Fix GitHub Actions sync failure with upstream due to merge conflicts in fastlane/Fastfile

[Copilot]

Problem

The GitHub Actions workflow was consistently failing when attempting to sync upstream changes from LoopKit/LoopWorkspace due to merge conflicts in fastlane/Fastfile:

Auto-merging fastlane/Fastfile
CONFLICT (content): Merge conflict in fastlane/Fastfile
Automatic merge failed; fix conflicts and then commit the result.
ERROR: exit 1
New commits could not be pulled.

This prevented the repository from staying synchronized with important updates from the upstream LoopKit repository, breaking the automated build and sync process.

Root Cause

The aormsby/[email protected] action cannot handle merge conflicts automatically. When the upstream repository updates files like fastlane/Fastfile with formatting changes, documentation updates, or structural modifications that conflict with the fork's version, the sync fails completely.

Solution

This PR replaces the failing sync action with custom bash scripts that intelligently handle merge conflicts:

🔧 Custom Sync Scripts

1. Scripts/sync_with_upstream.sh - Main sync script with automatic conflict resolution

   • Detects merge conflicts and resolves them systematically
   • Prefers upstream versions for known conflict files (fastlane/Fastfile, workflows, dependencies)
   • Handles submodule conflicts gracefully
   • Provides detailed colored logging for debugging

2. Scripts/check_upstream_changes.sh - Lightweight upstream change detection

   • Checks for new commits without attempting complex merges
   • Updates alive timestamps to keep repository active
   • Used for initial workflow checks

🎯 Conflict Resolution Strategy

The scripts automatically resolve conflicts by taking upstream versions for:

• fastlane/Fastfile - Ensures latest Loop build process compatibility
• .github/workflows/* - Gets latest workflow improvements
• Gemfile, Gemfile.lock - Maintains current dependencies
• Configuration and workspace files - Preserves project structure integrity
• Submodules - Stays current with component updates

🔄 GitHub Actions Integration

• Drop-in replacement: Uses same environment variables (UPSTREAM_REPO, UPSTREAM_BRANCH, TARGET_BRANCH, GH_PAT)
• Compatible outputs: Generates has_new_commits output for existing workflow logic
• Error handling: Proper exit codes and detailed logging for troubleshooting

Testing

Comprehensive testing confirmed the solution works correctly:

• ✅ Successfully resolves actual fastlane/Fastfile conflicts
• ✅ Handles multi-file conflicts (workflows, dependencies, submodules)
• ✅ Maintains GitHub Actions workflow compatibility
• ✅ Generates correct outputs for downstream steps

Result

The automated sync process now works reliably even with merge conflicts, ensuring the fork stays synchronized with upstream LoopKit/LoopWorkspace updates while maintaining the automated build functionality.

Before: Sync failures blocked all automation
After: Intelligent conflict resolution keeps sync working automatically

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