diff --git a/apps/web/src/components/ChatMarkdown.tsx b/apps/web/src/components/ChatMarkdown.tsx
index f4298fc22..a3d8329ad 100644
--- a/apps/web/src/components/ChatMarkdown.tsx
+++ b/apps/web/src/components/ChatMarkdown.tsx
@@ -213,8 +213,12 @@ function SuspenseShikiCodeBlock({
   const highlightedHtml = useMemo(() => {
     try {
       return highlighter.codeToHtml(code, { lang: language, theme: themeName });
-    } catch {
-      // If highlighting fails for this language, render as plain text
+    } catch (error) {
+      // Log highlighting failures for debugging while falling back to plain text
+      console.warn(
+        `Code highlighting failed for language "${language}", falling back to plain text.`,
+        error instanceof Error ? error.message : error,
+      );
       return highlighter.codeToHtml(code, { lang: "text", theme: themeName });
     }
   }, [code, highlighter, language, themeName]);
diff --git a/apps/web/src/components/PlanSidebar.tsx b/apps/web/src/components/PlanSidebar.tsx
index c465f3989..3b455bd8c 100644
--- a/apps/web/src/components/PlanSidebar.tsx
+++ b/apps/web/src/components/PlanSidebar.tsx
@@ -1,4 +1,4 @@
-import { memo, useState, useCallback } from "react";
+import { memo, useState, useCallback, useRef, useEffect } from "react";
 import { Badge } from "./ui/badge";
 import { Button } from "./ui/button";
 import { ScrollArea } from "./ui/scroll-area";
@@ -66,6 +66,7 @@ const PlanSidebar = memo(function PlanSidebar({
   const [proposedPlanExpanded, setProposedPlanExpanded] = useState(false);
   const [isSavingToWorkspace, setIsSavingToWorkspace] = useState(false);
   const [copied, setCopied] = useState(false);
+  const copiedTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
 
   const planMarkdown = activeProposedPlan?.planMarkdown ?? null;
   const displayedPlanMarkdown = planMarkdown ? stripDisplayedPlanMarkdown(planMarkdown) : null;
@@ -74,8 +75,14 @@ const PlanSidebar = memo(function PlanSidebar({
   const handleCopyPlan = useCallback(() => {
     if (!planMarkdown) return;
     void navigator.clipboard.writeText(planMarkdown);
+    if (copiedTimerRef.current != null) {
+      clearTimeout(copiedTimerRef.current);
+    }
     setCopied(true);
-    setTimeout(() => setCopied(false), 2000);
+    copiedTimerRef.current = setTimeout(() => {
+      setCopied(false);
+      copiedTimerRef.current = null;
+    }, 2000);
   }, [planMarkdown]);
 
   const handleDownload = useCallback(() => {
@@ -115,6 +122,15 @@ const PlanSidebar = memo(function PlanSidebar({
       );
   }, [planMarkdown, workspaceRoot]);
 
+  // Cleanup timeout on unmount
+  useEffect(() => {
+    return () => {
+      if (copiedTimerRef.current != null) {
+        clearTimeout(copiedTimerRef.current);
+      }
+    };
+  }, []);
+
   return (
     <div className="flex h-full w-[340px] shrink-0 flex-col border-l border-border/70 bg-card/50">
       {/* Header */}
diff --git a/apps/web/src/session-logic.ts b/apps/web/src/session-logic.ts
index aa8f3ffc3..9c1f43dbf 100644
--- a/apps/web/src/session-logic.ts
+++ b/apps/web/src/session-logic.ts
@@ -373,7 +373,7 @@ export function findLatestProposedPlan(
       .filter((proposedPlan) => proposedPlan.turnId === latestTurnId)
       .toSorted(
         (left, right) =>
-          left.updatedAt.localeCompare(right.updatedAt) || left.id.localeCompare(right.id),
+          left.updatedAt.localeCompare(right.updatedAt) ?? left.id.localeCompare(right.id),
       )
       .at(-1);
     if (matchingTurnPlan) {
@@ -390,7 +390,7 @@ export function findLatestProposedPlan(
   const latestPlan = [...proposedPlans]
     .toSorted(
       (left, right) =>
-        left.updatedAt.localeCompare(right.updatedAt) || left.id.localeCompare(right.id),
+        left.updatedAt.localeCompare(right.updatedAt) ?? left.id.localeCompare(right.id),
     )
     .at(-1);
   if (!latestPlan) {
diff --git a/apps/web/src/wsTransport.ts b/apps/web/src/wsTransport.ts
index 2882098c4..46c74d909 100644
--- a/apps/web/src/wsTransport.ts
+++ b/apps/web/src/wsTransport.ts
@@ -186,8 +186,9 @@ export class WsTransport {
       this.scheduleReconnect();
     });
 
-    ws.addEventListener("error", () => {
-      // close will follow
+    ws.addEventListener("error", (event) => {
+      // Log WebSocket errors for debugging (close event will follow)
+      console.warn("WebSocket connection error", { type: event.type, url: this.url });
     });
   }