refactor(setting): Improve settings migration and tool loading (#7445)

Co-authored-by: psinha40898 <pyushsinha20@gmail.com>

packages/cli/src/config/settingsSchema.ts

@@ -13,6 +13,17 @@ import type {
 } from '@google/gemini-cli-core';
 import type { CustomTheme } from '../ui/themes/theme.js';
 
+export enum MergeStrategy {
+  // Replace the old value with the new value. This is the default.
+  REPLACE = 'replace',
+  // Concatenate arrays.
+  CONCAT = 'concat',
+  // Merge arrays, ensuring unique values.
+  UNION = 'union',
+  // Shallow merge objects.
+  SHALLOW_MERGE = 'shallow_merge',
+}
+
 export interface SettingDefinition {
   type: 'boolean' | 'string' | 'number' | 'array' | 'object';
   label: string;
@@ -25,6 +36,7 @@ export interface SettingDefinition {
   key?: string;
   properties?: SettingsSchema;
   showInDialog?: boolean;
+  mergeStrategy?: MergeStrategy;
 }
 
 export interface SettingsSchema {
@@ -49,6 +61,7 @@ export const SETTINGS_SCHEMA = {
     default: {} as Record<string, MCPServerConfig>,
     description: 'Configuration for MCP servers.',
     showInDialog: false,
+    mergeStrategy: MergeStrategy.SHALLOW_MERGE,
   },
 
   general: {
@@ -485,6 +498,7 @@ export const SETTINGS_SCHEMA = {
         description:
           'Additional directories to include in the workspace context. Missing directories will be skipped with a warning.',
         showInDialog: false,
+        mergeStrategy: MergeStrategy.CONCAT,
       },
       loadMemoryFromIncludeDirectories: {
         type: 'boolean',
@@ -796,6 +810,7 @@ export const SETTINGS_SCHEMA = {
         default: ['DEBUG', 'DEBUG_MODE'] as string[],
         description: 'Environment variables to exclude from project context.',
         showInDialog: false,
+        mergeStrategy: MergeStrategy.UNION,
       },
       bugCommand: {
         type: 'object',
@@ -847,6 +862,7 @@ export const SETTINGS_SCHEMA = {
         default: [] as string[],
         description: 'List of disabled extensions.',
         showInDialog: false,
+        mergeStrategy: MergeStrategy.UNION,
       },
       workspacesWithMigrationNudge: {
         type: 'array',
@@ -857,6 +873,7 @@ export const SETTINGS_SCHEMA = {
         description:
           'List of workspaces for which the migration nudge has been shown.',
         showInDialog: false,
+        mergeStrategy: MergeStrategy.UNION,
       },
     },
   },