Add Host-global thinking and reply language controls.

Inject systemPrompt sections from Netx Ops settings so every preset can switch CoT and final-reply language without changing API/alarm lang.

Co-authored-by: Cursor <cursoragent@cursor.com>

test/model-language.test.mjs

@@ -0,0 +1,52 @@
+import assert from 'node:assert/strict'
+import { test } from 'node:test'
+
+import {
+  languageFromLocale,
+  normalizeReplyLanguage,
+  normalizeThinkingLanguage,
+  replyInstruction,
+  resolveThinkingLanguage,
+  thinkingInstruction,
+  thinkingReminder,
+} from '../src/netx/model-language.ts'
+
+test('normalizeThinkingLanguage accepts aliases and defaults to auto', () => {
+  assert.equal(normalizeThinkingLanguage(undefined), 'auto')
+  assert.equal(normalizeThinkingLanguage('zh'), 'zh-CN')
+  assert.equal(normalizeThinkingLanguage('zh-CN'), 'zh-CN')
+  assert.equal(normalizeThinkingLanguage('en-US'), 'en')
+  assert.equal(normalizeThinkingLanguage('nope'), 'auto')
+})
+
+test('normalizeReplyLanguage accepts aliases and defaults to follow-user', () => {
+  assert.equal(normalizeReplyLanguage(undefined), 'follow-user')
+  assert.equal(normalizeReplyLanguage('auto'), 'follow-user')
+  assert.equal(normalizeReplyLanguage('zh-CN'), 'zh')
+  assert.equal(normalizeReplyLanguage('english'), 'en')
+})
+
+test('resolveThinkingLanguage follows locale when auto', () => {
+  assert.equal(resolveThinkingLanguage('auto', 'zh-CN'), 'zh-CN')
+  assert.equal(resolveThinkingLanguage('auto', 'en-US'), 'en')
+  assert.equal(resolveThinkingLanguage('en', 'zh-CN'), 'en')
+  assert.equal(resolveThinkingLanguage('auto', 'de-DE'), 'en')
+})
+
+test('languageFromLocale covers chinese and english tags', () => {
+  assert.equal(languageFromLocale('zh-Hans-CN'), 'zh-CN')
+  assert.equal(languageFromLocale('en'), 'en')
+  assert.equal(languageFromLocale(''), undefined)
+})
+
+test('thinkingInstruction and reminder mention the target language', () => {
+  const instruction = thinkingInstruction('zh-CN')
+  assert.match(instruction, /Simplified Chinese/)
+  assert.match(thinkingReminder('en'), /English/)
+})
+
+test('replyInstruction is empty for follow-user and forces otherwise', () => {
+  assert.equal(replyInstruction('follow-user'), '')
+  assert.match(replyInstruction('en'), /English/)
+  assert.match(replyInstruction('zh'), /简体中文/)
+})