The DeepSeek Search API returns a short `snippet` for display and a longer
`summary` written for model reading. Carry `summary` on `WebSearchSource`,
map it from the Search API, and render it in place of the snippet in
`web_search` output while the search card keeps the snippet.
`tool-web` collapses summary whitespace and caps each summary at the new
`searchSummaryMaxChars` setting (800 characters by default, the upper end of
the guide's typical range; live summaries measured 1,000-2,300). The cut keeps
surrogate pairs intact and ends in an ellipsis. The PTC tool output type gains
the optional field, so the affected system-prompt sidecars are refreshed, and
the web search round now exercises a multi-line summary.
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