feat: add session persistence to CLI

- Add save-only endpoint (POST /conversations/{id}/save) for persisting
  messages without triggering agent execution
- Add sessions command to list previous conversation sessions
- Add --resume flag to chat command for resuming sessions by ID
- Buffer streamed responses and save after completion
- Update AGENTS.md with session commands and remove outdated limitation
- Add 3 new tests for save endpoint (208 total)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

webber-cli/webber_cli/client.py

@@ -7,7 +7,8 @@ Supports permission modes for controlling agent tool access.
 import json
 import httpx
 from collections.abc import AsyncIterator
-from dataclasses import dataclass
+from dataclasses import dataclass, field
+from datetime import datetime
 from enum import Enum
 from typing import Any
 
@@ -42,6 +43,47 @@ class AgentInfo:
     description: str
 
 
+@dataclass
+class Message:
+    """A message in a conversation."""
+    id: str
+    role: str
+    content: str
+    token_count: int
+    is_summary: bool
+    created_at: datetime
+
+
+@dataclass
+class Conversation:
+    """A conversation session."""
+    id: str
+    agent_type: str
+    title: str | None
+    working_dir: str
+    total_tokens: int
+    created_at: datetime
+    updated_at: datetime | None
+    messages: list[Message] = field(default_factory=list)
+
+
+@dataclass
+class AddMessageResult:
+    """Result of adding a message to a conversation."""
+    user_message: Message
+    assistant_message: Message
+    total_tokens: int
+    summarized: bool
+
+
+@dataclass
+class SaveMessagesResult:
+    """Result of saving a message pair without agent execution."""
+    user_message: Message
+    assistant_message: Message
+    total_tokens: int
+
+
 class WebberClient:
     """
     Client for the Webber API.
@@ -203,6 +245,193 @@ class WebberClient:
                         except json.JSONDecodeError:
                             continue
 
+    # === Conversation API ===
+
+    def _parse_message(self, data: dict) -> Message:
+        """Parse a Message from API response data."""
+        return Message(
+            id=data["id"],
+            role=data["role"],
+            content=data["content"],
+            token_count=data["token_count"],
+            is_summary=data["is_summary"],
+            created_at=datetime.fromisoformat(data["created_at"].replace("Z", "+00:00")),
+        )
+
+    def _parse_conversation(self, data: dict, with_messages: bool = False) -> Conversation:
+        """Parse a Conversation from API response data."""
+        messages = []
+        if with_messages and "messages" in data:
+            messages = [self._parse_message(m) for m in data["messages"]]
+
+        updated_at = None
+        if data.get("updated_at"):
+            updated_at = datetime.fromisoformat(data["updated_at"].replace("Z", "+00:00"))
+
+        return Conversation(
+            id=data["id"],
+            agent_type=data["agent_type"],
+            title=data.get("title"),
+            working_dir=data["working_dir"],
+            total_tokens=data["total_tokens"],
+            created_at=datetime.fromisoformat(data["created_at"].replace("Z", "+00:00")),
+            updated_at=updated_at,
+            messages=messages,
+        )
+
+    async def list_conversations(
+        self,
+        limit: int = 50,
+        offset: int = 0,
+    ) -> tuple[list[Conversation], int]:
+        """
+        List user's conversations.
+
+        Args:
+            limit: Maximum number of conversations to return
+            offset: Offset for pagination
+
+        Returns:
+            Tuple of (conversations, total_count)
+        """
+        client = await self._get_client()
+        response = await client.get(
+            "/conversations/",
+            params={"limit": limit, "offset": offset},
+        )
+        response.raise_for_status()
+        data = response.json()
+        conversations = [self._parse_conversation(c) for c in data["conversations"]]
+        return conversations, data["total"]
+
+    async def get_conversation(self, conversation_id: str) -> Conversation | None:
+        """
+        Get a conversation with all messages.
+
+        Args:
+            conversation_id: UUID of the conversation
+
+        Returns:
+            Conversation with messages, or None if not found
+        """
+        client = await self._get_client()
+        response = await client.get(f"/conversations/{conversation_id}")
+        if response.status_code == 404:
+            return None
+        response.raise_for_status()
+        return self._parse_conversation(response.json(), with_messages=True)
+
+    async def create_conversation(
+        self,
+        agent_type: str = "task",
+        working_dir: str = ".",
+        title: str | None = None,
+    ) -> Conversation:
+        """
+        Create a new conversation.
+
+        Args:
+            agent_type: Type of agent to use
+            working_dir: Working directory for the agent
+            title: Optional title for the conversation
+
+        Returns:
+            The created conversation
+        """
+        client = await self._get_client()
+        response = await client.post(
+            "/conversations/",
+            json={
+                "agent_type": agent_type,
+                "working_dir": working_dir,
+                "title": title,
+            },
+        )
+        response.raise_for_status()
+        return self._parse_conversation(response.json())
+
+    async def add_message(
+        self,
+        conversation_id: str,
+        content: str,
+    ) -> AddMessageResult:
+        """
+        Add a message to a conversation and get agent response.
+
+        Args:
+            conversation_id: UUID of the conversation
+            content: Message content
+
+        Returns:
+            AddMessageResult with user and assistant messages
+        """
+        client = await self._get_client()
+        response = await client.post(
+            f"/conversations/{conversation_id}/messages",
+            json={"content": content},
+        )
+        response.raise_for_status()
+        data = response.json()
+        return AddMessageResult(
+            user_message=self._parse_message(data["user_message"]),
+            assistant_message=self._parse_message(data["assistant_message"]),
+            total_tokens=data["total_tokens"],
+            summarized=data.get("summarized", False),
+        )
+
+    async def save_messages(
+        self,
+        conversation_id: str,
+        user_content: str,
+        assistant_content: str,
+    ) -> SaveMessagesResult:
+        """
+        Save a user/assistant message pair without triggering agent execution.
+
+        Used when streaming responses separately via run_agent_stream().
+        Allows persisting the exchange after streaming completes.
+
+        Args:
+            conversation_id: UUID of the conversation
+            user_content: User message content
+            assistant_content: Assistant response content
+
+        Returns:
+            SaveMessagesResult with both messages
+        """
+        client = await self._get_client()
+        response = await client.post(
+            f"/conversations/{conversation_id}/save",
+            json={
+                "user_content": user_content,
+                "assistant_content": assistant_content,
+            },
+        )
+        response.raise_for_status()
+        data = response.json()
+        return SaveMessagesResult(
+            user_message=self._parse_message(data["user_message"]),
+            assistant_message=self._parse_message(data["assistant_message"]),
+            total_tokens=data["total_tokens"],
+        )
+
+    async def delete_conversation(self, conversation_id: str) -> bool:
+        """
+        Delete a conversation.
+
+        Args:
+            conversation_id: UUID of the conversation
+
+        Returns:
+            True if deleted, False if not found
+        """
+        client = await self._get_client()
+        response = await client.delete(f"/conversations/{conversation_id}")
+        if response.status_code == 404:
+            return False
+        response.raise_for_status()
+        return True
+
     async def __aenter__(self) -> "WebberClient":
         """Async context manager entry."""
         return self