diff --git a/packages/ui/src/components/chat/ChatInput.tsx b/packages/ui/src/components/chat/ChatInput.tsx
index 2f04f958..6c93cb21 100644
--- a/packages/ui/src/components/chat/ChatInput.tsx
+++ b/packages/ui/src/components/chat/ChatInput.tsx
@@ -1463,14 +1463,21 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
                 return;
             }
             else if (commandName === 'compact' && currentSessionId) {
-                const { opencodeClient } = await import('@/lib/opencode/client');
-                const sdk = opencodeClient.getSdkClient();
-                const configState = useConfigStore.getState();
-                await sdk.session.summarize({
-                    sessionID: currentSessionId,
-                    modelID: configState.currentModelId || '',
-                    providerID: configState.currentProviderId || '',
-                });
+                try {
+                    if (!useConfigStore.getState().isConnected) {
+                        throw new Error("Connection lost. Please wait for reconnection.");
+                    }
+                    const { opencodeClient } = await import('@/lib/opencode/client');
+                    const sdk = opencodeClient.getSdkClient();
+                    const configState = useConfigStore.getState();
+                    await sdk.session.summarize({
+                        sessionID: currentSessionId,
+                        modelID: configState.currentModelId || '',
+                        providerID: configState.currentProviderId || '',
+                    });
+                } catch (error) {
+                    toast.error(error instanceof Error ? error.message : 'Failed to compact session');
+                }
                 return;
             }
         }
diff --git a/packages/ui/src/sync/event-pipeline.ts b/packages/ui/src/sync/event-pipeline.ts
index 6ebb2e41..7b7a25e1 100644
--- a/packages/ui/src/sync/event-pipeline.ts
+++ b/packages/ui/src/sync/event-pipeline.ts
@@ -33,6 +33,8 @@ export type EventPipelineInput = {
   routeDirectory?: (directory: string, payload: Event) => string
   /** Called after stream reconnects (visibility restore or heartbeat timeout). */
   onReconnect?: () => void
+  /** Called when the stream disconnects (heartbeat timeout, network error, or transport failure). */
+  onDisconnect?: () => void
   transport?: "auto" | "ws" | "sse"
 }
 
@@ -142,9 +144,10 @@ type DirectoryQueue = {
 }
 
 export function createEventPipeline(input: EventPipelineInput) {
-  const { sdk, onEvent, onReconnect, routeDirectory, transport = "auto" } = input
+  const { sdk, onEvent, onReconnect, onDisconnect, routeDirectory, transport = "auto" } = input
   const abort = new AbortController()
   let hasConnected = false
+  let disconnected = false
   let lastEventId: string | undefined
   let wsFallbackUntil = 0
 
@@ -242,6 +245,7 @@ export function createEventPipeline(input: EventPipelineInput) {
   let heartbeat: ReturnType<typeof setTimeout> | undefined
 
   const markConnected = () => {
+    disconnected = false
     if (hasConnected) {
       onReconnect?.()
       return
@@ -506,9 +510,19 @@ export function createEventPipeline(input: EventPipelineInput) {
         const code = typeof error === "object" && error !== null ? (error as { code?: unknown }).code : undefined
         if (currentTransport === "ws" && code === "WS_FALLBACK") {
           retryDelayMs = 0
-        } else if (!isAbortError(error) && !streamErrorLogged) {
-          streamErrorLogged = true
-          console.error("[event-pipeline] stream failed", error)
+        } else if (!isAbortError(error)) {
+          if (!streamErrorLogged) {
+            streamErrorLogged = true
+            console.error("[event-pipeline] stream failed", error)
+          }
+          // Notify consumer that the stream has disconnected, so it can
+          // update connection state (e.g. set isConnected = false).
+          // Guard: only fire once per disconnection cycle to avoid repeated
+          // setState calls on every failed retry attempt.
+          if (!disconnected) {
+            disconnected = true
+            onDisconnect?.()
+          }
         }
       } finally {
         abort.signal.removeEventListener("abort", onAbort)
diff --git a/packages/ui/src/sync/session-actions.ts b/packages/ui/src/sync/session-actions.ts
index e4a05890..d3d6a357 100644
--- a/packages/ui/src/sync/session-actions.ts
+++ b/packages/ui/src/sync/session-actions.ts
@@ -10,6 +10,7 @@ import { useInputStore } from "./input-store"
 import type { ChildStoreManager } from "./child-store"
 import { opencodeClient } from "@/lib/opencode/client"
 import { useGlobalSessionsStore } from "@/stores/useGlobalSessionsStore"
+import { useConfigStore } from "@/stores/useConfigStore"
 import { registerSessionDirectory } from "./sync-refs"
 
 // Reference set by SyncProvider — allows actions to access SDK and stores
@@ -325,6 +326,10 @@ export async function optimisticSend(input: {
     throw new Error("Optimistic refs not set — is useSync() mounted?")
   }
 
+  if (!useConfigStore.getState().isConnected) {
+    throw new Error("Connection lost. Please wait for reconnection.")
+  }
+
   const store = dirStore()
   const messageID = ascendingId("msg")
   const textPartId = ascendingId("prt")
@@ -408,6 +413,9 @@ export async function respondToPermission(
   requestId: string,
   response: "once" | "always" | "reject",
 ): Promise<void> {
+  if (!useConfigStore.getState().isConnected) {
+    throw new Error("Connection lost. Please wait for reconnection.")
+  }
   const result = await getRequestReplyClient("permission", sessionId, requestId).permission.reply({
     requestID: requestId,
     reply: response,
@@ -439,6 +447,9 @@ export async function respondToQuestion(
   requestId: string,
   answers: string[] | string[][],
 ): Promise<void> {
+  if (!useConfigStore.getState().isConnected) {
+    throw new Error("Connection lost. Please wait for reconnection.")
+  }
   const result = await getRequestReplyClient("question", sessionId, requestId).question.reply({
     requestID: requestId,
     answers: answers as Array<Array<string>>,
diff --git a/packages/ui/src/sync/sync-context.tsx b/packages/ui/src/sync/sync-context.tsx
index 5b41cd99..7a586fa7 100644
--- a/packages/ui/src/sync/sync-context.tsx
+++ b/packages/ui/src/sync/sync-context.tsx
@@ -1318,6 +1318,7 @@ export function SyncProvider(props: {
         handleEvent(directory, payload, childStores, routingIndex)
       },
       onReconnect: () => {
+        useConfigStore.setState({ isConnected: true })
         for (const [dir, store] of childStores.children) {
           if (reconnectResyncing.has(dir)) continue
           if (getReconnectCandidateSessionIds(store.getState()).length === 0) continue
@@ -1332,6 +1333,9 @@ export function SyncProvider(props: {
             })
         }
       },
+      onDisconnect: () => {
+        useConfigStore.setState({ isConnected: false })
+      },
     })
     return cleanup
   }, [props.sdk, childStores, routingIndex, messageStreamTransport])
diff --git a/packages/web/server/index.js b/packages/web/server/index.js
index 4a5aea38..ec8dcfdf 100644
--- a/packages/web/server/index.js
+++ b/packages/web/server/index.js
@@ -870,6 +870,7 @@ const waitForOpenCodeReady = (...args) => openCodeLifecycleRuntime.waitForOpenCo
 const waitForAgentPresence = (...args) => openCodeLifecycleRuntime.waitForAgentPresence(...args);
 const refreshOpenCodeAfterConfigChange = (...args) => openCodeLifecycleRuntime.refreshOpenCodeAfterConfigChange(...args);
 const startHealthMonitoring = () => openCodeLifecycleRuntime.startHealthMonitoring(HEALTH_CHECK_INTERVAL);
+const triggerHealthCheck = () => openCodeLifecycleRuntime.triggerHealthCheck();
 const scheduledTasksRuntime = createScheduledTasksRuntime({
   projectConfigRuntime,
   listProjects: async () => {
@@ -1155,6 +1156,7 @@ async function main(options = {}) {
     setupProxy,
     scheduleOpenCodeApiDetection,
     bootstrapOpenCodeAtStartup,
+    triggerHealthCheck,
     staticRoutesRuntime,
     process,
     crypto,
diff --git a/packages/web/server/lib/event-stream/runtime.js b/packages/web/server/lib/event-stream/runtime.js
index a25895dc..3eefdea9 100644
--- a/packages/web/server/lib/event-stream/runtime.js
+++ b/packages/web/server/lib/event-stream/runtime.js
@@ -54,6 +54,7 @@ export function createMessageStreamWsRuntime({
   getOpenCodeAuthHeaders,
   processForwardedEventPayload,
   wsClients,
+  triggerHealthCheck,
   fetchImpl = fetch,
 }) {
   const wsServer = new WebSocketServer({
@@ -136,6 +137,10 @@ export function createMessageStreamWsRuntime({
         if (!controller.signal.aborted) {
           sendMessageStreamWsFrame(socket, { type: 'error', message: 'Failed to connect to OpenCode event stream' });
           socket.close(1011, 'Failed to connect to OpenCode event stream');
+          // Trigger immediate health check so the server detects and
+          // restarts a dead OpenCode process without waiting for the next
+          // periodic interval (up to 15 s).
+          triggerHealthCheck?.();
         }
         return;
       }
@@ -146,6 +151,7 @@ export function createMessageStreamWsRuntime({
           message: `OpenCode event stream unavailable (${upstream.status})`,
         });
         socket.close(1011, 'OpenCode event stream unavailable');
+        triggerHealthCheck?.();
         return;
       }
 
diff --git a/packages/web/server/lib/opencode/lifecycle.js b/packages/web/server/lib/opencode/lifecycle.js
index 9d85d028..a4be1884 100644
--- a/packages/web/server/lib/opencode/lifecycle.js
+++ b/packages/web/server/lib/opencode/lifecycle.js
@@ -714,6 +714,25 @@ export const createOpenCodeLifecycleRuntime = (deps) => {
     }
   };
 
+  /**
+   * Perform an immediate (one-shot) health check and restart OpenCode if it's
+   * not healthy.  Callers on the SSE / WS proxy path use this to trigger
+   * recovery without waiting for the next periodic interval (up to 15 s).
+   */
+  const triggerHealthCheck = async () => {
+    if (!state.openCodeProcess || state.isShuttingDown || state.isRestartingOpenCode) return;
+
+    try {
+      const healthy = await isOpenCodeProcessHealthy();
+      if (!healthy) {
+        console.log('[lifecycle] immediate health check: OpenCode not healthy, restarting...');
+        await restartOpenCode();
+      }
+    } catch (error) {
+      console.error(`[lifecycle] immediate health check error: ${error.message}`);
+    }
+  };
+
   const startHealthMonitoring = (healthCheckIntervalMs) => {
     if (state.healthCheckInterval) {
       clearInterval(state.healthCheckInterval);
@@ -743,6 +762,7 @@ export const createOpenCodeLifecycleRuntime = (deps) => {
     refreshOpenCodeAfterConfigChange,
     bootstrapOpenCodeAtStartup,
     startHealthMonitoring,
+    triggerHealthCheck,
     waitForPortRelease,
   };
 };
diff --git a/packages/web/server/lib/opencode/startup-pipeline-runtime.js b/packages/web/server/lib/opencode/startup-pipeline-runtime.js
index 697f0d3c..5860a3e3 100644
--- a/packages/web/server/lib/opencode/startup-pipeline-runtime.js
+++ b/packages/web/server/lib/opencode/startup-pipeline-runtime.js
@@ -22,6 +22,7 @@ export const createStartupPipelineRuntime = (dependencies) => {
       getOpenCodeAuthHeaders,
       processForwardedEventPayload,
       messageStreamWsClients,
+      triggerHealthCheck,
       terminalHeartbeatIntervalMs,
       terminalRebindWindowMs,
       terminalMaxRebindsPerWindow,
@@ -76,6 +77,7 @@ export const createStartupPipelineRuntime = (dependencies) => {
       getOpenCodeAuthHeaders,
       processForwardedEventPayload,
       wsClients: messageStreamWsClients,
+      triggerHealthCheck,
     });
 
     setupProxy(app);