Detect and validate shared workflows missing 'on' field

[Copilot]

Workflows without an on trigger field now validate against included_file_schema instead of failing main_workflow_schema validation. Compilation is skipped with an informative message.

Detection

• Check for missing on field before schema validation
• Validate with included_file_schema (allows optional markdown content)
• Return SharedWorkflowError to signal skip

CLI handling

• Recognize SharedWorkflowError as info, not error
• Print usage instructions, mark as successful (skipped)
• No lock file generated

Example output

$ gh aw compile shared/mcp/deepwiki.md
ℹ️  Shared agentic workflow detected: deepwiki.md

This workflow is missing the 'on' field and will be treated as a shared workflow component.
Shared workflows are reusable components meant to be imported by other workflows.

To use this shared workflow:
  1. Import it in another workflow's frontmatter:
     ---
     on: issues
     imports:
       - shared/mcp/deepwiki.md
     ---

  2. Compile the workflow that imports it

Skipping compilation.
✓ Compiled 1 workflow(s): 0 error(s), 0 warning(s)

Files

• pkg/workflow/compiler_orchestrator.go - detection logic
• pkg/workflow/shared_workflow_error.go - error type (new)
• pkg/workflow/shared_workflow_test.go - tests (new)
• pkg/cli/compile_workflow_processor.go - CLI handling

Original prompt

When an agentic workflow is missing the "on" field, implicitly assume it is a shared agentic workflow and validate with the imported JSON schema (not the main schema). Skip compilation with info message.

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.