Initial commit: AI Dungeon clone (FastAPI backend + React frontend)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KFsGHju9szibJJa2YJcdbg

backend/app/providers/base.py

@@ -0,0 +1,27 @@
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from typing import AsyncIterator
+
+
+@dataclass
+class PromptParts:
+    """Assembled context, provider-agnostic. Providers map this to their wire format."""
+
+    system: str  # narrator prompt + AI instructions + memory
+    story: str  # the story text so far (already token-budgeted)
+
+
+class ProviderError(Exception):
+    """User-presentable provider failure (connection refused, bad key, model not found…)."""
+
+
+class Provider(ABC):
+    @abstractmethod
+    def generate(
+        self,
+        parts: PromptParts,
+        *,
+        temperature: float,
+        max_tokens: int,
+    ) -> AsyncIterator[tuple[str, str]]:
+        """Yield ("text" | "reasoning", chunk) pairs. Raises ProviderError on failure."""