fix(backend): Make Redis connection lazy in cache module (#11775)

## Summary
- Makes Redis connection lazy in the cache module - connection is only
established when `shared_cache=True` is actually used
- Fixes DatabaseManager failing to start because it imports
`onboarding.py` which imports `cache.py`, triggering Redis connection at
module load time even though it only uses in-memory caching

## Root Cause
Commit `b01ea3fcb` (merged today) added `increment_onboarding_runs` to
DatabaseManager, which imports from `onboarding.py`. That module imports
`@cached` decorator from `cache.py`, which was creating a Redis
connection at module import time:

```python
# Old code - ran at import time!
redis = Redis(connection_pool=_get_cache_pool())
```

Since `onboarding.py` only uses `@cached(shared_cache=False)` (in-memory
caching), it doesn't actually need Redis. But the import triggered the
connection attempt.

## Changes
- Wrapped Redis connection in a singleton class with lazy initialization
- Connection is only established when `_get_redis()` is first called
(i.e., when `shared_cache=True` is used)
- Services using only in-memory caching can now import `cache.py`
without Redis configuration

## Test plan
- [ ] Services using `shared_cache=False` work without Redis configured
- [ ] Services using `shared_cache=True` still work correctly with Redis
- [ ] Existing cache tests pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

autogpt_platform/backend/backend/util/cache.py

@@ -16,7 +16,7 @@ import pickle
 import threading
 import time
 from dataclasses import dataclass
-from functools import wraps
+from functools import cache, wraps
 from typing import Any, Callable, ParamSpec, Protocol, TypeVar, cast, runtime_checkable
 
 from redis import ConnectionPool, Redis
@@ -38,29 +38,34 @@ settings = Settings()
 #   maxmemory 2gb                   # Set memory limit (adjust based on your needs)
 #   save ""                         # Disable persistence if using Redis purely for caching
 
-# Create a dedicated Redis connection pool for caching (binary mode for pickle)
-_cache_pool: ConnectionPool | None = None
 
-
-@conn_retry("Redis", "Acquiring cache connection pool")
+@cache
 def _get_cache_pool() -> ConnectionPool:
-    """Get or create a connection pool for cache operations."""
-    global _cache_pool
-    if _cache_pool is None:
-        _cache_pool = ConnectionPool(
-            host=settings.config.redis_host,
-            port=settings.config.redis_port,
-            password=settings.config.redis_password or None,
-            decode_responses=False,  # Binary mode for pickle
-            max_connections=50,
-            socket_keepalive=True,
-            socket_connect_timeout=5,
-            retry_on_timeout=True,
-        )
-    return _cache_pool
+    """Get or create a connection pool for cache operations (lazy, thread-safe)."""
+    return ConnectionPool(
+        host=settings.config.redis_host,
+        port=settings.config.redis_port,
+        password=settings.config.redis_password or None,
+        decode_responses=False,  # Binary mode for pickle
+        max_connections=50,
+        socket_keepalive=True,
+        socket_connect_timeout=5,
+        retry_on_timeout=True,
+    )
 
 
-redis = Redis(connection_pool=_get_cache_pool())
+@cache
+@conn_retry("Redis", "Acquiring cache connection")
+def _get_redis() -> Redis:
+    """
+    Get the lazily-initialized Redis client for shared cache operations.
+    Uses @cache for thread-safe singleton behavior - connection is only
+    established when first accessed, allowing services that only use
+    in-memory caching to work without Redis configuration.
+    """
+    r = Redis(connection_pool=_get_cache_pool())
+    r.ping()  # Verify connection
+    return r
 
 
 @dataclass
@@ -179,9 +184,9 @@ def cached(
             try:
                 if refresh_ttl_on_get:
                     # Use GETEX to get value and refresh expiry atomically
-                    cached_bytes = redis.getex(redis_key, ex=ttl_seconds)
+                    cached_bytes = _get_redis().getex(redis_key, ex=ttl_seconds)
                 else:
-                    cached_bytes = redis.get(redis_key)
+                    cached_bytes = _get_redis().get(redis_key)
 
                 if cached_bytes and isinstance(cached_bytes, bytes):
                     return pickle.loads(cached_bytes)
@@ -195,7 +200,7 @@ def cached(
             """Set value in Redis with TTL."""
             try:
                 pickled_value = pickle.dumps(value, protocol=pickle.HIGHEST_PROTOCOL)
-                redis.setex(redis_key, ttl_seconds, pickled_value)
+                _get_redis().setex(redis_key, ttl_seconds, pickled_value)
             except Exception as e:
                 logger.error(
                     f"Redis error storing cache for {target_func.__name__}: {e}"
@@ -333,14 +338,18 @@ def cached(
                 if pattern:
                     # Clear entries matching pattern
                     keys = list(
-                        redis.scan_iter(f"cache:{target_func.__name__}:{pattern}")
+                        _get_redis().scan_iter(
+                            f"cache:{target_func.__name__}:{pattern}"
+                        )
                     )
                 else:
                     # Clear all cache keys
-                    keys = list(redis.scan_iter(f"cache:{target_func.__name__}:*"))
+                    keys = list(
+                        _get_redis().scan_iter(f"cache:{target_func.__name__}:*")
+                    )
 
                 if keys:
-                    pipeline = redis.pipeline()
+                    pipeline = _get_redis().pipeline()
                     for key in keys:
                         pipeline.delete(key)
                     pipeline.execute()
@@ -355,7 +364,9 @@ def cached(
 
         def cache_info() -> dict[str, int | None]:
             if shared_cache:
-                cache_keys = list(redis.scan_iter(f"cache:{target_func.__name__}:*"))
+                cache_keys = list(
+                    _get_redis().scan_iter(f"cache:{target_func.__name__}:*")
+                )
                 return {
                     "size": len(cache_keys),
                     "maxsize": None,  # Redis manages its own size
@@ -373,10 +384,8 @@ def cached(
             key = _make_hashable_key(args, kwargs)
             if shared_cache:
                 redis_key = _make_redis_key(key, target_func.__name__)
-                if redis.exists(redis_key):
-                    redis.delete(redis_key)
-                    return True
-                return False
+                deleted_count = cast(int, _get_redis().delete(redis_key))
+                return deleted_count > 0
             else:
                 if key in cache_storage:
                     del cache_storage[key]