docs(design): define spawn plugin user stories

design/user-stories/us-008-reward-spawn-progression.md

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+---
+type: User Story
+title: "US-008: Reward and encourage spawn progression"
+description: Remind players how to improve spawn access and reward each newly credited unique boss kill with an immediate cooldown reset.
+status: backlog
+---
+
+# US-008: Reward and encourage spawn progression
+
+As a **player**, I want `/spawn` to explain how I can improve its cooldown and reward new boss progress so that the benefit of defeating each remaining boss is clear and immediately useful.
+
+## Acceptance criteria
+
+- [ ] After every successful `/spawn`, a player who has not defeated all three unique qualifying enemies receives a reminder that defeating the remaining bosses permanently reduces the cooldown.
+- [ ] The reminder identifies the remaining eligible bosses and shows the next cooldown tier.
+- [ ] A player who has completed all three unique qualifying kills does not receive the progression reminder.
+- [ ] Each newly credited unique Warden, Ender Dragon, or Wither kill immediately clears the player's active `/spawn` cooldown.
+- [ ] Clearing the cooldown makes `/spawn` immediately available as a progression reward.
+- [ ] The newly credited kill also permanently applies the improved boss-based cooldown tier.
+- [ ] Repeated kills of an already credited enemy do not clear the cooldown.
+- [ ] The on-screen kill message states that `/spawn` is immediately available and displays the new cooldown tier.
+- [ ] Banned players cannot earn kill credit, a cooldown reset, or an improved tier.
+
+## Related
+
+- [US-001: Earn progressive spawn access](us-001-earn-progressive-spawn-access.md)
+- [US-002: Teleport safely to spawn](us-002-teleport-safely-to-spawn.md)
+- [US-005: Ban and unban spawn access](us-005-manage-spawn-bans.md)