment. That is the kind of output customization I would like to support in issue-ops/validator.

Why This Would Help

• It would let repositories keep validation logic and comment-formatting logic in the same place.
• It would make validator comments much more readable for structured inputs.
• It would avoid forcing repositories to fork the action just to customize comment output.

Compatibility and Safety

I think this can follow the same trust model as custom validators, since both features execute repository-defined scripts from the checked-out workspace.

To keep the behavior predictable, it would also make sense to:

• keep the feature optional
• prevent custom helpers from overriding built-in helper names
• preserve the current behavior when no helpers are configured

Thanks for considering this feature.