# Refactor Plan: upgrade-effects.ts

## Current State
- **File:** `src/lib/game/upgrade-effects.ts`
- **Lines:** 466
- **Target:** ≤400 lines (reduce by ~66 lines)

## Proposed File Structure

### 1. `src/lib/game/upgrade-effects.ts` (≈220 lines)
**Keeps:**
- `upgradeDefinitionsById` (cache)
- `buildUpgradeCache` function
- `getActiveUpgrades` function
- `computeEffects` function (core orchestrator)
- Evolution path dependency (`SKILL_EVOLUTION_PATHS`, `getUpgradesForSkillAtMilestone`)

**Rationale:** This remains the core orchestration module that ties together evolution paths with upgrade computation.

### 2. `src/lib/game/upgrade-effects.types.ts` (≈60 lines)
**Contains:**
- `ActiveUpgradeEffect` interface
- `ComputedEffects` interface  
- Re-exports for type consumers

**Rationale:** Pure type definitions separated for clarity.

### 3. `src/lib/game/special-effects.ts` (≈80 lines)
**Contains:**
- `SPECIAL_EFFECTS` constant record
- `hasSpecial` function

**Rationale:** Isolates special effect keys and the simple predicate function.

### 4. `src/lib/game/dynamic-compute.ts` (≈100 lines)
**Contains:**
- `computeDynamicRegen` function
- `computeDynamicClickMana` function
- `computeDynamicDamage` function

**Rationale:** Groups the three dynamic computation functions that all depend on `SPECIAL_EFFECTS` and share similar patterns.

## Circular Import Risks

**LOW RISK:**
- `upgrade-effects.ts` depends on `skill-evolution` - one-way dependency.
- New files import types from `upgrade-effects.types.ts` and `special-effects.ts`.
- `dynamic-compute.ts` depends on `special-effects.ts` and types - safe.

**MITIGATION:**
- Keep type re-exports clean.
- If `computeEffects` needs dynamic functions, import them from `dynamic-compute.ts`.

## Extraction Order

**1 → 2 → 3 → 4**

1. Create `upgrade-effects.types.ts`, move type interfaces, update imports.
2. Create `special-effects.ts`, move `SPECIAL_EFFECTS` + `hasSpecial`, update imports.
3. Create `dynamic-compute.ts`, move the three `computeDynamic*` functions, update imports.
4. Trim `upgrade-effects.ts` - remove moved items, update internal imports.

## Import Updates Required

Files importing from `upgrade-effects.ts` need updates:
- Types → `upgrade-effects.types.ts`
- Special effects → `special-effects.ts`
- Dynamic compute → `dynamic-compute.ts`
- Core functions → `upgrade-effects.ts`