continue first full balancing round

docs/progression_design.md

@@ -373,3 +373,15 @@ in `requirements.md` and the git history). Still open:
    one matching deposit tile). Touches REQ-BLD-MINER ("every asteroid
    tile is equivalent" no longer holds), REQ-GW-ASTEROID-EXPAND /
    REQ-EXP-*, `world.toml`, and `visuals.toml`.
+6. **Investigate team-1 bias in balancing arenas.** In arena round 1
+   (July 2026), team 1 won all three mirror matches with large margins
+   (8/20, 3/6, 1/2 survivors). Re-run mirrors repeatedly; if team 1
+   wins consistently, find and fix the asymmetry (spawn geometry, tick
+   processing order, target-selection tie-breaking). Mirror matches
+   must be statistically symmetric or every arena result carries a
+   side-dependent error.
+7. **Log remaining HP in the balancing arena results.** Win/loss alone
+   hides the margin ("1/1 battleship" can mean 95% or 5% HP left). Add
+   the surviving entities' remaining HP fraction (or a per-team total
+   EHP percentage) to the arena end state, so equal-threat matchups can
+   be tuned toward near-draws quantitatively.