Clarify chat state reset and placeholders

src/features/chat/chat-state.ts

@@ -210,41 +210,22 @@ export function createChatState(): ChatState {
     activeThreadId: null,
     activeThreadCwd: null,
     turnLifecycle: { kind: "idle" },
-    activeModel: null,
-    activeReasoningEffort: null,
-    activeCollaborationMode: "default",
-    activeServiceTier: null,
-    activeApprovalPolicy: null,
-    activeApprovalsReviewer: null,
-    activePermissionProfile: null,
+    ...initialActiveRuntimeState(),
     activeThreadCreationCliVersion: null,
     appServerDiagnostics: createAppServerDiagnostics(),
-    requestedModel: unchangedRuntimeSetting(),
-    requestedReasoningEffort: unchangedRuntimeSetting(),
-    requestedApprovalsReviewer: unchangedRuntimeSetting(),
-    selectedCollaborationMode: "default",
-    requestedServiceTier: unchangedRuntimeSetting(),
+    ...initialRequestedRuntimeState(),
     tokenUsage: null,
     rateLimit: null,
-    displayItems: [],
-    turnDiffs: new Map(),
-    approvals: [],
-    pendingUserInputs: [],
-    userInputDrafts: new Map(),
+    ...initialDisplayState(),
+    ...initialPendingRequestState(),
     listedThreads: [],
     threadsLoaded: false,
-    historyCursor: null,
-    loadingHistory: false,
-    composerDraft: "",
-    runtimePicker: null,
+    ...initialHistoryState(),
+    ...initialComposerState(),
+    ...initialPanelUiState(),
     availableModels: [],
     availableSkills: [],
     reportedLogs: new Set(),
-    composerSuggestSelected: 0,
-    composerSuggestions: [],
-    composerSuggestionsDismissedSignature: null,
-    messagesPinnedToBottom: true,
-    openDetails: new Set(),
   };
 }
 
@@ -340,16 +321,10 @@ function reduceThreadState(state: ChatState, action: ThreadAction): ChatState {
         activePermissionProfile: action.activePermissionProfile,
         activeThreadCreationCliVersion: action.thread.cliVersion,
         tokenUsage: null,
-        historyCursor: null,
-        loadingHistory: false,
+        ...initialHistoryState(),
+        ...initialPendingRequestState(),
+        ...initialComposerState(),
         turnDiffs: new Map(),
-        approvals: [],
-        pendingUserInputs: [],
-        userInputDrafts: new Map(),
-        composerDraft: "",
-        composerSuggestSelected: 0,
-        composerSuggestions: [],
-        composerSuggestionsDismissedSignature: null,
         displayItems: action.displayItems ?? [],
         listedThreads: action.listedThreads ?? state.listedThreads,
         messagesPinnedToBottom: action.forceMessagesToBottom ?? true,
@@ -386,17 +361,10 @@ function reduceThreadState(state: ChatState, action: ThreadAction): ChatState {
         patchChatState(state, {
           activeThreadId: action.threadId,
           activeThreadCwd: null,
-          activeModel: null,
-          activeReasoningEffort: null,
-          activeCollaborationMode: "default",
-          activeServiceTier: null,
-          activeApprovalPolicy: null,
-          activeApprovalsReviewer: null,
-          activePermissionProfile: null,
+          ...initialActiveRuntimeState(),
           activeThreadCreationCliVersion: null,
           tokenUsage: null,
-          historyCursor: null,
-          loadingHistory: false,
+          ...initialHistoryState(),
           displayItems: [action.item],
           turnDiffs: new Map(),
           messagesPinnedToBottom: true,
@@ -565,9 +533,7 @@ function reduceRuntimeState(state: ChatState, action: RuntimeAction): ChatState
 export function clearActiveTurnState(state: ChatState): ChatState {
   return patchChatState(state, {
     turnLifecycle: transitionChatTurnLifecycleState(state.turnLifecycle, { type: "cleared" }),
-    approvals: [],
-    pendingUserInputs: [],
-    userInputDrafts: new Map(),
+    ...initialPendingRequestState(),
   });
 }
 
@@ -576,37 +542,19 @@ export function clearActiveThreadState(state: ChatState): ChatState {
     patchChatState(state, {
       activeThreadId: null,
       activeThreadCwd: null,
-      activeModel: null,
-      activeReasoningEffort: null,
-      activeCollaborationMode: "default",
-      activeServiceTier: null,
-      activeApprovalPolicy: null,
-      activeApprovalsReviewer: null,
-      activePermissionProfile: null,
+      ...initialActiveRuntimeState(),
       activeThreadCreationCliVersion: null,
       tokenUsage: null,
-      historyCursor: null,
-      loadingHistory: false,
-      displayItems: [],
-      turnDiffs: new Map(),
-      composerDraft: "",
-      composerSuggestSelected: 0,
-      composerSuggestions: [],
-      composerSuggestionsDismissedSignature: null,
-      messagesPinnedToBottom: true,
+      ...initialHistoryState(),
+      ...initialDisplayState(),
+      ...initialComposerState(),
     }),
   );
 }
 
 export function clearConnectionScopedState(state: ChatState): ChatState {
   return patchChatState(clearActiveTurnState(state), {
-    activeModel: null,
-    activeReasoningEffort: null,
-    activeCollaborationMode: "default",
-    activeServiceTier: null,
-    activeApprovalPolicy: null,
-    activeApprovalsReviewer: null,
-    activePermissionProfile: null,
+    ...initialActiveRuntimeState(),
     activeThreadCreationCliVersion: null,
     rateLimit: null,
     listedThreads: [],
@@ -618,6 +566,82 @@ export function clearConnectionScopedState(state: ChatState): ChatState {
   });
 }
 
+function initialActiveRuntimeState(): Pick<
+  ChatState,
+  | "activeModel"
+  | "activeReasoningEffort"
+  | "activeCollaborationMode"
+  | "activeServiceTier"
+  | "activeApprovalPolicy"
+  | "activeApprovalsReviewer"
+  | "activePermissionProfile"
+> {
+  return {
+    activeModel: null,
+    activeReasoningEffort: null,
+    activeCollaborationMode: "default",
+    activeServiceTier: null,
+    activeApprovalPolicy: null,
+    activeApprovalsReviewer: null,
+    activePermissionProfile: null,
+  };
+}
+
+function initialRequestedRuntimeState(): Pick<
+  ChatState,
+  "requestedModel" | "requestedReasoningEffort" | "requestedApprovalsReviewer" | "selectedCollaborationMode" | "requestedServiceTier"
+> {
+  return {
+    requestedModel: unchangedRuntimeSetting(),
+    requestedReasoningEffort: unchangedRuntimeSetting(),
+    requestedApprovalsReviewer: unchangedRuntimeSetting(),
+    selectedCollaborationMode: "default",
+    requestedServiceTier: unchangedRuntimeSetting(),
+  };
+}
+
+function initialDisplayState(): Pick<ChatState, "displayItems" | "turnDiffs" | "messagesPinnedToBottom"> {
+  return {
+    displayItems: [],
+    turnDiffs: new Map(),
+    messagesPinnedToBottom: true,
+  };
+}
+
+function initialPendingRequestState(): Pick<ChatState, "approvals" | "pendingUserInputs" | "userInputDrafts"> {
+  return {
+    approvals: [],
+    pendingUserInputs: [],
+    userInputDrafts: new Map(),
+  };
+}
+
+function initialHistoryState(): Pick<ChatState, "historyCursor" | "loadingHistory"> {
+  return {
+    historyCursor: null,
+    loadingHistory: false,
+  };
+}
+
+function initialComposerState(): Pick<
+  ChatState,
+  "composerDraft" | "composerSuggestSelected" | "composerSuggestions" | "composerSuggestionsDismissedSignature"
+> {
+  return {
+    composerDraft: "",
+    composerSuggestSelected: 0,
+    composerSuggestions: [],
+    composerSuggestionsDismissedSignature: null,
+  };
+}
+
+function initialPanelUiState(): Pick<ChatState, "runtimePicker" | "openDetails"> {
+  return {
+    runtimePicker: null,
+    openDetails: new Set(),
+  };
+}
+
 export function cloneChatState(state: ChatState): ChatState {
   return {
     ...state,

tests/features/chat/chat-state-reducer.test.ts

@@ -115,6 +115,48 @@ describe("chatReducer", () => {
     expect(next.displayItems).toEqual([]);
   });
 
+  it("keeps composer state when restoring a thread placeholder", () => {
+    const state = createChatState();
+    state.activeThreadId = "previous-thread";
+    state.turnLifecycle = { kind: "running", turnId: "previous-turn" };
+    state.activeModel = "gpt-5.1";
+    state.historyCursor = "cursor";
+    state.loadingHistory = true;
+    state.composerDraft = "draft in this panel";
+    state.composerSuggestSelected = 1;
+    state.composerSuggestions = [suggestion("/resume")];
+    state.composerSuggestionsDismissedSignature = "dismissed";
+    state.displayItems = [message("previous-message")];
+    state.turnDiffs = new Map([["previous-turn", "@@"]]);
+    state.approvals = [approval(1)];
+    state.pendingUserInputs = [userInput(2)];
+    state.userInputDrafts = new Map([["2:note", "answer"]]);
+    state.messagesPinnedToBottom = false;
+    const placeholder = message("placeholder");
+
+    const next = chatReducer(state, {
+      type: "thread/restored-placeholder",
+      threadId: "restored-thread",
+      item: placeholder,
+    });
+
+    expect(next.activeThreadId).toBe("restored-thread");
+    expect(activeTurnId(next)).toBeNull();
+    expect(next.activeModel).toBeNull();
+    expect(next.historyCursor).toBeNull();
+    expect(next.loadingHistory).toBe(false);
+    expect(next.displayItems).toEqual([placeholder]);
+    expect(next.turnDiffs.size).toBe(0);
+    expect(next.approvals).toEqual([]);
+    expect(next.pendingUserInputs).toEqual([]);
+    expect(next.userInputDrafts.size).toBe(0);
+    expect(next.messagesPinnedToBottom).toBe(true);
+    expect(next.composerDraft).toBe("draft in this panel");
+    expect(next.composerSuggestSelected).toBe(1);
+    expect(next.composerSuggestions).toEqual([suggestion("/resume")]);
+    expect(next.composerSuggestionsDismissedSignature).toBe("dismissed");
+  });
+
   it("clones map and set backed state when updating turn diffs and open panels", () => {
     const state = createChatState();
     state.turnDiffs = new Map([["turn", "old"]]);