feat(vscode-ide-companion/diff): implement diff auto-open functionality in preferred editor group

packages/vscode-ide-companion/src/diff-manager.ts

@@ -12,6 +12,10 @@ import { type JSONRPCNotification } from '@modelcontextprotocol/sdk/types.js';
 import * as path from 'node:path';
 import * as vscode from 'vscode';
 import { DIFF_SCHEME } from './extension.js';
+import {
+  findLeftGroupOfChatWebview,
+  ensureLeftGroupOfChatWebview,
+} from './utils/editorGroupUtils.js';
 
 export class DiffContentProvider implements vscode.TextDocumentContentProvider {
   private content = new Map<string, string>();
@@ -110,13 +114,28 @@ export class DiffManager {
       true,
     );
 
+    // Prefer opening the diff adjacent to the chat webview (so we don't
+    // replace content inside the locked webview group). We try the group to
+    // the left of the chat webview first; if none exists we fall back to
+    // ViewColumn.Beside. With the chat locked in the leftmost group, this
+    // fallback opens diffs to the right of the chat.
+    let targetViewColumn = findLeftGroupOfChatWebview();
+    if (targetViewColumn === undefined) {
+      // If there is no left neighbor, create one to satisfy the requirement of
+      // opening diffs to the left of the chat webview.
+      targetViewColumn = await ensureLeftGroupOfChatWebview();
+    }
+
     await vscode.commands.executeCommand(
       'vscode.diff',
       leftDocUri,
       rightDocUri,
       diffTitle,
       {
-        viewColumn: vscode.ViewColumn.Beside,
+        // If a left-of-webview group was found, target it explicitly so the
+        // diff opens there while keeping focus on the webview. Otherwise, use
+        // the default "open to side" behavior.
+        viewColumn: targetViewColumn ?? vscode.ViewColumn.Beside,
         preview: false,
         preserveFocus: true,
       },