diff --git a/frontend/src/App.css b/frontend/src/App.css
index 3b7e89f4..dad5103e 100644
--- a/frontend/src/App.css
+++ b/frontend/src/App.css
@@ -209,6 +209,16 @@ body,
 	}
 }
 
+/* Spinner for in-progress deterministic merges */
+@keyframes spin {
+	from {
+		transform: rotate(0deg);
+	}
+	to {
+		transform: rotate(360deg);
+	}
+}
+
 /* Agent lozenge appearance animation (simulates arriving from agents panel) */
 @keyframes agentAppear {
 	from {
diff --git a/frontend/src/api/client.test.ts b/frontend/src/api/client.test.ts
index 9c03cab7..dbd2ff5f 100644
--- a/frontend/src/api/client.test.ts
+++ b/frontend/src/api/client.test.ts
@@ -267,6 +267,7 @@ describe("ChatWebSocket", () => {
 			qa: [],
 			merge: [],
 			done: [],
+			deterministic_merges_in_flight: [],
 		};
 		instances[1].simulateMessage({ type: "pipeline_state", ...freshState });
 
diff --git a/frontend/src/api/client/types.ts b/frontend/src/api/client/types.ts
index 1cff0982..71448b20 100644
--- a/frontend/src/api/client/types.ts
+++ b/frontend/src/api/client/types.ts
@@ -69,6 +69,8 @@ export interface PipelineState {
 	qa: PipelineStageItem[];
 	merge: PipelineStageItem[];
 	done: PipelineStageItem[];
+	/** Story IDs that currently have a deterministic merge in progress. */
+	deterministic_merges_in_flight: string[];
 }
 
 /** A message received from the Huskies server over WebSocket. */
@@ -84,6 +86,7 @@ export type WsResponse =
 			qa: PipelineStageItem[];
 			merge: PipelineStageItem[];
 			done: PipelineStageItem[];
+			deterministic_merges_in_flight: string[];
 	  }
 	| {
 			type: "permission_request";
diff --git a/frontend/src/api/client/websocket.ts b/frontend/src/api/client/websocket.ts
index 7ce62541..8367a092 100644
--- a/frontend/src/api/client/websocket.ts
+++ b/frontend/src/api/client/websocket.ts
@@ -123,6 +123,8 @@ export class ChatWebSocket {
 						qa: data.qa,
 						merge: data.merge,
 						done: data.done,
+						deterministic_merges_in_flight:
+							data.deterministic_merges_in_flight ?? [],
 					});
 				if (data.type === "permission_request")
 					this.onPermissionRequest?.(
diff --git a/frontend/src/components/ChatPipelinePanel.tsx b/frontend/src/components/ChatPipelinePanel.tsx
index d095722a..28fbc37b 100644
--- a/frontend/src/components/ChatPipelinePanel.tsx
+++ b/frontend/src/components/ChatPipelinePanel.tsx
@@ -110,52 +110,66 @@ export function ChatPipelinePanel({
 							configVersion={agentConfigVersion}
 							stateVersion={agentStateVersion}
 						/>
-						<StagePanel
-							title="Done"
-							items={pipeline.done ?? []}
-							costs={storyTokenCosts}
-							onItemClick={(item) => onSelectWorkItem(item.story_id)}
-							onStopAgent={onStopAgent}
-							onDeleteItem={onDeleteItem}
-						/>
-						<StagePanel
-							title="To Merge"
-							items={pipeline.merge}
-							costs={storyTokenCosts}
-							onItemClick={(item) => onSelectWorkItem(item.story_id)}
-							onStopAgent={onStopAgent}
-							onDeleteItem={onDeleteItem}
-						/>
-						<StagePanel
-							title="QA"
-							items={pipeline.qa}
-							costs={storyTokenCosts}
-							onItemClick={(item) => onSelectWorkItem(item.story_id)}
-							onStopAgent={onStopAgent}
-							onDeleteItem={onDeleteItem}
-						/>
-						<StagePanel
-							title="Current"
-							items={pipeline.current}
-							costs={storyTokenCosts}
-							onItemClick={(item) => onSelectWorkItem(item.story_id)}
-							agentRoster={agentRoster}
-							busyAgentNames={busyAgentNames}
-							onStartAgent={onStartAgent}
-							onStopAgent={onStopAgent}
-							onDeleteItem={onDeleteItem}
-						/>
-						<StagePanel
-							title="Backlog"
-							items={pipeline.backlog}
-							costs={storyTokenCosts}
-							onItemClick={(item) => onSelectWorkItem(item.story_id)}
-							agentRoster={agentRoster}
-							busyAgentNames={busyAgentNames}
-							onStartAgent={onStartAgent}
-							onStopAgent={onStopAgent}
-							onDeleteItem={onDeleteItem}
-						/>
+						{(() => {
+							const mergesInFlight = new Set(
+								pipeline.deterministic_merges_in_flight ?? [],
+							);
+							return (
+								<>
+									<StagePanel
+										title="Done"
+										items={pipeline.done ?? []}
+										costs={storyTokenCosts}
+										onItemClick={(item) => onSelectWorkItem(item.story_id)}
+										onStopAgent={onStopAgent}
+										onDeleteItem={onDeleteItem}
+										mergesInFlight={mergesInFlight}
+									/>
+									<StagePanel
+										title="To Merge"
+										items={pipeline.merge}
+										costs={storyTokenCosts}
+										onItemClick={(item) => onSelectWorkItem(item.story_id)}
+										onStopAgent={onStopAgent}
+										onDeleteItem={onDeleteItem}
+										mergesInFlight={mergesInFlight}
+									/>
+									<StagePanel
+										title="QA"
+										items={pipeline.qa}
+										costs={storyTokenCosts}
+										onItemClick={(item) => onSelectWorkItem(item.story_id)}
+										onStopAgent={onStopAgent}
+										onDeleteItem={onDeleteItem}
+										mergesInFlight={mergesInFlight}
+									/>
+									<StagePanel
+										title="Current"
+										items={pipeline.current}
+										costs={storyTokenCosts}
+										onItemClick={(item) => onSelectWorkItem(item.story_id)}
+										agentRoster={agentRoster}
+										busyAgentNames={busyAgentNames}
+										onStartAgent={onStartAgent}
+										onStopAgent={onStopAgent}
+										onDeleteItem={onDeleteItem}
+										mergesInFlight={mergesInFlight}
+									/>
+									<StagePanel
+										title="Backlog"
+										items={pipeline.backlog}
+										costs={storyTokenCosts}
+										onItemClick={(item) => onSelectWorkItem(item.story_id)}
+										agentRoster={agentRoster}
+										busyAgentNames={busyAgentNames}
+										onStartAgent={onStartAgent}
+										onStopAgent={onStopAgent}
+										onDeleteItem={onDeleteItem}
+										mergesInFlight={mergesInFlight}
+									/>
+								</>
+							);
+						})()}
 						<ServerLogsPanel logs={combinedLogs} />
 					</>
 				)}
diff --git a/frontend/src/components/LozengeFlyContext.agentlozenge.test.tsx b/frontend/src/components/LozengeFlyContext.agentlozenge.test.tsx
index 50316cc8..c8cf9706 100644
--- a/frontend/src/components/LozengeFlyContext.agentlozenge.test.tsx
+++ b/frontend/src/components/LozengeFlyContext.agentlozenge.test.tsx
@@ -14,6 +14,7 @@ function makePipeline(overrides: Partial<PipelineState> = {}): PipelineState {
 		qa: [],
 		merge: [],
 		done: [],
+		deterministic_merges_in_flight: [],
 		...overrides,
 	};
 }
diff --git a/frontend/src/components/LozengeFlyContext.flyin.test.tsx b/frontend/src/components/LozengeFlyContext.flyin.test.tsx
index c730ef4b..26a5629d 100644
--- a/frontend/src/components/LozengeFlyContext.flyin.test.tsx
+++ b/frontend/src/components/LozengeFlyContext.flyin.test.tsx
@@ -14,6 +14,7 @@ function makePipeline(overrides: Partial<PipelineState> = {}): PipelineState {
 		qa: [],
 		merge: [],
 		done: [],
+		deterministic_merges_in_flight: [],
 		...overrides,
 	};
 }
diff --git a/frontend/src/components/LozengeFlyContext.flyout.test.tsx b/frontend/src/components/LozengeFlyContext.flyout.test.tsx
index 59326fc4..0f0c2b9e 100644
--- a/frontend/src/components/LozengeFlyContext.flyout.test.tsx
+++ b/frontend/src/components/LozengeFlyContext.flyout.test.tsx
@@ -14,6 +14,7 @@ function makePipeline(overrides: Partial<PipelineState> = {}): PipelineState {
 		qa: [],
 		merge: [],
 		done: [],
+		deterministic_merges_in_flight: [],
 		...overrides,
 	};
 }
diff --git a/frontend/src/components/LozengeFlyContext.hidden.test.tsx b/frontend/src/components/LozengeFlyContext.hidden.test.tsx
index 34466dd5..e1e4abbb 100644
--- a/frontend/src/components/LozengeFlyContext.hidden.test.tsx
+++ b/frontend/src/components/LozengeFlyContext.hidden.test.tsx
@@ -14,6 +14,7 @@ function makePipeline(overrides: Partial<PipelineState> = {}): PipelineState {
 		qa: [],
 		merge: [],
 		done: [],
+		deterministic_merges_in_flight: [],
 		...overrides,
 	};
 }
diff --git a/frontend/src/components/StagePanel.test.tsx b/frontend/src/components/StagePanel.test.tsx
index db3a83d7..82f5ec5c 100644
--- a/frontend/src/components/StagePanel.test.tsx
+++ b/frontend/src/components/StagePanel.test.tsx
@@ -324,4 +324,71 @@ describe("StagePanel", () => {
 			screen.queryByTestId("merge-failure-reason-31_story_no_failure"),
 		).not.toBeInTheDocument();
 	});
+
+	it("shows merge-in-flight icon when story is in mergesInFlight set", () => {
+		const items: PipelineStageItem[] = [
+			{
+				story_id: "40_story_merging",
+				name: "Merging Story",
+				error: null,
+				merge_failure: null,
+				agent: null,
+				review_hold: null,
+				qa: null,
+				depends_on: null,
+			},
+		];
+		const mergesInFlight = new Set(["40_story_merging"]);
+		render(
+			<StagePanel title="To Merge" items={items} mergesInFlight={mergesInFlight} />,
+		);
+		expect(
+			screen.getByTestId("merge-in-flight-icon-40_story_merging"),
+		).toBeInTheDocument();
+	});
+
+	it("does not show merge-in-flight icon when story is not in mergesInFlight set", () => {
+		const items: PipelineStageItem[] = [
+			{
+				story_id: "41_story_not_merging",
+				name: "Idle Story",
+				error: null,
+				merge_failure: null,
+				agent: null,
+				review_hold: null,
+				qa: null,
+				depends_on: null,
+			},
+		];
+		const mergesInFlight = new Set(["99_story_other"]);
+		render(
+			<StagePanel
+				title="To Merge"
+				items={items}
+				mergesInFlight={mergesInFlight}
+			/>,
+		);
+		expect(
+			screen.queryByTestId("merge-in-flight-icon-41_story_not_merging"),
+		).not.toBeInTheDocument();
+	});
+
+	it("does not show merge-in-flight icon when mergesInFlight prop is absent", () => {
+		const items: PipelineStageItem[] = [
+			{
+				story_id: "42_story_no_prop",
+				name: "No Prop Story",
+				error: null,
+				merge_failure: null,
+				agent: null,
+				review_hold: null,
+				qa: null,
+				depends_on: null,
+			},
+		];
+		render(<StagePanel title="To Merge" items={items} />);
+		expect(
+			screen.queryByTestId("merge-in-flight-icon-42_story_no_prop"),
+		).not.toBeInTheDocument();
+	});
 });
diff --git a/frontend/src/components/StagePanel.tsx b/frontend/src/components/StagePanel.tsx
index 14e06111..699fcb81 100644
--- a/frontend/src/components/StagePanel.tsx
+++ b/frontend/src/components/StagePanel.tsx
@@ -53,6 +53,8 @@ interface StagePanelProps {
 	busyAgentNames?: Set<string>;
 	/** Called when the user requests to start an agent on a story. */
 	onStartAgent?: (storyId: string, agentName?: string) => void;
+	/** Set of story IDs that currently have a deterministic merge in progress. */
+	mergesInFlight?: Set<string>;
 }
 
 function AgentLozenge({
@@ -259,6 +261,7 @@ export function StagePanel({
 	agentRoster,
 	busyAgentNames,
 	onStartAgent,
+	mergesInFlight,
 }: StagePanelProps) {
 	const showStartButton =
 		Boolean(onStartAgent) &&
@@ -355,6 +358,19 @@ export function StagePanel({
 												✕
 											</span>
 										)}
+										{mergesInFlight?.has(item.story_id) && (
+											<span
+												data-testid={`merge-in-flight-icon-${item.story_id}`}
+												title="Deterministic merge in progress"
+												style={{
+													display: "inline-block",
+													marginRight: "6px",
+													animation: "spin 1s linear infinite",
+												}}
+											>
+												⟳
+											</span>
+										)}
 										{itemNumber && (
 											<span
 												style={{
diff --git a/frontend/src/hooks/useChatWebSocket.ts b/frontend/src/hooks/useChatWebSocket.ts
index 2aa4216a..78b93064 100644
--- a/frontend/src/hooks/useChatWebSocket.ts
+++ b/frontend/src/hooks/useChatWebSocket.ts
@@ -103,6 +103,7 @@ export function useChatWebSocket({
 		qa: [],
 		merge: [],
 		done: [],
+		deterministic_merges_in_flight: [],
 	});
 	const [pipelineVersion, setPipelineVersion] = useState(0);
 	const [reconciliationActive, setReconciliationActive] = useState(false);
diff --git a/server/src/http/workflow/pipeline.rs b/server/src/http/workflow/pipeline.rs
index 089b9307..44f1b22d 100644
--- a/server/src/http/workflow/pipeline.rs
+++ b/server/src/http/workflow/pipeline.rs
@@ -57,6 +57,8 @@ pub struct PipelineState {
     pub qa: Vec<UpcomingStory>,
     pub merge: Vec<UpcomingStory>,
     pub done: Vec<UpcomingStory>,
+    /// Story IDs that currently have a deterministic merge in progress.
+    pub deterministic_merges_in_flight: Vec<String>,
 }
 
 /// Load the full pipeline state (all 5 active stages).
@@ -71,12 +73,19 @@ pub fn load_pipeline_state(ctx: &AppContext) -> Result<PipelineState, String> {
 
     let typed_items = crate::pipeline_state::read_all_typed();
 
+    let deterministic_merges_in_flight = ctx
+        .services
+        .agents
+        .list_running_merges()
+        .unwrap_or_default();
+
     let mut state = PipelineState {
         backlog: Vec::new(),
         current: Vec::new(),
         qa: Vec::new(),
         merge: Vec::new(),
         done: Vec::new(),
+        deterministic_merges_in_flight,
     };
 
     for item in typed_items {
diff --git a/server/src/service/ws/message/convert.rs b/server/src/service/ws/message/convert.rs
index f9bd60fd..06b61d8f 100644
--- a/server/src/service/ws/message/convert.rs
+++ b/server/src/service/ws/message/convert.rs
@@ -53,6 +53,7 @@ pub fn pipeline_state_to_response(s: PipelineState) -> WsResponse {
         qa: s.qa,
         merge: s.merge,
         done: s.done,
+        deterministic_merges_in_flight: s.deterministic_merges_in_flight,
     }
 }
 
@@ -238,6 +239,7 @@ mod tests {
                 blocked: None,
                 depends_on: None,
             }],
+            deterministic_merges_in_flight: vec![],
         };
         let resp = pipeline_state_to_response(state);
         let json = serde_json::to_value(&resp).unwrap();
@@ -260,6 +262,7 @@ mod tests {
             qa: vec![],
             merge: vec![],
             done: vec![],
+            deterministic_merges_in_flight: vec![],
         };
         let resp = pipeline_state_to_response(state);
         let json = serde_json::to_value(&resp).unwrap();
@@ -294,6 +297,7 @@ mod tests {
             qa: vec![],
             merge: vec![],
             done: vec![],
+            deterministic_merges_in_flight: vec![],
         };
         let resp: WsResponse = state.into();
         let json = serde_json::to_value(&resp).unwrap();
diff --git a/server/src/service/ws/message/response.rs b/server/src/service/ws/message/response.rs
index 259b3b5b..4292b930 100644
--- a/server/src/service/ws/message/response.rs
+++ b/server/src/service/ws/message/response.rs
@@ -54,6 +54,8 @@ pub enum WsResponse {
         qa: Vec<UpcomingStory>,
         merge: Vec<UpcomingStory>,
         done: Vec<UpcomingStory>,
+        /// Story IDs that currently have a deterministic merge in progress.
+        deterministic_merges_in_flight: Vec<String>,
     },
     /// `.huskies/project.toml` was modified; the frontend should re-fetch the
     /// agent roster. Does NOT trigger a pipeline state refresh.
@@ -215,6 +217,7 @@ mod tests {
             qa: vec![],
             merge: vec![],
             done: vec![],
+            deterministic_merges_in_flight: vec![],
         };
         let json = serde_json::to_value(&resp).unwrap();
         assert_eq!(json["type"], "pipeline_state");