``search_sources`` (a provider list, ``["deepseek", "bing"]`` by default,
``[]`` to not offer the tool at all) names what the local ``web_search`` tool
searches with, in fallback order: ``search_in_order`` asks each source in turn
and keeps the first answer, so a source that errors — a rate limit, a rejected
key — or finds nothing hands over to the next instead of failing the tool. The
handler reports the failures only when every source came up empty.
The Bing leg answers with its RSS results (``?format=rss``), which need no key
and carry a description — the snippet DeepSeek's own index does not hand out —
and it goes through the ``fetch`` client, so the SSRF and host-grant policy
applies to it too (a host that binds tool instance state, as the CLI does).
Only DeepSeek's Anthropic-compatible surface runs a hosted ``web_search``: the
Responses and chat-completions surfaces answer "I can't browse the web" with
``{"type": "web_search"}`` and with the server-tool shape alike, so a DeepSeek
provider that talks them had no search at all.
``config.routing.local_web_search`` decides per provider: a DeepSeek provider
whose ``provider_tools`` ask for ``web_search`` and whose convention is not
``anthropic`` gets the local tool (``tools/net/search.py``), which asks the
search-capable endpoint behind the scenes and hands the model one ``title —
url`` line per hit — read a page with ``fetch``, the bodies stay server-side.
DeepSeek's preset asks for no hosted tool by default, so this stays opt-in.
NCBM