feat: Add light/dark mode support with backend persistence

backend/alembic/versions/2473a00afb70_add_theme_preference_to_user.py

@@ -0,0 +1,28 @@
+"""Add theme preference to user
+
+Revision ID: 2473a00afb70
+Revises: 63886baa1255
+Create Date: 2026-02-16 17:00:25.537643
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '2473a00afb70'
+down_revision: Union[str, Sequence[str], None] = '63886baa1255'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    op.add_column('users', sa.Column('theme_preference', sa.String(), nullable=False, server_default='light'))
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    op.drop_column('users', 'theme_preference')

backend/src/ea_chatbot/api/routers/agent.py

@@ -91,7 +91,7 @@ async def stream_agent_events(
                         encoded_plots: list[str] = []
                         for fig in plots:
                             buf = io.BytesIO()
-                            fig.savefig(buf, format="png")
+                            fig.savefig(buf, format="png", transparent=True)
                             plot_bytes = buf.getvalue()
                             assistant_plots.append(plot_bytes)
                             encoded_plots.append(base64.b64encode(plot_bytes).decode('utf-8'))

backend/src/ea_chatbot/api/routers/auth.py

@@ -4,7 +4,7 @@ from fastapi.security import OAuth2PasswordRequestForm
 from ea_chatbot.api.utils import create_access_token, settings
 from ea_chatbot.api.dependencies import history_manager, oidc_client, get_current_user
 from ea_chatbot.history.models import User as UserDB
-from ea_chatbot.api.schemas import Token, UserCreate, UserResponse
+from ea_chatbot.api.schemas import Token, UserCreate, UserResponse, ThemeUpdate
 from ea_chatbot.auth import OIDCSession
 import logging
 
@@ -45,7 +45,8 @@ async def register(user_in: UserCreate, response: Response):
     return {
         "id": str(user.id),
         "email": user.username,
-        "display_name": user.display_name
+        "display_name": user.display_name,
+        "theme_preference": user.theme_preference
     }
 
 @router.post("/login", response_model=Token)
@@ -155,5 +156,25 @@ async def get_me(current_user: UserDB = Depends(get_current_user)):
     return {
         "id": str(current_user.id),
         "email": current_user.username,
-        "display_name": current_user.display_name
+        "display_name": current_user.display_name,
+        "theme_preference": current_user.theme_preference
+    }
+
+@router.patch("/theme", response_model=UserResponse)
+async def update_theme(
+    theme_in: ThemeUpdate, 
+    current_user: UserDB = Depends(get_current_user)
+):
+    """Update the current user's theme preference."""
+    user = history_manager.update_user_theme(current_user.id, theme_in.theme)
+    if not user:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="User not found"
+        )
+    return {
+        "id": str(user.id),
+        "email": user.username,
+        "display_name": user.display_name,
+        "theme_preference": user.theme_preference
     }

backend/src/ea_chatbot/api/schemas.py

@@ -17,6 +17,10 @@ class UserResponse(BaseModel):
     id: str
     email: str
     display_name: str
+    theme_preference: str
+
+class ThemeUpdate(BaseModel):
+    theme: str
 
 # --- History Schemas ---
 

backend/src/ea_chatbot/app.py

@@ -420,7 +420,7 @@ def main():
                     st.pyplot(fig)
                     # Convert fig to bytes
                     buf = io.BytesIO()
-                    fig.savefig(buf, format="png")
+                    fig.savefig(buf, format="png", transparent=True)
                     plot_bytes_list.append(buf.getvalue())
             
             if final_state.get("dfs"):

backend/src/ea_chatbot/history/manager.py

@@ -70,6 +70,16 @@ class HistoryManager:
         except VerifyMismatchError:
             return None
 
+    def update_user_theme(self, user_id: str, theme: str) -> Optional[User]:
+        """Update the user's theme preference."""
+        with self.get_session() as session:
+            user = session.get(User, user_id)
+            if user:
+                user.theme_preference = theme
+                session.commit()
+                session.refresh(user)
+            return user
+
     def sync_user_from_oidc(self, email: str, display_name: Optional[str] = None) -> User:
         """
         Synchronize a user from an OIDC provider. 

backend/src/ea_chatbot/history/models.py

@@ -14,6 +14,7 @@ class User(Base):
     username: Mapped[str] = mapped_column(String, unique=True, index=True)
     password_hash: Mapped[Optional[str]] = mapped_column(String, nullable=True)
     display_name: Mapped[Optional[str]] = mapped_column(String, nullable=True)
+    theme_preference: Mapped[str] = mapped_column(String, default="light")
     
     conversations: Mapped[List["Conversation"]] = relationship(back_populates="user", cascade="all, delete-orphan")
 

backend/tests/api/test_api_auth.py

@@ -15,7 +15,8 @@ def mock_user():
         id="user-123",
         username="test@example.com",
         display_name="Test User",
-        password_hash="hashed_password"
+        password_hash="hashed_password",
+        theme_preference="light"
     )
 
 def test_register_user_success():
@@ -23,7 +24,7 @@ def test_register_user_success():
     # We mock it where it is used in the router
     with patch("ea_chatbot.api.routers.auth.history_manager") as mock_hm:
         mock_hm.get_user.return_value = None
-        mock_hm.create_user.return_value = User(id="1", username="new@example.com", display_name="New")
+        mock_hm.create_user.return_value = User(id="1", username="new@example.com", display_name="New", theme_preference="light")
         
         response = client.post(
             "/api/v1/auth/register",
@@ -93,7 +94,7 @@ def test_oidc_callback_success():
         }
         mock_oidc.exchange_code_for_token.return_value = {"id_token": "fake_id_token"}
         mock_oidc.validate_id_token.return_value = {"email": "sso@example.com", "name": "SSO User"}
-        mock_hm.sync_user_from_oidc.return_value = User(id="sso-123", username="sso@example.com", display_name="SSO User")
+        mock_hm.sync_user_from_oidc.return_value = User(id="sso-123", username="sso@example.com", display_name="SSO User", theme_preference="light")
         
         client.cookies.set("oidc_session", "fake_token")
         response = client.get(
@@ -110,7 +111,7 @@ def test_get_me_success():
     token = create_access_token(data={"sub": "123"})
     
     with patch("ea_chatbot.api.dependencies.history_manager") as mock_hm:
-        mock_hm.get_user_by_id.return_value = User(id="123", username="test@example.com", display_name="Test")
+        mock_hm.get_user_by_id.return_value = User(id="123", username="test@example.com", display_name="Test", theme_preference="light")
         
         response = client.get(
             "/api/v1/auth/me",

backend/tests/api/test_theme.py

@@ -0,0 +1,73 @@
+import pytest
+from fastapi.testclient import TestClient
+from unittest.mock import patch
+from ea_chatbot.api.main import app
+from ea_chatbot.history.models import User
+from ea_chatbot.api.utils import create_access_token
+
+client = TestClient(app)
+
+@pytest.fixture
+def test_user():
+    return User(
+        id="user-123",
+        username="test@example.com",
+        display_name="Test User",
+        theme_preference="light"
+    )
+
+@pytest.fixture
+def auth_token():
+    return create_access_token(data={"sub": "user-123"})
+
+def test_get_me_includes_theme(test_user, auth_token):
+    """Test that /auth/me returns the theme_preference."""
+    with patch("ea_chatbot.api.dependencies.history_manager") as mock_hm:
+        mock_hm.get_user_by_id.return_value = test_user
+        
+        response = client.get(
+            "/api/v1/auth/me",
+            cookies={"access_token": auth_token}
+        )
+        
+        assert response.status_code == 200
+        data = response.json()
+        assert "theme_preference" in data
+        assert data["theme_preference"] == "light"
+
+def test_update_theme_success(test_user, auth_token):
+    """Test successful theme update via PATCH /auth/theme."""
+    updated_user = User(
+        id="user-123",
+        username="test@example.com",
+        display_name="Test User",
+        theme_preference="dark"
+    )
+    
+    with patch("ea_chatbot.api.dependencies.history_manager") as mock_hm_dep, \
+         patch("ea_chatbot.api.routers.auth.history_manager") as mock_hm_router:
+        
+        # Dependency injection uses the one from dependencies
+        mock_hm_dep.get_user_by_id.return_value = test_user
+        
+        # The router uses its own reference to history_manager
+        mock_hm_router.update_user_theme.return_value = updated_user
+        
+        response = client.patch(
+            "/api/v1/auth/theme",
+            json={"theme": "dark"},
+            cookies={"access_token": auth_token}
+        )
+        
+        assert response.status_code == 200
+        data = response.json()
+        assert data["theme_preference"] == "dark"
+        mock_hm_router.update_user_theme.assert_called_once_with("user-123", "dark")
+
+def test_update_theme_unauthorized():
+    """Test that theme update requires authentication."""
+    response = client.patch(
+        "/api/v1/auth/theme",
+        json={"theme": "dark"}
+    )
+    assert response.status_code == 401