update_relationship_dynamics runs once per game-minute (10 ticks). Edges inactive for 1+ game-hours (600 ticks) decay trust 1 point toward 0 per minute. Creates social texture: NPCs who haven't interacted drift to neutral without active maintenance. Blocks #249 (social propagation, Sprint 15). Constants: DECAY_INTERVAL_TICKS=10, DECAY_INACTIVITY_THRESHOLD_TICKS=600, DECAY_DELTA=1. Integer arithmetic only (D-010 determinism). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>