The issue: variables sourced in cmd_delegate were not being passed
to child processes (subagents) because 'source' doesn't automatically
export variables to child processes.
Fix:
1. Use 'set -a' before sourcing to auto-export all variables
2. Use 'set +a' after sourcing to disable auto-export
3. Updated template comments to recommend 'export' prefix
Also added unit test to verify env pass-through works.
Verified with tests that child processes now see the exported variables.
163160cef4