For adapter plugins, ``PlatformEntry.check_fn`` doubles as a lazy installer:
calling it pip-installs the platform SDK as a side effect (see e.g.
``plugins/platforms/discord/adapter.py::check_discord_requirements``). The
enablement sweep in ``_apply_env_overrides`` called ``check_fn`` for every
registered plugin platform unconditionally, so a single
``load_gateway_config()`` — which the desktop/dashboard readiness probe
``GET /api/status`` awaits synchronously — pip-installed Discord, Telegram,
Slack, Feishu and Dingtalk even when the user configured none of them
(``platforms: none``). On a slow or restricted network the installs ran long
enough to block the event loop past the desktop's readiness timeouts, so the
app timed out, killed and re-spawned the backend, and boot-looped (stuck at
94%).
Consult the cheap ``is_connected`` credential check FIRST and only run the
install-triggering ``check_fn`` for platforms that are already enabled or
actually configured. Auto-enable-by-credentials is unchanged: a platform with
its token set still gets its SDK installed and enabled.
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