diff --git a/src/app/api/chat/route.ts b/src/app/api/chat/route.ts
index 20438e84..05b6758b 100644
--- a/src/app/api/chat/route.ts
+++ b/src/app/api/chat/route.ts
@@ -4,6 +4,8 @@ import { logger } from "@/lib/utils/logger";
 import { auth } from "@/lib/auth";
 import { headers } from "next/headers";
 import { createChatTools } from "@/lib/ai/tools";
+import { loadWorkspaceState } from "@/lib/workspace/state-loader";
+import { formatSelectedCardsContext } from "@/lib/utils/format-workspace-context";
 
 /**
  * Extract workspaceId from system context or request body
@@ -101,6 +103,39 @@ function cleanMessages(messages: any[]): any[] {
   });
 }
 
+/**
+ * Build selected cards context from card IDs
+ * Fetches workspace state and formats the selected cards for the system prompt
+ */
+async function buildSelectedCardsContext(
+  workspaceId: string | null,
+  selectedCardIds: string[]
+): Promise<string> {
+  if (!workspaceId || !selectedCardIds || selectedCardIds.length === 0) {
+    return "";
+  }
+
+  try {
+    const state = await loadWorkspaceState(workspaceId);
+    const selectedItems = state.items.filter((item) =>
+      selectedCardIds.includes(item.id)
+    );
+
+    if (selectedItems.length === 0) {
+      return "";
+    }
+
+    return formatSelectedCardsContext(selectedItems, state.items);
+  } catch (error) {
+    logger.error("❌ [CHAT-API] Failed to load selected cards context:", {
+      error: error instanceof Error ? error.message : String(error),
+      workspaceId,
+      selectedCardIds,
+    });
+    return "";
+  }
+}
+
 /**
  * Build the enhanced system prompt with guidelines and detection hints
  */
@@ -188,8 +223,27 @@ export async function POST(req: Request) {
     // Clean messages
     const cleanedMessages = cleanMessages(convertedMessages);
 
+    // Build selected cards context
+    const selectedCardIds = body.selectedCardIds || [];
+    const selectedCardsContext = await buildSelectedCardsContext(workspaceId, selectedCardIds);
+
     // Build system prompt
-    const finalSystemPrompt = buildSystemPrompt(system, fileUrls, urlContextUrls);
+    let finalSystemPrompt = buildSystemPrompt(system, fileUrls, urlContextUrls);
+
+    // Inject selected cards context if available
+    if (selectedCardsContext) {
+      finalSystemPrompt = `${finalSystemPrompt}\n\n${selectedCardsContext}`;
+    }
+
+    // Inject reply context if available
+    const replySelections = body.replySelections || [];
+    if (replySelections.length > 0) {
+      const replyContext = replySelections
+        .map((sel: { text: string }) => `> ${sel.text}`)
+        .join("\n");
+
+      finalSystemPrompt = `${finalSystemPrompt}\n\nREPLY CONTEXT:\nThe user is replying specifically to these parts of the previous message:\n${replyContext}`;
+    }
 
     // Get model
     const modelId = body.modelId || "gemini-2.5-pro";
diff --git a/src/components/assistant-ui/WorkspaceRuntimeProvider.tsx b/src/components/assistant-ui/WorkspaceRuntimeProvider.tsx
index ff7bf515..4f35b28a 100644
--- a/src/components/assistant-ui/WorkspaceRuntimeProvider.tsx
+++ b/src/components/assistant-ui/WorkspaceRuntimeProvider.tsx
@@ -14,6 +14,8 @@ interface WorkspaceRuntimeProviderProps {
   children: React.ReactNode;
 }
 
+import { useShallow } from "zustand/react/shallow";
+
 export function WorkspaceRuntimeProvider({
   workspaceId,
   children
@@ -21,6 +23,13 @@ export function WorkspaceRuntimeProvider({
 
   const selectedModelId = useUIStore((state) => state.selectedModelId);
   const activeFolderId = useUIStore((state) => state.activeFolderId);
+  /* 
+    FIX for "Maximum update depth exceeded":
+    We select the Set directly because Array.from() inside the selector creates a new reference on every render,
+    triggering an infinite update loop. The Set reference is stable until changed.
+  */
+  const selectedCardIdsSet = useUIStore((state) => state.selectedCardIds);
+  const replySelections = useUIStore(useShallow((state) => state.replySelections));
   const { data: session } = useSession();
 
   // Create AssistantCloud instance - use anonymous mode for anonymous users
@@ -100,13 +109,15 @@ export function WorkspaceRuntimeProvider({
           workspaceId,
           modelId: selectedModelId,
           activeFolderId,
+          selectedCardIds: Array.from(selectedCardIdsSet),
+          replySelections,
         },
         headers: {
           // Headers for static context if needed
         },
       });
       return transport;
-    }, [workspaceId, selectedModelId, activeFolderId]),
+    }, [workspaceId, selectedModelId, activeFolderId, selectedCardIdsSet, replySelections]),
     onError: handleChatError,
   });
 
diff --git a/src/components/assistant-ui/thread.tsx b/src/components/assistant-ui/thread.tsx
index 4251e666..b9a4c0e0 100644
--- a/src/components/assistant-ui/thread.tsx
+++ b/src/components/assistant-ui/thread.tsx
@@ -629,19 +629,6 @@ const Composer: FC<ComposerProps> = ({ items }) => {
         // Combine all context: selected cards, reply texts, and user message
         let modifiedText = currentText;
 
-        // Add selected cards context with markers (no UI representation, but sent to LLM)
-        // Always append this so LLM knows the selection state (even when nothing is selected)
-        const cardsContext = formatSelectedCardsContext(selectedItems, items);
-        const cardsMarker = "[[SELECTED_CARDS_MARKER]]";
-        modifiedText = modifiedText + `\n\n${cardsMarker}${cardsContext}${cardsMarker}`;
-
-        // Add reply texts with pipe separator if there are replies
-        if (replySelections.length > 0) {
-          const replyTexts = replySelections.map(sel => sel.text).join('|');
-          const specialMarker = "[[REPLY_MARKER]]";
-          modifiedText = modifiedText + `\n\n${specialMarker}${replyTexts}${specialMarker}`;
-        }
-
         // Set the modified text and send
         api.composer().setText(modifiedText);
         api.composer().send();