adventure: Tier 6 postgame "Mythic" dungeons (P1–P7 calibration)

Five post-game dungeons above the T5 ceiling, gated on both T5 bosses beaten
+ level 18. Opt-in endgame: deadly solo, clearable by a party with Pete + pets.

- P1 gating: postgameUnlocked (T5 clears + level floor), zonesForLevel excludes
  T6 unconditionally; wired into startZoneRun, !zone/!expedition, party accept,
  boredom picker, and the list dividers.
- P2 bestiary: 15 elites + 5 signature bosses (Layer-1 stat blocks).
- P3 zone defs + 4-region registries; ZoneLootEntry.BossOnly.
- P4 five zone graphs on a shared builder (44–52 rooms, no soft-lock; Ossuary
  secret Verse nodes).
- P5 loot: BossOnly enforced; signature items are real registry magic items;
  five Thom pity recipes off the per-zone crafting anchors.
- P6 narration/flavor (5 files), T6 achievements, Pete stays zone-parametric.
- P7 (in progress): sim can now reach gated T6 (SimRunner.SeedPostgameUnlock +
  IsPostgameZone). First calibration pass on millenia — hardened ossuary +
  drowned_star, softened first_hoard + unplace; last_meridian in band.

Fix: party members were refused from every T6 zone because expeditionCmdAccept
ran the level gate (which excludes T6) before the postgame check — the intended
party endgame was unreachable. Route T6 through postgameUnlocked. Regression
tests added.

internal/plugin/dnd_economy_test.go

@@ -18,6 +18,11 @@ func TestRecipeRegistry_IngredientsExistInResources(t *testing.T) {
 		}
 	}
 	for _, r := range thomCraftRecipes {
+		// AlwaysKnown pity recipes consume zone-loot crafting anchors, not
+		// gather-resource materials — validated separately below.
+		if r.AlwaysKnown {
+			continue
+		}
 		for ing := range r.Ingredients {
 			if !known[ing] {
 				t.Errorf("recipe %s references unknown ingredient %q", r.ID, ing)
@@ -26,12 +31,59 @@ func TestRecipeRegistry_IngredientsExistInResources(t *testing.T) {
 	}
 }
 
+// TestPityRecipes_AnchorsAndOutputsResolve — the T6 signature-item pity
+// recipes consume a zone-loot UniqueAlways crafting anchor and emit a real
+// registry magic item. Validate both ends: every ingredient name matches a
+// UniqueAlways zone-loot drop's inventory name, and every OutputSkillSource
+// points at a magicItemRegistry ID.
+func TestPityRecipes_AnchorsAndOutputsResolve(t *testing.T) {
+	anchorNames := map[string]bool{}
+	for _, z := range allZones() {
+		for _, e := range z.Loot {
+			if e.UniqueAlways {
+				anchorNames[titleCaseUnderscored(e.ItemID)] = true
+			}
+		}
+	}
+	pity := 0
+	for _, r := range thomCraftRecipes {
+		if !r.AlwaysKnown {
+			continue
+		}
+		pity++
+		for ing := range r.Ingredients {
+			if !anchorNames[ing] {
+				t.Errorf("pity recipe %s ingredient %q is not a zone-loot anchor name", r.ID, ing)
+			}
+		}
+		if r.OutputType != "magic_item" {
+			t.Errorf("pity recipe %s OutputType = %q, want magic_item", r.ID, r.OutputType)
+		}
+		id, ok := strings.CutPrefix(r.OutputSkillSource, "magic_item:")
+		if !ok {
+			t.Errorf("pity recipe %s OutputSkillSource %q missing magic_item: prefix", r.ID, r.OutputSkillSource)
+			continue
+		}
+		if _, ok := magicItemRegistry[id]; !ok {
+			t.Errorf("pity recipe %s output %q not in magicItemRegistry", r.ID, id)
+		}
+	}
+	if pity != 5 {
+		t.Errorf("expected 5 T6 pity recipes, found %d", pity)
+	}
+}
+
 // TestRecipeRegistry_OutputValuesMatchTier — outputs should land in §8.1
 // rarity brackets given their tier (rare 100–300, very rare 500–1200,
 // epic 500–1200 in §8.1 — recipes here lean tier 3–4, so 200..1200 is the
 // reasonable band).
 func TestRecipeRegistry_OutputValuesInBand(t *testing.T) {
 	for _, r := range thomCraftRecipes {
+		// Pity recipes emit Legendary magic items priced well above the §8.1
+		// crafting band by design — excluded from this invariant.
+		if r.AlwaysKnown {
+			continue
+		}
 		if r.OutputValue < 200 || r.OutputValue > 1200 {
 			t.Errorf("recipe %s output value %d outside band [200,1200] (tier %d)",
 				r.ID, r.OutputValue, r.OutputTier)