INJURY_LEVELS: readonly ["NA", "M1", "S2", "S3", "G4", "G5"] = ...

Injury severity levels, indexed by numeric level: INJURY_LEVELS[0] is "NA" (no injury), then M1 (1), S2 (2), S3 (3), G4 (4), G5 (5). The leading letter is the severity band (Minor / Serious / Grievous) and the digit is the level. Effective impact maps to a level via the bands in the injury-resolution pipeline.