Initial project structure

Scaffold all modules, route stubs, data models, and config.
No logic implemented yet — all core methods raise NotImplementedError.
Establishes the full directory layout matching the architecture in CLAUDE.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fellowship/core/loop.py

@@ -0,0 +1,66 @@
+"""
+Session loop — the core driver for each active session.
+One SessionLoop instance runs per session as an asyncio Task.
+Never dispatches two LLM calls simultaneously.
+Starts immediately for autonomous mode; waits for first talker message otherwise.
+"""
+
+import asyncio
+import logging
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from fellowship.core.session import Session
+
+logger = logging.getLogger(__name__)
+
+
+class SessionLoop:
+    def __init__(self, session: "Session") -> None:
+        self.session = session
+        self._task: asyncio.Task | None = None
+        self._pause_event = asyncio.Event()
+        self._pause_event.set()  # Not paused by default
+
+    def start(self) -> None:
+        """Start the loop as a background asyncio Task."""
+        self._task = asyncio.create_task(self._run(), name=f"loop-{self.session.token[:8]}")
+
+    def stop(self) -> None:
+        """Cancel the loop task."""
+        if self._task:
+            self._task.cancel()
+
+    def pause(self) -> None:
+        """Pause the loop. Clears the internal event so the loop blocks."""
+        self._pause_event.clear()
+
+    def resume(self) -> None:
+        """Resume a paused loop."""
+        self._pause_event.set()
+
+    async def _run(self) -> None:
+        """
+        Main loop body. Runs until the session ends or the task is cancelled.
+        Each iteration:
+          1. Wait if paused.
+          2. Check for pending talker messages (all modes).
+          3. Determine next bot speaker (round_robin or orchestrator).
+          4. Execute bot turn.
+          5. Check end conditions.
+        """
+        raise NotImplementedError
+
+    async def _handle_talker_message(self) -> bool:
+        """
+        Drain one message from the talker queue into history.
+        Returns True if a message was processed.
+        """
+        raise NotImplementedError
+
+    async def _check_end_conditions(self) -> bool:
+        """
+        Check all configured end conditions (max_turns, max_time, max_context_tokens).
+        Returns True if the session should end.
+        """
+        raise NotImplementedError