feat: persistent chat history with clear button

- Add dashboard/store.py: MessageLog dataclass singleton tracking
  user/agent/error messages for the lifetime of the server process
- agents.py: write each chat turn to MessageLog; add GET and DELETE
  /agents/timmy/history routes returning the history.html partial
- partials/history.html: render stored messages by role (YOU / TIMMY /
  SYSTEM); falls back to the Mission Control init message when empty
- index.html: chat-log loads history via hx-get on page start; new
  CLEAR button in panel header sends hx-delete to reset the log
- style.css: add .mc-btn-clear (muted, red-on-hover for the header)
- tests: autouse reset_message_log fixture in conftest; 5 new history
  tests covering empty state, recording, offline errors, clear, and
  post-clear state → 32 tests total, all passing

https://claude.ai/code/session_01KZMfwBpLuiv6x9GbzTqbys

src/dashboard/routes/agents.py

@@ -6,6 +6,7 @@ from fastapi.responses import HTMLResponse
 from fastapi.templating import Jinja2Templates
 
 from timmy.agent import create_timmy
+from dashboard.store import message_log
 
 router = APIRouter(prefix="/agents", tags=["agents"])
 templates = Jinja2Templates(directory=str(Path(__file__).parent.parent / "templates"))
@@ -27,6 +28,25 @@ async def list_agents():
     return {"agents": list(AGENT_REGISTRY.values())}
 
 
+@router.get("/timmy/history", response_class=HTMLResponse)
+async def get_history(request: Request):
+    return templates.TemplateResponse(
+        request,
+        "partials/history.html",
+        {"messages": message_log.all()},
+    )
+
+
+@router.delete("/timmy/history", response_class=HTMLResponse)
+async def clear_history(request: Request):
+    message_log.clear()
+    return templates.TemplateResponse(
+        request,
+        "partials/history.html",
+        {"messages": []},
+    )
+
+
 @router.post("/timmy/chat", response_class=HTMLResponse)
 async def chat_timmy(request: Request, message: str = Form(...)):
     timestamp = datetime.now().strftime("%H:%M:%S")
@@ -40,6 +60,12 @@ async def chat_timmy(request: Request, message: str = Form(...)):
     except Exception as exc:
         error_text = f"Timmy is offline: {exc}"
 
+    message_log.append(role="user", content=message, timestamp=timestamp)
+    if response_text is not None:
+        message_log.append(role="agent", content=response_text, timestamp=timestamp)
+    else:
+        message_log.append(role="error", content=error_text, timestamp=timestamp)
+
     return templates.TemplateResponse(
         request,
         "partials/chat_message.html",

src/dashboard/store.py

@@ -0,0 +1,31 @@
+from dataclasses import dataclass, field
+
+
+@dataclass
+class Message:
+    role: str       # "user" | "agent" | "error"
+    content: str
+    timestamp: str
+
+
+class MessageLog:
+    """In-memory chat history for the lifetime of the server process."""
+
+    def __init__(self) -> None:
+        self._entries: list[Message] = []
+
+    def append(self, role: str, content: str, timestamp: str) -> None:
+        self._entries.append(Message(role=role, content=content, timestamp=timestamp))
+
+    def all(self) -> list[Message]:
+        return list(self._entries)
+
+    def clear(self) -> None:
+        self._entries.clear()
+
+    def __len__(self) -> int:
+        return len(self._entries)
+
+
+# Module-level singleton shared across the app
+message_log = MessageLog()

src/dashboard/templates/index.html

@@ -46,15 +46,20 @@
     <!-- Chat Panel -->
     <div class="col-12 col-md-9 d-flex flex-column mc-chat-panel">
       <div class="card mc-panel flex-grow-1 d-flex flex-column min-h-0">
-        <div class="card-header mc-panel-header">// TIMMY INTERFACE</div>
-
-        <div class="chat-log flex-grow-1 overflow-auto p-3" id="chat-log">
-          <div class="chat-message agent">
-            <div class="msg-meta">TIMMY // SYSTEM</div>
-            <div class="msg-body">Mission Control initialized. Timmy ready — awaiting input.</div>
-          </div>
+        <div class="card-header mc-panel-header d-flex justify-content-between align-items-center">
+          <span>// TIMMY INTERFACE</span>
+          <button class="mc-btn-clear"
+                  hx-delete="/agents/timmy/history"
+                  hx-target="#chat-log"
+                  hx-swap="innerHTML"
+                  hx-confirm="Clear conversation history?">CLEAR</button>
         </div>
 
+        <div class="chat-log flex-grow-1 overflow-auto p-3" id="chat-log"
+             hx-get="/agents/timmy/history"
+             hx-trigger="load"
+             hx-swap="innerHTML"></div>
+
         <div class="card-footer mc-chat-footer">
           <form hx-post="/agents/timmy/chat"
                 hx-target="#chat-log"

src/dashboard/templates/partials/history.html

@@ -0,0 +1,25 @@
+{% if messages %}
+  {% for msg in messages %}
+    {% if msg.role == "user" %}
+    <div class="chat-message user">
+      <div class="msg-meta">YOU // {{ msg.timestamp }}</div>
+      <div class="msg-body">{{ msg.content }}</div>
+    </div>
+    {% elif msg.role == "agent" %}
+    <div class="chat-message agent">
+      <div class="msg-meta">TIMMY // {{ msg.timestamp }}</div>
+      <div class="msg-body">{{ msg.content }}</div>
+    </div>
+    {% else %}
+    <div class="chat-message error-msg">
+      <div class="msg-meta">SYSTEM // {{ msg.timestamp }}</div>
+      <div class="msg-body">{{ msg.content }}</div>
+    </div>
+    {% endif %}
+  {% endfor %}
+{% else %}
+<div class="chat-message agent">
+  <div class="msg-meta">TIMMY // SYSTEM</div>
+  <div class="msg-body">Mission Control initialized. Timmy ready — awaiting input.</div>
+</div>
+{% endif %}