Add prompt artifact upload step to compiled workflows

[Copilot]

Summary

This PR adds a step to upload the generated prompt as a workflow artifact (prompt.txt) after the prompt is rendered. This makes it easier to debug and inspect the exact instructions that were sent to the AI engine.

Changes

Added a new generateUploadPrompt() function in the compiler that generates an artifact upload step using actions/upload-artifact@v4. This step is inserted immediately after the prompt generation phase, before agent version capture, ensuring the prompt file is available as a downloadable artifact from the workflow run.

Generated Step

The compiled workflows now include:

- name: Upload prompt
  if: always()
  uses: actions/upload-artifact@v4
  with:
    name: prompt.txt
    path: /tmp/gh-aw/aw-prompts/prompt.txt
    if-no-files-found: warn

Key Features

• Always runs: The if: always() condition ensures the prompt is uploaded even if the workflow fails, making it useful for debugging failed runs
• Consistent pattern: Follows the same approach as other artifact uploads (aw_info.json, agent logs, etc.)
• Universal compatibility: Works with all AI engines (copilot, claude, codex, custom)
• Non-breaking: No changes to workflow frontmatter syntax or existing functionality

Testing

• Added TestPromptUploadArtifact to validate the upload step generation
• All existing unit and integration tests pass
• Successfully recompiled all 64 workflows in the repository
• Verified 35+ workflows now include the prompt upload step

Benefits

Users can now:

• Download the exact prompt that was sent to the AI engine from the workflow run artifacts
• Debug issues by inspecting the generated prompt content
• Audit what instructions were provided to the AI for compliance and review purposes

Original prompt

Update the compiler to add a step after rendering the prompt that uploads it as an artifact (prompt.txt).

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