WebUI Architecture Cleanup (#19541)

* webui: architecture foundation (non-MCP core refactors)

* chore: update webui build output

tools/server/webui/src/lib/contexts/message-edit.context.ts

@@ -0,0 +1,39 @@
+import { getContext, setContext } from 'svelte';
+
+export interface MessageEditState {
+	readonly isEditing: boolean;
+	readonly editedContent: string;
+	readonly editedExtras: DatabaseMessageExtra[];
+	readonly editedUploadedFiles: ChatUploadedFile[];
+	readonly originalContent: string;
+	readonly originalExtras: DatabaseMessageExtra[];
+	readonly showSaveOnlyOption: boolean;
+}
+
+export interface MessageEditActions {
+	setContent: (content: string) => void;
+	setExtras: (extras: DatabaseMessageExtra[]) => void;
+	setUploadedFiles: (files: ChatUploadedFile[]) => void;
+	save: () => void;
+	saveOnly: () => void;
+	cancel: () => void;
+	startEdit: () => void;
+}
+
+export type MessageEditContext = MessageEditState & MessageEditActions;
+
+const MESSAGE_EDIT_KEY = Symbol.for('chat-message-edit');
+
+/**
+ * Sets the message edit context. Call this in the parent component (ChatMessage.svelte).
+ */
+export function setMessageEditContext(ctx: MessageEditContext): MessageEditContext {
+	return setContext(MESSAGE_EDIT_KEY, ctx);
+}
+
+/**
+ * Gets the message edit context. Call this in child components.
+ */
+export function getMessageEditContext(): MessageEditContext {
+	return getContext(MESSAGE_EDIT_KEY);
+}