* feat: normalize web search output contract
* refactor(agents): promote web_search contract from a dedicated output module
* fix(agents): wrap unwrapped web_search text and pass unknown provider payloads through as raw
* fix(agents): gate web_search results branch on conforming rows and cover metadata fields
* fix(agents): gate every provider text path at the web_search boundary
* test(agents): align web_search fixtures with boundary-owned wrapping
* fix(agents): make the web_search boundary own the untrusted-content envelope
* fix(agents): report declared web_search errors first and align the documented contract
* fix(agents): bind envelope stripping to real markers and densify result rows
* fix(agents): emit canonical urls and a closed error code from web_search
* fix(agents): keep structured provider error diagnostics in the wrapped message
* fix(agents): satisfy production export and lint gates for the web_search contract