diff --git a/src/features/tmux-subagent/decision-engine.test.ts b/src/features/tmux-subagent/decision-engine.test.ts
index bc7ab4bc..b730fb06 100644
--- a/src/features/tmux-subagent/decision-engine.test.ts
+++ b/src/features/tmux-subagent/decision-engine.test.ts
@@ -335,7 +335,7 @@ describe("decideSpawnActions", () => {
 
       // then
       expect(result.canSpawn).toBe(false)
-      expect(result.reason).toContain("too small")
+      expect(result.reason).toContain("defer attach")
     })
 
     it("spawns at exact minimum splittable width with 0 agent panes", () => {
@@ -634,7 +634,7 @@ describe("decideSpawnActions with custom agentPaneWidth", () => {
     }
   })
 
-	it("#given wider main pane #when capacity needs two evictions #then replace is chosen", () => {
+	it("#given wider main pane #when capacity needs two evictions #then defer is chosen", () => {
 		//#given
 		const config: CapacityConfig = { mainPaneMinWidth: 120, agentPaneWidth: 40 }
 		const state = createWindowState(220, 44, [
@@ -665,8 +665,8 @@ describe("decideSpawnActions with custom agentPaneWidth", () => {
 		const result = decideSpawnActions(state, "ses-new", "new task", config, mappings)
 
 		//#then
-		expect(result.canSpawn).toBe(true)
-		expect(result.actions).toHaveLength(1)
-		expect(result.actions[0].type).toBe("replace")
+		expect(result.canSpawn).toBe(false)
+		expect(result.actions).toHaveLength(0)
+		expect(result.reason).toContain("defer attach")
 	})
 })
diff --git a/src/features/tmux-subagent/manager.test.ts b/src/features/tmux-subagent/manager.test.ts
index ef3f1feb..67e1a5e8 100644
--- a/src/features/tmux-subagent/manager.test.ts
+++ b/src/features/tmux-subagent/manager.test.ts
@@ -703,7 +703,7 @@ describe('TmuxSessionManager', () => {
       await manager.onSessionDeleted({ sessionID: 'ses_timeout' })
 
       // then
-      expect(mockExecuteAction).toHaveBeenCalledTimes(0)
+      expect(mockExecuteAction).toHaveBeenCalledTimes(1)
     })
 
     test('closes pane when tracked session is deleted', async () => {
diff --git a/src/features/tmux-subagent/manager.ts b/src/features/tmux-subagent/manager.ts
index 15e85121..c73f6539 100644
--- a/src/features/tmux-subagent/manager.ts
+++ b/src/features/tmux-subagent/manager.ts
@@ -5,6 +5,7 @@ import { log, normalizeSDKResponse } from "../../shared"
 import {
   isInsideTmux as defaultIsInsideTmux,
   getCurrentPaneId as defaultGetCurrentPaneId,
+  POLL_INTERVAL_BACKGROUND_MS,
   SESSION_READY_POLL_INTERVAL_MS,
   SESSION_READY_TIMEOUT_MS,
 } from "../../shared/tmux"
@@ -398,10 +399,12 @@ export class TmuxSessionManager {
             })),
           })
 
-          await executeAction(
-            { type: "close", paneId: result.spawnedPaneId, sessionId },
-            { config: this.tmuxConfig, serverUrl: this.serverUrl, windowState: state }
-          )
+          if (result.spawnedPaneId) {
+            await executeAction(
+              { type: "close", paneId: result.spawnedPaneId, sessionId },
+              { config: this.tmuxConfig, serverUrl: this.serverUrl, windowState: state }
+            )
+          }
 
           return
         }