FASE 4-5-6: Infraestructura, CRM, Service Orders, Notificaciones, Ahorro, Logistica, API Publica

FASE 4:
- Redis cache de stock con fallback graceful
- Multi-moneda (MXN/USD) con contabilidad en MXN
- Proveedores y ordenes de compra completo
- Meilisearch 1.5M+ partes indexadas
- Metabase KPIs con dashboard auto-generado

FASE 5:
- CRM mejorado: activities, tags, loyalty program, analytics
- Imagenes de partes: upload, resize, thumbnails WebP
- Ordenes de servicio Kanban: received->diagnosis->repair->ready->delivered
- Garantias/RMA, alertas de reorden, multi-sucursal
- Stubs BNPL (APLAZO) y ERP Sync (Aspel/Contpaqi)

FASE 6:
- Notificaciones automaticas: push/WhatsApp/email/in-app
- Reportes de ahorro vs retail_price
- Logistica + tracking: DHL, FedEx, Estafeta, 99min, Uber
- API Publica: API keys, rate limiting, catalog search

Migraciones: v1.9-v3.0
Tests: 93/93 pasando
Backup: nexus_backup_20260427_045859.tar.gz

pos/services/redis_stock_cache.py

@@ -0,0 +1,120 @@
+# /home/Autopartes/pos/services/redis_stock_cache.py
+"""Redis cache layer for inventory stock calculations.
+
+Provides sub-millisecond stock lookups by caching SUM(inventory_operations)
+results in Redis. Cache is invalidated on every stock mutation.
+
+Fallback: if Redis is unavailable, queries PostgreSQL directly.
+"""
+
+import os
+import json
+import redis
+from decimal import Decimal
+
+# Connection settings from environment
+REDIS_URL = os.environ.get('REDIS_URL', 'redis://localhost:6379/0')
+REDIS_STOCK_TTL = int(os.environ.get('REDIS_STOCK_TTL', '300'))  # 5 minutes default
+REDIS_ENABLED = os.environ.get('REDIS_ENABLED', 'true').lower() == 'true'
+
+# Lazy connection
+_redis_client = None
+
+
+def _get_redis():
+    """Get or create Redis connection (lazy singleton)."""
+    global _redis_client
+    if _redis_client is None and REDIS_ENABLED:
+        try:
+            _redis_client = redis.from_url(REDIS_URL, decode_responses=True)
+            _redis_client.ping()
+        except Exception as e:
+            print(f"[redis_stock_cache] Redis unavailable: {e}")
+            _redis_client = False  # Disable for this session
+    return _redis_client if _redis_client is not False else None
+
+
+def _stock_key(inventory_id, branch_id=None):
+    """Generate Redis key for a stock entry."""
+    if branch_id:
+        return f"nexus:stock:{inventory_id}:b{branch_id}"
+    return f"nexus:stock:{inventory_id}"
+
+
+def get_cached_stock(inventory_id, branch_id=None):
+    """Get stock from Redis cache.
+
+    Returns:
+        int/None: Stock quantity if cached, None if miss or Redis down.
+    """
+    r = _get_redis()
+    if not r:
+        return None
+    try:
+        val = r.get(_stock_key(inventory_id, branch_id))
+        if val is not None:
+            return int(val)
+    except Exception as e:
+        print(f"[redis_stock_cache] GET error: {e}")
+    return None
+
+
+def set_cached_stock(inventory_id, quantity, branch_id=None):
+    """Store stock in Redis cache with TTL."""
+    r = _get_redis()
+    if not r:
+        return
+    try:
+        key = _stock_key(inventory_id, branch_id)
+        r.set(key, int(quantity), ex=REDIS_STOCK_TTL)
+    except Exception as e:
+        print(f"[redis_stock_cache] SET error: {e}")
+
+
+def invalidate_stock(inventory_id, branch_id=None):
+    """Remove stock entry from Redis cache.
+
+    Called after any inventory mutation (sale, purchase, adjust, transfer).
+    If branch_id is None, invalidates both global and branch-specific keys.
+    """
+    r = _get_redis()
+    if not r:
+        return
+    try:
+        keys = [_stock_key(inventory_id)]
+        if branch_id:
+            keys.append(_stock_key(inventory_id, branch_id))
+        else:
+            # Wildcard invalidation for all branches of this item
+            pattern = _stock_key(inventory_id, '*')
+            keys = r.keys(pattern)
+            keys.append(_stock_key(inventory_id))
+        if keys:
+            r.delete(*keys)
+    except Exception as e:
+        print(f"[redis_stock_cache] DELETE error: {e}")
+
+
+def invalidate_all_stock():
+    """Flush all stock keys from Redis. Use with caution (e.g., after bulk import)."""
+    r = _get_redis()
+    if not r:
+        return
+    try:
+        keys = r.keys('nexus:stock:*')
+        if keys:
+            r.delete(*keys)
+            print(f"[redis_stock_cache] Flushed {len(keys)} stock keys")
+    except Exception as e:
+        print(f"[redis_stock_cache] FLUSH error: {e}")
+
+
+def health_check():
+    """Return True if Redis is reachable."""
+    r = _get_redis()
+    if not r:
+        return False
+    try:
+        return r.ping()
+    except Exception:
+        return False