docs: Add Docker Optimization & Build Cache Management section

DOCUMENTATION UPDATE (Nov 26, 2025):
User quote: "ok. dont forget the documentation"

Added comprehensive Docker Optimization section covering:

1. MULTI-STAGE BUILDS (already implemented):
   - Verified Dockerfile uses builder → runner pattern
   - Benefits: Smaller images, faster builds, better layer reuse

2. BUILDKIT AUTO-CLEANUP (just configured):
   - Updated /etc/docker/daemon.json with 20GB threshold
   - Auto garbage collection when cache exceeds limit
   - Docker restarted, BuildKit v0.14.1 active
   - Current baseline: 11.13GB cache (healthy)

3. AUTOMATED CLEANUP SCRIPT (ready to use):
   - Script: /home/icke/traderv4/cleanup_trading_bot.sh (94 lines)
   - Features: Keeps last 2 images, prunes cache, protects volumes
   - Usage: Manual (after builds) or automated (cron daily)
   - Typical savings: 40-50 GB per run

WHY THIS MATTERS:
- User previously hit 40GB cache accumulation
- BuildKit auto-cleanup provides 20GB safety net
- Manual script gives on-demand control
- Documented process for team reference

IMPLEMENTATION STATUS:
 Multi-stage builds confirmed in Dockerfile
 BuildKit configured in daemon.json (20GB threshold)
 Cleanup script exists and executable
 Docker daemon restarted with new config
 Current disk usage healthy (11.13GB < 20GB)

Files documented:
- /etc/docker/daemon.json (BuildKit config)
- /home/icke/traderv4/cleanup_trading_bot.sh (manual cleanup)
- Dockerfile (multi-stage builds)

Added monitoring commands, usage recommendations, safety measures,
and typical space savings data for team reference.

.github/copilot-instructions.md

@@ -614,6 +614,129 @@ docker system df
 - Active containers
 - Tagged images currently in use
 
+### Docker Optimization & Build Cache Management (Nov 26, 2025)
+
+**Purpose:** Prevent Docker cache accumulation (40+ GB) through automated cleanup and BuildKit optimizations
+
+**Three-Layer Optimization Strategy:**
+
+**1. Multi-Stage Builds (ALREADY IMPLEMENTED)**
+```dockerfile
+# Dockerfile already uses multi-stage pattern:
+FROM node:20-alpine AS deps      # Install dependencies
+FROM node:20-alpine AS builder   # Build application
+FROM node:20-alpine AS runner    # Final minimal image
+
+# Benefits:
+# - Smaller final images (only runtime dependencies)
+# - Faster builds (caches each stage independently)
+# - Better layer reuse
+```
+
+**2. BuildKit Auto-Cleanup (Nov 26, 2025)**
+```bash
+# /etc/docker/daemon.json configuration:
+{
+  "features": {
+    "buildkit": true
+  },
+  "builder": {
+    "gc": {
+      "enabled": true,
+      "defaultKeepStorage": "20GB"
+    }
+  }
+}
+
+# Restart Docker to apply:
+sudo systemctl restart docker
+
+# Verify BuildKit active:
+docker buildx version  # Should show v0.14.1+
+```
+
+**Auto-Cleanup Behavior:**
+- **Threshold:** 20GB build cache limit
+- **Action:** Automatically garbage collects when exceeded
+- **Safety:** Keeps recent layers for build speed
+- **Monitoring:** Check current usage: `docker system df`
+
+**Current Disk Usage Baseline (Nov 26, 2025):**
+- Build Cache: 11.13GB (healthy, under 20GB threshold)
+- Images: 59.2GB (33.3GB reclaimable)
+- Volumes: 8.5GB (7.9GB reclaimable)
+- Containers: 232.9MB
+
+**3. Automated Cleanup Script (READY TO USE)**
+```bash
+# Script: /home/icke/traderv4/cleanup_trading_bot.sh (94 lines)
+# Executable: -rwxr-xr-x (already set)
+
+# Features:
+# - Step 1: Keeps last 2 trading-bot images (rollback safety)
+# - Step 2: Removes dangling images (untagged layers)
+# - Step 3: Prunes build cache (biggest space saver)
+# - Step 4: Safe volume handling (protects postgres)
+# - Reporting: Shows disk space before/after
+
+# Manual usage (recommended after builds):
+cd /home/icke/traderv4
+docker compose build trading-bot && ./cleanup_trading_bot.sh
+
+# Automated usage (daily cleanup at 2 AM):
+# Add to crontab: crontab -e
+0 2 * * * /home/icke/traderv4/cleanup_trading_bot.sh
+
+# Check current disk usage:
+docker system df
+```
+
+**Script Safety Measures:**
+- **Never removes:** Named volumes (trading-bot-postgres, etc.)
+- **Never removes:** Running containers
+- **Never removes:** Tagged images currently in use
+- **Keeps:** Last 2 trading-bot images for quick rollback
+- **Reports:** Space freed after cleanup (typical: 40-50 GB)
+
+**When to Run Cleanup:**
+1. **After builds:** Most effective, immediate cleanup
+2. **Weekly:** If building frequently during development
+3. **On demand:** When disk space warnings appear
+4. **Before deployments:** Clean slate for major updates
+
+**Typical Space Savings:**
+- Manual script run: 40-50 GB (build cache + dangling images)
+- BuildKit auto-cleanup: Maintains 20GB cap automatically
+- Combined approach: Prevents accumulation entirely
+
+**Monitoring Commands:**
+```bash
+# Check current disk usage
+docker system df
+
+# Detailed breakdown
+docker system df -v
+
+# Check BuildKit cache
+docker buildx du
+
+# Verify auto-cleanup threshold
+grep -A10 "builder" /etc/docker/daemon.json
+```
+
+**Why This Matters:**
+- **Problem:** User previously hit 40GB cache accumulation
+- **Solution:** BuildKit auto-cleanup (20GB cap) + manual script (on-demand)
+- **Result:** System self-maintains, prevents disk full scenarios
+- **Team benefit:** Documented process for all developers
+
+**Implementation Status:**
+- ✅ Multi-stage builds: Already present in Dockerfile (builder → runner)
+- ✅ BuildKit auto-cleanup: Configured in daemon.json (20GB threshold)
+- ✅ Cleanup script: Exists and ready (/home/icke/traderv4/cleanup_trading_bot.sh)
+- ✅ Docker daemon: Restarted with new config (BuildKit v0.14.1 active)
+- ✅ Current state: Healthy (11.13GB cache, under threshold)
+
 ---
 
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