coder(pending): new-file-from-RightRail create endpoint + modal

POST /api/sessions/:sessionId/pending/create queues a pending_changes create via queueCreate (WriteGuardError -> 422 with the guard message). RightRail gains a 'New file from pasted text' modal (path + content) wired through api.coder.createPendingFile; sessionId is threaded down from App.tsx. The staged change shows in the CoderPane DiffPanel for explicit apply.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/api/client.ts

@@ -346,6 +346,23 @@ export const api = {
           user_message: userMessage,
         }),
       }),
+    // Queue a new-file create from the RightRail browser → BooCoder
+    // pending_changes (operation='create'). Surfaces in the CoderPane DiffPanel
+    // for explicit apply. A WriteGuardError comes back as a 422 whose { error }
+    // body ApiError exposes as .message for inline display.
+    createPendingFile: (sessionId: string, file_path: string, content: string) =>
+      request<{
+        id: string;
+        session_id: string;
+        task_id: string | null;
+        file_path: string;
+        operation: string;
+        status: string;
+        created_at: string;
+      }>(`/api/coder/sessions/${sessionId}/pending/create`, {
+        method: 'POST',
+        body: JSON.stringify({ file_path, content }),
+      }),
   },
 
   agents: {