feat(web): support slash commands in gateway web chat input

web/src/contexts/AgentContext.tsx

@@ -22,6 +22,13 @@ export interface ChatMessage {
   markdown?: boolean;
   toolCall?: ToolCallInfo;
   timestamp: Date;
+  /**
+   * Locally-generated info/system message produced by web slash-command
+   * handlers (`/help`, `/model`, unknown-command notices). Excluded from
+   * persistence so command output does not pollute localStorage and reappear
+   * as fake assistant replies on reload. See #7137.
+   */
+  local?: boolean;
 }
 
 interface AgentContextValue {
@@ -40,6 +47,13 @@ interface AgentContextValue {
   refreshModels: () => void;
   deleteMessage: (id: string) => void;
   clearAllMessages: () => void;
+  /**
+   * Append a locally-generated info/system message to the transcript without
+   * sending anything to the gateway. Used by web slash-command handlers
+   * (`/help`, `/model`, unknown-command notices) to surface feedback inline.
+   * See #7137.
+   */
+  addLocalMessage: (content: string) => void;
   abortSession: () => Promise<void>;
   /**
    * Pending supervised-mode tool-approval prompt, or null. Populated when the
@@ -723,6 +737,21 @@ export function AgentProvider({ agentAlias, children }: AgentProviderProps) {
     })();
   }, [agentAlias, attachSocketCallbacks]);
 
+  const addLocalMessage = useCallback((content: string) => {
+    localMessageMutationVersionRef.current += 1;
+    setMessages((prev) => [
+      ...prev,
+      {
+        id: generateUUID(),
+        role: 'agent',
+        content,
+        markdown: true,
+        timestamp: new Date(),
+        local: true,
+      },
+    ]);
+  }, []);
+
   const respondToApproval = useCallback((decision: ApprovalDecision) => {
     setPendingApproval((current) => {
       if (!current) return null;
@@ -750,6 +779,7 @@ export function AgentProvider({ agentAlias, children }: AgentProviderProps) {
     refreshModels: () => setModelInfoVersion((v) => v + 1),
     deleteMessage,
     clearAllMessages,
+    addLocalMessage,
     abortSession: async () => {
       // Clear local approval state immediately — the in-flight request_id
       // belongs to the turn we're cancelling and will be rejected by the

web/src/lib/chatHistoryStorage.ts

@@ -107,15 +107,21 @@ export function uiMessagesToPersisted(
     markdown?: boolean;
     toolCall?: { name: string; args?: unknown; output?: string };
     timestamp: Date;
+    local?: boolean;
   }>,
 ): PersistedChatBubble[] {
-  return messages.map((m) => ({
-    id: m.id,
-    role: m.role,
-    content: m.content,
-    thinking: m.thinking,
-    markdown: m.markdown,
-    toolCall: m.toolCall,
-    timestamp: m.timestamp.toISOString(),
-  }));
+  return messages
+    // Skip messages flagged `local: true` (web slash-command output like /help,
+    // /model banners, unknown-command notices). They are ephemeral UI feedback
+    // and must not be re-hydrated as fake assistant replies on reload. #7137
+    .filter((m) => !m.local)
+    .map((m) => ({
+      id: m.id,
+      role: m.role,
+      content: m.content,
+      thinking: m.thinking,
+      markdown: m.markdown,
+      toolCall: m.toolCall,
+      timestamp: m.timestamp.toISOString(),
+    }));
 }