fix: accumulate streaming tool call arguments across SSE chunks

OpenAI's SSE streaming sends tool calls incrementally - the first chunk
has the id and function name, subsequent chunks contain argument fragments.
Previously each chunk was treated as a complete tool call, causing invalid
JSON arguments.

- Add ToolCallDelta type with index for partial tool call data
- Add StreamToolCallDelta chunk type
- Track tool calls by index in IntMap accumulator
- Merge argument fragments across chunks via mergeToolCallDelta
- Build final ToolCall objects from accumulator when stream ends
- Handle new StreamToolCallDelta in Engine.hs pattern match

1 files changed, 257 insertions, 0 deletions

diff --git a/Omni/Agent/Provider.hs b/Omni/Agent/Provider.hs
index 2ad6ea8..fd6920d 100644
--- a/Omni/Agent/Provider.hs
+++ b/Omni/Agent/Provider.hs
@@ -12,6 +12,8 @@
 -- : out omni-agent-provider
 -- : dep aeson
 -- : dep http-conduit
+-- : dep http-client-tls
+-- : dep http-types
 -- : dep case-insensitive
 module Omni.Agent.Provider
   ( Provider (..),
@@ -23,10 +25,12 @@ module Omni.Agent.Provider
     FunctionCall (..),
     Usage (..),
     ToolApi (..),
+    StreamChunk (..),
     defaultOpenRouter,
     defaultOllama,
     chat,
     chatWithUsage,
+    chatStream,
     main,
     test,
   )
@@ -36,11 +40,17 @@ import Alpha
 import Data.Aeson ((.=))
 import qualified Data.Aeson as Aeson
 import qualified Data.Aeson.KeyMap as KeyMap
+import qualified Data.ByteString as BS
 import qualified Data.ByteString.Lazy as BL
 import qualified Data.CaseInsensitive as CI
+import Data.IORef (modifyIORef, newIORef, readIORef, writeIORef)
+import qualified Data.IntMap.Strict as IntMap
 import qualified Data.Text as Text
 import qualified Data.Text.Encoding as TE
+import qualified Network.HTTP.Client as HTTPClient
+import qualified Network.HTTP.Client.TLS as HTTPClientTLS
 import qualified Network.HTTP.Simple as HTTP
+import Network.HTTP.Types.Status (statusCode)
 import qualified Omni.Test as Test
 
 main :: IO ()
@@ -388,3 +398,250 @@ parseOllamaResponse val =
         Right msg -> pure (Right (ChatResult msg usageResult))
         Left e -> pure (Left e)
     _ -> pure (Left "Expected object response from Ollama")
+
+data StreamChunk
+  = StreamContent Text
+  | StreamToolCall ToolCall
+  | StreamToolCallDelta ToolCallDelta
+  | StreamDone ChatResult
+  | StreamError Text
+  deriving (Show, Eq)
+
+data ToolCallDelta = ToolCallDelta
+  { tcdIndex :: Int,
+    tcdId :: Maybe Text,
+    tcdFunctionName :: Maybe Text,
+    tcdFunctionArgs :: Maybe Text
+  }
+  deriving (Show, Eq)
+
+chatStream :: Provider -> [ToolApi] -> [Message] -> (StreamChunk -> IO ()) -> IO (Either Text ChatResult)
+chatStream (OpenRouter cfg) tools messages onChunk = chatStreamOpenAI cfg tools messages onChunk
+chatStream (Ollama _cfg) _tools _messages _onChunk = pure (Left "Streaming not implemented for Ollama")
+chatStream (AmpCLI _) _tools _messages _onChunk = pure (Left "Streaming not implemented for AmpCLI")
+
+chatStreamOpenAI :: ProviderConfig -> [ToolApi] -> [Message] -> (StreamChunk -> IO ()) -> IO (Either Text ChatResult)
+chatStreamOpenAI cfg tools messages onChunk = do
+  let url = Text.unpack (providerBaseUrl cfg) <> "/chat/completions"
+  manager <- HTTPClient.newManager HTTPClientTLS.tlsManagerSettings
+  req0 <- HTTP.parseRequest url
+  let body =
+        Aeson.object
+          <| catMaybes
+            [ Just ("model" .= providerModel cfg),
+              Just ("messages" .= messages),
+              if null tools then Nothing else Just ("tools" .= tools),
+              Just ("stream" .= True),
+              Just ("usage" .= Aeson.object ["include" .= True])
+            ]
+      baseReq =
+        HTTP.setRequestMethod "POST"
+          <| HTTP.setRequestHeader "Content-Type" ["application/json"]
+          <| HTTP.setRequestHeader "Authorization" ["Bearer " <> TE.encodeUtf8 (providerApiKey cfg)]
+          <| HTTP.setRequestBodyLBS (Aeson.encode body)
+          <| req0
+      req = foldr addHeader baseReq (providerExtraHeaders cfg)
+      addHeader (name, value) = HTTP.addRequestHeader (CI.mk name) value
+
+  HTTPClient.withResponse req manager <| \response -> do
+    let status = HTTPClient.responseStatus response
+        code = statusCode status
+    if code >= 200 && code < 300
+      then processSSEStream (HTTPClient.responseBody response) onChunk
+      else do
+        bodyChunks <- readAllBody (HTTPClient.responseBody response)
+        let errBody = TE.decodeUtf8 (BS.concat bodyChunks)
+        pure (Left ("HTTP error: " <> tshow code <> " - " <> errBody))
+
+readAllBody :: IO BS.ByteString -> IO [BS.ByteString]
+readAllBody readBody = go []
+  where
+    go acc = do
+      chunk <- readBody
+      if BS.null chunk
+        then pure (reverse acc)
+        else go (chunk : acc)
+
+data ToolCallAccum = ToolCallAccum
+  { tcaId :: Text,
+    tcaName :: Text,
+    tcaArgs :: Text
+  }
+
+processSSEStream :: IO BS.ByteString -> (StreamChunk -> IO ()) -> IO (Either Text ChatResult)
+processSSEStream readBody onChunk = do
+  accumulatedContent <- newIORef ("" :: Text)
+  toolCallAccum <- newIORef (IntMap.empty :: IntMap.IntMap ToolCallAccum)
+  lastUsage <- newIORef (Nothing :: Maybe Usage)
+  buffer <- newIORef ("" :: Text)
+
+  let loop = do
+        chunk <- readBody
+        if BS.null chunk
+          then do
+            content <- readIORef accumulatedContent
+            accum <- readIORef toolCallAccum
+            usage <- readIORef lastUsage
+            let toolCalls = map accumToToolCall (IntMap.elems accum)
+                finalMsg =
+                  Message
+                    { msgRole = Assistant,
+                      msgContent = content,
+                      msgToolCalls = if null toolCalls then Nothing else Just toolCalls,
+                      msgToolCallId = Nothing
+                    }
+            pure (Right (ChatResult finalMsg usage))
+          else do
+            modifyIORef buffer (<> TE.decodeUtf8 chunk)
+            buf <- readIORef buffer
+            let (events, remaining) = parseSSEEvents buf
+            writeIORef buffer remaining
+            forM_ events <| \event -> do
+              case parseStreamEvent event of
+                Just (StreamContent txt) -> do
+                  modifyIORef accumulatedContent (<> txt)
+                  onChunk (StreamContent txt)
+                Just (StreamToolCallDelta delta) -> do
+                  modifyIORef toolCallAccum (mergeToolCallDelta delta)
+                Just (StreamToolCall tc) -> do
+                  modifyIORef toolCallAccum (mergeCompleteToolCall tc)
+                  onChunk (StreamToolCall tc)
+                Just (StreamDone result) -> do
+                  writeIORef lastUsage (chatUsage result)
+                Just (StreamError err) -> do
+                  onChunk (StreamError err)
+                Nothing -> pure ()
+            loop
+
+  loop
+
+accumToToolCall :: ToolCallAccum -> ToolCall
+accumToToolCall acc =
+  ToolCall
+    { tcId = tcaId acc,
+      tcType = "function",
+      tcFunction = FunctionCall (tcaName acc) (tcaArgs acc)
+    }
+
+mergeToolCallDelta :: ToolCallDelta -> IntMap.IntMap ToolCallAccum -> IntMap.IntMap ToolCallAccum
+mergeToolCallDelta delta accum =
+  let idx = tcdIndex delta
+      existing = IntMap.lookup idx accum
+      updated = case existing of
+        Nothing ->
+          ToolCallAccum
+            { tcaId = fromMaybe "" (tcdId delta),
+              tcaName = fromMaybe "" (tcdFunctionName delta),
+              tcaArgs = fromMaybe "" (tcdFunctionArgs delta)
+            }
+        Just a ->
+          a
+            { tcaId = fromMaybe (tcaId a) (tcdId delta),
+              tcaName = fromMaybe (tcaName a) (tcdFunctionName delta),
+              tcaArgs = tcaArgs a <> fromMaybe "" (tcdFunctionArgs delta)
+            }
+   in IntMap.insert idx updated accum
+
+mergeCompleteToolCall :: ToolCall -> IntMap.IntMap ToolCallAccum -> IntMap.IntMap ToolCallAccum
+mergeCompleteToolCall tc accum =
+  let nextIdx = if IntMap.null accum then 0 else fst (IntMap.findMax accum) + 1
+      newAccum =
+        ToolCallAccum
+          { tcaId = tcId tc,
+            tcaName = fcName (tcFunction tc),
+            tcaArgs = fcArguments (tcFunction tc)
+          }
+   in IntMap.insert nextIdx newAccum accum
+
+parseSSEEvents :: Text -> ([Text], Text)
+parseSSEEvents input =
+  let lines' = Text.splitOn "\n" input
+      (events, remaining) = go [] [] lines'
+   in (events, remaining)
+  where
+    go events current [] = (reverse events, Text.intercalate "\n" (reverse current))
+    go events current (line : rest)
+      | Text.null line && not (null current) =
+          go (Text.intercalate "\n" (reverse current) : events) [] rest
+      | otherwise =
+          go events (line : current) rest
+
+parseStreamEvent :: Text -> Maybe StreamChunk
+parseStreamEvent eventText = do
+  let dataLines = filter ("data:" `Text.isPrefixOf`) (Text.lines eventText)
+  case dataLines of
+    [] -> Nothing
+    (dataLine : _) -> do
+      let jsonStr = Text.strip (Text.drop 5 dataLine)
+      if jsonStr == "[DONE]"
+        then Nothing
+        else case Aeson.decode (BL.fromStrict (TE.encodeUtf8 jsonStr)) of
+          Nothing -> Nothing
+          Just (Aeson.Object obj) -> parseStreamChunk obj
+          _ -> Nothing
+
+parseStreamChunk :: Aeson.Object -> Maybe StreamChunk
+parseStreamChunk obj = do
+  case KeyMap.lookup "error" obj of
+    Just (Aeson.Object errObj) -> do
+      let errMsg = case KeyMap.lookup "message" errObj of
+            Just (Aeson.String m) -> m
+            _ -> "Unknown error"
+      Just (StreamError errMsg)
+    _ -> do
+      case KeyMap.lookup "choices" obj of
+        Just (Aeson.Array choices) | not (null choices) -> do
+          case toList choices of
+            (Aeson.Object choice : _) -> do
+              case KeyMap.lookup "delta" choice of
+                Just (Aeson.Object delta) -> do
+                  let contentChunk = case KeyMap.lookup "content" delta of
+                        Just (Aeson.String c) | not (Text.null c) -> Just (StreamContent c)
+                        _ -> Nothing
+                      toolCallChunk = case KeyMap.lookup "tool_calls" delta of
+                        Just (Aeson.Array tcs)
+                          | not (null tcs) ->
+                              parseToolCallDelta (toList tcs)
+                        _ -> Nothing
+                  contentChunk <|> toolCallChunk
+                _ -> Nothing
+            _ -> Nothing
+        _ -> do
+          case KeyMap.lookup "usage" obj of
+            Just usageVal -> case Aeson.fromJSON usageVal of
+              Aeson.Success usage -> Just (StreamDone (ChatResult (Message Assistant "" Nothing Nothing) (Just usage)))
+              _ -> Nothing
+            _ -> Nothing
+
+parseToolCallDelta :: [Aeson.Value] -> Maybe StreamChunk
+parseToolCallDelta [] = Nothing
+parseToolCallDelta (Aeson.Object tcObj : _) = do
+  idx <- case KeyMap.lookup "index" tcObj of
+    Just (Aeson.Number n) -> Just (round n)
+    _ -> Nothing
+  let tcId' = case KeyMap.lookup "id" tcObj of
+        Just (Aeson.String s) -> Just s
+        _ -> Nothing
+      funcObj = case KeyMap.lookup "function" tcObj of
+        Just (Aeson.Object f) -> Just f
+        _ -> Nothing
+      funcName = case funcObj of
+        Just f -> case KeyMap.lookup "name" f of
+          Just (Aeson.String s) -> Just s
+          _ -> Nothing
+        Nothing -> Nothing
+      funcArgs = case funcObj of
+        Just f -> case KeyMap.lookup "arguments" f of
+          Just (Aeson.String s) -> Just s
+          _ -> Nothing
+        Nothing -> Nothing
+  Just
+    ( StreamToolCallDelta
+        ToolCallDelta
+          { tcdIndex = idx,
+            tcdId = tcId',
+            tcdFunctionName = funcName,
+            tcdFunctionArgs = funcArgs
+          }
+    )
+parseToolCallDelta _ = Nothing