docs(design): add OKF user story catalog

design/us-004-minecraft-validation.md

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+---
+type: User Story
+title: Validate Minecraft accounts
+description: Java Edition usernames resolve to canonical Mojang identities with controlled override behavior.
+tags: [player, minecraft, mojang, identity]
+timestamp: 2026-08-01T18:43:58Z
+story_id: US-004
+status: verified
+---
+
+# User Story
+
+As a player, I want submitted Minecraft usernames checked against Mojang, so that the server can identify my online-mode Java account reliably.
+
+# Acceptance Criteria
+
+- [x] Given a syntactically valid username, when it is submitted, then validation occurs server-side against the fixed Mojang endpoint.
+- [x] Given a Mojang match, then the canonical username and compact UUID are stored.
+- [x] Given no Mojang match, then the user or administrator must explicitly confirm an unverified override.
+- [x] Given malformed input, then it cannot be stored even through an override.
+- [x] Given an active UUID or case-insensitive username already registered, then another active registration is rejected.
+- [x] Given a later online-mode game login for an unverified account, then its UUID can be safely backfilled after username matching.
+
+# Implementation
+
+- [`packages/minecraft/src/index.ts`](../packages/minecraft/src/index.ts)
+- [`packages/database/src/schema.ts`](../packages/database/src/schema.ts)
+- User and administrator account actions under [`apps/web/src/app`](../apps/web/src/app)
+
+# Validation
+
+- [`packages/minecraft/test/minecraft.test.ts`](../packages/minecraft/test/minecraft.test.ts)
+- Database partial unique indexes preserve active identity invariants.
+
+# Related Stories
+
+- [First-time onboarding](us-003-onboarding.md)
+- [Velocity game admission](us-009-velocity-admission.md)