diff --git a/frontend/src/components/Chat.tsx b/frontend/src/components/Chat.tsx
index 6c765c8..02ec9e3 100644
--- a/frontend/src/components/Chat.tsx
+++ b/frontend/src/components/Chat.tsx
@@ -798,6 +798,12 @@ export function Chat({ projectPath, onCloseProject }: ChatProps) {
 		setQueuedMessages([...queuedMessagesRef.current]);
 	}, []);
 
+	const handleStopAgent = useCallback((storyId: string, agentName: string) => {
+		agentsApi.stopAgent(storyId, agentName).catch((err: unknown) => {
+			console.error("Failed to stop agent:", err);
+		});
+	}, []);
+
 	return (
 		<div
 			className="chat-container"
@@ -1077,18 +1083,21 @@ export function Chat({ projectPath, onCloseProject }: ChatProps) {
 									items={pipeline.done ?? []}
 									costs={storyTokenCosts}
 									onItemClick={(item) => setSelectedWorkItemId(item.story_id)}
+									onStopAgent={handleStopAgent}
 								/>
 								<StagePanel
 									title="To Merge"
 									items={pipeline.merge}
 									costs={storyTokenCosts}
 									onItemClick={(item) => setSelectedWorkItemId(item.story_id)}
+									onStopAgent={handleStopAgent}
 								/>
 								<StagePanel
 									title="QA"
 									items={pipeline.qa}
 									costs={storyTokenCosts}
 									onItemClick={(item) => setSelectedWorkItemId(item.story_id)}
+									onStopAgent={handleStopAgent}
 								/>
 								<StagePanel
 									title="Current"
@@ -1098,6 +1107,7 @@ export function Chat({ projectPath, onCloseProject }: ChatProps) {
 									agentRoster={agentRoster}
 									busyAgentNames={busyAgentNames}
 									onStartAgent={handleStartAgent}
+									onStopAgent={handleStopAgent}
 								/>
 								<StagePanel
 									title="Backlog"
@@ -1107,6 +1117,7 @@ export function Chat({ projectPath, onCloseProject }: ChatProps) {
 									agentRoster={agentRoster}
 									busyAgentNames={busyAgentNames}
 									onStartAgent={handleStartAgent}
+									onStopAgent={handleStopAgent}
 								/>
 								<ServerLogsPanel logs={serverLogs} />
 							</>
diff --git a/frontend/src/components/StagePanel.tsx b/frontend/src/components/StagePanel.tsx
index d0b7766..7189f5a 100644
--- a/frontend/src/components/StagePanel.tsx
+++ b/frontend/src/components/StagePanel.tsx
@@ -43,6 +43,7 @@ interface StagePanelProps {
 	items: PipelineStageItem[];
 	emptyMessage?: string;
 	onItemClick?: (item: PipelineStageItem) => void;
+	onStopAgent?: (storyId: string, agentName: string) => void;
 	/** Map of story_id → total_cost_usd for displaying cost badges. */
 	costs?: Map<string, number>;
 	/** Agent roster to populate the start agent dropdown. */
@@ -56,9 +57,11 @@ interface StagePanelProps {
 function AgentLozenge({
 	agent,
 	storyId,
+	onStop,
 }: {
 	agent: AgentAssignment;
 	storyId: string;
+	onStop?: () => void;
 }) {
 	const { saveSlotRect, pendingFlyIns } = useLozengeFly();
 	const lozengeRef = useRef<HTMLDivElement>(null);
@@ -128,6 +131,31 @@ function AgentLozenge({
 				/>
 			)}
 			{label}
+			{isRunning && onStop && (
+				<button
+					type="button"
+					data-testid={`stop-agent-${storyId}`}
+					onClick={(e) => {
+						e.stopPropagation();
+						onStop();
+					}}
+					title="Stop agent"
+					style={{
+						marginLeft: "4px",
+						padding: "0 3px",
+						background: "transparent",
+						border: "none",
+						color,
+						cursor: "pointer",
+						fontSize: "0.9em",
+						lineHeight: 1,
+						opacity: 0.8,
+						flexShrink: 0,
+					}}
+				>
+					■
+				</button>
+			)}
 		</div>
 	);
 }
@@ -224,6 +252,7 @@ export function StagePanel({
 	items,
 	emptyMessage = "Empty.",
 	onItemClick,
+	onStopAgent,
 	costs,
 	agentRoster,
 	busyAgentNames,
@@ -391,7 +420,19 @@ export function StagePanel({
 									)}
 								</div>
 								{item.agent && (
-									<AgentLozenge agent={item.agent} storyId={item.story_id} />
+									<AgentLozenge
+										agent={item.agent}
+										storyId={item.story_id}
+										onStop={
+											onStopAgent && item.agent.status === "running"
+												? () =>
+														onStopAgent(
+															item.story_id,
+															item.agent?.agent_name ?? "",
+														)
+												: undefined
+										}
+									/>
 								)}
 								{canStart && onStartAgent && (
 									<StartAgentControl