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_zone_cmd.go

@@ -118,6 +118,25 @@ func (p *AdventurePlugin) zoneCmdList(ctx MessageContext, c *DnDCharacter) error
 			i+1, z.Display, int(z.Tier), z.LevelMin, z.LevelMax, z.ID))
 		b.WriteString(fmt.Sprintf("    %s\n", z.Atmosphere))
 	}
+	// Post-game zones render under a divider once any exist. Unlocked players
+	// see enterable entries (indexed continuing from the list above, matching
+	// availableZonesFor); locked players see aspiration + the unlock hint.
+	if pg := postgameZones(); len(pg) > 0 {
+		unlocked, reason := postgameUnlocked(ctx.Sender, c.Level)
+		b.WriteString("\n— Beyond the Map —\n")
+		if !unlocked {
+			b.WriteString(fmt.Sprintf("_%s_\n", reason))
+		}
+		for j, z := range pg {
+			if unlocked {
+				b.WriteString(fmt.Sprintf("**%d.** %s — _T%d, L%d+_  `!zone enter %s`\n",
+					len(zones)+j+1, z.Display, int(z.Tier), z.LevelMin, z.ID))
+			} else {
+				b.WriteString(fmt.Sprintf("🔒 %s — _T%d, L%d+_\n", z.Display, int(z.Tier), z.LevelMin))
+			}
+			b.WriteString(fmt.Sprintf("    %s\n", z.Atmosphere))
+		}
+	}
 	if active, isLeader, _ := activeZoneRunFor(ctx.Sender); active != nil {
 		zone := zoneOrFallback(active.ZoneID)
 		tail := "Use `!zone status` or `!zone abandon`."
@@ -200,9 +219,12 @@ func (p *AdventurePlugin) zoneCmdEnter(ctx MessageContext, c *DnDCharacter, rest
 			"🛌 You're still resting — %s remaining. The dungeon won't go anywhere.",
 			formatRespecDuration(remaining)))
 	}
-	available := zonesForLevel(c.Level)
+	available := availableZonesFor(ctx.Sender, c.Level)
 	id, ok := resolveZoneInput(rest, available)
 	if !ok {
+		if reason := postgameLockReason(rest, ctx.Sender, c.Level); reason != "" {
+			return p.SendDM(ctx.Sender, reason)
+		}
 		return p.SendDM(ctx.Sender,
 			"Unknown zone for your level. Try `!zone list` to see what's available.")
 	}
@@ -762,7 +784,7 @@ func (p *AdventurePlugin) advanceOnceWithOpts(ctx MessageContext, compact, inlin
 			b.WriteString(line)
 			b.WriteString("\n\n")
 		}
-		if granted := p.rollZoneLoot(ctx.Sender, run, zone); len(granted) > 0 {
+		if granted := p.rollZoneLoot(ctx.Sender, run, zone, !midZone); len(granted) > 0 {
 			b.WriteString("**Loot:**\n")
 			for _, id := range granted {
 				b.WriteString("• " + id + "\n")