fix: 构建时替换 feature flags，修复 CoStrict provider 递归解析，默认启用 BUDDY

- build.ts: 构建产物中手动替换 feature('FLAG_NAME') 为 true/false，
  使构建后的产物正确响应 feature flag，不再依赖运行时环境变量。
- src/utils/model/model.ts: 修复 CoStrict provider 下 getDefaultSonnetModel
  和 getDefaultHaikuModel 的递归调用问题，返回具体模型名。
- src/buddy/useBuddyNotification.tsx: 移除 BUDDY 功能的日期限制，默认启用。

build.ts

@@ -1,7 +1,6 @@
 import { readdir, readFile, writeFile, cp } from 'fs/promises'
 import { join } from 'path'
-import { getMacroDefines } from './scripts/defines.ts'
-import { DEFAULT_BUILD_FEATURES } from './scripts/defines.ts'
+import { getMacroDefines, DEFAULT_BUILD_FEATURES } from './scripts/defines.ts'
 
 const outdir = 'dist'
 
@@ -52,6 +51,26 @@ for (const file of files) {
   }
 }
 
+// Step 3.5: Replace feature('FLAG_NAME') with true/false at build time
+// Bun.build does not natively replace feature flags, so we do it manually here
+// to match the behavior of vite-plugin-feature-flags.ts.
+const FEATURE_CALL_RE = /feature\s*\(\s*['"]([\w]+)['"]\s*\)/g
+let featureReplaced = 0
+for (const file of files) {
+  if (!file.endsWith('.js')) continue
+  const filePath = join(outdir, file)
+  const content = await readFile(filePath, 'utf-8')
+  let matchCount = 0
+  const transformed = content.replace(FEATURE_CALL_RE, (match, flagName) => {
+    matchCount++
+    return features.includes(flagName) ? 'true' : 'false'
+  })
+  if (matchCount > 0) {
+    await writeFile(filePath, transformed)
+    featureReplaced += matchCount
+  }
+}
+
 // Also patch unguarded globalThis.Bun destructuring from third-party deps
 // (e.g. @anthropic-ai/sandbox-runtime) so Node.js doesn't crash at import time.
 let bunPatched = 0
@@ -72,7 +91,7 @@ for (const file of files) {
 BUN_DESTRUCTURE.lastIndex = 0
 
 console.log(
-  `Bundled ${result.outputs.length} files to ${outdir}/ (patched ${patched} for import.meta.require, ${bunPatched} for Bun destructure)`,
+  `Bundled ${result.outputs.length} files to ${outdir}/ (patched ${patched} for import.meta.require, ${bunPatched} for Bun destructure, ${featureReplaced} feature flags)`,
 )
 
 // Step 4: Copy native .node addon files (audio-capture) and vendored binaries (ripgrep)

src/buddy/useBuddyNotification.tsx

@@ -15,11 +15,8 @@ export function isBuddyTeaserWindow(): boolean {
 }
 
 export function isBuddyLive(): boolean {
-  if (process.env.USER_TYPE === 'ant') return true
-  const d = new Date()
-  return (
-    d.getFullYear() > 2026 || (d.getFullYear() === 2026 && d.getMonth() >= 3)
-  )
+  // BUDDY 功能已默认启用，不再受日期限制
+  return true
 }
 
 function RainbowText({ text }: { text: string }): React.ReactNode {

src/utils/model/model.ts

@@ -153,8 +153,9 @@ export function getDefaultOpusModel(): ModelName {
 // @[MODEL LAUNCH]: Update the default Sonnet model (3P providers may lag so keep defaults unchanged).
 export function getDefaultSonnetModel(): ModelName {
   const provider = getAPIProvider()
-  // CoStrict has no sonnet alias — use the main loop model to stay on the same provider
-  if (provider === 'costrict') return getMainLoopModel()
+  // CoStrict has no sonnet alias — return a concrete default to avoid recursive
+  // resolution (getMainLoopModel → getDefaultMainLoopModel → getDefaultSonnetModel).
+  if (provider === 'costrict') return getModelStrings().sonnet46
   // For OpenAI provider, check OPENAI_DEFAULT_SONNET_MODEL first
   if (provider === 'openai' && process.env.OPENAI_DEFAULT_SONNET_MODEL) {
     return process.env.OPENAI_DEFAULT_SONNET_MODEL
@@ -177,8 +178,9 @@ export function getDefaultSonnetModel(): ModelName {
 // @[MODEL LAUNCH]: Update the default Haiku model (3P providers may lag so keep defaults unchanged).
 export function getDefaultHaikuModel(): ModelName {
   const provider = getAPIProvider()
-  // CoStrict has no haiku alias — use the main loop model to stay on the same provider
-  if (provider === 'costrict') return getMainLoopModel()
+  // CoStrict has no haiku alias — return a concrete default to avoid recursive
+  // resolution (getMainLoopModel → getDefaultMainLoopModel → getDefaultHaikuModel).
+  if (provider === 'costrict') return getModelStrings().haiku45
   // For OpenAI provider, check OPENAI_DEFAULT_HAIKU_MODEL first
   if (provider === 'openai' && process.env.OPENAI_DEFAULT_HAIKU_MODEL) {
     return process.env.OPENAI_DEFAULT_HAIKU_MODEL