[googio]

web_search: Serply as an API key service

Adds serply-api to the search services catalogue, next to serper-api. agentty has a matching PR that moves its submodule to this commit and adds the id to its registry list, so this one needs to be merged first.

Disclosure: I work with Serply.

What it does

Serply returns Google results as JSON (docs). The row is built the same way as Serper's:

• Request: GET https://api.serply.io/v1/search/?q=...&num=... with the key in the x-api-key header, so the key never appears in the URL.
• Country: defaults to United States. Without gl the request is served from whichever proxy region is free and the results can change country between calls, so gl=us is sent when the dial is empty. The dial is the shared list with "United States (default)" as its first row and no second US row; any other choice is sent as gl (lower case).
• Freshness: Past hour to Past year, sent as tbs=qdr:h|d|w|m|y. These are the same values Serper offers.
• Excluded sites: not in has_native_exclude, so -site: stays in the query text, as it does for Serper. Google honours it.
• Reply: read from results[], using link, title and description. A 2xx reply without results is reported as unreadable.
• Out of credits: Serply's gateway answers a zero balance (expired free credits included) with 402 and {"detail":"Insufficient prepaid credits"}, which classify_http already reports as quota exhausted.
• Token links: now and then a reply row carries an opaque token in link instead of a URL. Rows whose link is not http(s) are dropped before counting.
• Empty results on a 200: Serply's Pagination guide says this also happens during transient upstream failures. No header or field tells it apart from a genuine "no results"; the documented advice is to retry. mcp-cpp reports it as no results and moves to the next service.

Things that differ from Serper:

• max_count is 10. num above 10 returns the same page as num=10.
• No language. hl did not change the results, so the row leaves language off and does not claim it.
• No spell-correction dial. Serply has no autocorrect parameter.
• A user-agent: mcp-cpp header is sent. Cloudflare in front of the API refuses some default client user-agents, so the request names itself.

The builder comment marks this [L]: the exact URL the test pins, ?q=rust%20async&num=5&gl=nz&tbs=qdr%3Ad, returns 200 from the live API, and tbs=qdr:h narrowed the results.

Tests

tests/web_search_services_test.cpp:

• the catalogue count goes from 10 to 11;
• Serply's Freshness values are checked against the same hourly tbs list Serper uses;
• a new case covers the request (URL, key header, user-agent, no hl, cap of 10, gl=us with no dials, no second US row) and the reply parser (a recorded result, and a reply without results);
• the reply parser skips a row whose link is a token and does not count it;
• "failures are told apart" pins Serply's 402 body as quota exhausted.

The full mcp_tests run passes (96 cases, 2269 assertions) with GCC 13, and the build has no warnings.