diff --git a/src/client/src/components/ChatView.ts b/src/client/src/components/ChatView.ts
index a0ea093..edd56b8 100644
--- a/src/client/src/components/ChatView.ts
+++ b/src/client/src/components/ChatView.ts
@@ -27,6 +27,8 @@ export class ChatView extends LitElement {
   @property({ type: Number }) messageTotal = 0;
   @property({ type: Boolean }) hasMore = false;
   @property({ type: Boolean }) loadingMore = false;
+  @property({ type: Boolean }) isCompacting = false;
+  @property({ type: Number }) pendingMessageCount = 0;
   @property({ attribute: false }) onLoadMore?: () => void;
   @query(".chat") private chat?: HTMLDivElement;
   @state() private pinnedToBottom = true;
@@ -60,11 +62,23 @@ export class ChatView extends LitElement {
           ${groupChatMessages(this.messages, this.messageStart).map((group) => group.kind === "message"
             ? this.renderMessage(group.message, group.index)
             : this.renderMessageGroup(group.messages, group.startIndex))}
+          ${this.renderSessionActivity()}
         </div>
       </div>
     `;
   }
 
+  private renderSessionActivity() {
+    if (!this.isCompacting) return null;
+    return html`
+      <aside class="session-activity compacting" aria-live="polite">
+        <strong>Compacting history…</strong>
+        <span>The agent is summarizing earlier context. New prompts will be queued until compaction finishes.</span>
+        ${this.pendingMessageCount > 0 ? html`<small>${this.pendingMessageCount} queued ${this.pendingMessageCount === 1 ? "message" : "messages"}</small>` : null}
+      </aside>
+    `;
+  }
+
   private renderHistoryIndicator() {
     if (!this.messages.length || this.messageTotal <= 0) return null;
     const loadedCount = this.messages.length;
diff --git a/src/client/src/components/PiWebApp.ts b/src/client/src/components/PiWebApp.ts
index c050ddc..c5b5672 100644
--- a/src/client/src/components/PiWebApp.ts
+++ b/src/client/src/components/PiWebApp.ts
@@ -114,8 +114,8 @@ export class PiWebApp extends LitElement {
         <main>
           ${state.error ? html`<div class="error">${state.error}</div>` : null}
           ${state.selectedSession ? html`
-            <chat-view .sessionId=${state.selectedSession.id} .messages=${state.messages} .messageStart=${state.messagePageStart} .messageTotal=${state.messagePageTotal} .hasMore=${state.messagePageStart > 0} .loadingMore=${state.isLoadingEarlierMessages} .onLoadMore=${() => this.withChatPrependTransition(() => this.sessions.loadEarlierMessages())}></chat-view>
-            <prompt-editor .sessionId=${state.selectedSession.id} .cwd=${state.selectedWorkspace?.path} .canSteer=${state.status?.isStreaming === true} .onSend=${(text: string, streamingBehavior?: "steer" | "followUp") => this.sessions.send(text, streamingBehavior)} .onStopSession=${() => this.sessions.stopSession()}></prompt-editor>
+            <chat-view .sessionId=${state.selectedSession.id} .messages=${state.messages} .messageStart=${state.messagePageStart} .messageTotal=${state.messagePageTotal} .hasMore=${state.messagePageStart > 0} .loadingMore=${state.isLoadingEarlierMessages} .isCompacting=${state.status?.isCompacting === true} .pendingMessageCount=${state.status?.pendingMessageCount ?? 0} .onLoadMore=${() => this.withChatPrependTransition(() => this.sessions.loadEarlierMessages())}></chat-view>
+            <prompt-editor .sessionId=${state.selectedSession.id} .cwd=${state.selectedWorkspace?.path} .canSteer=${state.status?.isStreaming === true} .isCompacting=${state.status?.isCompacting === true} .onSend=${(text: string, streamingBehavior?: "steer" | "followUp") => this.sessions.send(text, streamingBehavior)} .onStopSession=${() => this.sessions.stopSession()}></prompt-editor>
             <status-bar .status=${state.status} .activity=${state.activity} .workspace=${state.selectedWorkspace}></status-bar>
             ${state.commandDialog !== undefined ? html`<command-picker .title=${state.commandDialog.title} .options=${state.commandDialog.options} .onPick=${(value: string) => this.sessions.respondToCommand(state.commandDialog?.requestId ?? "", value)} .onCancel=${() => { this.sessions.cancelCommand(); }}></command-picker>` : null}
           ` : html`<div class="empty">Select or start a session.</div>`}
diff --git a/src/client/src/components/PromptEditor.ts b/src/client/src/components/PromptEditor.ts
index 46f1bed..01041b7 100644
--- a/src/client/src/components/PromptEditor.ts
+++ b/src/client/src/components/PromptEditor.ts
@@ -11,6 +11,7 @@ export class PromptEditor extends LitElement {
   @property() sessionId?: string;
   @property() cwd?: string;
   @property({ type: Boolean }) canSteer = false;
+  @property({ type: Boolean }) isCompacting = false;
   @property({ attribute: false }) onSend?: (text: string, streamingBehavior?: "steer" | "followUp") => void;
   @property({ attribute: false }) onStopSession?: () => void;
   @query("textarea") private textarea?: HTMLTextAreaElement;
@@ -35,6 +36,7 @@ export class PromptEditor extends LitElement {
   override render() {
     const inputMode = inputModeForDraft(this.draft);
     const shellMode = inputMode.kind === "shell";
+    const queuesInput = this.canSteer || this.isCompacting;
     return html`
       <footer class=${shellMode ? "shell-mode" : ""}>
         <div class="editor-wrap">
@@ -48,11 +50,12 @@ export class PromptEditor extends LitElement {
             placeholder="Message pi... Use / for commands, @ for files"
           ></textarea>
           ${shellMode ? html`<div class="mode-hint">Shell command${inputMode.excludeFromContext ? " · excluded from context" : ""}</div>` : null}
+          ${this.isCompacting && !shellMode ? html`<div class="mode-hint">Compacting history · message will be queued</div>` : null}
           <autocomplete-menu .items=${this.completions} .selectedIndex=${this.selectedIndex} .onPick=${(item: CompletionItem) => { this.pick(item); }}></autocomplete-menu>
         </div>
         <div class="actions">
-          <button ?disabled=${this.disabled} title=${this.canSteer ? "Queue after the current response" : "Send message"} @click=${() => { this.send("followUp"); }}>${this.canSteer ? "Queue" : "Send"}</button>
-          ${this.canSteer ? html`<button ?disabled=${this.disabled} title="Steer the current response before the next model call" @click=${() => { this.send("steer"); }}>Steer</button>` : null}
+          <button ?disabled=${this.disabled} title=${queuesInput ? "Queue until the current activity finishes" : "Send message"} @click=${() => { this.send("followUp"); }}>${queuesInput ? "Queue" : "Send"}</button>
+          ${this.canSteer && !this.isCompacting ? html`<button ?disabled=${this.disabled} title="Steer the current response before the next model call" @click=${() => { this.send("steer"); }}>Steer</button>` : null}
           <button ?disabled=${this.disabled} title="Stop only this Pi session from continuing" @click=${() => this.onStopSession?.()}>Stop session</button>
         </div>
       </footer>
@@ -144,7 +147,7 @@ export class PromptEditor extends LitElement {
     }
     if (event.key === "Enter" && !event.shiftKey) {
       event.preventDefault();
-      this.send(this.canSteer ? "followUp" : undefined);
+      this.send(this.canSteer || this.isCompacting ? "followUp" : undefined);
     }
   }
 
@@ -160,7 +163,7 @@ export class PromptEditor extends LitElement {
     this.draft = "";
     if (this.sessionId !== undefined && this.sessionId !== "") clearDraft(this.sessionId);
     this.completions = [];
-    this.onSend?.(text, this.canSteer ? streamingBehavior : undefined);
+    this.onSend?.(text, this.canSteer || this.isCompacting ? streamingBehavior : undefined);
   }
 
   static override styles = promptEditorStyles;
diff --git a/src/client/src/components/shared.ts b/src/client/src/components/shared.ts
index ad06ab5..9514ded 100644
--- a/src/client/src/components/shared.ts
+++ b/src/client/src/components/shared.ts
@@ -69,6 +69,10 @@ export const chatStyles = css`
   .group-msg.system { color: #ff7b72; }
   .group-msg.bash { color: #3fb950; }
   .history-boundary { display: grid; gap: 3px; margin: 0 0 14px; color: #8b949e; font-size: 12px; text-align: center; }
+  .session-activity { display: grid; gap: 4px; margin: 0 0 14px; padding: 12px; border: 1px solid #30363d; border-radius: 10px; background: #161b22; color: #e6edf3; }
+  .session-activity.compacting { border-color: #a371f7; background: #21132f; }
+  .session-activity strong { color: #d2a8ff; }
+  .session-activity span, .session-activity small { color: #8b949e; }
   .history-boundary small { color: #6e7681; }
   .label { display: block; margin-bottom: 8px; color: #8b949e; font-size: 12px; text-transform: uppercase; }
   formatted-text.part { display: block; }
diff --git a/src/server/sessions/piSessionService.ts b/src/server/sessions/piSessionService.ts
index 4968013..5a7b9f5 100644
--- a/src/server/sessions/piSessionService.ts
+++ b/src/server/sessions/piSessionService.ts
@@ -105,8 +105,8 @@ export class PiSessionService {
 
   async prompt(sessionId: string, text: string, streamingBehavior?: "steer" | "followUp"): Promise<void> {
     const session = await this.getOrOpen(sessionId);
-    const behavior = session.isStreaming ? streamingBehavior ?? "followUp" : undefined;
-    this.publishActivity(session, behavior === "steer" ? "steering queued" : behavior === "followUp" ? "message queued" : "prompt accepted", "active");
+    const behavior = session.isStreaming || session.isCompacting ? streamingBehavior ?? "followUp" : undefined;
+    this.publishActivity(session, session.isCompacting ? "message queued during compaction" : behavior === "steer" ? "steering queued" : behavior === "followUp" ? "message queued" : "prompt accepted", "active");
     void session.prompt(text, behavior === undefined ? undefined : { streamingBehavior: behavior }).catch((error: unknown) => {
       const message = error instanceof Error ? error.message : String(error);
       this.publishActivity(session, "error", "error", message);