refactor(db): use shared pooled DatabaseClient singleton instead of per-call instances

- Replace get_db_client() creating new DatabaseClient on every call with a
  module-level singleton initialized once at startup via init_db_client()
- Add init_db_client() and close_db_client() lifecycle functions called
  from FastAPI lifespan handler
- Migrate all DatabaseClient methods from legacy self.connect()/self.conn
  to pooled self.get_conn() context manager for thread-safe connection reuse
- Pool is properly torn down on application shutdown

Closes leeworks-agents/SPARC#7

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SPARC/api.py

@@ -21,11 +21,13 @@ from SPARC.auth import (
     TokenResponse,
     UserResponse,
     check_jwt_secret,
+    close_db_client,
     create_tokens,
     decode_token,
     get_current_admin,
     get_current_user,
     get_db_client,
+    init_db_client,
 )
 from SPARC.types import BatchAnalysisResult, CompanyAnalysisResult
 
@@ -155,6 +157,7 @@ async def lifespan(app: FastAPI):
     """Initialize resources on startup, clean up on shutdown."""
     global _analyzer
     check_jwt_secret()
+    init_db_client()
     _analyzer = CompanyAnalyzer()
     # Mark any jobs that were running/pending before the restart as failed
     from SPARC.database import DatabaseClient
@@ -167,8 +170,9 @@ async def lifespan(app: FastAPI):
         logging.getLogger(__name__).warning("Marked %d stale jobs as failed on startup", stale)
     _db.close()
     yield
-    # Cleanup if needed
+    # Cleanup
     _analyzer = None
+    close_db_client()
 
 
 app = FastAPI(

SPARC/auth.py

@@ -146,11 +146,36 @@ def decode_token(token: str) -> Optional[TokenPayload]:
         return None
 
 
+# Shared database client singleton, initialized at startup via init_db_client()
+_db_client: DatabaseClient | None = None
+
+
+def init_db_client() -> None:
+    """Initialize the shared database client. Call once at app startup."""
+    global _db_client
+    _db_client = DatabaseClient(config.database_url)
+    _db_client.connect()
+
+
+def close_db_client() -> None:
+    """Close the shared database client. Call at app shutdown."""
+    global _db_client
+    if _db_client:
+        _db_client.close()
+        _db_client = None
+
+
 def get_db_client() -> DatabaseClient:
-    """Get database client for auth operations."""
+    """Get the shared pooled database client for auth operations.
-    client = DatabaseClient(config.database_url)
+
-    client.connect()
+    Returns the module-level singleton DatabaseClient. If not yet initialized
-    return client
+    (e.g., during tests), creates a new instance as a fallback.
+    """
+    global _db_client
+    if _db_client is None:
+        _db_client = DatabaseClient(config.database_url)
+        _db_client.connect()
+    return _db_client
 
 
 async def get_current_user(

SPARC/database.py

@@ -221,8 +221,6 @@ class DatabaseClient:
         Returns:
             Cached message dict if found, None otherwise
         """
-        self.connect()
-
         prompt_hash = self.hash_prompt(prompt)
 
         query = """
@@ -245,7 +243,8 @@ class DatabaseClient:
 
         query += " ORDER BY timestamp DESC LIMIT 1"
 
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
                 cursor.execute(query, params)
                 result = cursor.fetchone()
                 return dict(result) if result else None
@@ -276,11 +275,10 @@ class DatabaseClient:
         Returns:
             The ID of the inserted record
         """
-        self.connect()
-
         prompt_hash = self.hash_prompt(prompt)
 
-        with self.conn.cursor() as cursor:
+        with self.get_conn() as conn:
+            with conn.cursor() as cursor:
                 cursor.execute(
                     """
                     INSERT INTO llm_messages
@@ -302,7 +300,7 @@ class DatabaseClient:
                 )
 
                 message_id = cursor.fetchone()[0]
-            self.conn.commit()
+            conn.commit()
 
             return message_id
 
@@ -324,8 +322,6 @@ class DatabaseClient:
         Returns:
             List of message dictionaries
         """
-        self.connect()
-
         query = "SELECT * FROM llm_messages WHERE 1=1"
         params = []
 
@@ -340,7 +336,8 @@ class DatabaseClient:
         query += " ORDER BY timestamp DESC LIMIT %s OFFSET %s"
         params.extend([limit, offset])
 
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
                 cursor.execute(query, params)
                 return [dict(row) for row in cursor.fetchall()]
 
@@ -353,9 +350,8 @@ class DatabaseClient:
         Returns:
             Dictionary with analytics data
         """
-        self.connect()
+        with self.get_conn() as conn:
-
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
                 # Total messages
                 cursor.execute(
                     """
@@ -650,12 +646,11 @@ class DatabaseClient:
         Returns:
             Created user dict or None if email exists
         """
-        self.connect()
-
         password_hash = self.hash_password(password)
 
         try:
-            with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
+            with self.get_conn() as conn:
+                with conn.cursor(cursor_factory=RealDictCursor) as cursor:
                     cursor.execute(
                         """
                         INSERT INTO users (email, password_hash, role)
@@ -665,10 +660,9 @@ class DatabaseClient:
                         (email, password_hash, role),
                     )
                     user = cursor.fetchone()
-                self.conn.commit()
+                conn.commit()
                 return dict(user) if user else None
         except psycopg2.errors.UniqueViolation:
-            self.conn.rollback()
             return None
 
     def authenticate_user(self, email: str, password: str) -> Optional[Dict]:
@@ -681,9 +675,8 @@ class DatabaseClient:
         Returns:
             User dict if authenticated, None otherwise
         """
-        self.connect()
+        with self.get_conn() as conn:
-
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
                 cursor.execute(
                     "SELECT * FROM users WHERE email = %s",
                     (email,),
@@ -708,9 +701,8 @@ class DatabaseClient:
         Returns:
             User dict or None
         """
-        self.connect()
+        with self.get_conn() as conn:
-
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
                 cursor.execute(
                     "SELECT id, email, role, created_at FROM users WHERE id = %s",
                     (user_id,),
@@ -727,9 +719,8 @@ class DatabaseClient:
         Returns:
             User dict or None
         """
-        self.connect()
+        with self.get_conn() as conn:
-
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
                 cursor.execute(
                     "SELECT id, email, role, created_at FROM users WHERE email = %s",
                     (email,),
@@ -747,9 +738,8 @@ class DatabaseClient:
         Returns:
             List of user dicts
         """
-        self.connect()
+        with self.get_conn() as conn:
-
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
                 cursor.execute(
                     """
                     SELECT id, email, role, created_at
@@ -771,9 +761,8 @@ class DatabaseClient:
         Returns:
             Updated user dict or None
         """
-        self.connect()
+        with self.get_conn() as conn:
-
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
                 cursor.execute(
                     """
                     UPDATE users
@@ -784,7 +773,7 @@ class DatabaseClient:
                     (role, user_id),
                 )
                 user = cursor.fetchone()
-            self.conn.commit()
+            conn.commit()
             return dict(user) if user else None
 
     def delete_user(self, user_id: int) -> bool:
@@ -796,12 +785,11 @@ class DatabaseClient:
         Returns:
             True if deleted
         """
-        self.connect()
+        with self.get_conn() as conn:
-
+            with conn.cursor() as cursor:
-        with self.conn.cursor() as cursor:
                 cursor.execute("DELETE FROM users WHERE id = %s", (user_id,))
                 deleted = cursor.rowcount > 0
-            self.conn.commit()
+            conn.commit()
             return deleted
 
     def get_user_count(self) -> int:
@@ -810,8 +798,7 @@ class DatabaseClient:
         Returns:
             Number of users
         """
-        self.connect()
+        with self.get_conn() as conn:
-
+            with conn.cursor() as cursor:
-        with self.conn.cursor() as cursor:
                 cursor.execute("SELECT COUNT(*) FROM users")
                 return cursor.fetchone()[0]