web_search provider validation errors on valid Brave/Kagi responses

[spences10]

Summary

web_search can return provider validation errors for otherwise valid searches when Brave or Kagi returns a response shape containing missing/undefined result fields.

This looks like a genuine adapter/schema robustness issue rather than caller misuse: the tool calls used valid provider, query, limit, and large_result_mode arguments. Similar Brave calls succeeded in the same session, but some queries failed during response parsing.

Repro examples

These calls failed:

{
  "provider": "brave",
  "query": "\"pi-prompt-shelf\" pi extension prompt",
  "limit": 10,
  "large_result_mode": "inline"
}

Error:

Malformed brave response: × Invalid key: Expected "web" but received undefined
  → at web

Another Brave query with the same shape also failed:

{
  "provider": "brave",
  "query": "\"prompt templates with model skill thinking frontmatter\" pi",
  "limit": 10,
  "large_result_mode": "inline"
}

Same error:

Malformed brave response: × Invalid key: Expected "web" but received undefined
  → at web

Kagi also failed for valid searches:

{
  "provider": "kagi",
  "query": "\"pi-prompt-shelf\" \"pi-packs\"",
  "limit": 10,
  "large_result_mode": "inline"
}

Error:

Malformed kagi response: × Invalid key: Expected "title" but received undefined
  → at data.2.title
× Invalid key: Expected "url" but received undefined
  → at data.2.url
× Invalid key: Expected "snippet" but received undefined
  → at data.2.snippet
× Invalid key: Expected "total_hits" but received undefined
  → at meta.total_hits

Other Kagi queries failed similarly, but at different data indexes, e.g. data.5 and data.14.

Expected behavior

The provider adapters should tolerate provider responses that contain no web block, non-result rows, omitted snippets, or missing total_hits metadata. Ideally:

• return an empty result list for no-result Brave responses instead of throwing
• filter/skip Kagi entries without title/url
• make snippet and meta.total_hits optional if the upstream provider omits them
• include raw provider response details in debug logs, if available, to aid diagnosis

Context

This came up while researching Pi extensions. Some Brave searches succeeded immediately before these failures, so the issue appears response-shape-specific rather than a broken MCP invocation or unavailable provider.