ui/phase-27: root-cause aggregation of duplicate (race, className) rows

Legacy reports list the same `(race, className)` pair across several
roster rows; the engine likewise creates one ShipGroup per arrival.
Both the legacy parser and `TransformBattle` were keyed on shipClass
without summing — only the last row / group's counts survived, so a
protocol's destroy count appeared to exceed the recorded initial
roster. The UI worked around this with phantom-frame logic.

Both parser and engine now SUM `Number`/`NumberLeft` across rows /
groups sharing the same class; the phantom-frame workaround is gone.
KNNTS041 turn 41 planet #7 reconciles: `Nails:pup` 1168 initial −
86 survivors = 1082 destroys.

The engine's previously latent nil-map write on `bg.Tech` (would
have paniced on any group with non-empty Tech) is fixed in the same
patch — it blocked the aggregation regression test.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

game/internal/controller/battle_test.go

@@ -8,6 +8,7 @@ import (
 	"galaxy/calc"
 	"galaxy/game/internal/controller"
 	"galaxy/game/internal/model/game"
+	"galaxy/model/report"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -184,3 +185,89 @@ func TestProduceBattles(t *testing.T) {
 		assert.Zero(t, c.ShipGroup(3).Number)
 	}
 }
+
+// TestTransformBattleAggregatesSameShipClass guards against the
+// engine-side variant of the duplicate-class bug. Several ShipGroups
+// of the same ShipClass.ID can take part in the same battle (arrivals
+// from different planets, tech splits, etc.); they must collapse into
+// a single BattleReportGroup with summed Number and NumberLeft. The
+// pre-fix engine cached the first group's index and silently dropped
+// every subsequent group's initial / survivor counts, which manifested
+// downstream as more Destroyed shots in the protocol than the
+// recorded initial roster could account for.
+func TestTransformBattleAggregatesSameShipClass(t *testing.T) {
+	c, g := newCache()
+
+	assert.NoError(t, g.RaceRelation(Race_0.Name, Race_1.Name, game.RelationWar.String()))
+	assert.NoError(t, g.RaceRelation(Race_1.Name, Race_0.Name, game.RelationWar.String()))
+
+	// Two Race_0 groups of the SAME ship class (Race_0_Gunship) plus
+	// one Race_1 group of Race_1_Gunship — all parked on Planet_0
+	// (owned by Race_0; the Race_1 group lands there via the Unsafe
+	// helper that bypasses the ownership check). Group indices land
+	// at 0, 1, 2 in creation order.
+	assert.NoError(t, c.CreateShips(Race_0_idx, Race_0_Gunship, R0_Planet_0_num, 10))
+	assert.NoError(t, c.CreateShips(Race_0_idx, Race_0_Gunship, R0_Planet_0_num, 10))
+	c.CreateShipsUnsafe_T(Race_1_idx, c.MustShipClass(Race_1_idx, Race_1_Gunship).ID, R0_Planet_0_num, 5)
+
+	// Simulate post-battle survivor counts: Group 0 ended the battle
+	// with 8 ships, Group 1 with 6. The aggregated BattleReportGroup
+	// must report NumberLeft = 8 + 6 = 14 (not just the last cached
+	// group's 6 — that's the regression).
+	c.ShipGroup(0).Number = 8
+	c.ShipGroup(1).Number = 6
+
+	b := &controller.Battle{
+		Planet:         R0_Planet_0_num,
+		ObserverGroups: map[int]bool{0: true, 1: true, 2: true},
+		InitialNumbers: map[int]uint{0: 10, 1: 10, 2: 5},
+		// Protocol must reference every in-battle group at least once
+		// (otherwise TransformBattle won't register it through the
+		// `ship()` path). Two shots from Race_1 against each Race_0
+		// group hits both groupIds.
+		Protocol: []controller.BattleAction{
+			{Attacker: 2, Defender: 0, Destroyed: true},
+			{Attacker: 2, Defender: 1, Destroyed: true},
+		},
+	}
+
+	r := controller.TransformBattle(c, b)
+
+	// Two BattleReportGroup entries total: one merged Race_0_Gunship
+	// (groups 0 + 1) and one Race_1_Gunship. NOT three.
+	if got, want := len(r.Ships), 2; got != want {
+		t.Fatalf("len(r.Ships) = %d, want %d (duplicate ShipClass.ID must merge)", got, want)
+	}
+
+	var gunship0, gunship1 *report.BattleReportGroup
+	for i := range r.Ships {
+		grp := r.Ships[i]
+		switch grp.Race {
+		case Race_0.Name:
+			gunship0 = &grp
+		case Race_1.Name:
+			gunship1 = &grp
+		}
+	}
+	if gunship0 == nil || gunship1 == nil {
+		t.Fatalf("missing race entry: race0=%v race1=%v", gunship0, gunship1)
+	}
+
+	if gunship0.ClassName != Race_0_Gunship {
+		t.Errorf("race0.ClassName = %q, want %q", gunship0.ClassName, Race_0_Gunship)
+	}
+	if gunship0.Number != 20 {
+		t.Errorf("race0.Number = %d, want 20 (10+10)", gunship0.Number)
+	}
+	if gunship0.NumberLeft != 14 {
+		t.Errorf("race0.NumberLeft = %d, want 14 (8+6)", gunship0.NumberLeft)
+	}
+	if !gunship0.InBattle {
+		t.Errorf("race0.InBattle = false, want true (both source groups were in-battle)")
+	}
+
+	if gunship1.Number != 5 || gunship1.NumberLeft != 5 {
+		t.Errorf("race1 = (Number=%d, NumberLeft=%d), want (5, 5)",
+			gunship1.Number, gunship1.NumberLeft)
+	}
+}