refactor: simplify message rendering

docs/architecture.md

@@ -10,7 +10,7 @@ src/agent_chat_cli/
 ├── core/
 │   ├── actions.py             # User action handlers
 │   ├── agent_loop.py          # Claude Agent SDK client wrapper
-│   ├── message_bus.py         # Message routing from agent to UI
+│   ├── renderer.py              # Message routing from agent to UI
 │   ├── ui_state.py            # Centralized UI state management
 │   └── styles.tcss            # Textual CSS styles
 ├── components/
@@ -43,7 +43,7 @@ The application follows a loosely coupled architecture with four main orchestrat
 ┌─────────────────────────────────────────────────────────────┐
 │                     AgentChatCLIApp                         │
 │  ┌───────────┐  ┌───────────┐  ┌─────────┐  ┌───────────┐  │
-│  │  UIState  │  │MessageBus │  │ Actions │  │ AgentLoop │  │
+│  │  UIState  │  │  Renderer   │  │ Actions │  │ AgentLoop │  │
 │  └─────┬─────┘  └─────┬─────┘  └────┬────┘  └─────┬─────┘  │
 │        │              │             │              │        │
 │        └──────────────┴─────────────┴──────────────┘        │
@@ -63,9 +63,9 @@ Centralized management of UI state behaviors. Handles:
 - Tool permission prompt display/hide
 - Interrupt state tracking
 
-This class was introduced in PR #9 to consolidate scattered UI state logic from Actions and MessageBus into a single cohesive module.
+This class was introduced in PR #9 to consolidate scattered UI state logic from Actions and Renderer into a single cohesive module.
 
-**MessageBus** (`core/message_bus.py`)
+**Renderer** (`core/renderer.py`)
 Routes messages from the AgentLoop to appropriate UI components:
 - `STREAM_EVENT`: Streaming text chunks to AgentMessage widgets
 - `ASSISTANT`: Complete assistant responses with tool use blocks
@@ -92,7 +92,7 @@ Manages the Claude Agent SDK client lifecycle:
 1. User types in `UserInput` and presses Enter
 2. `Actions.submit_user_message()` posts to UI and enqueues to `AgentLoop.query_queue`
 3. `AgentLoop` sends query to Claude Agent SDK and streams responses
-4. Responses flow through `MessageBus.handle_agent_message()` to update UI
+4. Responses flow through `Actions.render_message()` to update UI
 5. Tool use triggers permission prompt via `UIState.show_permission_prompt()`
 6. User response flows back through `Actions.respond_to_tool_permission()`
 
@@ -118,7 +118,7 @@ Modal prompt for tool permission requests:
 - Manages focus to prevent input elsewhere while visible
 
 **ChatHistory** (`components/chat_history.py`)
-Container for message widgets, handles `MessagePosted` events.
+Container for message widgets.
 
 **ThinkingIndicator** (`components/thinking_indicator.py`)
 Animated indicator shown during agent processing.

src/agent_chat_cli/app.py

@@ -5,12 +5,12 @@
 from textual.binding import Binding
 
 from agent_chat_cli.components.header import Header
-from agent_chat_cli.components.chat_history import ChatHistory, MessagePosted
+from agent_chat_cli.components.chat_history import ChatHistory
 from agent_chat_cli.components.thinking_indicator import ThinkingIndicator
 from agent_chat_cli.components.tool_permission_prompt import ToolPermissionPrompt
 from agent_chat_cli.components.user_input import UserInput
 from agent_chat_cli.core.agent_loop import AgentLoop
-from agent_chat_cli.core.message_bus import MessageBus
+from agent_chat_cli.core.renderer import Renderer
 from agent_chat_cli.core.actions import Actions
 from agent_chat_cli.core.ui_state import UIState
 from agent_chat_cli.utils.logger import setup_logging
@@ -34,7 +34,7 @@ def __init__(self) -> None:
         super().__init__()
 
         self.ui_state = UIState(app=self)
-        self.message_bus = MessageBus(app=self)
+        self.renderer = Renderer(app=self)
         self.actions = Actions(app=self)
         self.agent_loop = AgentLoop(app=self)
 
@@ -49,9 +49,6 @@ def compose(self) -> ComposeResult:
     async def on_mount(self) -> None:
         asyncio.create_task(self.agent_loop.start())
 
-    async def on_message_posted(self, event: MessagePosted) -> None:
-        await self.message_bus.on_message_posted(event)
-
     async def action_interrupt(self) -> None:
         await self.actions.interrupt()
 

src/agent_chat_cli/components/chat_history.py

@@ -1,6 +1,5 @@
 import json
 from textual.containers import Container
-from textual.message import Message as TextualMessage
 
 from agent_chat_cli.components.messages import (
     AgentMessage,
@@ -48,9 +47,3 @@ def _create_message_widget(
                     tool_widget.tool_input = {"raw": message.content}
 
                 return tool_widget
-
-
-class MessagePosted(TextualMessage):
-    def __init__(self, message: Message) -> None:
-        self.message = message
-        super().__init__()

src/agent_chat_cli/core/actions.py

@@ -1,8 +1,8 @@
 from typing import TYPE_CHECKING
 
 from agent_chat_cli.utils.enums import ControlCommand
-from agent_chat_cli.components.chat_history import ChatHistory, MessagePosted
-from agent_chat_cli.components.messages import Message
+from agent_chat_cli.components.chat_history import ChatHistory
+from agent_chat_cli.components.messages import Message, MessageType
 from agent_chat_cli.components.tool_permission_prompt import ToolPermissionPrompt
 from agent_chat_cli.utils.logger import log_json
 
@@ -17,16 +17,32 @@ def __init__(self, app: "AgentChatCLIApp") -> None:
     def quit(self) -> None:
         self.app.exit()
 
+    async def add_message_to_chat(self, type: MessageType, content: str) -> None:
+        match type:
+            case MessageType.USER:
+                message = Message.user(content)
+            case MessageType.SYSTEM:
+                message = Message.system(content)
+            case MessageType.AGENT:
+                message = Message.agent(content)
+            case _:
+                raise ValueError(f"Unsupported message type: {type}")
+
+        chat_history = self.app.query_one(ChatHistory)
+        chat_history.add_message(message)
+
     async def submit_user_message(self, message: str) -> None:
-        self.app.post_message(MessagePosted(Message.user(message)))
+        chat_history = self.app.query_one(ChatHistory)
+        chat_history.add_message(Message.user(message))
         self.app.ui_state.start_thinking()
+        await self.app.ui_state.scroll_to_bottom()
         await self._query(message)
 
-    def post_system_message(self, message: str) -> None:
-        self.app.post_message(MessagePosted(Message.system(message)))
+    async def post_system_message(self, message: str) -> None:
+        await self.add_message_to_chat(MessageType.SYSTEM, message)
 
-    async def handle_agent_message(self, message) -> None:
-        await self.app.message_bus.handle_agent_message(message)
+    async def render_message(self, message) -> None:
+        await self.app.renderer.render_message(message)
 
     async def interrupt(self) -> None:
         permission_prompt = self.app.query_one(ToolPermissionPrompt)

src/agent_chat_cli/core/agent_loop.py

@@ -92,7 +92,7 @@ async def start(self) -> None:
 
                 await self._handle_message(message)
 
-            await self.app.actions.handle_agent_message(
+            await self.app.actions.render_message(
                 AgentMessage(type=AgentMessageType.RESULT, data=None)
             )
 
@@ -135,7 +135,7 @@ async def _handle_message(self, message: Message) -> None:
                     text_chunk = delta.get("text", "")
 
                     if text_chunk:
-                        await self.app.actions.handle_agent_message(
+                        await self.app.actions.render_message(
                             AgentMessage(
                                 type=AgentMessageType.STREAM_EVENT,
                                 data={"text": text_chunk},
@@ -163,7 +163,7 @@ async def _handle_message(self, message: Message) -> None:
                         )
 
             # Finally, post the agent assistant response
-            await self.app.actions.handle_agent_message(
+            await self.app.actions.render_message(
                 AgentMessage(
                     type=AgentMessageType.ASSISTANT,
                     data={"content": content},
@@ -180,7 +180,7 @@ async def _can_use_tool(
 
         # Handle permission request queue sequentially
         async with self.permission_lock:
-            await self.app.actions.handle_agent_message(
+            await self.app.actions.render_message(
                 AgentMessage(
                     type=AgentMessageType.TOOL_PERMISSION_REQUEST,
                     data={
@@ -213,7 +213,7 @@ async def _can_use_tool(
                 )
 
             if rejected_tool:
-                self.app.actions.post_system_message(
+                await self.app.actions.post_system_message(
                     f"Permission denied for {tool_name}"
                 )