- Add comprehensive JSONL Issue Schema section to docs/ARCHITECTURE.md
documenting all exported fields including close_reason
- Add TestCloseReasonRoundTrip test in export_import_test.go to verify
close_reason is preserved through JSONL export/import cycle
Closes: bd-lxzx
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>