- Kills grant the hostile type's own `xp` (the roster sets XP-per-threat;
the curve lives in data/progression.json, 100 x n^2, capped at level 80)
- Each crossed level fires one `levelup` event: +3 hull / +2 shields with
a full heal, cyan burst + a distinct voice, and a kill-feed line — the
placeholder toughness the skill layer will subscribe to later
- Combat bar gains an XP row below the orbs (level, live gold fill,
banked / next cost; hidden when the snapshot carries no xp, so the
range bar keeps its old face)
- Kills show a gold "+N" reward floater; the level-up's SFX is the new
8th combat event (solar_flare_01)
- XpManager is pure and tested headless (node dev/xp.test.mjs); the
ledger saves as { level, xp } and old saves load fresh at level 0
- dev hooks (xp/grantXp), sfxcheck (range seven, main eight), shot
captures, and README all follow along
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