first commit

app/exceptions.py

@@ -0,0 +1,52 @@
+"""Application exception hierarchy.
+
+All custom exceptions inherit from AppError. The global exception handler
+in middleware.py catches these and returns the appropriate JSON envelope.
+"""
+
+
+class AppError(Exception):
+    """Base application error."""
+
+    status_code: int = 500
+    message: str = "Internal server error"
+
+    def __init__(self, message: str | None = None):
+        if message is not None:
+            self.message = message
+        super().__init__(self.message)
+
+
+class ValidationError(AppError):
+    status_code = 400
+    message = "Validation error"
+
+
+class NotFoundError(AppError):
+    status_code = 404
+    message = "Resource not found"
+
+
+class DuplicateError(AppError):
+    status_code = 409
+    message = "Resource already exists"
+
+
+class AuthenticationError(AppError):
+    status_code = 401
+    message = "Authentication required"
+
+
+class AuthorizationError(AppError):
+    status_code = 403
+    message = "Insufficient permissions"
+
+
+class ProviderError(AppError):
+    status_code = 502
+    message = "Market data provider unavailable"
+
+
+class RateLimitError(AppError):
+    status_code = 429
+    message = "Rate limited"