Fix/ripgrep fallback (#1273)

* fix: tmp 目录改用 os.tmpdir() + ripgrep 缺失时自动 fallback 系统 rg

1. Shell.ts / imagePaste.ts / filesystem.ts: Linux/macOS 默认 tmp 路径
   从硬编码 '/tmp' 改为 os.tmpdir()，自动适配 Termux/Android 等无 /tmp
   的环境；macOS 桌面零变化；CLAUDE_CODE_TMPDIR 仍优先级最高。

2. ripgrep.ts: builtin rg 二进制缺失时（Android/Termux、不完整安装）
   自动 fallback 到 PATH 上的系统 rg，通过 note 字段携带人读提示；
   /doctor 渲染 note；init 启动时写一行 stderr warning。

Co-Authored-By: glm-5.2 <zai-org@claude-code-best.win>

* fix: review fix — ripgrep note 文案修正 + init catch 加调试日志

- ripgrep "no ripgrep available" note 去掉无意义的 USE_BUILTIN_RIPGREP=0 建议
- init.ts ripgrep status check 的空 catch 加 logForDebugging

Co-Authored-By: glm-5.2 <zai-org@claude-code-best.win>

---------

Co-authored-by: glm-5.2 <zai-org@claude-code-best.win>

src/utils/ripgrep.ts

@@ -1,5 +1,6 @@
 import type { ChildProcess, ExecFileException } from 'child_process'
 import { execFile, spawn } from 'child_process'
+import { existsSync } from 'fs'
 import memoize from 'lodash-es/memoize.js'
 import { homedir } from 'os'
 import * as path from 'path'
@@ -24,9 +25,10 @@ type RipgrepConfig = {
   command: string
   args: string[]
   argv0?: string
+  note?: string
 }
 
-const getRipgrepConfig = memoize((): RipgrepConfig => {
+export const getRipgrepConfig = memoize((): RipgrepConfig => {
   const userWantsSystemRipgrep = isEnvDefinedFalsy(
     process.env.USE_BUILTIN_RIPGREP,
   )
@@ -59,9 +61,61 @@ const getRipgrepConfig = memoize((): RipgrepConfig => {
       ? path.resolve(rgRoot, `${process.arch}-win32`, 'rg.exe')
       : path.resolve(rgRoot, `${process.arch}-${process.platform}`, 'rg')
 
-  return { mode: 'builtin', command, args: [] }
+  return resolveBuiltinWithFallback(command)
 })
 
+/**
+ * Pure function: decide what to do when the builtin rg binary may be missing.
+ * Extracted so it can be tested without any module mocking.
+ *
+ * @param builtinPath  Path to the vendored rg binary.
+ * @param systemRgPath  When omitted, calls `findExecutable('rg')` (production path).
+ *                     Pass a string to force a specific system path, or `null` to
+ *                     simulate "system rg not found".
+ * @param platform     Override for `process.platform` (tests only).
+ */
+export function resolveBuiltinWithFallback(
+  builtinPath: string,
+  systemRgPath?: string | null,
+  platform?: string,
+): {
+  mode: 'system' | 'builtin'
+  command: string
+  args: string[]
+  note?: string
+} {
+  const p = platform ?? process.platform
+
+  // Builtin exists — use it, no note.
+  if (existsSync(builtinPath)) {
+    return { mode: 'builtin', command: builtinPath, args: [] }
+  }
+
+  // Builtin missing — check system rg.
+  // When systemRgPath is explicitly passed (including null), use it directly.
+  // When undefined, call findExecutable (production path).
+  const resolvedSystem =
+    systemRgPath === undefined
+      ? findExecutable('rg', []).cmd
+      : (systemRgPath ?? 'rg')
+  if (resolvedSystem !== 'rg') {
+    return {
+      mode: 'system',
+      command: 'rg',
+      args: [],
+      note: `fallback: builtin rg unavailable on ${p}, using system rg`,
+    }
+  }
+
+  // Neither available.
+  return {
+    mode: 'builtin',
+    command: builtinPath,
+    args: [],
+    note: `no ripgrep available on ${p}; install ripgrep via apt/pkg/brew`,
+  }
+}
+
 export function ripgrepCommand(): {
   rgPath: string
   rgArgs: string[]
@@ -524,6 +578,7 @@ let ripgrepStatus: {
   working: boolean
   lastTested: number
   config: RipgrepConfig
+  note?: string
 } | null = null
 
 /**
@@ -534,12 +589,14 @@ export function getRipgrepStatus(): {
   mode: 'system' | 'builtin' | 'embedded'
   path: string
   working: boolean | null // null if not yet tested
+  note?: string
 } {
   const config = getRipgrepConfig()
   return {
     mode: config.mode,
     path: config.command,
     working: ripgrepStatus?.working ?? null,
+    note: ripgrepStatus?.note ?? config.note,
   }
 }
 
@@ -593,6 +650,7 @@ const testRipgrepOnFirstUse = memoize(async (): Promise<void> => {
       working,
       lastTested: Date.now(),
       config,
+      note: config.note,
     }
 
     logForDebugging(
@@ -609,6 +667,7 @@ const testRipgrepOnFirstUse = memoize(async (): Promise<void> => {
       working: false,
       lastTested: Date.now(),
       config,
+      note: config.note,
     }
     logError(error)
   }