feat(chat): convert turn state from useReducer to Zustand store with createSelectors

apps/web/CONVENTIONS.md

@@ -341,6 +341,20 @@ References:
 - [Zustand — Reading/writing state outside components](https://zustand.docs.pmnd.rs/guides/reading-and-writing-state-outside-components)
 - [React Router — Middleware](https://reactrouter.com/how-to/middleware)
 
+### Turn state lives in `domains/messaging/turn-store.ts`
+
+Turn lifecycle (sending, thinking, streaming, idle, errored), queue
+depth, active tool-call count, and current turn identity are managed
+by the turn store. Use `useTurnStore(selector)` in React components
+and `useTurnStore.getState()` in non-React code (stream handlers,
+reconciliation). Do not prop-drill turn state or dispatch functions.
+
+Action naming follows the
+[Flux-inspired practice](https://zustand.docs.pmnd.rs/learn/guides/flux-inspired-practice):
+`on*` for SSE-event reactions (`onTextDelta`, `onStreamError`,
+`onPollReconciled`), imperative for user/system-initiated actions
+(`requestSend`, `cancelGeneration`, `resetTurn`).
+
 ### Selector patterns and `useShallow`
 
 Selectors control re-render granularity. Choose the right pattern based

apps/web/src/domains/chat/chat-page.tsx

@@ -2,6 +2,7 @@ import {
   type MutableRefObject,
   type RefObject,
   useCallback,
+  useEffect,
   useReducer,
   useRef,
   useState,
@@ -15,8 +16,8 @@ import {
   INITIAL_INTERACTION_STATE,
 } from "@/domains/interactions/interaction-store.js";
 import {
-  turnReducer,
   INITIAL_TURN_STATE,
+  useTurnStore,
 } from "@/domains/messaging/turn-store.js";
 import type { DisplayMessage } from "@/domains/chat/lib/reconcile.js";
 import { useSyncChatStore } from "@/domains/chat/chat-store.js";
@@ -54,7 +55,10 @@ export function ChatPage() {
   const { assistantState, assistantId } = lifecycle;
 
   const [messages, setMessages] = useState<DisplayMessage[]>([]);
-  const [turnState, dispatchTurn] = useReducer(turnReducer, INITIAL_TURN_STATE);
+  useEffect(() => {
+    useTurnStore.setState(INITIAL_TURN_STATE);
+  }, []);
+
   const [interactionState, dispatchInteraction] = useReducer(
     interactionReducer,
     INITIAL_INTERACTION_STATE,
@@ -94,7 +98,6 @@ export function ChatPage() {
     activeConversationKey: null,
     assistantId,
     sendMessage,
-    dispatchTurn,
     dispatchInteraction,
   });
 
@@ -128,8 +131,6 @@ export function ChatPage() {
     isKeyboardOpen: false,
     messages,
     setMessages,
-    turnState,
-    dispatchTurn,
     input,
     setInput,
     error,

apps/web/src/domains/chat/chat-store.test.ts

@@ -8,7 +8,6 @@ beforeEach(() => {
     activeConversationKey: null,
     assistantId: null,
     sendMessage: async () => {},
-    dispatchTurn: () => {},
     dispatchInteraction: () => {},
   }, true);
 });
@@ -24,7 +23,6 @@ describe("useChatStore", () => {
   it("initializes with noop action refs", () => {
     const state = useChatStore.getState();
     expect(typeof state.sendMessage).toBe("function");
-    expect(typeof state.dispatchTurn).toBe("function");
     expect(typeof state.dispatchInteraction).toBe("function");
   });
 
@@ -59,7 +57,6 @@ describe("useChatStore", () => {
       activeConversationKey: "conv-abc",
       assistantId: "ast-new",
       sendMessage: async () => {},
-      dispatchTurn: () => {},
       dispatchInteraction: () => {},
     };
     useChatStore.setState(fullState, true);

apps/web/src/domains/chat/chat-store.ts

@@ -22,7 +22,6 @@ import { create } from "zustand";
 import { useShallow } from "zustand/shallow";
 
 import type { DisplayAttachment, DisplayMessage } from "@/domains/chat/lib/reconcile.js";
-import type { DomainEvent } from "@/domains/messaging/turn-store.js";
 import type { InteractionEvent } from "@/domains/interactions/interaction-store.js";
 
 // ---------------------------------------------------------------------------
@@ -41,8 +40,6 @@ export interface ChatState {
 export interface ChatActions {
   /** Send a user message (with optional attachments) to the active conversation. */
   sendMessage: (content: string, attachments?: DisplayAttachment[]) => Promise<void>;
-  /** Dispatch a turn state-machine event. */
-  dispatchTurn: Dispatch<DomainEvent>;
   /** Dispatch an interaction state-machine event. */
   dispatchInteraction: Dispatch<InteractionEvent>;
 }
@@ -61,7 +58,6 @@ export const useChatStore = create<ChatStore>()(() => ({
   activeConversationKey: null,
   assistantId: null,
   sendMessage: NOOP_SEND,
-  dispatchTurn: NOOP_DISPATCH as Dispatch<DomainEvent>,
   dispatchInteraction: NOOP_DISPATCH as Dispatch<InteractionEvent>,
 }));
 
@@ -74,7 +70,6 @@ export interface ChatStoreSyncProps {
   activeConversationKey: string | null;
   assistantId: string | null;
   sendMessage: (content: string, attachments?: DisplayAttachment[]) => Promise<void>;
-  dispatchTurn: Dispatch<DomainEvent>;
   dispatchInteraction: Dispatch<InteractionEvent>;
 }
 
@@ -89,7 +84,6 @@ export function useSyncChatStore(props: ChatStoreSyncProps): void {
     activeConversationKey,
     assistantId,
     sendMessage,
-    dispatchTurn,
     dispatchInteraction,
   } = props;
 
@@ -104,10 +98,9 @@ export function useSyncChatStore(props: ChatStoreSyncProps): void {
   useEffect(() => {
     useChatStore.setState({
       sendMessage,
-      dispatchTurn,
       dispatchInteraction,
     });
-  }, [sendMessage, dispatchTurn, dispatchInteraction]);
+  }, [sendMessage, dispatchInteraction]);
 }
 
 // ---------------------------------------------------------------------------
@@ -130,14 +123,13 @@ export function useChatState(): ChatState {
 }
 
 /**
- * Stable action dispatchers (sendMessage, dispatchTurn, dispatchInteraction).
+ * Stable action dispatchers (sendMessage, dispatchInteraction).
  * Does **not** re-render when messages or active conversation change.
  */
 export function useChatActions(): ChatActions {
   return useChatStore(
     useShallow((s) => ({
       sendMessage: s.sendMessage,
-      dispatchTurn: s.dispatchTurn,
       dispatchInteraction: s.dispatchInteraction,
     })),
   );

apps/web/src/domains/chat/components/chat-composer/chat-composer.test.tsx

@@ -17,7 +17,7 @@ import { renderToStaticMarkup } from "react-dom/server";
 import {
   type ChatAttachment,
 } from "@/domains/chat/components/chat-attachments/index.js";
-import { INITIAL_TURN_STATE, type TurnState } from "@/domains/messaging/turn-store.js";
+import { INITIAL_TURN_STATE, type TurnState, useTurnStore } from "@/domains/messaging/turn-store.js";
 
 import { ChatComposer, computeGhostSuffix, shouldSubmitOnEnter } from "@/domains/chat/components/chat-composer/chat-composer.js";
 
@@ -294,7 +294,6 @@ function renderComposer(props: Partial<Parameters<typeof ChatComposer>[0]> = {})
       chatAttachments={[]}
       onAddAttachmentFiles={() => {}}
       onRemoveAttachment={() => {}}
-      turnState={INITIAL_TURN_STATE}
       onStopGenerating={() => {}}
       assistantId="asst_test"
       {...props}
@@ -316,41 +315,45 @@ describe("ChatComposer — placeholder", () => {
 
 describe("ChatComposer — send/stop button visibility", () => {
   test("idle state renders a Send button (aria-label='Send message')", () => {
-    const html = renderComposer({ turnState: INITIAL_TURN_STATE });
+    useTurnStore.setState(INITIAL_TURN_STATE);
+    const html = renderComposer();
     expect(html).toContain('aria-label="Send message"');
     expect(html).not.toContain('aria-label="Stop generating"');
   });
 
-  test("isSending(turnState)=true on desktop renders only the Stop button (send/attach/voice hidden)", () => {
+  test("isSending=true on desktop renders only the Stop button (send/attach/voice hidden)", () => {
     mockIsMobile = false;
     const sending: TurnState = {
       ...INITIAL_TURN_STATE,
       phase: "streaming",
     };
-    const html = renderComposer({ turnState: sending });
+    useTurnStore.setState(sending);
+    const html = renderComposer();
     expect(html).toContain('aria-label="Stop generating"');
     expect(html).not.toContain('aria-label="Send message"');
   });
 
-  test("isSending(turnState)=true on mobile with no input renders only Stop button", () => {
+  test("isSending=true on mobile with no input renders only Stop button", () => {
     mockIsMobile = true;
     const sending: TurnState = {
       ...INITIAL_TURN_STATE,
       phase: "streaming",
     };
-    const html = renderComposer({ turnState: sending, input: "" });
+    useTurnStore.setState(sending);
+    const html = renderComposer({ input: "" });
     expect(html).toContain('aria-label="Stop generating"');
     expect(html).not.toContain('aria-label="Send message"');
     mockIsMobile = false;
   });
 
-  test("isSending(turnState)=true on mobile with user input renders only Send button", () => {
+  test("isSending=true on mobile with user input renders only Send button", () => {
     mockIsMobile = true;
     const sending: TurnState = {
       ...INITIAL_TURN_STATE,
       phase: "streaming",
     };
-    const html = renderComposer({ turnState: sending, input: "hello" });
+    useTurnStore.setState(sending);
+    const html = renderComposer({ input: "hello" });
     expect(html).not.toContain('aria-label="Stop generating"');
     expect(html).toContain('aria-label="Send message"');
     mockIsMobile = false;
@@ -363,7 +366,8 @@ describe("ChatComposer — send/stop button visibility", () => {
       ...INITIAL_TURN_STATE,
       phase: "awaiting_user_input",
     };
-    const html = renderComposer({ turnState: awaiting });
+    useTurnStore.setState(awaiting);
+    const html = renderComposer();
     expect(html).toContain('aria-label="Send message"');
     expect(html).not.toContain('aria-label="Stop generating"');
   });
@@ -431,7 +435,6 @@ describe("ChatComposer — Stop button click invokes onStopGenerating", () => {
     // captured callback directly.
     const onStopGenerating = mock(() => {});
     renderComposer({
-      turnState: { ...INITIAL_TURN_STATE, phase: "streaming" },
       onStopGenerating,
     });
     onStopGenerating();

apps/web/src/domains/chat/components/chat-composer/chat-composer.tsx

@@ -23,7 +23,7 @@ import {
   VoiceInputButton,
   type VoiceInputButtonHandle,
 } from "@/domains/chat/components/voice-input-button.js";
-import { isSending, type TurnState } from "@/domains/messaging/turn-store.js";
+import { isSending, useTurnStore } from "@/domains/messaging/turn-store.js";
 import { useIsMobile } from "@/hooks/use-is-mobile.js";
 import { isPointerCoarse } from "@/utils/pointer.js";
 import { useAudioAmplitude } from "@/domains/voice/use-audio-amplitude.js";
@@ -188,8 +188,6 @@ export interface ChatComposerProps {
   onVoiceError?: (code: string | null) => void;
   onVoiceBeforeStart?: () => boolean | Promise<boolean>;
 
-  // turn state
-  turnState: TurnState;
   onStopGenerating: () => void;
 
   // assistant id used by AttachFileButton's disabled guard
@@ -249,7 +247,6 @@ export function ChatComposer({
   voiceInterim,
   onVoiceError,
   onVoiceBeforeStart,
-  turnState,
   onStopGenerating,
   assistantId,
   thresholdPickerSlot,
@@ -360,6 +357,7 @@ export function ChatComposer({
     [emojiState, input, inputRef, setInput, onTextChange],
   );
 
+  const turnState = useTurnStore();
   const isGenerating =
     isSending(turnState) && turnState.phase !== "awaiting_user_input";
 

apps/web/src/domains/chat/components/chat-route-content.tsx

@@ -73,7 +73,7 @@ import { buildTranscriptItems } from "@/domains/chat/lib/transcript/build-items.
 import type { TranscriptPaginationState } from "@/domains/chat/lib/transcript/types.js";
 import { getThinkingStatusText, isSendDisabled, shouldShowThinkingIndicator, type UIContext } from "@/domains/chat/lib/turn-selectors.js";
 import { isSurfaceInteractive } from "@/domains/chat/lib/types.js";
-import type { TurnState } from "@/domains/messaging/turn-store.js";
+
 import type { MainView, OpenedAppState, OpenedDocumentState, ViewerState } from "@/stores/viewer-store.js";
 import { submitQuestionResponse } from "@/domains/chat/lib/api.js";
 import { useActiveProfileModel } from "@/domains/chat/lib/use-active-profile-model.js";
@@ -85,7 +85,7 @@ import { isChannelConversation as _isChannelConversation } from "@/domains/chat/
 import { getDiskPressureChatBlockReason } from "@/domains/assistant/disk-pressure.js";
 import type { DiskPressureStatusEventPayload } from "@/domains/assistant/use-disk-pressure-monitor.js";
 import type { InteractionEvent } from "@/domains/interactions/interaction-store.js";
-import type { DomainEvent } from "@/domains/messaging/turn-store.js";
+import { useTurnStore } from "@/domains/messaging/turn-store.js";
 import type { QuestionResponseEntry, AllowlistOption, ScopeOption, DirectoryScopeOption, ConfirmationDecision } from "@/domains/chat/lib/event-types.js";
 import type { CharacterComponents, CharacterTraits } from "@/domains/avatar/types.js";
 import { DiskPressureBanner, type DiskPressureBannerMode } from "@/domains/chat/components/disk-pressure-banner.js";
@@ -223,7 +223,7 @@ export interface ChatRouteRefs {
   requestIdToStableIdRef: MutableRefObject<Map<string, string>>;
   pendingLocalDeletionsRef: MutableRefObject<Set<string>>;
   confirmationToolCallMapRef: MutableRefObject<Map<string, string>>;
-  turnStateRef: MutableRefObject<TurnState>;
+
   interactionStateRef: MutableRefObject<InteractionState>;
   reconcileAfterNextStreamOpenRef: MutableRefObject<boolean>;
 }
@@ -251,10 +251,6 @@ export interface ChatRouteContentProps {
   messages: DisplayMessage[];
   setMessages: Dispatch<SetStateAction<DisplayMessage[]>>;
 
-  // Turn state
-  turnState: TurnState;
-  dispatchTurn: Dispatch<DomainEvent>;
-
   // Input
   input: string;
   setInput: Dispatch<SetStateAction<string>>;
@@ -383,8 +379,6 @@ export function ChatRouteContent({
   isKeyboardOpen,
   messages,
   setMessages,
-  turnState,
-  dispatchTurn: _dispatchTurn,
   input,
   setInput,
   error,
@@ -509,11 +503,15 @@ export function ChatRouteContent({
     requestIdToStableIdRef: _requestIdToStableIdRef,
     pendingLocalDeletionsRef: _pendingLocalDeletionsRef,
     confirmationToolCallMapRef: _confirmationToolCallMapRef,
-    turnStateRef: _turnStateRef,
     interactionStateRef,
     reconcileAfterNextStreamOpenRef: _reconcileAfterNextStreamOpenRef,
   } = refs;
 
+  // -------------------------------------------------------------------------
+  // Turn state (read from Zustand store)
+  // -------------------------------------------------------------------------
+  const turnState = useTurnStore();
+
   // -------------------------------------------------------------------------
   // Derived interaction state
   // -------------------------------------------------------------------------
@@ -1212,7 +1210,6 @@ export function ChatRouteContent({
     onVoiceRecordingChange: handleVoiceRecordingChange,
     onVoiceError: _setVoiceError,
     onVoiceBeforeStart: handleVoiceBeforeStart,
-    turnState,
     onStopGenerating: handleStopGenerating,
     assistantId,
     modelSupportsVision: activeModelSupportsVision,

apps/web/src/domains/chat/hooks/use-conversation-history.ts

@@ -28,7 +28,7 @@ import {
 } from "@/domains/chat/lib/diagnostics.js";
 import type { TranscriptPaginationState } from "@/domains/chat/lib/transcript/types.js";
 import type { ContextWindowUsage } from "@/domains/chat/components/context-window-indicator.js";
-import type { DomainEvent } from "@/domains/messaging/turn-store.js";
+import { useTurnStore } from "@/domains/messaging/turn-store.js";
 import type { InteractionEvent, InteractionState } from "@/domains/interactions/interaction-store.js";
 import type { ConversationListAction } from "@/domains/conversations/conversation-list-store.js";
 import type { SubagentAction } from "@/domains/subagents/subagent-store.js";
@@ -130,7 +130,7 @@ interface UseConversationHistoryParams {
   setSuggestion: Dispatch<SetStateAction<string | null>>;
   setCompactionCircuitOpenUntil: Dispatch<SetStateAction<Date | null>>;
   setInput: Dispatch<SetStateAction<string>>;
-  dispatchTurn: Dispatch<DomainEvent>;
+
   dispatchSubagent: Dispatch<SubagentAction>;
 
   // Callbacks
@@ -207,7 +207,6 @@ export function useConversationHistory({
   setSuggestion,
   setCompactionCircuitOpenUntil,
   setInput,
-  dispatchTurn,
   dispatchSubagent,
   resetChatAttachments,
   syncNeedsNewBubbleFromMessages,
@@ -326,7 +325,7 @@ export function useConversationHistory({
       previousPagination: transcriptPaginationRef.current,
       cacheSize: conversationCacheRef.current.size,
     });
-    dispatchTurn({ type: "TURN_RESET" });
+    useTurnStore.getState().resetTurn();
     setIsLoadingHistory(true);
     needsNewBubbleRef.current = true;
     setMessages([]);
@@ -672,7 +671,6 @@ export function useConversationHistory({
     setSuggestion,
     setCompactionCircuitOpenUntil,
     setInput,
-    dispatchTurn,
     dispatchSubagent,
     onDraftRestored,
     shouldSuppressGenericChatErrorNotice,