Add comprehensive tests for sandbox-formatters.ts (20 tests):
- formatStatus: running/stopped with emojis
- formatSimpleStatus: running/stopped without emojis
- formatImageMatch: match/mismatch indicators
- formatAge: seconds, minutes, hours, days with edge cases
- countRunning: count items by running state
- countMismatches: count items by image mismatch
All pure functions now covered. 152 LOC tests added.
Total test count: 39 tests (19 integration + 20 unit)
Test coverage increased from ~66% to ~80%.
