Step 1: Migrate console-formatted logging from fmt.Println to stderr

[Copilot]

This PR completes Step 1 of the multi-step migration to using the golang log package with stderr output, as outlined in the project's logging guidelines.

Problem

The codebase was using fmt.Println() for console-formatted logging output, which writes to stdout. According to the AGENTS.md guidelines, all CLI logging should go to stderr using fmt.Fprintln(os.Stderr, ...) to properly separate user output from diagnostic/informational messages.

Changes

Migrated 40 occurrences of fmt.Println to fmt.Fprintln(os.Stderr, ...) across 4 files in the workflow package:

• pkg/workflow/compiler.go (31 occurrences) - All verbose compilation messages including file reading, parsing, validation, and success messages
• pkg/workflow/custom_engine.go (3 occurrences) - Log parsing fallback messages
• pkg/workflow/mcp-config.go (3 occurrences) - MCP server type warnings
• pkg/workflow/stop_after.go (3 occurrences) - Stop-after time resolution messages

All migrated calls use console formatting helpers (console.FormatInfoMessage, console.FormatWarningMessage, console.FormatSuccessMessage) and now correctly output to stderr.

Testing

Verified that verbose compilation output now goes to stderr:

# Output only appears on stderr, not stdout
./gh-aw compile workflow.md --verbose 2>&1 1>/dev/null
# Shows verbose output

./gh-aw compile workflow.md --verbose 1>/dev/null 2>&1  
# No output (redirected stderr to stdout which is then redirected to /dev/null)

All existing tests pass without modification, confirming backward compatibility.

Future Work

This is Step 1 of a phased migration. Remaining work includes migrating fmt.Printf calls (32 occurrences) in subsequent PRs to complete the transition to proper stderr-based logging throughout the codebase.

Related

• Follows guidelines documented in AGENTS.md
• Part of multi-step logging migration initiative

Original prompt

We are going to do a multiple step migration to using the golang log package. Use stderr.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.