Add agent observability: event logging and storage

- Add Omni/Agent/Event.hs with AgentEvent types
- Add agent_events table schema and CRUD functions to Core.hs
- Add new callbacks to Engine.hs: onAssistant, onToolResult, onComplete, onError
- Wire event logging into Worker.hs with session tracking

Events are now persisted to SQLite for each agent work session,
enabling visibility into agent reasoning and tool usage.

Task-Id: t-197.1
Task-Id: t-197.2
Task-Id: t-197.3

1 files changed, 27 insertions, 3 deletions

diff --git a/Omni/Agent/Worker.hs b/Omni/Agent/Worker.hs
index 61c392b..1c69b15 100644
--- a/Omni/Agent/Worker.hs
+++ b/Omni/Agent/Worker.hs
@@ -243,6 +243,15 @@ runWithEngine repo task = do
       -- Select model based on task complexity (simple heuristic)
       let model = selectModel task
 
+      -- Generate session ID for event logging
+      sessionId <- TaskCore.generateSessionId
+      let tid = TaskCore.taskId task
+
+      -- Helper to log events to DB
+      let logEvent eventType content = do
+            let contentJson = TE.decodeUtf8 (BSL.toStrict (Aeson.encode content))
+            TaskCore.insertAgentEvent tid sessionId eventType contentJson
+
       -- Build Engine config with callbacks
       totalCostRef <- newIORef (0 :: Int)
       let engineCfg =
@@ -253,11 +262,26 @@ runWithEngine repo task = do
                     },
                 Engine.engineOnCost = \tokens cost -> do
                   modifyIORef' totalCostRef (+ cost)
-                  AgentLog.log <| "Cost: " <> tshow cost <> " cents (" <> tshow tokens <> " tokens)",
+                  AgentLog.log <| "Cost: " <> tshow cost <> " cents (" <> tshow tokens <> " tokens)"
+                  logEvent "cost" (Aeson.object [("tokens", Aeson.toJSON tokens), ("cents", Aeson.toJSON cost)]),
                 Engine.engineOnActivity = \activity -> do
                   AgentLog.log <| "[engine] " <> activity,
-                Engine.engineOnToolCall = \toolName result -> do
-                  AgentLog.log <| "[tool] " <> toolName <> ": " <> Text.take 100 result
+                Engine.engineOnToolCall = \toolName args -> do
+                  AgentLog.log <| "[tool] " <> toolName
+                  logEvent "tool_call" (Aeson.object [("tool", Aeson.toJSON toolName), ("args", Aeson.toJSON args)]),
+                Engine.engineOnAssistant = \msg -> do
+                  AgentLog.log <| "[assistant] " <> Text.take 200 msg
+                  logEvent "assistant" (Aeson.String msg),
+                Engine.engineOnToolResult = \toolName success output -> do
+                  let statusStr = if success then "ok" else "failed"
+                  AgentLog.log <| "[result] " <> toolName <> " (" <> statusStr <> "): " <> Text.take 100 output
+                  logEvent "tool_result" (Aeson.object [("tool", Aeson.toJSON toolName), ("success", Aeson.toJSON success), ("output", Aeson.toJSON output)]),
+                Engine.engineOnComplete = do
+                  AgentLog.log "[engine] Complete"
+                  logEvent "complete" Aeson.Null,
+                Engine.engineOnError = \err -> do
+                  AgentLog.log <| "[error] " <> err
+                  logEvent "error" (Aeson.String err)
               }
 
       -- Build Agent config