010: Fix Agent Modifying Workflow Files Breaks Agent Pipelines

Problem

The fix agent has unrestricted write access to all files, including .github/workflows/. When it modifies workflow files to address review feedback, it can introduce YAML syntax errors or behavioral regressions that break the agent pipelines — including the review agent that governs it.

Observed (PR #14)

1. Review agent requested changes on a workflow restructuring PR
2. Fix agent pushed commit d165c91 addressing feedback
3. Next review agent run failed: Invalid format 'SCRIPT_EOF Syntax Errors: [ 'Error node: "<" at 0:0' ]'
4. Autonomous loop halted until manual intervention

Proposed Fix

Combine prompt constraint with validation:

1. Prompt constraint — instruct fix agent not to modify .github/workflows/, .github/scripts/, or GEMINI.md unless review explicitly requests workflow changes
2. actionlint validation — run syntax checking on any modified workflow files before pushing
3. Escalate — if workflow changes are needed, post a comment and let a human implement them