diff --git a/apps/server/trpc/routers/chat-session.ts b/apps/server/trpc/routers/chat-session.ts
index 6f3fb5e..9c2625e 100644
--- a/apps/server/trpc/routers/chat-session.ts
+++ b/apps/server/trpc/routers/chat-session.ts
@@ -8,8 +8,6 @@ import type { ProcedureBuilder } from '../trpc.js';
 import {
   requireAgentManager,
   requireInitiativeRepository,
-  requirePhaseRepository,
-  requirePageRepository,
   requireTaskRepository,
   requireChatSessionRepository,
 } from './_helpers.js';
@@ -83,22 +81,12 @@ export function chatSessionProcedures(publicProcedure: ProcedureBuilder) {
           }
         }
 
-        // Spawn fresh agent with chat history + context
+        // Gather data needed for spawn (fast DB reads) before returning
         const messages = await chatRepo.findMessagesBySessionId(session.id);
         const chatHistory: ChatHistoryEntry[] = messages
           .slice(-MAX_HISTORY_MESSAGES)
           .map(m => ({ role: m.role as 'user' | 'assistant' | 'system', content: m.content }));
 
-        const context = await gatherInitiativeContext(
-          ctx.phaseRepository,
-          ctx.taskRepository,
-          ctx.pageRepository,
-          input.initiativeId,
-        );
-
-        const prompt = buildChatPrompt(input.targetType, input.targetId, chatHistory, input.message);
-
-        // Create a task for the chat agent
         const targetName = input.targetType === 'phase'
           ? (await ctx.phaseRepository?.findById(input.targetId))?.name ?? input.targetId
           : (await ctx.taskRepository?.findById(input.targetId))?.name ?? input.targetId;
@@ -111,34 +99,68 @@ export function chatSessionProcedures(publicProcedure: ProcedureBuilder) {
           status: 'in_progress',
         });
 
-        // Determine target phase/task for input context
-        const targetPhase = input.targetType === 'phase'
-          ? await ctx.phaseRepository?.findById(input.targetId)
-          : undefined;
-        const targetTask = input.targetType === 'task'
-          ? await ctx.taskRepository?.findById(input.targetId)
-          : undefined;
+        const prompt = buildChatPrompt(input.targetType, input.targetId, chatHistory, input.message);
 
-        const agent = await agentManager.spawn({
-          taskId: task.id,
-          prompt,
-          mode: 'chat',
-          provider: input.provider,
-          initiativeId: input.initiativeId,
-          inputContext: {
-            initiative,
-            phase: targetPhase ?? undefined,
-            task: targetTask ?? undefined,
-            pages: context.pages.length > 0 ? context.pages : undefined,
-            phases: context.phases.length > 0 ? context.phases : undefined,
-            tasks: context.tasks.length > 0 ? context.tasks : undefined,
-          },
-        });
+        // Spawn agent in background — worktree creation + file I/O is heavy
+        // and blocks the event loop, causing ECONNREFUSED on the SSE connection.
+        // The UI detects the agent via SSE events (agent:spawned) + query invalidation.
+        const sessionId = session.id;
+        void (async () => {
+          try {
+            const context = await gatherInitiativeContext(
+              ctx.phaseRepository,
+              ctx.taskRepository,
+              ctx.pageRepository,
+              input.initiativeId,
+            );
 
-        // Link agent to session
-        await chatRepo.updateSession(session.id, { agentId: agent.id });
+            const targetPhase = input.targetType === 'phase'
+              ? await ctx.phaseRepository?.findById(input.targetId)
+              : undefined;
+            const targetTask = input.targetType === 'task'
+              ? await ctx.taskRepository?.findById(input.targetId)
+              : undefined;
 
-        return { sessionId: session.id, agentId: agent.id, action: 'spawned' as const };
+            const agent = await agentManager.spawn({
+              taskId: task.id,
+              prompt,
+              mode: 'chat',
+              provider: input.provider,
+              initiativeId: input.initiativeId,
+              inputContext: {
+                initiative,
+                phase: targetPhase ?? undefined,
+                task: targetTask ?? undefined,
+                pages: context.pages.length > 0 ? context.pages : undefined,
+                phases: context.phases.length > 0 ? context.phases : undefined,
+                tasks: context.tasks.length > 0 ? context.tasks : undefined,
+              },
+            });
+
+            await chatRepo.updateSession(sessionId, { agentId: agent.id });
+
+            ctx.eventBus.emit({
+              type: 'chat:message_created' as const,
+              timestamp: new Date(),
+              payload: { chatSessionId: sessionId, role: 'system' as const },
+            });
+          } catch (err) {
+            const msg = err instanceof Error ? err.message : String(err);
+            // Store error as system message so the UI can display it
+            await chatRepo.createMessage({
+              chatSessionId: sessionId,
+              role: 'system',
+              content: `Failed to start agent: ${msg}`,
+            });
+            ctx.eventBus.emit({
+              type: 'chat:message_created' as const,
+              timestamp: new Date(),
+              payload: { chatSessionId: sessionId, role: 'system' as const },
+            });
+          }
+        })();
+
+        return { sessionId: session.id, agentId: null, action: 'spawned' as const };
       }),
 
     getChatSession: publicProcedure