N7/B3: the Omen — one rotating world modifier per ISO week

activeOmen() is a pure function of the UTC ISO (year, week): omenTable
indexed by (year*53+week)%len, so it advances weekly with no schema, no
ticker state, no persistence. Five non-combat seams read it — harvest yield,
supply freebie, expedition start mood, arena payout (scales gross earnings
before the pot tax), and ingredient drop chance. TwinBee reveals the active
omen in the existing morning DM (no net-new scheduled message).

Launch set is buffs-with-texture on non-combat levers only: Bountiful
Harvest, Quartermaster's Blessing, Golden Purse, Overflowing Satchels, Still
Waters. Nothing touches SimulateCombat or the turn engine — the omen is keyed
on the real clock, so a combat mutator would make the golden and the balance
corpus week-dependent. The plan's "elites +2 ATK" is deliberately dropped for
that reason.

The balance sim drives the real expedition loop and would otherwise traverse
all five seams, making corpus sweeps depend on the wall-clock week. NewSimRunner
sets simOmenDisabled (mirrors simAutoArmEnabled), so activeOmen returns a
no-effect omen under the sim. Still Waters subtracts from the daily threat
*rise* only, floored at hold-steady — it never forces active decay.

Claude-Session: https://claude.ai/code/session_017mEwUmmS7aQTP2NQXj6rUa

internal/plugin/adventure_omen_test.go

@@ -0,0 +1,86 @@
+package plugin
+
+import "testing"
+
+// TestOmenForWeek_Deterministic — the same ISO week always yields the same omen.
+func TestOmenForWeek_Deterministic(t *testing.T) {
+	a := omenForWeek(2026, 28)
+	b := omenForWeek(2026, 28)
+	if a.Key != b.Key {
+		t.Fatalf("omenForWeek not deterministic: %q vs %q", a.Key, b.Key)
+	}
+}
+
+// TestOmenForWeek_AdvancesEachWeek — consecutive weeks step by exactly one table
+// entry, so the schedule rotates rather than sticking or skipping.
+func TestOmenForWeek_AdvancesEachWeek(t *testing.T) {
+	n := len(omenTable)
+	for w := 1; w <= n; w++ {
+		cur := omenForWeek(2026, w)
+		next := omenForWeek(2026, w+1)
+		wantNext := omenTable[((2026*53)+w+1)%n]
+		if next.Key != wantNext.Key {
+			t.Errorf("week %d→%d: got %q, want %q", w, w+1, next.Key, wantNext.Key)
+		}
+		if cur.Key == next.Key {
+			t.Errorf("week %d and %d produced the same omen %q (should advance)", w, w+1, cur.Key)
+		}
+	}
+}
+
+// TestOmenForWeek_TotalOverYearBoundary — never panics across week/year edges,
+// including ISO week 53.
+func TestOmenForWeek_TotalOverYearBoundary(t *testing.T) {
+	for y := 2020; y <= 2030; y++ {
+		for w := 1; w <= 53; w++ {
+			o := omenForWeek(y, w)
+			if o.Key == "" {
+				t.Fatalf("omenForWeek(%d,%d) returned zero omen", y, w)
+			}
+		}
+	}
+}
+
+// TestOmenTable_NonCombatOnly — every omen carries at least one effect and the
+// struct has no combat lever, so the launch set can never move the golden or the
+// balance corpus. §B3.
+func TestOmenTable_NonCombatOnly(t *testing.T) {
+	for _, o := range omenTable {
+		hasEffect := o.HarvestYieldBonus > 0 || o.SupplyFreebiePacks > 0 ||
+			o.StartMoodBonus > 0 || o.ArenaPayoutMult > 1.0 ||
+			o.ConsumableChanceMult > 1.0 || o.ThreatDriftReduce > 0
+		if !hasEffect {
+			t.Errorf("omen %q has no active effect", o.Key)
+		}
+		if o.Name == "" || o.TwinBee == "" {
+			t.Errorf("omen %q missing player-facing copy", o.Key)
+		}
+	}
+}
+
+// TestActiveOmen_SimDisabled — the balance sim neutralizes the omen so corpus
+// results are wall-clock-independent. §B3.
+func TestActiveOmen_SimDisabled(t *testing.T) {
+	defer func() { simOmenDisabled = false }()
+	simOmenDisabled = true
+	o := activeOmen()
+	if o.Key != "none" {
+		t.Errorf("sim-disabled omen = %q, want none", o.Key)
+	}
+	if o.HarvestYieldBonus != 0 || o.SupplyFreebiePacks != 0 || o.StartMoodBonus != 0 ||
+		o.ArenaPayoutMult != 0 || o.ConsumableChanceMult != 0 || o.ThreatDriftReduce != 0 {
+		t.Errorf("sim-disabled omen must have no effect, got %+v", o)
+	}
+}
+
+// TestOmenKeysUnique — no duplicate keys (a dup would make the rotation land on
+// the same omen two of every len(omenTable) weeks).
+func TestOmenKeysUnique(t *testing.T) {
+	seen := map[string]bool{}
+	for _, o := range omenTable {
+		if seen[o.Key] {
+			t.Errorf("duplicate omen key %q", o.Key)
+		}
+		seen[o.Key] = true
+	}
+}