feat: add reminder service for todos

Adds a background reminder loop that checks every 5 minutes for overdue
todos and sends Telegram notifications.

Changes:
- Add last_reminded_at column to todos table with auto-migration
- Add listTodosDueForReminder to find overdue, unreminded todos
- Add markReminderSent to update reminder timestamp
- Add user_chats table to map user_id -> chat_id for notifications
- Add recordUserChat called on each message to track chat IDs
- Add reminderLoop forked in runTelegramBot
- 24-hour anti-spam interval between reminders per todo

2 files changed, 133 insertions, 9 deletions

diff --git a/Omni/Agent/Telegram.hs b/Omni/Agent/Telegram.hs
index f1c71e6..27b3ccf 100644
--- a/Omni/Agent/Telegram.hs
+++ b/Omni/Agent/Telegram.hs
@@ -43,6 +43,12 @@ module Omni.Agent.Telegram
     checkOllama,
     pullEmbeddingModel,
 
+    -- * Reminders
+    reminderLoop,
+    checkAndSendReminders,
+    recordUserChat,
+    lookupChatId,
+
     -- * System Prompt
     telegramSystemPrompt,
 
@@ -62,6 +68,7 @@ import qualified Data.Text as Text
 import Data.Time (getCurrentTime, utcToLocalTime)
 import Data.Time.Format (defaultTimeLocale, formatTime)
 import Data.Time.LocalTime (getCurrentTimeZone)
+import qualified Database.SQLite.Simple as SQL
 import qualified Network.HTTP.Client as HTTPClient
 import qualified Network.HTTP.Simple as HTTP
 import qualified Omni.Agent.Engine as Engine
@@ -578,12 +585,78 @@ telegramSystemPrompt =
       "ALWAYS include a text response to the user after using tools. never end your turn with only tool calls."
     ]
 
+initUserChatsTable :: SQL.Connection -> IO ()
+initUserChatsTable conn =
+  SQL.execute_
+    conn
+    "CREATE TABLE IF NOT EXISTS user_chats (\
+    \  user_id TEXT PRIMARY KEY,\
+    \  chat_id INTEGER NOT NULL,\
+    \  last_seen_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP\
+    \)"
+
+recordUserChat :: Text -> Int -> IO ()
+recordUserChat uid chatId = do
+  now <- getCurrentTime
+  Memory.withMemoryDb <| \conn -> do
+    initUserChatsTable conn
+    SQL.execute
+      conn
+      "INSERT INTO user_chats (user_id, chat_id, last_seen_at) \
+      \VALUES (?, ?, ?) \
+      \ON CONFLICT(user_id) DO UPDATE SET \
+      \  chat_id = excluded.chat_id, \
+      \  last_seen_at = excluded.last_seen_at"
+      (uid, chatId, now)
+
+lookupChatId :: Text -> IO (Maybe Int)
+lookupChatId uid =
+  Memory.withMemoryDb <| \conn -> do
+    initUserChatsTable conn
+    rows <-
+      SQL.query
+        conn
+        "SELECT chat_id FROM user_chats WHERE user_id = ?"
+        (SQL.Only uid)
+    pure (listToMaybe (map SQL.fromOnly rows))
+
+reminderLoop :: TelegramConfig -> IO ()
+reminderLoop tgConfig =
+  forever <| do
+    threadDelay (5 * 60 * 1000000)
+    checkAndSendReminders tgConfig
+
+checkAndSendReminders :: TelegramConfig -> IO ()
+checkAndSendReminders tgConfig = do
+  todos <- Todos.listTodosDueForReminder
+  forM_ todos <| \td -> do
+    mChatId <- lookupChatId (Todos.todoUserId td)
+    case mChatId of
+      Nothing -> pure ()
+      Just chatId -> do
+        let title = Todos.todoTitle td
+            dueStr = case Todos.todoDueDate td of
+              Just d -> " (due: " <> tshow d <> ")"
+              Nothing -> ""
+            msg =
+              "⏰ reminder: \""
+                <> title
+                <> "\""
+                <> dueStr
+                <> "\nreply when you finish and i'll mark it complete."
+        sendMessage tgConfig chatId msg
+        Todos.markReminderSent (Todos.todoId td)
+        putText <| "Sent reminder for todo " <> tshow (Todos.todoId td) <> " to chat " <> tshow chatId
+
 -- | Run the Telegram bot main loop.
 runTelegramBot :: TelegramConfig -> Provider.Provider -> IO ()
 runTelegramBot tgConfig provider = do
   putText "Starting Telegram bot..."
   offsetVar <- newTVarIO 0
 
+  _ <- forkIO (reminderLoop tgConfig)
+  putText "Reminder loop started (checking every 5 minutes)"
+
   let engineCfg =
         Engine.defaultEngineConfig
           { Engine.engineOnToolCall = \toolName args ->
@@ -639,6 +712,8 @@ handleAuthorizedMessage ::
   Int ->
   IO ()
 handleAuthorizedMessage tgConfig provider engineCfg msg uid userName chatId = do
+  recordUserChat uid chatId
+
   pdfContent <- case tmDocument msg of
     Just doc | isPdf doc -> do
       putText <| "Processing PDF: " <> fromMaybe "(unnamed)" (tdFileName doc)
diff --git a/Omni/Agent/Tools/Todos.hs b/Omni/Agent/Tools/Todos.hs
index 81253c1..4c7d2be 100644
--- a/Omni/Agent/Tools/Todos.hs
+++ b/Omni/Agent/Tools/Todos.hs
@@ -27,6 +27,11 @@ module Omni.Agent.Tools.Todos
     completeTodo,
     deleteTodo,
 
+    -- * Reminders
+    listTodosDueForReminder,
+    markReminderSent,
+    reminderInterval,
+
     -- * Database
     initTodosTable,
 
@@ -40,7 +45,7 @@ import Alpha
 import Data.Aeson ((.!=), (.:), (.:?), (.=))
 import qualified Data.Aeson as Aeson
 import qualified Data.Text as Text
-import Data.Time (UTCTime, getCurrentTime)
+import Data.Time (NominalDiffTime, UTCTime, addUTCTime, getCurrentTime)
 import Data.Time.Format (defaultTimeLocale, parseTimeM)
 import qualified Database.SQLite.Simple as SQL
 import qualified Omni.Agent.Engine as Engine
@@ -75,7 +80,8 @@ test =
                   todoTitle = "Buy milk",
                   todoDueDate = Just now,
                   todoCompleted = False,
-                  todoCreatedAt = now
+                  todoCreatedAt = now,
+                  todoLastRemindedAt = Nothing
                 }
         case Aeson.decode (Aeson.encode td) of
           Nothing -> Test.assertFailure "Failed to decode Todo"
@@ -93,7 +99,8 @@ data Todo = Todo
     todoTitle :: Text,
     todoDueDate :: Maybe UTCTime,
     todoCompleted :: Bool,
-    todoCreatedAt :: UTCTime
+    todoCreatedAt :: UTCTime,
+    todoLastRemindedAt :: Maybe UTCTime
   }
   deriving (Show, Eq, Generic)
 
@@ -105,7 +112,8 @@ instance Aeson.ToJSON Todo where
         "title" .= todoTitle td,
         "due_date" .= todoDueDate td,
         "completed" .= todoCompleted td,
-        "created_at" .= todoCreatedAt td
+        "created_at" .= todoCreatedAt td,
+        "last_reminded_at" .= todoLastRemindedAt td
       ]
 
 instance Aeson.FromJSON Todo where
@@ -117,6 +125,7 @@ instance Aeson.FromJSON Todo where
         <*> (v .:? "due_date")
         <*> (v .: "completed")
         <*> (v .: "created_at")
+        <*> (v .:? "last_reminded_at")
 
 instance SQL.FromRow Todo where
   fromRow =
@@ -126,6 +135,7 @@ instance SQL.FromRow Todo where
       <*> SQL.field
       <*> SQL.field
       <*> SQL.field
+      <*> SQL.field
 
 initTodosTable :: SQL.Connection -> IO ()
 initTodosTable conn = do
@@ -137,7 +147,8 @@ initTodosTable conn = do
     \  title TEXT NOT NULL,\
     \  due_date TIMESTAMP,\
     \  completed INTEGER NOT NULL DEFAULT 0,\
-    \  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP\
+    \  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,\
+    \  last_reminded_at TIMESTAMP\
     \)"
   SQL.execute_
     conn
@@ -145,6 +156,14 @@ initTodosTable conn = do
   SQL.execute_
     conn
     "CREATE INDEX IF NOT EXISTS idx_todos_due ON todos(user_id, due_date)"
+  migrateTodosTable conn
+
+migrateTodosTable :: SQL.Connection -> IO ()
+migrateTodosTable conn = do
+  cols <- SQL.query_ conn "PRAGMA table_info(todos)" :: IO [(Int, Text, Text, Int, Maybe Text, Int)]
+  let colNames = map (\(_, name, _, _, _, _) -> name) cols
+  unless ("last_reminded_at" `elem` colNames) <| do
+    SQL.execute_ conn "ALTER TABLE todos ADD COLUMN last_reminded_at TIMESTAMP"
 
 parseDueDate :: Text -> Maybe UTCTime
 parseDueDate txt =
@@ -172,7 +191,8 @@ createTodo uid title maybeDueDateStr = do
           todoTitle = title,
           todoDueDate = dueDate,
           todoCompleted = False,
-          todoCreatedAt = now
+          todoCreatedAt = now,
+          todoLastRemindedAt = Nothing
         }
 
 listTodos :: Text -> Int -> IO [Todo]
@@ -181,7 +201,7 @@ listTodos uid limit =
     initTodosTable conn
     SQL.query
       conn
-      "SELECT id, user_id, title, due_date, completed, created_at \
+      "SELECT id, user_id, title, due_date, completed, created_at, last_reminded_at \
       \FROM todos WHERE user_id = ? \
       \ORDER BY completed ASC, due_date ASC NULLS LAST, created_at DESC LIMIT ?"
       (uid, limit)
@@ -192,7 +212,7 @@ listPendingTodos uid limit =
     initTodosTable conn
     SQL.query
       conn
-      "SELECT id, user_id, title, due_date, completed, created_at \
+      "SELECT id, user_id, title, due_date, completed, created_at, last_reminded_at \
       \FROM todos WHERE user_id = ? AND completed = 0 \
       \ORDER BY due_date ASC NULLS LAST, created_at DESC LIMIT ?"
       (uid, limit)
@@ -204,11 +224,40 @@ listOverdueTodos uid = do
     initTodosTable conn
     SQL.query
       conn
-      "SELECT id, user_id, title, due_date, completed, created_at \
+      "SELECT id, user_id, title, due_date, completed, created_at, last_reminded_at \
       \FROM todos WHERE user_id = ? AND completed = 0 AND due_date < ? \
       \ORDER BY due_date ASC"
       (uid, now)
 
+reminderInterval :: NominalDiffTime
+reminderInterval = 24 * 60 * 60
+
+listTodosDueForReminder :: IO [Todo]
+listTodosDueForReminder = do
+  now <- getCurrentTime
+  let cutoff = addUTCTime (negate reminderInterval) now
+  Memory.withMemoryDb <| \conn -> do
+    initTodosTable conn
+    SQL.query
+      conn
+      "SELECT id, user_id, title, due_date, completed, created_at, last_reminded_at \
+      \FROM todos \
+      \WHERE completed = 0 \
+      \  AND due_date IS NOT NULL \
+      \  AND due_date < ? \
+      \  AND (last_reminded_at IS NULL OR last_reminded_at < ?)"
+      (now, cutoff)
+
+markReminderSent :: Int -> IO ()
+markReminderSent tid = do
+  now <- getCurrentTime
+  Memory.withMemoryDb <| \conn -> do
+    initTodosTable conn
+    SQL.execute
+      conn
+      "UPDATE todos SET last_reminded_at = ? WHERE id = ?"
+      (now, tid)
+
 completeTodo :: Text -> Int -> IO Bool
 completeTodo uid tid =
   Memory.withMemoryDb <| \conn -> do