docs: add armor plating mechanics - 7 slots, plates take damage first

- Documented shield layer mechanics (Plate → Armor → Player)
- 7 armor pieces, 1 plate per piece
- Plates have lower decay than armor
- Specialization strategy for damage types

docs/ATTACHMENT_MECHANICS.md

@@ -132,3 +132,101 @@ Base cost + enhancer_decay
 5. **Double Sights:** Support weapon sight + scope sight combination
 
 **Key Insight:** Amps increase DPS but cost more per shot. Scopes/Absorbers are situational. Enhancers are high-risk endgame.
+
+---
+
+# Armor Plating Mechanics
+
+**Source:** Domain expert knowledge from user (@ImpulsiveFPS)  
+**Date:** 2026-02-09
+
+## How It Works (The "Shield" Layer)
+
+When a monster hits you, damage flows through layers in specific order:
+
+```
+Incoming Damage → PLATE → ARMOR → PLAYER HEALTH
+```
+
+### Example:
+- **Armor:** Protects against 10 Impact damage
+- **Plate:** Protects against 15 Impact damage  
+- **Monster hits:** 20 Impact damage
+
+**Result:**
+- Plate absorbs 15 → Plate takes decay
+- Armor absorbs remaining 5 → Armor takes decay  
+- Player takes **0 damage**
+
+---
+
+## Why Use Plating?
+
+### 1. Specialization
+Don't buy "Acid Armor" - just add **Acid Plates** to your current suit.
+
+### 2. Saving Money (Efficiency)
+- Plates usually have **lower decay** cost than high-end armor
+- Plates are **easier to repair** than armor
+- Cheaper to let plate take damage than armor itself
+
+### 3. Boosting Weak Armor
+Make "weak" starter armor viable for mid-level monsters by adding strong plating.
+
+---
+
+## The Rules of Plating
+
+### Rule 1: One Plate Per Piece
+- You have **7 armor pieces:** Head, Chest, Arms (2), Hands (2), Legs, Feet
+- **Maximum:** 1 plate per piece = 7 plates total
+
+### Rule 2: Matching Types (CRITICAL)
+- **You want all 7 plates to be the same type**
+- If you only plate your chest, and monster hits your leg → **Plate does nothing!**
+- Partial plating = wasted protection
+
+### Rule 3: Drag and Drop
+- Drag plate onto armor piece in inventory to "slot" it
+- Just like weapon attachments
+
+---
+
+## Armor Piece Breakdown
+
+| Slot | Can Have Plate? |
+|------|----------------|
+| Head | Yes |
+| Chest/Harness | Yes |
+| Left Arm | Yes |
+| Right Arm | Yes |
+| Left Hand | Yes |
+| Right Hand | Yes |
+| Thighs/Legs | Yes |
+| Feet | Yes |
+
+**Total:** 7 plate slots
+
+---
+
+## Decay Mechanics
+
+### When Damage is Absorbed:
+1. **Plate takes decay first** (primary layer)
+2. **Armor takes decay second** (overflow only)
+3. **Player health reduced** (if damage exceeds both)
+
+### Cost Optimization Strategy:
+- **Cheap plates:** High protection, low decay
+- **Use plates for:** Specific damage types (Acid, Cold, etc.)
+- **Use armor for:** General protection + cosmetic looks
+
+---
+
+## Implementation Notes for Lemontropia Suite
+
+1. **Plate Selection:** Show 7 plate slots (one per armor piece)
+2. **Protection Stacking:** Plate protection + Armor protection = Total
+3. **Decay Order:** Plate decays first, armor decays second
+4. **Matching Warning:** Alert if player has mismatched plates
+5. **Cost Calculation:** Track plate decay separately from armor decay

memory/2026-02-09.md

@@ -73,8 +73,9 @@ User feedback:
 
 - Kill tracking: 1 per loot event (estimated, not exact)
 - Shrapnel handling: included in loot, not kill count
-- Cost tracking: weapon decay per shot + armor decay per hit
+- Cost tracking: weapon decay per shot + armor decay per hit + plate decay per hit
 - Agent swarm effective for parallel development but needs verification
+- **Armor Plating:** 7 pieces, 1 plate per piece, plates take damage FIRST
 
 ## Technical Debt