[instructions] Sync github-agentic-workflows.md with latest schema features

[github-actions]

Instructions Update - Synchronized with v0.36.0

This PR updates the github-agentic-workflows.md file to document previously undocumented schema features that are actively used in workflows but were missing from the instructions.

Changes Made

Added documentation for 4 undocumented features:

1. serena tool - AI-powered code intelligence with language service integration

   • Documented array format for quick setup: ["go", "typescript"]
   • Documented object format for advanced configuration with version control
   • Listed all supported languages: go, typescript, python, java, rust, csharp

2. messages field in safe-outputs - Custom message templates for footer and notification messages

   • Documented 8 message types: footer, footer-install, run-started, run-success, run-failure, detection-failure, staged-title, staged-description
   • Listed all available placeholders: {workflow_name}, {run_url}, {triggering_number}, {workflow_source}, {workflow_source_url}, {operation}, {event_type}, {status}
   • Provided example configuration

3. mentions field in safe-outputs - @mention filtering configuration

   • Documented boolean format (simple mode)
   • Documented object format with fine-grained controls: allow-team-members, allow-context, allowed list, max count
   • Explained team member and context mention behavior

4. runs-on field in safe-outputs - Runner specification for safe-output jobs

   • Documented default value: ubuntu-slim (1-vCPU runner)
   • Listed common runner options
   • Explained scope: applies to all safe-output jobs

Documentation Review

• ✅ Followed prompting best practices (imperative mood, minimal examples)
• ✅ Maintained technical tone and brevity
• ✅ Updated only necessary sections
• ✅ Verified accuracy against current codebase (main_workflow_schema.json)
• ✅ Examples match real usage patterns in repository workflows

Analysis

Reviewed 20+ workflows using these features:

• serena: Used in 20 workflows (archie, cloclo, go-fan, etc.)
• mentions: Used throughout workflows with @mention requirements
• messages: Used in 22 workflows (archie, brave, ci-doctor, etc.)
• runs-on: Available for performance optimization in safe-outputs

All features are production-ready and actively used but were undocumented, creating confusion for workflow authors.

AI generated by Instructions Janitor