Merge remote-tracking branch 'origin/likun' into ji

# Conflicts:
#	frontend-web/src/components/workspace/artifacts/artifact-file-detail.tsx
#	frontend-web/src/components/workspace/code-editor.tsx
#	frontend-web/src/components/workspace/input-box.tsx
#	frontend-web/src/pages/ChatPage.tsx
#	offline-backend-20260512/backend/app/gateway/routers/artifacts.py

frontend-web/src/pages/ChatPage.tsx

@@ -4,7 +4,7 @@ import { useCallback, useEffect, useMemo, useState } from "react";
 
 import { type PromptInputMessage } from "@/components/ai-elements/prompt-input";
 import { usePromptPrefixSettings } from "@/core/system-settings/hooks";
-import { ArtifactTrigger } from "@/components/workspace/artifacts";
+import { ArtifactTrigger, useArtifacts } from "@/components/workspace/artifacts";
 import {
   ChatBox,
   useSpecificChatMode,
@@ -44,6 +44,7 @@ export default function ChatPage() {
   const { tokenUsageEnabled } = useModels();
   const { data: promptPrefixSettings } = usePromptPrefixSettings();
   const [promptPrefixOn, setPromptPrefixOn] = useState(false);
+  const { selectedArtifact } = useArtifacts();
   useSpecificChatMode();
 
   useEffect(() => {
@@ -91,6 +92,17 @@ export default function ChatPage() {
     },
   });
 
+  const writingArtifactPath = useMemo(() => {
+    const isMarkdown = (path: string | null | undefined) =>
+      !!path && /\.(md|markdown)(?:$|[?#])/i.test(path);
+    if (isMarkdown(selectedArtifact)) {
+      return selectedArtifact ?? undefined;
+    }
+    return [...(thread.values.artifacts ?? [])]
+      .reverse()
+      .find((path) => isMarkdown(path));
+  }, [selectedArtifact, thread.values.artifacts]);
+
   const handleSubmit = useCallback(
     (message: PromptInputMessage) => {
       // Only the opening turn of a brand-new thread may carry the prefix.
@@ -106,14 +118,31 @@ export default function ChatPage() {
       // The prefix is intentionally NOT concatenated into the message text:
       // doing so would make the user see it. We only flag the request via
       // context; the backend tags the message and PromptPrefixMiddleware
-      // injects the prefix into the LLM request only.
+      // injects the prefix into the LLM request only. Writing mode adds the
+      // active markdown artifact path so the agent keeps editing the canvas.
+      const extraContext: Record<string, unknown> = {};
+      if (shouldApplyPrefix) {
+        extraContext.prompt_prefix_enabled = true;
+      }
+      if (settings.context.writing_mode && writingArtifactPath) {
+        extraContext.writing_artifact_path = writingArtifactPath;
+      }
       void sendMessage(
         threadId,
         message,
-        shouldApplyPrefix ? { prompt_prefix_enabled: true } : undefined,
+        Object.keys(extraContext).length > 0 ? extraContext : undefined,
       );
     },
-    [sendMessage, threadId, isNewThread, hasStartedConversation, promptPrefixOn, promptPrefixSettings],
+    [
+      sendMessage,
+      threadId,
+      isNewThread,
+      hasStartedConversation,
+      promptPrefixOn,
+      promptPrefixSettings,
+      settings.context.writing_mode,
+      writingArtifactPath,
+    ],
   );
 
   const handleClarificationSubmit = useCallback(