From f1897501de4e0312d1e1ff93d4bb611acac60247 Mon Sep 17 00:00:00 2001
From: Alexander Zielonka <zielonka@zeasy.software>
Date: Mon, 27 Apr 2026 14:06:09 +0200
Subject: [PATCH] feat(01-02): implement skill-increase-cap (LVL-06)
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Task 2 GREEN phase. PF2e skill-increase cap rule:
- UNTRAINED → TRAINED at any level
- TRAINED → EXPERT requires L3+
- EXPERT → MASTER requires L7+
- MASTER → LEGENDARY requires L15+

Pure function, no NestJS, no Prisma. 9 tests passing.
---
 .../leveling/lib/skill-increase-cap.ts        | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 server/src/modules/leveling/lib/skill-increase-cap.ts

diff --git a/server/src/modules/leveling/lib/skill-increase-cap.ts b/server/src/modules/leveling/lib/skill-increase-cap.ts
new file mode 100644
index 0000000..b8c0fa3
--- /dev/null
+++ b/server/src/modules/leveling/lib/skill-increase-cap.ts
@@ -0,0 +1,31 @@
+import type { Proficiency } from './types';
+
+/** Levels at which a skill-increase step occurs (PF2e CRB). */
+export const SKILL_INCREASE_LEVELS: readonly number[] = [3, 5, 7, 9, 11, 13, 15, 17, 19];
+
+/**
+ * Minimum character level required to advance a skill from `currentRank`.
+ * UNTRAINED → TRAINED is unrestricted (any level >= 1 with a skill-increase step).
+ * LEGENDARY is `null` because it is the maximum rank — no further increases possible.
+ */
+const SKILL_RANK_LEVEL_REQUIREMENTS: Record<Proficiency, number | null> = {
+  UNTRAINED: 1, // → TRAINED
+  TRAINED: 3, // → EXPERT (PF2e CRB)
+  EXPERT: 7, // → MASTER
+  MASTER: 15, // → LEGENDARY
+  LEGENDARY: null, // already maxed
+};
+
+/**
+ * PF2e skill-increase cap rule (LVL-06).
+ * Returns true if a character at `characterLevel` may advance a skill that is
+ * currently at `currentRank` to the next rank.
+ */
+export function canIncreaseSkill(
+  currentRank: Proficiency,
+  characterLevel: number,
+): boolean {
+  const required = SKILL_RANK_LEVEL_REQUIREMENTS[currentRank];
+  if (required === null) return false;
+  return characterLevel >= required;
+}