Apply close-older-issues logic to discussion fallbacks

[Copilot]

When create-discussion with close-older-discussions: true falls back to creating an issue (permissions failure), older fallback issues were accumulating without cleanup.

Changes

Handler (create_discussion.cjs):

• Map close_older_discussions config to close_older_issues when initializing fallback handler
• Enables automatic cleanup of older fallback issues via workflow-id marker matching

Schema (main_workflow_schema.json):

• Add fallback-to-issue property to create-discussion schema
• Update close-older-discussions description to document fallback behavior

Tests (create_discussion_fallback.test.cjs):

• Verify close-older-issues applies on fallback when enabled
• Verify no cleanup when disabled
• Verify permissions errors trigger fallback with cleanup

Example

safe-outputs:
  create-discussion:
    close-older-discussions: true
    fallback-to-issue: true  # default

When discussion creation fails, fallback issue is created and older fallback issues with matching workflow-id are automatically closed as "not planned".

Original prompt

When a failed create-discussion safe outout is converted to an issue (like #13704) and it has the close-older-discussions, apply the close-order-issues code to close older fallback issues.

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[Copilot]

Pull request overview

This PR resolves an issue where fallback issues created from failed discussion creation were accumulating without cleanup. When create-discussion with close-older-discussions: true falls back to creating an issue due to permissions errors, the PR ensures that older fallback issues are automatically closed using the existing close-older-issues logic.

Changes:

• Maps close_older_discussions configuration to close_older_issues when initializing the fallback issue handler
• Adds fallback-to-issue property to the create-discussion schema for explicit configuration
• Updates documentation to clarify that the close-older-issues behavior applies to fallback issues

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pkg/parser/schemas/main_workflow_schema.json	Added fallback-to-issue property and updated close-older-discussions description to document fallback behavior
docs/src/content/docs/reference/frontmatter-full.md	Updated documentation to match schema changes and clarify fallback behavior
actions/setup/js/create_discussion.cjs	Maps close_older_discussions config to close_older_issues when initializing fallback handler, enabling automatic cleanup
actions/setup/js/create_discussion_fallback.test.cjs	Comprehensive test coverage verifying close-older-issues applies correctly during fallback scenarios

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