diff --git a/eslint.config.mjs b/eslint.config.mjs
index 11a46f96..43b85581 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -49,7 +49,7 @@ const removedChatStateEscapeHatchRestrictions = [
 const chatSignalAdapterRestrictions = [
   {
     selector: "ImportDeclaration[source.value='@preact/signals']",
-    message: "Keep chat signals in panel/shell-state.tsx as a reducer-to-Preact notification adapter.",
+    message: "Keep chat signals in panel/shell-state.tsx as a reducer-to-Preact notification and derived projection adapter.",
   },
 ];
 const chatDomainLayerRestrictions = [
diff --git a/src/features/chat/application/runtime/snapshot.ts b/src/features/chat/application/runtime/snapshot.ts
index 243b4d14..de17cf27 100644
--- a/src/features/chat/application/runtime/snapshot.ts
+++ b/src/features/chat/application/runtime/snapshot.ts
@@ -8,10 +8,14 @@ interface RuntimeSnapshotInput {
   activeThread: Pick<ChatState["activeThread"], "id" | "tokenUsage">;
   runtime: ChatState["runtime"];
   rateLimit: ChatState["connection"]["rateLimit"];
-  items: readonly MessageStreamItem[];
+  hasThreadTurns: boolean;
   availableModels: ChatState["connection"]["availableModels"];
 }
 
+export function messageItemsHaveThreadTurns(items: readonly MessageStreamItem[]): boolean {
+  return items.some((item) => item.turnId);
+}
+
 export function runtimeSnapshotForChatSlices(input: RuntimeSnapshotInput): RuntimeSnapshot {
   return {
     runtimeConfig: input.runtimeConfig,
@@ -30,7 +34,7 @@ export function runtimeSnapshotForChatSlices(input: RuntimeSnapshotInput): Runti
     requestedFastMode: input.runtime.requestedFastMode,
     tokenUsage: input.activeThread.tokenUsage,
     rateLimit: input.rateLimit,
-    hasThreadTurns: input.items.some((item) => item.turnId),
+    hasThreadTurns: input.hasThreadTurns,
     availableModels: input.availableModels,
   };
 }
@@ -41,7 +45,7 @@ export function runtimeSnapshotForChatState(state: ChatState): RuntimeSnapshot {
     activeThread: state.activeThread,
     runtime: state.runtime,
     rateLimit: state.connection.rateLimit,
-    items: messageStreamItems(state.messageStream),
+    hasThreadTurns: messageItemsHaveThreadTurns(messageStreamItems(state.messageStream)),
     availableModels: state.connection.availableModels,
   });
 }
diff --git a/src/features/chat/host/session-graph.ts b/src/features/chat/host/session-graph.ts
index efe9c2bb..83175b38 100644
--- a/src/features/chat/host/session-graph.ts
+++ b/src/features/chat/host/session-graph.ts
@@ -18,7 +18,7 @@ import type { ComposerSubmitActions } from "../application/conversation/composer
 import { reconnectPanel, type ChatReconnectActionsHost } from "../application/connection/reconnect-actions";
 import { runtimeSnapshotForChatState } from "../application/runtime/snapshot";
 import { createChatRuntimeSettingsActions } from "../application/runtime/settings-actions";
-import { activeTurnId, chatTurnBusy, type ChatAction, type ChatConnectionPhase } from "../application/state/root-reducer";
+import { chatTurnBusy, type ChatAction, type ChatConnectionPhase } from "../application/state/root-reducer";
 import { messageStreamItems } from "../application/state/message-stream";
 import type { ChatStateStore } from "../application/state/store";
 import type { ChatResumeWorkTracker, ChatViewDeferredTasks } from "../application/lifecycle";
@@ -694,7 +694,7 @@ function createSessionComposerController(
     sendShortcut: () => environment.plugin.settingsRef.settings.sendShortcut,
     scrollThreadFromComposerEdges: () => environment.plugin.settingsRef.settings.scrollThreadFromComposerEdges,
     canInterrupt: (state) => {
-      return state.turn.lifecycle.kind !== "idle" && Boolean(state.activeThread.id && activeTurnId(state));
+      return state.turnBusy && Boolean(state.activeThread.id && state.activeTurnId);
     },
     composerProjection: (state) => chatPanelComposerProjection(composerSurface, state),
     currentModelForSuggestions: () => {
diff --git a/src/features/chat/panel/composer-controller.ts b/src/features/chat/panel/composer-controller.ts
index 0be9b38f..b13f7700 100644
--- a/src/features/chat/panel/composer-controller.ts
+++ b/src/features/chat/panel/composer-controller.ts
@@ -1,7 +1,7 @@
 import type { CodexInput } from "../../../domain/chat/input";
 import { isComposerSendKey, type SendShortcut } from "../../../shared/ui/keyboard";
 import { textareaCursorAtVisualBoundary } from "../../../shared/ui/textarea-caret";
-import { chatTurnBusy, type ChatAction, type ChatState } from "../application/state/root-reducer";
+import type { ChatAction, ChatState } from "../application/state/root-reducer";
 import type { ChatStateStore } from "../application/state/store";
 import type { ComposerShellProps } from "../ui/composer";
 import { syncComposerHeight, type ComposerCallbacks } from "../ui/composer";
@@ -64,7 +64,7 @@ export class ChatComposerController {
     return {
       viewId: this.options.viewId,
       draft: state.composer.draft,
-      busy: chatTurnBusy(state),
+      busy: state.turnBusy,
       canInterrupt: this.options.canInterrupt(state),
       normalPlaceholder: projection.placeholder,
       suggestions: state.composer.suggestions,
diff --git a/src/features/chat/panel/shell-state.tsx b/src/features/chat/panel/shell-state.tsx
index a952662d..a06cf1f5 100644
--- a/src/features/chat/panel/shell-state.tsx
+++ b/src/features/chat/panel/shell-state.tsx
@@ -1,8 +1,11 @@
 import { createContext } from "preact";
 import { useContext } from "preact/hooks";
-import { batch, signal, type Signal } from "@preact/signals";
+import { batch, computed, signal, type ReadonlySignal, type Signal } from "@preact/signals";
 
-import type { ChatState } from "../application/state/root-reducer";
+import type { RuntimeSnapshot } from "../domain/runtime/snapshot";
+import { messageItemsHaveThreadTurns, runtimeSnapshotForChatSlices } from "../application/runtime/snapshot";
+import { activeTurnId, chatTurnBusy, type ChatState } from "../application/state/root-reducer";
+import { messageStreamItems } from "../application/state/message-stream";
 
 export interface ChatPanelShellState {
   connection: Signal<ChatState["connection"]>;
@@ -14,6 +17,10 @@ export interface ChatPanelShellState {
   requests: Signal<ChatState["requests"]>;
   composer: Signal<ChatState["composer"]>;
   ui: Signal<ChatState["ui"]>;
+  turnBusy: ReadonlySignal<boolean>;
+  activeTurnId: ReadonlySignal<string | null>;
+  hasThreadTurns: ReadonlySignal<boolean>;
+  composerRuntimeSnapshot: ReadonlySignal<RuntimeSnapshot>;
 }
 
 export type ChatPanelToolbarShellState = Pick<ChatState, "connection" | "threadList" | "activeThread" | "runtime" | "turn" | "ui">;
@@ -22,24 +29,51 @@ export type ChatPanelGoalShellState = Pick<ChatState, "activeThread" | "ui">;
 
 export type ChatPanelMessageStreamShellState = Pick<ChatState, "activeThread" | "runtime" | "turn" | "messageStream" | "requests" | "ui">;
 
-export type ChatPanelComposerShellState = Pick<
+export interface ChatPanelComposerShellState extends Pick<
   ChatState,
-  "connection" | "threadList" | "activeThread" | "runtime" | "turn" | "messageStream" | "composer"
->;
+  "connection" | "threadList" | "activeThread" | "runtime" | "composer"
+> {
+  readonly turnBusy: boolean;
+  readonly activeTurnId: string | null;
+  readonly runtimeSnapshot: RuntimeSnapshot;
+}
 
 export const ChatPanelShellStateContext = createContext<ChatPanelShellState | null>(null);
 
 export function createChatPanelShellState(initialState: ChatState): ChatPanelShellState {
+  const connection = signal(initialState.connection);
+  const threadList = signal(initialState.threadList);
+  const activeThread = signal(initialState.activeThread);
+  const runtime = signal(initialState.runtime);
+  const turn = signal(initialState.turn);
+  const messageStream = signal(initialState.messageStream);
+  const requests = signal(initialState.requests);
+  const composer = signal(initialState.composer);
+  const ui = signal(initialState.ui);
+  const hasThreadTurns = computed(() => messageItemsHaveThreadTurns(messageStreamItems(messageStream.value)));
   return {
-    connection: signal(initialState.connection),
-    threadList: signal(initialState.threadList),
-    activeThread: signal(initialState.activeThread),
-    runtime: signal(initialState.runtime),
-    turn: signal(initialState.turn),
-    messageStream: signal(initialState.messageStream),
-    requests: signal(initialState.requests),
-    composer: signal(initialState.composer),
-    ui: signal(initialState.ui),
+    connection,
+    threadList,
+    activeThread,
+    runtime,
+    turn,
+    messageStream,
+    requests,
+    composer,
+    ui,
+    turnBusy: computed(() => chatTurnBusy({ turn: turn.value })),
+    activeTurnId: computed(() => activeTurnId({ turn: turn.value })),
+    hasThreadTurns,
+    composerRuntimeSnapshot: computed(() =>
+      runtimeSnapshotForChatSlices({
+        runtimeConfig: connection.value.runtimeConfig,
+        activeThread: activeThread.value,
+        runtime: runtime.value,
+        rateLimit: connection.value.rateLimit,
+        hasThreadTurns: hasThreadTurns.value,
+        availableModels: connection.value.availableModels,
+      }),
+    ),
   };
 }
 
@@ -92,9 +126,10 @@ export function composerStateFromShellState(shellState: ChatPanelShellState): Ch
     threadList: shellState.threadList.value,
     activeThread: shellState.activeThread.value,
     runtime: shellState.runtime.value,
-    turn: shellState.turn.value,
-    messageStream: shellState.messageStream.value,
     composer: shellState.composer.value,
+    turnBusy: shellState.turnBusy.value,
+    activeTurnId: shellState.activeTurnId.value,
+    runtimeSnapshot: shellState.composerRuntimeSnapshot.value,
   };
 }
 
diff --git a/src/features/chat/panel/surface/composer-projection.tsx b/src/features/chat/panel/surface/composer-projection.tsx
index cb605615..72aa5000 100644
--- a/src/features/chat/panel/surface/composer-projection.tsx
+++ b/src/features/chat/panel/surface/composer-projection.tsx
@@ -17,7 +17,6 @@ import type { RuntimeSnapshot } from "../../domain/runtime/snapshot";
 import { ComposerShell, type ComposerShellProps } from "../../ui/composer";
 import { composerStateFromShellState, useChatPanelShellState, type ChatPanelComposerShellState } from "../shell-state";
 import { explicitThreadName } from "../../../../domain/threads/model";
-import { runtimeSnapshotForShellState } from "./runtime-snapshot";
 
 interface RestoredThreadTitleSnapshot {
   threadId: string;
@@ -105,7 +104,7 @@ export function chatPanelComposerProjection(
   surface: ChatPanelComposerSurface,
   state: ChatPanelComposerShellState,
 ): ChatPanelComposerProjection {
-  const snapshot = runtimeSnapshotForShellState(state);
+  const snapshot = state.runtimeSnapshot;
   return {
     placeholder: composerPlaceholder(activeComposerThreadName(state, surface.thread.restoredPlaceholder())),
     meta: {
diff --git a/src/features/chat/panel/surface/runtime-snapshot.ts b/src/features/chat/panel/surface/runtime-snapshot.ts
index 9f7f88bf..1b76e569 100644
--- a/src/features/chat/panel/surface/runtime-snapshot.ts
+++ b/src/features/chat/panel/surface/runtime-snapshot.ts
@@ -1,15 +1,10 @@
-import { messageStreamItems } from "../../application/state/message-stream";
 import type { RuntimeSnapshot } from "../../domain/runtime/snapshot";
 import { runtimeSnapshotForChatSlices } from "../../application/runtime/snapshot";
-import type { ChatPanelComposerShellState, ChatPanelToolbarShellState } from "../shell-state";
-
-export function runtimeSnapshotForShellState(state: ChatPanelComposerShellState): RuntimeSnapshot {
-  return runtimeSnapshotForSurfaceState(state, messageStreamItems(state.messageStream));
-}
+import type { ChatPanelToolbarShellState } from "../shell-state";
 
 export function runtimeSnapshotForToolbarShellState(state: ChatPanelToolbarShellState): RuntimeSnapshot {
   // Toolbar shell state intentionally avoids subscribing to messageStream.
-  return runtimeSnapshotForSurfaceState(state, []);
+  return runtimeSnapshotForSurfaceState(state, false);
 }
 
 function runtimeSnapshotForSurfaceState(
@@ -18,14 +13,14 @@ function runtimeSnapshotForSurfaceState(
     readonly activeThread: ChatPanelToolbarShellState["activeThread"];
     readonly runtime: ChatPanelToolbarShellState["runtime"];
   },
-  items: Parameters<typeof runtimeSnapshotForChatSlices>[0]["items"],
+  hasThreadTurns: boolean,
 ): RuntimeSnapshot {
   return runtimeSnapshotForChatSlices({
     runtimeConfig: state.connection.runtimeConfig,
     activeThread: state.activeThread,
     runtime: state.runtime,
     rateLimit: state.connection.rateLimit,
-    items,
+    hasThreadTurns,
     availableModels: state.connection.availableModels,
   });
 }
diff --git a/tests/features/chat/conversation/composer/controller.test.ts b/tests/features/chat/conversation/composer/controller.test.ts
index eb685525..e54b26e1 100644
--- a/tests/features/chat/conversation/composer/controller.test.ts
+++ b/tests/features/chat/conversation/composer/controller.test.ts
@@ -12,6 +12,7 @@ import type { SkillMetadata } from "../../../../../src/domain/catalog/metadata";
 import { installObsidianDomShims } from "../../../../support/dom";
 import type { ChatPanelComposerShellState } from "../../../../../src/features/chat/panel/shell-state";
 import type { NoteCandidateProvider } from "../../../../../src/features/chat/application/composer/note-context";
+import { composerShellStateFromChatState } from "../../support/shell-state";
 
 installObsidianDomShims();
 
@@ -21,7 +22,7 @@ function renderComposerController(
   stateStore: ChatStateStore,
   actions: ChatComposerRenderActions = { submit: vi.fn() },
 ): void {
-  renderUiRoot(parent, h(ComposerShell, controller.renderState(stateStore.getState(), actions)));
+  renderUiRoot(parent, h(ComposerShell, controller.renderState(composerShellStateFromChatState(stateStore.getState()), actions)));
 }
 
 describe("ChatComposerController", () => {
@@ -49,7 +50,7 @@ describe("ChatComposerController", () => {
       onHeightChange: vi.fn(),
     });
 
-    const props = controller.renderState(stateStore.getState(), { submit: vi.fn() });
+    const props = controller.renderState(composerShellStateFromChatState(stateStore.getState()), { submit: vi.fn() });
 
     expect(props.normalPlaceholder).toBe("Projected empty");
     expect(props.meta.statusSummary).toBe(
diff --git a/tests/features/chat/panel/shell.test.tsx b/tests/features/chat/panel/shell.test.tsx
index d902a42d..37571d2f 100644
--- a/tests/features/chat/panel/shell.test.tsx
+++ b/tests/features/chat/panel/shell.test.tsx
@@ -68,6 +68,51 @@ describe("ChatPanelShell", () => {
     });
   });
 
+  it("keeps composer rendering off message stream updates until turn presence changes", async () => {
+    const store = createChatStateStore();
+    const container = document.createElement("div");
+    document.body.appendChild(container);
+    const parts = shellParts();
+    const renderComposerState = vi.fn(parts.composer.renderer.renderState.bind(parts.composer.renderer));
+    parts.composer.renderer.renderState = renderComposerState;
+
+    await act(async () => {
+      renderChatPanelShell(container, { ...shellProps(store), parts });
+      await settleShellEffects();
+    });
+    renderComposerState.mockClear();
+
+    await act(async () => {
+      store.dispatch({
+        type: "message-stream/system-item-added",
+        item: { id: "system-1", kind: "system", role: "system", text: "Status only." },
+      });
+      await settleShellEffects();
+    });
+    expect(renderComposerState).not.toHaveBeenCalled();
+
+    await act(async () => {
+      store.dispatch({
+        type: "message-stream/item-added",
+        item: {
+          id: "assistant-1",
+          turnId: "turn-1",
+          kind: "message",
+          messageKind: "assistantResponse",
+          messageState: "completed",
+          role: "assistant",
+          text: "Turn response.",
+        },
+      });
+      await settleShellEffects();
+    });
+    expect(renderComposerState).toHaveBeenCalledTimes(1);
+
+    await act(async () => {
+      unmountChatPanelShell(container);
+    });
+  });
+
   it("removes and restores the toolbar from shell props without replacing the body regions", async () => {
     const store = createChatStateStore();
     const container = document.createElement("div");
diff --git a/tests/features/chat/panel/surface/projection.test.ts b/tests/features/chat/panel/surface/projection.test.ts
index a1644eb2..4e33038c 100644
--- a/tests/features/chat/panel/surface/projection.test.ts
+++ b/tests/features/chat/panel/surface/projection.test.ts
@@ -22,6 +22,7 @@ import { ChatPanelShellStateContext, createChatPanelShellState } from "../../../
 import type { ToolbarActions } from "../../../../../src/features/chat/ui/toolbar";
 import { renderUiRoot, unmountUiRoot } from "../../../../../src/shared/ui/ui-root";
 import { installObsidianDomShims } from "../../../../support/dom";
+import { composerShellStateFromChatState } from "../../support/shell-state";
 
 installObsidianDomShims();
 
@@ -110,7 +111,7 @@ describe("chat panel surface projections", () => {
       },
     });
 
-    expect(chatPanelComposerProjection(composerSurfaceFixture(), state).meta).toMatchObject({
+    expect(composerProjectionFromState(composerSurfaceFixture(), state).meta).toMatchObject({
       fatal: null,
       context: {
         cells: [
@@ -145,7 +146,7 @@ describe("chat panel surface projections", () => {
     ]);
     state = chatStateWith(state, { connection: { runtimeConfig: runtimeConfigFixture({ model: "gpt-5.5" }) } });
 
-    expect(chatPanelComposerProjection(composerSurfaceFixture(), state).meta).toMatchObject({
+    expect(composerProjectionFromState(composerSurfaceFixture(), state).meta).toMatchObject({
       fatal: null,
       context: {
         cells: [
@@ -175,7 +176,7 @@ describe("chat panel surface projections", () => {
       },
     });
 
-    expect(chatPanelComposerProjection(composerSurfaceFixture(), state).meta).toMatchObject({
+    expect(composerProjectionFromState(composerSurfaceFixture(), state).meta).toMatchObject({
       context: {
         cells: [
           { text: "⣀", placeholder: true },
@@ -193,7 +194,7 @@ describe("chat panel surface projections", () => {
     let state = chatStateFixture();
     state = chatStateWith(state, { connection: { phase: { kind: "failed", message: "Connection failed." } } });
 
-    expect(chatPanelComposerProjection(composerSurfaceFixture(), state).meta).toMatchObject({
+    expect(composerProjectionFromState(composerSurfaceFixture(), state).meta).toMatchObject({
       fatal: "Codex app-server disconnected",
       context: {
         cells: [
@@ -263,7 +264,7 @@ describe("chat panel surface projections", () => {
     const selectedModels: string[] = [];
     const selectedEfforts: string[] = [];
 
-    const choices = chatPanelComposerProjection(
+    const choices = composerProjectionFromState(
       composerSurfaceFixture({
         runtime: {
           requestModel: async (model) => {
@@ -344,7 +345,7 @@ describe("chat panel surface projections", () => {
     });
     state = chatStateWith(state, { connection: { availableModels: [modelFixture("gpt-5.5")] } });
 
-    const projection = chatPanelComposerProjection(composerSurfaceFixture(), state);
+    const projection = composerProjectionFromState(composerSurfaceFixture(), state);
 
     expect(projection).toMatchObject({
       placeholder: "Ask Codex to work on this task...",
@@ -362,8 +363,8 @@ describe("chat panel surface projections", () => {
     activeState = chatStateWith(activeState, { activeThread: { id: "thread-1" } });
     activeState = chatStateWith(activeState, { threadList: { listedThreads: [threadFixture("thread-1", "Active")] } });
 
-    expect(chatPanelComposerProjection(composerSurfaceFixture(), activeState).placeholder).toBe("Ask Codex to work on “Active”...");
-    expect(chatPanelComposerProjection(composerSurfaceFixture(), chatStateFixture()).placeholder).toBe("Ask Codex to work on this task...");
+    expect(composerProjectionFromState(composerSurfaceFixture(), activeState).placeholder).toBe("Ask Codex to work on “Active”...");
+    expect(composerProjectionFromState(composerSurfaceFixture(), chatStateFixture()).placeholder).toBe("Ask Codex to work on this task...");
   });
 
   it("uses restored thread names in the composer projection", () => {
@@ -372,7 +373,7 @@ describe("chat panel surface projections", () => {
     state = chatStateWith(state, { threadList: { listedThreads: [threadFixture("thread-1", null)] } });
 
     expect(
-      chatPanelComposerProjection(
+      composerProjectionFromState(
         composerSurfaceFixture({
           thread: {
             restoredPlaceholder: () => ({ threadId: "thread-1", title: "Restored", explicitName: "Restored" }),
@@ -404,6 +405,10 @@ function renderWithShellState(state: ChatState, node: ComponentChild): HTMLEleme
   return parent;
 }
 
+function composerProjectionFromState(surface: ChatPanelComposerSurface, state: ChatState) {
+  return chatPanelComposerProjection(surface, composerShellStateFromChatState(state));
+}
+
 function clickLabeledButton(parent: HTMLElement, label: string): void {
   const button = Array.from(parent.querySelectorAll<HTMLButtonElement>("button")).find((item) => item.getAttribute("aria-label") === label);
   if (!button) throw new Error(`Expected button: ${label}`);
diff --git a/tests/features/chat/support/shell-state.ts b/tests/features/chat/support/shell-state.ts
new file mode 100644
index 00000000..8898b928
--- /dev/null
+++ b/tests/features/chat/support/shell-state.ts
@@ -0,0 +1,16 @@
+import { runtimeSnapshotForChatState } from "../../../../src/features/chat/application/runtime/snapshot";
+import { activeTurnId, chatTurnBusy, type ChatState } from "../../../../src/features/chat/application/state/root-reducer";
+import type { ChatPanelComposerShellState } from "../../../../src/features/chat/panel/shell-state";
+
+export function composerShellStateFromChatState(state: ChatState): ChatPanelComposerShellState {
+  return {
+    connection: state.connection,
+    threadList: state.threadList,
+    activeThread: state.activeThread,
+    runtime: state.runtime,
+    composer: state.composer,
+    turnBusy: chatTurnBusy(state),
+    activeTurnId: activeTurnId(state),
+    runtimeSnapshot: runtimeSnapshotForChatState(state),
+  };
+}