From 762824c590c7d548f6760a1e777896df2ec8c1f0 Mon Sep 17 00:00:00 2001
From: Pnant <73925474+Panniantong@users.noreply.github.com>
Date: Thu, 11 Jun 2026 15:48:33 +0800
Subject: [PATCH] feat(routing): ordered backend candidates + real-probing
 doctor
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

- backends is now an ordered candidate list (first = preferred); channels
  report the backend actually serving via active_backend, surfaced in the
  doctor text report and --json
- new agent_reach/probe.py really executes upstream commands and tells
  apart missing / broken (stale venv shebang after a system Python
  upgrade) / timeout, with a reinstall prescription for broken installs
- all 13 channels migrated off which()-only checks: fixes bilibili
  false-positive "bili-cli 可用" on broken shims, misleading xiaohongshu
  "连接失败", rdt OSError crashing doctor, mcporter breakage masquerading
  as "未配置"
- twitter: 15s probe + 1 retry (flaky 10s timeout), broken twitter-cli
  now falls back to bird instead of aborting the check
- doctor survives per-channel exceptions; config supports per-channel
  backend override (<channel>_backend / <CHANNEL>_BACKEND env)
- fix skill install/uninstall crash on symlinked skill dirs (the
  "[Errno None] None" warning from shutil.rmtree on a symlink)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 .gitignore                          |   1 +
 agent_reach/channels/base.py        |  40 +++-
 agent_reach/channels/bilibili.py    |  35 +++-
 agent_reach/channels/exa_search.py  |  36 ++--
 agent_reach/channels/github.py      |  36 ++--
 agent_reach/channels/linkedin.py    |  30 ++-
 agent_reach/channels/reddit.py      |  90 +++++---
 agent_reach/channels/rss.py         |  10 +-
 agent_reach/channels/twitter.py     | 132 +++++++-----
 agent_reach/channels/v2ex.py        |   2 +
 agent_reach/channels/web.py         |   2 +
 agent_reach/channels/xiaohongshu.py |  52 ++---
 agent_reach/channels/xiaoyuzhou.py  |  15 +-
 agent_reach/channels/xueqiu.py      |   2 +
 agent_reach/channels/youtube.py     |  15 +-
 agent_reach/cli.py                  |  12 +-
 agent_reach/doctor.py               |  29 ++-
 agent_reach/probe.py                |  99 +++++++++
 tests/test_channel_contracts.py     |  73 +++++++
 tests/test_channels.py              | 308 +++++++++++++++++++++++++++-
 tests/test_doctor.py                |  10 +-
 tests/test_probe.py                 |  90 ++++++++
 tests/test_twitter_channel.py       |  46 +++++
 23 files changed, 988 insertions(+), 177 deletions(-)
 create mode 100644 agent_reach/probe.py
 create mode 100644 tests/test_probe.py

diff --git a/.gitignore b/.gitignore
index 370ebd9..f3d65c6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,4 @@ build/
 
 # Claude Code personal permission settings — local only, never commit
 .claude/settings.local.json
+uv.lock
diff --git a/agent_reach/channels/base.py b/agent_reach/channels/base.py
index 21551cf..2afec0a 100644
--- a/agent_reach/channels/base.py
+++ b/agent_reach/channels/base.py
@@ -8,11 +8,22 @@ and provides:
   - check(config) → is the upstream tool installed and configured?
 
 After installation, agents call upstream tools directly.
+
+Backend routing semantics:
+  - `backends` is an ORDERED candidate list: backends[0] is the preferred
+    backend, the rest are fallbacks. "Switching backends" for a platform
+    means reordering this list (or a user override) — not rewriting code.
+  - check() must set `self.active_backend` to the backend that is actually
+    serving the channel right now (None when nothing usable is found).
+    shutil.which() alone is NOT proof of health — a stale venv shim passes
+    which() but cannot execute (see agent_reach.probe). Channels should
+    really execute a lightweight command before claiming a backend active.
+  - Users can force a backend with config key `<channel>_backend`
+    (or env var `<CHANNEL>_BACKEND`); ordered_backends() applies it.
 """
 
-import shutil
 from abc import ABC, abstractmethod
-from typing import List, Tuple
+from typing import List, Optional, Tuple
 
 
 class Channel(ABC):
@@ -20,17 +31,40 @@ class Channel(ABC):
 
     name: str = ""                    # e.g. "youtube"
     description: str = ""             # e.g. "YouTube 视频和字幕"
-    backends: List[str] = []          # e.g. ["yt-dlp"] — what upstream tool is used
+    backends: List[str] = []          # ordered candidates — backends[0] = preferred
     tier: int = 0                     # 0=zero-config, 1=needs free key, 2=needs setup
 
+    #: Backend currently serving this channel; set by check(), None = unavailable.
+    active_backend: Optional[str] = None
+
     @abstractmethod
     def can_handle(self, url: str) -> bool:
         """Check if this channel can handle this URL."""
         ...
 
+    def ordered_backends(self, config=None) -> List[str]:
+        """Candidate backends in probe order, honoring the user override.
+
+        The config key `<channel>_backend` (env `<CHANNEL>_BACKEND`) moves the
+        named backend to the front of the list; unknown values are ignored so
+        a stale override can never hide working backends.
+        """
+        candidates = list(self.backends)
+        override = config.get(f"{self.name}_backend") if config else None
+        if override:
+            for i, b in enumerate(candidates):
+                if b == override or b.startswith(override):
+                    candidates.insert(0, candidates.pop(i))
+                    break
+        return candidates
+
     def check(self, config=None) -> Tuple[str, str]:
         """
         Check if this channel's upstream tool is available.
         Returns (status, message) where status is 'ok'/'warn'/'off'/'error'.
+
+        Subclasses with external backends must really probe them (see
+        agent_reach.probe.probe_command) and set self.active_backend.
         """
+        self.active_backend = self.backends[0] if self.backends else "内置"
         return "ok", f"{'、'.join(self.backends) if self.backends else '内置'}"
diff --git a/agent_reach/channels/bilibili.py b/agent_reach/channels/bilibili.py
index cda844d..18e08c4 100644
--- a/agent_reach/channels/bilibili.py
+++ b/agent_reach/channels/bilibili.py
@@ -3,9 +3,10 @@
 
 import json
 import os
-import shutil
-import subprocess
 import urllib.request
+
+from agent_reach.probe import probe_command
+
 from .base import Channel
 
 _UA = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36"
@@ -36,11 +37,23 @@ class BilibiliChannel(Channel):
         return "bilibili.com" in d or "b23.tv" in d
 
     def check(self, config=None):
-        if not shutil.which("yt-dlp"):
+        self.active_backend = None
+
+        # 真跑 yt-dlp --version，区分 未装 / 断链 / 异常（which 命中不等于能用）
+        yt = probe_command("yt-dlp", ["--version"], timeout=10, package="yt-dlp")
+        if yt.status == "missing":
             return "off", "yt-dlp 未安装。安装：pip install yt-dlp"
+        if yt.status == "broken":
+            return "error", "yt-dlp 已安装但无法执行\n" + yt.hint
+        if not yt.ok:
+            detail = yt.hint or yt.output or yt.status
+            return "error", f"yt-dlp 探测失败（{yt.status}）：{detail}"
+
+        self.active_backend = "yt-dlp"
 
         proxy = (config.get("bilibili_proxy") if config else None) or os.environ.get("BILIBILI_PROXY")
-        has_bili_cli = bool(shutil.which("bili"))
+        # 真跑 bili --version——断链时旧的 which 检测会误报"bili-cli 可用"
+        bili = probe_command("bili", ["--version"], timeout=10, package="bilibili-cli")
 
         parts = []
 
@@ -51,16 +64,22 @@ class BilibiliChannel(Channel):
             parts.append("视频读取：yt-dlp")
 
         # bili-cli 增强
-        if has_bili_cli:
+        if bili.ok:
             parts.append("搜索/热门/排行：bili-cli 可用")
+            status = "ok"
         else:
-            # 检测搜索 API 连通性
+            if bili.status == "broken":
+                parts.append("bili-cli 已安装但无法执行，不计为可用\n" + bili.hint)
+            elif bili.status in ("timeout", "error"):
+                parts.append(f"bili-cli 探测失败（{bili.status}），不计为可用")
+            # 降级走搜索 API；只探测一次，message 和 status 共用结果
             api_ok = _search_api_ok()
             if api_ok:
                 parts.append("搜索：B站 API 可用")
             else:
                 parts.append("搜索：B站 API 不可达")
-            parts.append("提示：安装 bili-cli 可解锁热门/排行/动态：pipx install bilibili-cli")
+            if bili.status == "missing":
+                parts.append("提示：安装 bili-cli 可解锁热门/排行/动态：pipx install bilibili-cli")
+            status = "ok" if api_ok else "warn"
 
-        status = "ok" if has_bili_cli or _search_api_ok() else "warn"
         return status, "。".join(parts)
diff --git a/agent_reach/channels/exa_search.py b/agent_reach/channels/exa_search.py
index a1687dd..01a2fcf 100644
--- a/agent_reach/channels/exa_search.py
+++ b/agent_reach/channels/exa_search.py
@@ -1,10 +1,13 @@
 # -*- coding: utf-8 -*-
 """Exa Search — check if mcporter + Exa MCP is available."""
 
-import shutil
-import subprocess
+from agent_reach.probe import probe_command
+
 from .base import Channel
 
+#: mcporter 是 npm 包，断链处方与默认的 pipx/uv 不同
+_MCPORTER_BROKEN_HINT = "mcporter 无法执行（node 环境损坏），重装：\n  npm install -g mcporter"
+
 
 class ExaSearchChannel(Channel):
     name = "exa_search"
@@ -16,23 +19,22 @@ class ExaSearchChannel(Channel):
         return False  # Search-only channel
 
     def check(self, config=None):
-        mcporter = shutil.which("mcporter")
-        if not mcporter:
+        self.active_backend = None
+        probe = probe_command("mcporter", ["config", "list"], timeout=10, package="mcporter")
+        if probe.status == "missing":
             return "off", (
                 "需要 mcporter + Exa MCP。安装：\n"
                 "  npm install -g mcporter\n"
                 "  mcporter config add exa https://mcp.exa.ai/mcp"
             )
-        try:
-            r = subprocess.run(
-                [mcporter, "config", "list"], capture_output=True,
-                encoding="utf-8", errors="replace", timeout=5
-            )
-            if "exa" in r.stdout.lower():
-                return "ok", "全网语义搜索可用（免费，无需 API Key）"
-            return "off", (
-                "mcporter 已装但 Exa 未配置。运行：\n"
-                "  mcporter config add exa https://mcp.exa.ai/mcp"
-            )
-        except Exception:
-            return "off", "mcporter 连接异常"
+        if probe.status == "broken":
+            return "error", _MCPORTER_BROKEN_HINT
+        if not probe.ok:  # timeout / error
+            return "error", f"mcporter 执行异常：{probe.hint or probe.output or probe.status}"
+        if "exa" in probe.output.lower():
+            self.active_backend = self.backends[0]
+            return "ok", "全网语义搜索可用（免费，无需 API Key）"
+        return "off", (
+            "mcporter 已装但 Exa 未配置。运行：\n"
+            "  mcporter config add exa https://mcp.exa.ai/mcp"
+        )
diff --git a/agent_reach/channels/github.py b/agent_reach/channels/github.py
index 67ff75c..1908a98 100644
--- a/agent_reach/channels/github.py
+++ b/agent_reach/channels/github.py
@@ -1,8 +1,8 @@
 # -*- coding: utf-8 -*-
 """GitHub — check if gh CLI is available."""
 
-import shutil
-import subprocess
+from agent_reach.probe import probe_command
+
 from .base import Channel
 
 
@@ -17,16 +17,26 @@ class GitHubChannel(Channel):
         return "github.com" in urlparse(url).netloc.lower()
 
     def check(self, config=None):
-        gh = shutil.which("gh")
-        if not gh:
+        # 真跑 gh auth status 探活。注意：未登录时 rc!=0 是正常业务态（warn），不是 error。
+        probe = probe_command("gh", ["auth", "status"], timeout=10, package="gh")
+        if probe.status == "missing":
+            self.active_backend = None
             return "warn", "gh CLI 未安装。安装：https://cli.github.com"
-        try:
-            r = subprocess.run(
-                [gh, "auth", "status"],
-                capture_output=True, encoding="utf-8", errors="replace", timeout=5
+        if probe.status == "broken":
+            # gh 是二进制安装（brew/官方包），不是 pip 包——处方不用 pipx/uv 文案
+            self.active_backend = None
+            return "error", (
+                "gh 命令存在但无法执行——安装已损坏。重装即可修复：\n"
+                "  brew reinstall gh\n"
+                "或从 https://cli.github.com 重新安装 gh CLI"
             )
-            if r.returncode == 0:
-                return "ok", "完整可用（读取、搜索、Fork、Issue、PR 等）"
-            return "warn", "gh CLI 已安装但未认证。运行 gh auth login 可解锁完整功能"
-        except Exception:
-            return "warn", "gh CLI 状态检查失败，运行 gh auth status 查看详情"
+        if probe.status == "timeout":
+            # gh 本体能启动（工具是活的），只是状态检查超时
+            self.active_backend = "gh CLI"
+            return "warn", "gh CLI 状态检查超时，运行 gh auth status 查看详情"
+        if probe.ok:
+            self.active_backend = "gh CLI"
+            return "ok", "完整可用（读取、搜索、Fork、Issue、PR 等）"
+        # rc != 0：gh 活着但未认证（gh auth status 的正常业务态）
+        self.active_backend = "gh CLI"
+        return "warn", "gh CLI 已安装但未认证。运行 gh auth login 可解锁完整功能"
diff --git a/agent_reach/channels/linkedin.py b/agent_reach/channels/linkedin.py
index 1c95dc8..9b1bb5d 100644
--- a/agent_reach/channels/linkedin.py
+++ b/agent_reach/channels/linkedin.py
@@ -1,13 +1,13 @@
 # -*- coding: utf-8 -*-
 """LinkedIn — check if linkedin-scraper-mcp is available."""
 
-import shutil
-import subprocess
-
-from agent_reach.utils.process import utf8_subprocess_env
+from agent_reach.probe import probe_command
 
 from .base import Channel
 
+#: mcporter 是 npm 包，断链处方与默认的 pipx/uv 不同
+_MCPORTER_BROKEN_HINT = "mcporter 无法执行（node 环境损坏），重装：\n  npm install -g mcporter"
+
 
 class LinkedInChannel(Channel):
     name = "linkedin"
@@ -20,24 +20,22 @@ class LinkedInChannel(Channel):
         return "linkedin.com" in urlparse(url).netloc.lower()
 
     def check(self, config=None):
-        mcporter = shutil.which("mcporter")
-        if not mcporter:
+        self.active_backend = None
+        probe = probe_command("mcporter", ["config", "list"], timeout=10, package="mcporter")
+        if probe.status == "missing":
             return "off", (
                 "基本内容可通过 Jina Reader 读取。完整功能需要：\n"
                 "  pip install linkedin-scraper-mcp\n"
                 "  mcporter config add linkedin http://localhost:3000/mcp\n"
                 "  详见 https://github.com/stickerdaniel/linkedin-mcp-server"
             )
-        try:
-            r = subprocess.run(
-                [mcporter, "config", "list"], capture_output=True,
-                encoding="utf-8", errors="replace", timeout=5,
-                env=utf8_subprocess_env(),
-            )
-            if "linkedin" in r.stdout.lower():
-                return "ok", "完整可用（Profile、公司、职位搜索）"
-        except Exception:
-            pass
+        if probe.status == "broken":
+            return "error", _MCPORTER_BROKEN_HINT
+        if not probe.ok:  # timeout / error
+            return "error", f"mcporter 执行异常：{probe.hint or probe.output or probe.status}"
+        if "linkedin" in probe.output.lower():
+            self.active_backend = "linkedin-scraper-mcp"
+            return "ok", "完整可用（Profile、公司、职位搜索）"
         return "off", (
             "mcporter 已装但 LinkedIn MCP 未配置。运行：\n"
             "  pip install linkedin-scraper-mcp\n"
diff --git a/agent_reach/channels/reddit.py b/agent_reach/channels/reddit.py
index 3b51cc3..025b339 100644
--- a/agent_reach/channels/reddit.py
+++ b/agent_reach/channels/reddit.py
@@ -10,12 +10,24 @@ import json
 import shutil
 import subprocess
 
+from agent_reach.utils.process import utf8_subprocess_env
+
 from .base import Channel
 
 _CREDENTIAL_FILE = "~/.config/rdt-cli/credential.json"
 # Pinned to the 0.4.2 state — PyPI still only has 0.4.1 (upstream issue #10).
 _RDT_GIT_SOURCE = "git+https://github.com/public-clis/rdt-cli.git@5e4fb3720d5c174e976cd425ccc3b879d52cac66"
 
+#: shell 对"找到但不可执行/找不到"使用的退出码（对齐 agent_reach.probe）
+_BROKEN_EXIT_CODES = (126, 127)
+
+#: rdt 应从固定 git 源安装（PyPI 落后），断链处方与 probe 默认的 pipx/uv 不同
+_RDT_BROKEN_HINT = (
+    "rdt 命令存在但无法执行——通常是系统 Python 升级后 venv 解释器丢失。\n"
+    "PyPI 版本落后，推荐用固定 git 源强制重装：\n"
+    f"  pipx install --force '{_RDT_GIT_SOURCE}'"
+)
+
 
 class RedditChannel(Channel):
     name = "reddit"
@@ -30,6 +42,8 @@ class RedditChannel(Channel):
         return "reddit.com" in d or "redd.it" in d
 
     def check(self, config=None):
+        self.active_backend = None
+
         rdt = shutil.which("rdt")
         if not rdt:
             return "off", (
@@ -42,6 +56,10 @@ class RedditChannel(Channel):
                 "安装后运行 `rdt login` 登录（需先在浏览器登录 reddit.com）"
             )
 
+        # 不走 probe_command：实测 `rdt status --json` 成功时（rc=0）也会向 stderr
+        # 打网络重试日志，probe 把 stdout+stderr 合并后 JSON 解析必炸。
+        # 故保留手写 subprocess（stdout 单独捕获），但异常分类对齐 probe 语义：
+        # exec 失败/126/127 → broken（venv 断链处方），TimeoutExpired → 超时。
         try:
             r = subprocess.run(
                 [rdt, "status", "--json"],
@@ -49,31 +67,55 @@ class RedditChannel(Channel):
                 encoding="utf-8",
                 errors="replace",
                 timeout=10,
+                env=utf8_subprocess_env(),
             )
-            data = json.loads(r.stdout or "{}")
-            authenticated = data.get("data", {}).get("authenticated", False)
-            username = data.get("data", {}).get("username") or ""
+        except subprocess.TimeoutExpired:
+            return "error", "rdt 响应超时（>10s），Reddit 状态未知。稍后重试或运行 `rdt status` 查看详情"
+        except OSError:
+            # 含 FileNotFoundError：which 命中但 exec 失败 = venv 断链（probe 的 broken）
+            return "error", _RDT_BROKEN_HINT
 
-            if authenticated:
-                suffix = f"（已登录：{username}）" if username else ""
-                return "ok", (f"rdt-cli 可用{suffix}（搜索帖子、阅读全文、查看评论）")
+        if r.returncode in _BROKEN_EXIT_CODES:
+            return "error", _RDT_BROKEN_HINT
 
-            return "warn", (
-                "rdt-cli 已安装但未登录。Reddit 自 2024 年起要求认证，"
-                "未登录时所有请求均返回 403。\n\n"
-                "方法一（自动）：运行 `rdt login`\n"
-                "  先在浏览器登录 reddit.com，再运行此命令自动提取 Cookie。\n\n"
-                "方法二（手动，适用于 Chrome/Edge 127+ 无法自动提取时）：\n"
-                "  1. Chrome 应用商店安装 Cookie-Editor 扩展：\n"
-                "     https://chromewebstore.google.com/detail/cookie-editor/hlkenndednhfkekhgcdicdfddnkalmdm\n"
-                "  2. 在浏览器打开 reddit.com（确保已登录）\n"
-                "  3. 点击 Cookie-Editor 图标，找到 `reddit_session`，复制其 Value\n"
-                f"  4. 将以下内容写入 {_CREDENTIAL_FILE}：\n"
-                '     {"cookies": {"reddit_session": "<粘贴 Value>"}, '
-                '"source": "manual", "username": "<你的用户名>", '
-                '"modhash": null, "saved_at": 0, "last_verified_at": null}\n\n'
-                "验证：`rdt status --json` 确认 authenticated: true"
-            )
+        if r.returncode != 0:
+            detail = (r.stderr or r.stdout or "").strip().splitlines()
+            tail = detail[-1] if detail else "无输出"
+            return "error", f"rdt 异常退出（exit {r.returncode}）：{tail}。运行 `rdt status` 查看详情"
 
-        except (json.JSONDecodeError, FileNotFoundError, subprocess.TimeoutExpired):
-            return "warn", "rdt-cli 已安装但状态检查失败，运行 `rdt status` 查看详情"
+        # 进程正常退出 → rdt 本身是活的（无论登录与否），后端即为可用
+        self.active_backend = "rdt-cli"
+
+        try:
+            data = json.loads(r.stdout or "")
+        except json.JSONDecodeError:
+            data = None
+        if not isinstance(data, dict):
+            return "warn", "rdt-cli 可用但状态输出无法解析，运行 `rdt status` 查看登录状态"
+
+        info = data.get("data")
+        if not isinstance(info, dict):
+            info = {}
+        authenticated = info.get("authenticated", False)
+        username = info.get("username") or ""
+
+        if authenticated:
+            suffix = f"（已登录：{username}）" if username else ""
+            return "ok", (f"rdt-cli 可用{suffix}（搜索帖子、阅读全文、查看评论）")
+
+        return "warn", (
+            "rdt-cli 已安装但未登录。Reddit 自 2024 年起要求认证，"
+            "未登录时所有请求均返回 403。\n\n"
+            "方法一（自动）：运行 `rdt login`\n"
+            "  先在浏览器登录 reddit.com，再运行此命令自动提取 Cookie。\n\n"
+            "方法二（手动，适用于 Chrome/Edge 127+ 无法自动提取时）：\n"
+            "  1. Chrome 应用商店安装 Cookie-Editor 扩展：\n"
+            "     https://chromewebstore.google.com/detail/cookie-editor/hlkenndednhfkekhgcdicdfddnkalmdm\n"
+            "  2. 在浏览器打开 reddit.com（确保已登录）\n"
+            "  3. 点击 Cookie-Editor 图标，找到 `reddit_session`，复制其 Value\n"
+            f"  4. 将以下内容写入 {_CREDENTIAL_FILE}：\n"
+            '     {"cookies": {"reddit_session": "<粘贴 Value>"}, '
+            '"source": "manual", "username": "<你的用户名>", '
+            '"modhash": null, "saved_at": 0, "last_verified_at": null}\n\n'
+            "验证：`rdt status --json` 确认 authenticated: true"
+        )
diff --git a/agent_reach/channels/rss.py b/agent_reach/channels/rss.py
index a61d9d9..5f63072 100644
--- a/agent_reach/channels/rss.py
+++ b/agent_reach/channels/rss.py
@@ -15,7 +15,13 @@ class RSSChannel(Channel):
 
     def check(self, config=None):
         try:
-            import feedparser
-            return "ok", "可读取 RSS/Atom 源"
+            import feedparser  # noqa: F401
         except ImportError:
+            self.active_backend = None
             return "off", "feedparser 未安装。安装：pip install feedparser"
+        except Exception as e:
+            # 已安装但导入期崩溃（半残安装/版本冲突）→ 重装处方
+            self.active_backend = None
+            return "error", f"feedparser 导入失败：{e}\n修复：pip install --force-reinstall feedparser"
+        self.active_backend = self.backends[0]
+        return "ok", "可读取 RSS/Atom 源"
diff --git a/agent_reach/channels/twitter.py b/agent_reach/channels/twitter.py
index 6971edd..62cd588 100644
--- a/agent_reach/channels/twitter.py
+++ b/agent_reach/channels/twitter.py
@@ -1,9 +1,8 @@
 # -*- coding: utf-8 -*-
 """Twitter/X — check if twitter-cli or bird CLI is available."""
 
-import shutil
-import subprocess
 from .base import Channel
+from agent_reach.probe import probe_command
 
 
 class TwitterChannel(Channel):
@@ -18,56 +17,98 @@ class TwitterChannel(Channel):
         return "x.com" in d or "twitter.com" in d
 
     def check(self, config=None):
-        # Prefer twitter-cli, fallback to bird/birdx
-        twitter = shutil.which("twitter")
-        bird = shutil.which("bird") or shutil.which("birdx")
+        """按 backends 顺序真实探测，第一个活着的后端即为 active_backend。"""
+        self.active_backend = None
+        failures = []
 
-        if twitter:
-            return self._check_twitter_cli(twitter)
-        elif bird:
-            return self._check_bird(bird)
-        else:
+        for backend in self.ordered_backends(config):
+            if backend == "twitter-cli":
+                result = self._check_twitter_cli()
+            elif backend == "bird CLI (legacy)":
+                result = self._check_bird()
+            else:
+                continue
+
+            if result is None:
+                continue  # 未安装——继续尝试下一个后端
+
+            status, message = result
+            if status in ("ok", "warn"):
+                # 工具本身是活的（含已装但未登录的 warn）
+                self.active_backend = backend
+                return status, message
+            # broken/timeout —— 记下处方，继续尝试下一个后端
+            failures.append(message)
+
+        if failures:
+            return "error", "\n".join(failures)
+        return "warn", (
+            "Twitter CLI 未安装。安装方式：\n"
+            "  pipx install twitter-cli\n"
+            "或：\n"
+            "  uv tool install twitter-cli"
+        )
+
+    def _check_twitter_cli(self):
+        """探测 twitter-cli。返回 None 表示未安装，否则返回 (status, message)。
+
+        `twitter status` 才是健康信号：已登录时输出 "ok: true"，
+        未登录时以非零退出码输出 "not_authenticated"——工具本身是活的，
+        所以 probe 的 error 状态也要看 output 内容再分类。
+        """
+        probe = probe_command(
+            "twitter", ["status"], timeout=15, retries=1, package="twitter-cli"
+        )
+        if probe.status == "missing":
+            return None
+        if probe.status == "broken":
+            return "error", "twitter-cli 命令存在但无法执行。\n" + probe.hint
+        if probe.status == "timeout":
+            return "error", "twitter-cli 健康检查超时（已重试 1 次）。\n" + probe.hint
+
+        output = probe.output
+        if "ok: true" in output:
+            return "ok", (
+                "twitter-cli 完整可用（搜索、读推文、时间线、长文/Article、"
+                "用户查询、Thread）"
+            )
+        if "not_authenticated" in output:
             return "warn", (
-                "Twitter CLI 未安装。安装方式：\n"
-                "  pipx install twitter-cli\n"
-                "或：\n"
-                "  uv tool install twitter-cli"
+                "twitter-cli 已安装但未认证。设置方式：\n"
+                "  export TWITTER_AUTH_TOKEN=\"xxx\"\n"
+                "  export TWITTER_CT0=\"yyy\"\n"
+                "或确保已在浏览器中登录 x.com"
             )
+        return "warn", (
+            "twitter-cli 已安装但认证检查失败。运行：\n"
+            "  twitter -v status 查看详细信息"
+        )
 
-    def _check_twitter_cli(self, binary: str):
-        try:
-            r = subprocess.run(
-                [binary, "status"], capture_output=True,
-                encoding="utf-8", errors="replace", timeout=10
+    def _check_bird(self):
+        """探测 bird/birdx（legacy 回退）。返回 None 表示均未安装，否则返回 (status, message)。"""
+        last_failure = None
+        for cmd in ("bird", "birdx"):
+            probe = probe_command(
+                cmd, ["check"], timeout=15, retries=1, package="@steipete/bird"
             )
-            output = (r.stdout or "") + (r.stderr or "")
-            if r.returncode == 0 and "ok: true" in output:
-                return "ok", (
-                    "twitter-cli 完整可用（搜索、读推文、时间线、长文/Article、"
-                    "用户查询、Thread）"
+            if probe.status == "missing":
+                continue
+            if probe.status == "broken":
+                last_failure = (
+                    "error",
+                    f"{cmd} 命令存在但无法执行（bird 是 npm 包，可用 "
+                    "npm install -g @steipete/bird 重装）。\n" + probe.hint,
                 )
-            if "not_authenticated" in output:
-                return "warn", (
-                    "twitter-cli 已安装但未认证。设置方式：\n"
-                    "  export TWITTER_AUTH_TOKEN=\"xxx\"\n"
-                    "  export TWITTER_CT0=\"yyy\"\n"
-                    "或确保已在浏览器中登录 x.com"
+                continue  # bird 坏了再试 birdx
+            if probe.status == "timeout":
+                last_failure = (
+                    "error",
+                    f"{cmd} 健康检查超时（已重试 1 次）。\n" + probe.hint,
                 )
-            return "warn", (
-                "twitter-cli 已安装但认证检查失败。运行：\n"
-                "  twitter -v status 查看详细信息"
-            )
-        except Exception:
-            return "warn", "twitter-cli 已安装但连接失败"
+                continue
 
-    def _check_bird(self, binary: str):
-        try:
-            r = subprocess.run(
-                [binary, "check"], capture_output=True,
-                encoding="utf-8", errors="replace", timeout=10
-            )
-            output = (r.stdout or "") + (r.stderr or "")
-            if r.returncode == 0:
+            output = probe.output
+            if probe.ok:
                 return "ok", "bird CLI 可用（读取、搜索推文，含长文/X Article）"
             if "Missing credentials" in output or "missing" in output.lower():
                 return "warn", (
@@ -78,5 +119,4 @@ class TwitterChannel(Channel):
             return "warn", (
                 "bird CLI 已安装但认证检查失败。"
             )
-        except Exception:
-            return "warn", "bird CLI 已安装但连接失败"
+        return last_failure
diff --git a/agent_reach/channels/v2ex.py b/agent_reach/channels/v2ex.py
index 700b653..1b24561 100644
--- a/agent_reach/channels/v2ex.py
+++ b/agent_reach/channels/v2ex.py
@@ -41,8 +41,10 @@ class V2EXChannel(Channel):
             _get_json(
                 "https://www.v2ex.com/api/topics/show.json?node_name=python&page=1"
             )
+            self.active_backend = self.backends[0]
             return "ok", "公开 API 可用（热门主题、节点浏览、主题详情、用户信息）"
         except Exception as e:
+            self.active_backend = None
             return "warn", f"V2EX API 连接失败（可能需要代理）：{e}"
 
     # ------------------------------------------------------------------ #
diff --git a/agent_reach/channels/web.py b/agent_reach/channels/web.py
index dfdf10c..9d10dfe 100644
--- a/agent_reach/channels/web.py
+++ b/agent_reach/channels/web.py
@@ -17,6 +17,8 @@ class WebChannel(Channel):
         return True  # Fallback — handles any URL
 
     def check(self, config=None):
+        # 恒可用兜底渠道：无本地命令、不做网络探测（doctor 已有多个渠道触网），保持零开销
+        self.active_backend = self.backends[0]
         return "ok", "通过 Jina Reader 读取任意网页（curl https://r.jina.ai/URL）"
 
     def read(self, url: str) -> str:
diff --git a/agent_reach/channels/xiaohongshu.py b/agent_reach/channels/xiaohongshu.py
index 8a71df7..5549f19 100644
--- a/agent_reach/channels/xiaohongshu.py
+++ b/agent_reach/channels/xiaohongshu.py
@@ -1,8 +1,8 @@
 # -*- coding: utf-8 -*-
 """XiaoHongShu — check if xhs-cli (xiaohongshu-cli) is available."""
 
-import shutil
-import subprocess
+from agent_reach.probe import probe_command
+
 from .base import Channel
 
 
@@ -127,8 +127,12 @@ class XiaoHongShuChannel(Channel):
         return "xiaohongshu.com" in d or "xhslink.com" in d
 
     def check(self, config=None):
-        xhs = shutil.which("xhs")
-        if not xhs:
+        self.active_backend = None
+        probe = probe_command(
+            "xhs", ["status"], timeout=10, package="xiaohongshu-cli"
+        )
+
+        if probe.status == "missing":
             return "off", (
                 "需要安装 xhs-cli：\n"
                 "  pipx install xiaohongshu-cli\n"
@@ -136,27 +140,27 @@ class XiaoHongShuChannel(Channel):
                 "  uv tool install xiaohongshu-cli\n"
                 "安装后运行 `xhs login` 登录"
             )
+        if probe.status == "broken":
+            return "error", "xhs 命令存在但无法执行\n" + probe.hint
+        if probe.status == "timeout":
+            return "warn", "xhs-cli 已安装但状态检测超时\n" + probe.hint
 
-        try:
-            r = subprocess.run(
-                [xhs, "status"], capture_output=True,
-                encoding="utf-8", errors="replace", timeout=10,
+        # 进程是活的（执行成功或运行后非零退出）——按输出内容分类
+        if probe.ok and "ok: true" in probe.output:
+            self.active_backend = self.backends[0]
+            return "ok", (
+                "完整可用（搜索、阅读、评论、发帖、热门、"
+                "收藏、关注、用户查询）"
             )
-            output = (r.stdout or "") + (r.stderr or "")
-            if r.returncode == 0 and "ok: true" in output:
-                return "ok", (
-                    "完整可用（搜索、阅读、评论、发帖、热门、"
-                    "收藏、关注、用户查询）"
-                )
-            if "not_authenticated" in output or "expired" in output:
-                return "warn", (
-                    "xhs-cli 已安装但未登录。运行：\n"
-                    "  xhs login\n"
-                    "（自动从浏览器提取 Cookie，或扫码登录）"
-                )
+        if "not_authenticated" in probe.output or "expired" in probe.output:
+            self.active_backend = self.backends[0]
             return "warn", (
-                "xhs-cli 已安装但状态异常。运行：\n"
-                "  xhs -v status 查看详细信息"
+                "xhs-cli 已安装但未登录。运行：\n"
+                "  xhs login\n"
+                "（自动从浏览器提取 Cookie，或扫码登录）"
             )
-        except Exception:
-            return "warn", "xhs-cli 已安装但连接失败"
+        self.active_backend = self.backends[0]
+        return "warn", (
+            "xhs-cli 已安装但状态异常。运行：\n"
+            "  xhs -v status 查看详细信息"
+        )
diff --git a/agent_reach/channels/xiaoyuzhou.py b/agent_reach/channels/xiaoyuzhou.py
index 9507191..efc73b7 100644
--- a/agent_reach/channels/xiaoyuzhou.py
+++ b/agent_reach/channels/xiaoyuzhou.py
@@ -2,8 +2,8 @@
 """Xiaoyuzhou Podcast (小宇宙播客) — transcribe podcasts via Groq Whisper API."""
 
 import os
-import shutil
 from agent_reach.config import Config
+from agent_reach.probe import probe_command
 from .base import Channel
 
 
@@ -19,13 +19,21 @@ class XiaoyuzhouChannel(Channel):
         return "xiaoyuzhoufm.com" in d
 
     def check(self, config=None):
-        # Check ffmpeg
-        if not shutil.which("ffmpeg"):
+        self.active_backend = None
+
+        # Check ffmpeg — really execute it: a stale pip-installed ffmpeg shim
+        # passes shutil.which() but cannot run
+        probe = probe_command("ffmpeg", ["-version"], timeout=10, package="ffmpeg")
+        if probe.status == "missing":
             return "off", (
                 "需要 ffmpeg（音频转码和切片）。安装：\n"
                 "  Ubuntu/Debian: apt install -y ffmpeg\n"
                 "  macOS: brew install ffmpeg"
             )
+        if not probe.ok:
+            return "error", (
+                "ffmpeg 无法执行，重装：brew install ffmpeg（macOS）/ apt install ffmpeg（Linux）"
+            )
 
         # Check script exists
         script = os.path.expanduser("~/.agent-reach/tools/xiaoyuzhou/transcribe.sh")
@@ -51,4 +59,5 @@ class XiaoyuzhouChannel(Channel):
                 "  2. 运行: agent-reach configure groq-key gsk_xxxxx"
             )
 
+        self.active_backend = "groq-whisper"
         return "ok", "完整可用（播客下载 + Whisper 转录）"
diff --git a/agent_reach/channels/xueqiu.py b/agent_reach/channels/xueqiu.py
index 4bef961..f1ce444 100644
--- a/agent_reach/channels/xueqiu.py
+++ b/agent_reach/channels/xueqiu.py
@@ -162,12 +162,14 @@ class XueqiuChannel(Channel):
     # ------------------------------------------------------------------ #
 
     def check(self, config=None):
+        self.active_backend = None
         try:
             data = _get_json(
                 "https://stock.xueqiu.com/v5/stock/batch/quote.json?symbol=SH000001"
             )
             items = (data.get("data") or {}).get("items") or []
             if items:
+                self.active_backend = self.backends[0]
                 return "ok", "公开 API 可用（行情、搜索、热帖、热股）"
             return "warn", "API 响应异常（返回数据为空）"
         except Exception as e:
diff --git a/agent_reach/channels/youtube.py b/agent_reach/channels/youtube.py
index 5ee1e2b..69393ca 100644
--- a/agent_reach/channels/youtube.py
+++ b/agent_reach/channels/youtube.py
@@ -3,6 +3,7 @@
 
 import shutil
 
+from agent_reach.probe import probe_command
 from agent_reach.utils.paths import get_ytdlp_config_path, render_ytdlp_fix_command
 from agent_reach.utils.text import read_utf8_text
 
@@ -32,8 +33,20 @@ class YouTubeChannel(Channel):
         return "youtube.com" in d or "youtu.be" in d
 
     def check(self, config=None):
-        if not shutil.which("yt-dlp"):
+        # 真跑 yt-dlp --version 探活，区分未装 / venv 断链 / 跑不动
+        probe = probe_command("yt-dlp", ["--version"], timeout=10, package="yt-dlp")
+        if probe.status == "missing":
+            self.active_backend = None
             return "off", "yt-dlp 未安装。安装：pip install yt-dlp"
+        if probe.status == "broken":
+            self.active_backend = None
+            return "error", f"yt-dlp 已安装但无法执行\n{probe.hint}"
+        if not probe.ok:  # timeout / error：装了但跑不动
+            self.active_backend = None
+            detail = probe.hint or probe.output or probe.status
+            return "error", f"yt-dlp 无法正常运行：{detail}"
+        # yt-dlp 本体是活的；后面的 JS runtime/转写检查只影响 ok/warn，不影响后端归属
+        self.active_backend = "yt-dlp"
         # Check JS runtime
         has_js = shutil.which("deno") or shutil.which("node")
         if not has_js:
diff --git a/agent_reach/cli.py b/agent_reach/cli.py
index d257b72..ccda286 100644
--- a/agent_reach/cli.py
+++ b/agent_reach/cli.py
@@ -364,8 +364,11 @@ def _install_skill():
     def _copy_skill_dir(target: str) -> bool:
         """Copy entire skill directory (locale-specific SKILL.md + references/)."""
         try:
-            # Clear existing installation
-            if os.path.exists(target):
+            # Clear existing installation. A symlinked skill dir (dotfiles
+            # setups) breaks shutil.rmtree — unlink the link itself instead.
+            if os.path.islink(target):
+                os.unlink(target)
+            elif os.path.exists(target):
                 shutil.rmtree(target)
             os.makedirs(target, exist_ok=True)
 
@@ -454,7 +457,10 @@ def _uninstall_skill():
         skill_path = os.path.expanduser(skill_path_template)
         if os.path.isdir(skill_path):
             try:
-                shutil.rmtree(skill_path)
+                if os.path.islink(skill_path):
+                    os.unlink(skill_path)
+                else:
+                    shutil.rmtree(skill_path)
                 print(f"  Removed {platform_name} skill: {skill_path}")
                 removed = True
             except Exception as e:
diff --git a/agent_reach/doctor.py b/agent_reach/doctor.py
index 14e5fd1..0d56f24 100644
--- a/agent_reach/doctor.py
+++ b/agent_reach/doctor.py
@@ -10,20 +10,37 @@ from agent_reach.channels import get_all_channels
 
 
 def check_all(config: Config) -> Dict[str, dict]:
-    """Check all channels and return status dict."""
+    """Check all channels and return status dict.
+
+    A single misbehaving channel must never take the whole report down,
+    so per-channel exceptions degrade to status="error".
+    """
     results = {}
     for ch in get_all_channels():
-        status, message = ch.check(config)
+        try:
+            status, message = ch.check(config)
+        except Exception as e:  # noqa: BLE001 — doctor must survive any channel
+            status, message = "error", f"体检异常：{e}"
         results[ch.name] = {
             "status": status,
             "name": ch.description,
             "message": message,
             "tier": ch.tier,
             "backends": ch.backends,
+            "active_backend": getattr(ch, "active_backend", None),
         }
     return results
 
 
+def _name_msg(r: dict, escape) -> str:
+    """Render one channel line; show the active backend when there is a choice."""
+    text = f"[bold]{escape(r['name'])}[/bold] — {escape(r['message'])}"
+    active = r.get("active_backend")
+    if active and len(r.get("backends", [])) > 1:
+        text += f" [dim]（当前后端：{escape(active)}）[/dim]"
+    return text
+
+
 def format_report(results: Dict[str, dict]) -> str:
     """Format results as a readable text report (with Rich markup)."""
     try:
@@ -44,7 +61,7 @@ def format_report(results: Dict[str, dict]) -> str:
     lines.append("[bold]✅ 装好即用：[/bold]")
     for key, r in results.items():
         if r["tier"] == 0:
-            name_msg = f"[bold]{escape(r['name'])}[/bold] — {escape(r['message'])}"
+            name_msg = _name_msg(r, escape)
             if r["status"] == "ok":
                 lines.append(f"  [green]✅[/green] {name_msg}")
             elif r["status"] == "warn":
@@ -60,8 +77,7 @@ def format_report(results: Dict[str, dict]) -> str:
         lines.append("")
         lines.append("[bold]可选渠道（已安装）：[/bold]")
         for key, r in tier1_active.items():
-            name_msg = f"[bold]{escape(r['name'])}[/bold] — {escape(r['message'])}"
-            lines.append(f"  [green]✅[/green] {name_msg}")
+            lines.append(f"  [green]✅[/green] {_name_msg(r, escape)}")
 
     # Tier 2 — optional complex setup
     tier2 = {k: r for k, r in results.items() if r["tier"] == 2}
@@ -72,8 +88,7 @@ def format_report(results: Dict[str, dict]) -> str:
             lines.append("")
             lines.append("[bold]可选渠道（已安装）：[/bold]")
         for key, r in tier2_active.items():
-            name_msg = f"[bold]{escape(r['name'])}[/bold] — {escape(r['message'])}"
-            lines.append(f"  [green]✅[/green] {name_msg}")
+            lines.append(f"  [green]✅[/green] {_name_msg(r, escape)}")
 
     lines.append("")
     status_color = "green" if ok_count == total else ("yellow" if ok_count > 0 else "red")
diff --git a/agent_reach/probe.py b/agent_reach/probe.py
new file mode 100644
index 0000000..9f20c47
--- /dev/null
+++ b/agent_reach/probe.py
@@ -0,0 +1,99 @@
+# -*- coding: utf-8 -*-
+"""Lightweight upstream command probing.
+
+Distinguishes the three failure modes that look identical to shutil.which():
+  - missing: command not on PATH
+  - broken: command exists but cannot execute — most commonly a stale venv
+    shebang after a system Python upgrade (pipx/uv tool installs break this
+    way: which() finds the shim, but exec fails with FileNotFoundError
+    pointing at the shim itself)
+  - timeout/error: command runs but misbehaves
+
+Channels use probe_command() inside check() so doctor reports real health,
+not just file existence.
+"""
+
+import shutil
+import subprocess
+from dataclasses import dataclass
+from typing import Optional, Sequence
+
+from agent_reach.utils.process import utf8_subprocess_env
+
+#: Exit codes shells use for "found but not executable" / "not found".
+_BROKEN_EXIT_CODES = (126, 127)
+
+
+@dataclass
+class ProbeResult:
+    status: str  # "ok" | "missing" | "broken" | "timeout" | "error"
+    output: str = ""
+    hint: str = ""
+
+    @property
+    def ok(self) -> bool:
+        return self.status == "ok"
+
+
+def reinstall_hint(package: str) -> str:
+    """Prescription for a broken (stale-venv) CLI install."""
+    return (
+        f"命令存在但无法执行——通常是系统 Python 升级后 venv 解释器丢失。重装即可修复：\n"
+        f"  uv tool install --force {package}\n"
+        f"或：pipx reinstall {package}"
+    )
+
+
+def probe_command(
+    cmd: str,
+    args: Sequence[str] = ("--version",),
+    timeout: int = 10,
+    retries: int = 0,
+    package: Optional[str] = None,
+) -> ProbeResult:
+    """Actually execute `cmd *args` and classify the result.
+
+    package: pip/pipx package name used in the broken-install hint
+             (defaults to cmd).
+    """
+    path = shutil.which(cmd)
+    if not path:
+        return ProbeResult("missing")
+
+    last: Optional[ProbeResult] = None
+    for _ in range(retries + 1):
+        last = _run_once(path, args, timeout, package or cmd)
+        if last.ok:
+            return last
+        # missing/broken won't heal between retries — only transient
+        # failures (timeout/error) are worth a second attempt
+        if last.status in ("missing", "broken"):
+            return last
+    return last
+
+
+def _run_once(path: str, args: Sequence[str], timeout: int, package: str) -> ProbeResult:
+    try:
+        r = subprocess.run(
+            [path, *args],
+            capture_output=True,
+            encoding="utf-8",
+            errors="replace",
+            timeout=timeout,
+            env=utf8_subprocess_env(),
+        )
+    except FileNotFoundError:
+        # which() found it but exec failed: the shebang interpreter is gone
+        return ProbeResult("broken", hint=reinstall_hint(package))
+    except OSError:
+        return ProbeResult("broken", hint=reinstall_hint(package))
+    except subprocess.TimeoutExpired:
+        return ProbeResult("timeout", hint=f"`{path}` 响应超时（>{timeout}s）")
+
+    if r.returncode in _BROKEN_EXIT_CODES:
+        return ProbeResult("broken", hint=reinstall_hint(package))
+
+    output = (r.stdout or "") + (r.stderr or "")
+    if r.returncode != 0:
+        return ProbeResult("error", output=output.strip())
+    return ProbeResult("ok", output=output.strip())
diff --git a/tests/test_channel_contracts.py b/tests/test_channel_contracts.py
index d036c02..1733b3c 100644
--- a/tests/test_channel_contracts.py
+++ b/tests/test_channel_contracts.py
@@ -1,10 +1,17 @@
 # -*- coding: utf-8 -*-
 """Contract tests for channel adapters."""
 
+import subprocess
+
 from agent_reach.channels import get_all_channels
 from agent_reach.config import Config
 
 
+def _fake_run_ok(cmd, **kwargs):
+    """Pretend any probed CLI executes fine and prints a version."""
+    return subprocess.CompletedProcess(cmd, 0, "2026.06.09", "")
+
+
 def test_channel_registry_contract():
     channels = get_all_channels()
     assert channels, "channel registry must not be empty"
@@ -29,6 +36,67 @@ def test_channel_check_contract_with_minimal_runtime(monkeypatch, tmp_path):
         assert isinstance(message, str) and message.strip()
 
 
+def test_channel_active_backend_attribute_contract():
+    """Every channel exposes active_backend (default None, or str once set)."""
+    for ch in get_all_channels():
+        assert hasattr(ch, "active_backend")
+        # Fresh instances must default to None / str (class attribute on base)
+        fresh = type(ch)()
+        assert fresh.active_backend is None or isinstance(fresh.active_backend, str)
+
+
+def test_channel_active_backend_set_by_check(monkeypatch, tmp_path):
+    """After check(), active_backend is None or a str — never anything else."""
+    monkeypatch.setattr("shutil.which", lambda _cmd: None)
+
+    # Keep the network-based channels (V2EX/Xueqiu/Bilibili API) deterministic.
+    import urllib.request
+    from urllib.error import URLError
+
+    def _no_net(*_a, **_k):
+        raise URLError("offline")
+
+    monkeypatch.setattr(urllib.request, "urlopen", _no_net)
+    import agent_reach.channels.xueqiu as xueqiu_mod
+    monkeypatch.setattr(xueqiu_mod, "_cookies_initialized", True)
+    monkeypatch.setattr(xueqiu_mod._opener, "open", _no_net)
+
+    config = Config(config_path=tmp_path / "config.yaml")
+    for ch in get_all_channels():
+        ch.check(config)
+        assert ch.active_backend is None or isinstance(ch.active_backend, str), (
+            f"{ch.name}: active_backend must be None or str after check()"
+        )
+
+
+def test_ordered_backends_contract(tmp_path):
+    """ordered_backends(config) is a reordering (same multiset) of backends."""
+    config = Config(config_path=tmp_path / "config.yaml")
+    for ch in get_all_channels():
+        ordered = ch.ordered_backends(config)
+        assert isinstance(ordered, list)
+        assert sorted(ordered) == sorted(ch.backends), (
+            f"{ch.name}: ordered_backends must be a permutation of backends"
+        )
+        # And without any config at all
+        ordered_none = ch.ordered_backends(None)
+        assert sorted(ordered_none) == sorted(ch.backends)
+
+
+def test_ordered_backends_override_moves_backend_to_front():
+    """Config key <channel>_backend promotes the named backend to front."""
+    from agent_reach.channels.twitter import TwitterChannel
+
+    ch = TwitterChannel()
+    ordered = ch.ordered_backends({"twitter_backend": "bird"})
+    assert ordered[0] == "bird CLI (legacy)"
+    assert sorted(ordered) == sorted(ch.backends)
+
+    # Unknown override is ignored — never hides working backends
+    ordered_unknown = ch.ordered_backends({"twitter_backend": "no-such-tool"})
+    assert ordered_unknown == list(ch.backends)
+
+
 def test_youtube_warns_when_node_only_and_no_config(monkeypatch, tmp_path):
     """YouTube should warn when only Node.js is installed but no yt-dlp config exists."""
     from agent_reach.channels.youtube import YouTubeChannel
@@ -41,6 +109,7 @@ def test_youtube_warns_when_node_only_and_no_config(monkeypatch, tmp_path):
         return None  # deno not installed
 
     monkeypatch.setattr("shutil.which", fake_which)
+    monkeypatch.setattr("subprocess.run", _fake_run_ok)  # yt-dlp probe really executes now
     # Point to a non-existent config file
     monkeypatch.setattr("os.path.expanduser", lambda p: str(tmp_path / ".config/yt-dlp/config"))
 
@@ -48,6 +117,7 @@ def test_youtube_warns_when_node_only_and_no_config(monkeypatch, tmp_path):
     status, message = ch.check()
     assert status == "warn"
     assert "--js-runtimes" in message
+    assert ch.active_backend == "yt-dlp"  # 本体活着，warn 只关乎 JS runtime
 
 
 def test_youtube_warns_with_windows_specific_fix_command(monkeypatch, tmp_path):
@@ -62,6 +132,7 @@ def test_youtube_warns_with_windows_specific_fix_command(monkeypatch, tmp_path):
         return None
 
     monkeypatch.setattr("shutil.which", fake_which)
+    monkeypatch.setattr("subprocess.run", _fake_run_ok)  # yt-dlp probe really executes now
     monkeypatch.setattr("agent_reach.utils.paths.sys.platform", "win32")
     monkeypatch.setenv("APPDATA", str(tmp_path / "AppData" / "Roaming"))
 
@@ -84,10 +155,12 @@ def test_youtube_ok_when_deno_installed(monkeypatch):
         return None
 
     monkeypatch.setattr("shutil.which", fake_which)
+    monkeypatch.setattr("subprocess.run", _fake_run_ok)  # yt-dlp probe really executes now
 
     ch = YouTubeChannel()
     status, _msg = ch.check()
     assert status == "ok"
+    assert ch.active_backend == "yt-dlp"
 
 
 def test_channel_can_handle_contract():
diff --git a/tests/test_channels.py b/tests/test_channels.py
index 3ac24fa..88d79a2 100644
--- a/tests/test_channels.py
+++ b/tests/test_channels.py
@@ -670,9 +670,11 @@ class TestRedditChannel:
 
         monkeypatch.setattr(subprocess, "run", fake_run)
         from agent_reach.channels.reddit import RedditChannel
-        status, msg = RedditChannel().check()
+        ch = RedditChannel()
+        status, msg = ch.check()
         assert status == "ok"
         assert "testuser" in msg
+        assert ch.active_backend == "rdt-cli"
 
     def test_reports_warn_when_not_authenticated(self, monkeypatch):
         monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/rdt")
@@ -687,14 +689,18 @@ class TestRedditChannel:
 
         monkeypatch.setattr(subprocess, "run", fake_run)
         from agent_reach.channels.reddit import RedditChannel
-        status, msg = RedditChannel().check()
+        ch = RedditChannel()
+        status, msg = ch.check()
         assert status == "warn"
         assert "403" in msg
         assert "rdt login" in msg
         assert "Cookie-Editor" in msg
         assert "chromewebstore.google.com" in msg
+        # 未登录是业务态：进程活着，后端仍然算可用
+        assert ch.active_backend == "rdt-cli"
 
-    def test_reports_warn_when_status_check_fails(self, monkeypatch):
+    def test_reports_error_when_status_check_fails(self, monkeypatch):
+        """rdt 非零退出且输出不可解析 → 工具异常（error），不再算 warn。"""
         monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/rdt")
 
         def fake_run(cmd, **kwargs):
@@ -702,8 +708,43 @@ class TestRedditChannel:
 
         monkeypatch.setattr(subprocess, "run", fake_run)
         from agent_reach.channels.reddit import RedditChannel
-        status, msg = RedditChannel().check()
-        assert status == "warn"
+        ch = RedditChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "rdt 异常退出" in msg
+        assert ch.active_backend is None
+
+    def test_reports_error_with_reinstall_hint_when_broken(self, monkeypatch):
+        """which 命中但 exec 抛 FileNotFoundError（venv 断链）→ error + 重装处方。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/rdt")
+
+        def fake_run(cmd, **kwargs):
+            raise FileNotFoundError("/usr/local/bin/rdt")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.reddit import RedditChannel
+        ch = RedditChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "无法执行" in msg
+        assert "pipx install --force" in msg  # rdt 专用 git 源重装处方
+        assert "git+https://github.com/public-clis/rdt-cli.git" in msg
+        assert ch.active_backend is None
+
+    def test_reports_error_with_reinstall_hint_on_exit_127(self, monkeypatch):
+        """退出码 127（找到但跑不动）同样按断链处理。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/rdt")
+
+        def fake_run(cmd, **kwargs):
+            return subprocess.CompletedProcess(cmd, 127, "", "")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.reddit import RedditChannel
+        ch = RedditChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "pipx install --force" in msg
+        assert ch.active_backend is None
 
     def test_can_handle_reddit_urls(self):
         from agent_reach.channels.reddit import RedditChannel
@@ -723,9 +764,11 @@ class TestXiaoHongShuChannel:
 
         monkeypatch.setattr(subprocess, "run", fake_run)
 
-        status, msg = XiaoHongShuChannel().check()
+        ch = XiaoHongShuChannel()
+        status, msg = ch.check()
         assert status == "ok"
         assert "完整可用" in msg
+        assert ch.active_backend == "xhs-cli (xiaohongshu-cli)"
 
     def test_reports_warn_when_not_authenticated(self, monkeypatch):
         monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/xhs")
@@ -735,12 +778,261 @@ class TestXiaoHongShuChannel:
 
         monkeypatch.setattr(subprocess, "run", fake_run)
 
-        status, msg = XiaoHongShuChannel().check()
+        ch = XiaoHongShuChannel()
+        status, msg = ch.check()
         assert status == "warn"
         assert "xhs login" in msg
+        # 未登录是业务态：工具进程活着，后端仍可用
+        assert ch.active_backend == "xhs-cli (xiaohongshu-cli)"
 
     def test_reports_off_when_not_installed(self, monkeypatch):
         monkeypatch.setattr(shutil, "which", lambda _: None)
-        status, msg = XiaoHongShuChannel().check()
+        ch = XiaoHongShuChannel()
+        status, msg = ch.check()
         assert status == "off"
         assert "xiaohongshu-cli" in msg
+        assert ch.active_backend is None
+
+    def test_reports_error_with_reinstall_hint_when_broken(self, monkeypatch):
+        """which 命中但 exec 抛 FileNotFoundError（venv 断链）→ error + 重装处方。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/xhs")
+
+        def fake_run(cmd, **kwargs):
+            raise FileNotFoundError("/usr/local/bin/xhs")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+
+        ch = XiaoHongShuChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "无法执行" in msg
+        assert "uv tool install --force xiaohongshu-cli" in msg
+        assert "pipx reinstall xiaohongshu-cli" in msg
+        assert ch.active_backend is None
+
+
+class TestBilibiliChannel:
+    def test_reports_error_with_reinstall_hint_when_ytdlp_broken(self, monkeypatch):
+        """yt-dlp which 命中但 exec 失败（venv 断链）→ error + 重装处方。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/yt-dlp")
+
+        def fake_run(cmd, **kwargs):
+            raise FileNotFoundError(cmd[0])
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.bilibili import BilibiliChannel
+        ch = BilibiliChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "无法执行" in msg
+        assert "uv tool install --force yt-dlp" in msg
+        assert "pipx reinstall yt-dlp" in msg
+        assert ch.active_backend is None
+
+    def test_active_backend_set_when_ytdlp_and_bili_ok(self, monkeypatch):
+        monkeypatch.setattr(
+            shutil, "which",
+            lambda cmd: f"/usr/local/bin/{cmd}" if cmd in ("yt-dlp", "bili") else None,
+        )
+
+        def fake_run(cmd, **kwargs):
+            return subprocess.CompletedProcess(cmd, 0, "2026.06.09", "")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.bilibili import BilibiliChannel
+        ch = BilibiliChannel()
+        status, msg = ch.check()
+        assert status == "ok"
+        assert "bili-cli 可用" in msg
+        assert ch.active_backend == "yt-dlp"
+
+    def test_bili_broken_does_not_count_as_available(self, monkeypatch):
+        """bili-cli 断链时不计为可用，降级走搜索 API；yt-dlp 仍是 active_backend。"""
+        monkeypatch.setattr(
+            shutil, "which",
+            lambda cmd: f"/usr/local/bin/{cmd}" if cmd in ("yt-dlp", "bili") else None,
+        )
+
+        def fake_run(cmd, **kwargs):
+            if "yt-dlp" in cmd[0]:
+                return subprocess.CompletedProcess(cmd, 0, "2026.06.09", "")
+            raise FileNotFoundError(cmd[0])
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        import agent_reach.channels.bilibili as bilibili_mod
+        monkeypatch.setattr(bilibili_mod, "_search_api_ok", lambda: True)
+        ch = bilibili_mod.BilibiliChannel()
+        status, msg = ch.check()
+        assert status == "ok"  # 搜索 API 兜底
+        assert "不计为可用" in msg
+        assert ch.active_backend == "yt-dlp"
+
+
+class TestYouTubeChannel:
+    def test_reports_error_with_reinstall_hint_when_broken(self, monkeypatch):
+        """yt-dlp which 命中但 exec 抛 FileNotFoundError → error + 重装处方。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/yt-dlp")
+
+        def fake_run(cmd, **kwargs):
+            raise FileNotFoundError(cmd[0])
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.youtube import YouTubeChannel
+        ch = YouTubeChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "无法执行" in msg
+        assert "uv tool install --force yt-dlp" in msg
+        assert ch.active_backend is None
+
+
+class TestGitHubChannel:
+    def test_reports_error_with_reinstall_hint_when_broken(self, monkeypatch):
+        """gh which 命中但 exec 失败 → error + brew 重装处方（gh 不是 pip 包）。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/gh")
+
+        def fake_run(cmd, **kwargs):
+            raise FileNotFoundError(cmd[0])
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.github import GitHubChannel
+        ch = GitHubChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "无法执行" in msg
+        assert "brew reinstall gh" in msg
+        assert ch.active_backend is None
+
+    def test_active_backend_set_when_authenticated(self, monkeypatch):
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/gh")
+
+        def fake_run(cmd, **kwargs):
+            return subprocess.CompletedProcess(cmd, 0, "Logged in to github.com", "")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.github import GitHubChannel
+        ch = GitHubChannel()
+        status, msg = ch.check()
+        assert status == "ok"
+        assert ch.active_backend == "gh CLI"
+
+    def test_active_backend_set_when_unauthenticated(self, monkeypatch):
+        """gh auth status 非零退出是正常业务态（未登录）：warn 但后端可用。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/gh")
+
+        def fake_run(cmd, **kwargs):
+            return subprocess.CompletedProcess(cmd, 1, "", "You are not logged in")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.github import GitHubChannel
+        ch = GitHubChannel()
+        status, msg = ch.check()
+        assert status == "warn"
+        assert "gh auth login" in msg
+        assert ch.active_backend == "gh CLI"
+
+
+class TestLinkedInChannel:
+    def test_reports_error_with_reinstall_hint_when_broken(self, monkeypatch):
+        """mcporter which 命中但 exec 失败 → error + npm 重装处方。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/mcporter")
+
+        def fake_run(cmd, **kwargs):
+            raise FileNotFoundError(cmd[0])
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.linkedin import LinkedInChannel
+        ch = LinkedInChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "npm install -g mcporter" in msg
+        assert ch.active_backend is None
+
+    def test_active_backend_set_when_linkedin_configured(self, monkeypatch):
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/mcporter")
+
+        def fake_run(cmd, **kwargs):
+            return subprocess.CompletedProcess(cmd, 0, "linkedin  http://localhost:3000/mcp", "")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.linkedin import LinkedInChannel
+        ch = LinkedInChannel()
+        status, msg = ch.check()
+        assert status == "ok"
+        assert ch.active_backend == "linkedin-scraper-mcp"
+
+    def test_off_without_backend_when_linkedin_not_configured(self, monkeypatch):
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/mcporter")
+
+        def fake_run(cmd, **kwargs):
+            return subprocess.CompletedProcess(cmd, 0, "exa  https://mcp.exa.ai/mcp", "")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.linkedin import LinkedInChannel
+        ch = LinkedInChannel()
+        status, msg = ch.check()
+        assert status == "off"
+        assert ch.active_backend is None
+
+
+class TestExaSearchChannel:
+    def test_reports_error_with_reinstall_hint_when_broken(self, monkeypatch):
+        """mcporter which 命中但 exec 失败 → error + npm 重装处方。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/mcporter")
+
+        def fake_run(cmd, **kwargs):
+            raise FileNotFoundError(cmd[0])
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.exa_search import ExaSearchChannel
+        ch = ExaSearchChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "npm install -g mcporter" in msg
+        assert ch.active_backend is None
+
+    def test_active_backend_set_when_exa_configured(self, monkeypatch):
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/mcporter")
+
+        def fake_run(cmd, **kwargs):
+            return subprocess.CompletedProcess(cmd, 0, "exa  https://mcp.exa.ai/mcp", "")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.exa_search import ExaSearchChannel
+        ch = ExaSearchChannel()
+        status, msg = ch.check()
+        assert status == "ok"
+        assert ch.active_backend == "Exa via mcporter"
+
+
+class TestXiaoyuzhouChannel:
+    def test_reports_error_with_reinstall_hint_when_ffmpeg_broken(self, monkeypatch):
+        """ffmpeg which 命中但 exec 失败（pip 假 ffmpeg 断链）→ error + 重装处方。"""
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/ffmpeg")
+
+        def fake_run(cmd, **kwargs):
+            raise FileNotFoundError(cmd[0])
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        from agent_reach.channels.xiaoyuzhou import XiaoyuzhouChannel
+        ch = XiaoyuzhouChannel()
+        status, msg = ch.check()
+        assert status == "error"
+        assert "无法执行" in msg
+        assert "brew install ffmpeg" in msg
+        assert ch.active_backend is None
+
+    def test_active_backend_set_when_fully_configured(self, monkeypatch):
+        monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/ffmpeg")
+
+        def fake_run(cmd, **kwargs):
+            return subprocess.CompletedProcess(cmd, 0, "ffmpeg version 7.0", "")
+
+        monkeypatch.setattr(subprocess, "run", fake_run)
+        monkeypatch.setattr("os.path.isfile", lambda p: True)  # transcribe.sh 已安装
+        monkeypatch.setenv("GROQ_API_KEY", "gsk_test")
+        from agent_reach.channels.xiaoyuzhou import XiaoyuzhouChannel
+        ch = XiaoyuzhouChannel()
+        status, msg = ch.check()
+        assert status == "ok"
+        assert ch.active_backend == "groq-whisper"
diff --git a/tests/test_doctor.py b/tests/test_doctor.py
index f3aa77d..8ecdf57 100644
--- a/tests/test_doctor.py
+++ b/tests/test_doctor.py
@@ -8,13 +8,15 @@ from agent_reach.config import Config
 
 
 class _StubChannel:
-    def __init__(self, name, description, tier, status, message, backends=None):
+    def __init__(self, name, description, tier, status, message, backends=None,
+                 active_backend=None):
         self.name = name
         self.description = description
         self.tier = tier
         self._status = status
         self._message = message
         self.backends = backends or []
+        self.active_backend = active_backend
 
     def check(self, config=None):
         return self._status, self._message
@@ -31,7 +33,8 @@ class TestDoctor:
             doctor,
             "get_all_channels",
             lambda: [
-                _StubChannel("web", "网页", 0, "ok", "可抓取网页", ["requests"]),
+                _StubChannel("web", "网页", 0, "ok", "可抓取网页", ["requests"],
+                             active_backend="requests"),
                 _StubChannel("github", "GitHub", 0, "warn", "gh 未安装", ["gh"]),
                 _StubChannel("exa_search", "全网语义搜索", 1, "off", "mcporter 未配置", ["Exa"]),
             ],
@@ -46,6 +49,7 @@ class TestDoctor:
                 "message": "可抓取网页",
                 "tier": 0,
                 "backends": ["requests"],
+                "active_backend": "requests",
             },
             "github": {
                 "status": "warn",
@@ -53,6 +57,7 @@ class TestDoctor:
                 "message": "gh 未安装",
                 "tier": 0,
                 "backends": ["gh"],
+                "active_backend": None,
             },
             "exa_search": {
                 "status": "off",
@@ -60,6 +65,7 @@ class TestDoctor:
                 "message": "mcporter 未配置",
                 "tier": 1,
                 "backends": ["Exa"],
+                "active_backend": None,
             },
         }
 
diff --git a/tests/test_probe.py b/tests/test_probe.py
new file mode 100644
index 0000000..f1a673f
--- /dev/null
+++ b/tests/test_probe.py
@@ -0,0 +1,90 @@
+# -*- coding: utf-8 -*-
+"""Tests for agent_reach.probe — real-execution probing and failure classification."""
+
+import os
+import stat
+import sys
+
+import pytest
+
+from agent_reach.probe import ProbeResult, probe_command, reinstall_hint
+
+
+def _make_executable(path, content):
+    path.write_text(content)
+    path.chmod(path.stat().st_mode | stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH)
+    return str(path)
+
+
+def test_missing_command():
+    r = probe_command("definitely-not-a-real-command-xyz")
+    assert r.status == "missing"
+    assert not r.ok
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="shebang semantics are POSIX-only")
+def test_broken_shebang_detected_as_broken(tmp_path, monkeypatch):
+    """A stale venv shim: which() finds it, exec raises FileNotFoundError."""
+    script = _make_executable(
+        tmp_path / "stale-tool", "#!/nonexistent/venv/bin/python\nprint('hi')\n"
+    )
+    monkeypatch.setenv("PATH", str(tmp_path) + os.pathsep + os.environ.get("PATH", ""))
+
+    r = probe_command("stale-tool", package="stale-tool-pkg")
+    assert r.status == "broken"
+    assert "uv tool install --force stale-tool-pkg" in r.hint
+    assert "pipx reinstall stale-tool-pkg" in r.hint
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="shell script fixture is POSIX-only")
+def test_healthy_command_returns_ok_with_output(tmp_path, monkeypatch):
+    script = _make_executable(
+        tmp_path / "healthy-tool", "#!/bin/sh\necho 'healthy-tool 1.2.3'\n"
+    )
+    monkeypatch.setenv("PATH", str(tmp_path) + os.pathsep + os.environ.get("PATH", ""))
+
+    r = probe_command("healthy-tool")
+    assert r.ok
+    assert "1.2.3" in r.output
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="shell script fixture is POSIX-only")
+def test_nonzero_exit_classified_as_error(tmp_path, monkeypatch):
+    script = _make_executable(
+        tmp_path / "failing-tool", "#!/bin/sh\necho 'boom' >&2\nexit 3\n"
+    )
+    monkeypatch.setenv("PATH", str(tmp_path) + os.pathsep + os.environ.get("PATH", ""))
+
+    r = probe_command("failing-tool")
+    assert r.status == "error"
+    assert "boom" in r.output
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="shell script fixture is POSIX-only")
+def test_exit_127_classified_as_broken(tmp_path, monkeypatch):
+    script = _make_executable(tmp_path / "wrapper-tool", "#!/bin/sh\nexit 127\n")
+    monkeypatch.setenv("PATH", str(tmp_path) + os.pathsep + os.environ.get("PATH", ""))
+
+    r = probe_command("wrapper-tool", package="wrapper-pkg")
+    assert r.status == "broken"
+    assert "wrapper-pkg" in r.hint
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="shell script fixture is POSIX-only")
+def test_retries_help_transient_failures(tmp_path, monkeypatch):
+    """First call fails (exit 1), second succeeds — retries=1 should return ok."""
+    marker = tmp_path / "ran-once"
+    script = _make_executable(
+        tmp_path / "flaky-tool",
+        f"#!/bin/sh\nif [ -f {marker} ]; then echo ok; exit 0; fi\ntouch {marker}\nexit 1\n",
+    )
+    monkeypatch.setenv("PATH", str(tmp_path) + os.pathsep + os.environ.get("PATH", ""))
+
+    r = probe_command("flaky-tool", retries=1)
+    assert r.ok
+
+
+def test_reinstall_hint_mentions_both_installers():
+    hint = reinstall_hint("some-pkg")
+    assert "uv tool install --force some-pkg" in hint
+    assert "pipx reinstall some-pkg" in hint
diff --git a/tests/test_twitter_channel.py b/tests/test_twitter_channel.py
index a84b044..1f8c716 100644
--- a/tests/test_twitter_channel.py
+++ b/tests/test_twitter_channel.py
@@ -26,6 +26,7 @@ def test_check_twitter_cli_found_and_auth_ok():
     assert status == "ok"
     assert "twitter-cli" in message
     assert "完整可用" in message
+    assert channel.active_backend == "twitter-cli"
 
 
 def test_check_twitter_cli_found_auth_missing():
@@ -41,6 +42,8 @@ def test_check_twitter_cli_found_auth_missing():
         status, message = channel.check()
     assert status == "warn"
     assert "未认证" in message
+    # 未认证是业务态：工具进程活着，后端仍可用
+    assert channel.active_backend == "twitter-cli"
 
 
 # --- bird CLI fallback tests ---
@@ -59,6 +62,7 @@ def test_check_bird_fallback_auth_ok():
         status, message = channel.check()
     assert status == "ok"
     assert "bird" in message
+    assert channel.active_backend == "bird CLI (legacy)"
 
 
 def test_check_bird_fallback_auth_missing():
@@ -86,6 +90,7 @@ def test_check_nothing_installed():
         status, message = channel.check()
     assert status == "warn"
     assert "twitter-cli" in message
+    assert channel.active_backend is None
 
 
 # --- twitter-cli preferred over bird ---
@@ -106,3 +111,44 @@ def test_twitter_cli_preferred_over_bird():
         status, message = channel.check()
     assert status == "ok"
     assert "twitter-cli" in message
+    assert channel.active_backend == "twitter-cli"
+
+
+# --- broken install (stale venv shim) ---
+
+def test_check_twitter_cli_broken_reports_error_with_reinstall_hint():
+    """which 命中但 exec 抛 FileNotFoundError（venv 断链）→ error + 重装处方。"""
+    channel = TwitterChannel()
+    with patch(
+        "shutil.which",
+        side_effect=lambda name: "/usr/local/bin/twitter" if name == "twitter" else None,
+    ), patch("subprocess.run", side_effect=FileNotFoundError("/usr/local/bin/twitter")):
+        status, message = channel.check()
+    assert status == "error"
+    assert "无法执行" in message
+    assert "uv tool install --force twitter-cli" in message
+    assert "pipx reinstall twitter-cli" in message
+    assert channel.active_backend is None
+
+
+def test_check_twitter_cli_broken_falls_back_to_bird():
+    """twitter-cli 断链但 bird 健康 → 回退到 bird，后端正确归属。"""
+    channel = TwitterChannel()
+
+    def which_side_effect(name):
+        if name in ("twitter", "bird"):
+            return f"/usr/local/bin/{name}"
+        return None
+
+    def run_side_effect(cmd, **kwargs):
+        if "twitter" in cmd[0]:
+            raise FileNotFoundError(cmd[0])
+        return _cp(stdout="Authenticated as @user\n", returncode=0)
+
+    with patch("shutil.which", side_effect=which_side_effect), patch(
+        "subprocess.run", side_effect=run_side_effect
+    ):
+        status, message = channel.check()
+    assert status == "ok"
+    assert "bird" in message
+    assert channel.active_backend == "bird CLI (legacy)"