fix(ai): round-trip Anthropic tool_search_tool_result blocks

[lu-zero]

Issue for this PR

Fixes #45527.

Scope note: this is the protocol half only — the wire round-trip for Anthropic tool-search blocks. It does not add the config seam (defer_loading passthrough, declaring a provider-defined tool) that #45527 also asks for; happy to keep that issue open if maintainers prefer.

Targets beta. The same fix against dev is #48466, where the file lives at packages/llm/src/protocols/anthropic-messages.ts; beta has the identical gap at packages/ai/src/protocols/anthropic-messages.ts.

Type of change

• Bug fix

What does this PR do?

The native Anthropic protocol dropped tool_search_tool_result content blocks at stream-decode time and refused to lower them back onto the wire. Both gaps keyed off the same hardcoded three-entry server-tool list, which predates Anthropic's tool-search server tools.

A tool search puts signed thinking, server_tool_use, tool_search_tool_result and tool_use in one assistant turn. Dropping the result block means the replayed turn no longer matches the original response, and Anthropic rejects the signed thinking block:

`thinking` or `redacted_thinking` blocks in the latest assistant message cannot be modified.

One unhandled block type turns into a hard 400 for the rest of the conversation.

File	Change
ai/src/protocols/anthropic-messages.ts	Accept and re-emit tool_search_tool_result; record server_tool_use id → name in parser state, because tool_search_tool_bm25 and tool_search_tool_regex both report through one result block type that carries no name of its own.
ai/test/provider/anthropic-messages.test.ts	Round-trip coverage: decode the tool-search turn, then recompile it and assert every sibling of the signed thinking block survives.

How did you verify your code works?

Check	Result
bun test test/provider/anthropic-messages.test.ts	70 pass, 0 fail
Same test with the source change reverted	fails — the tool-result event is absent entirely
bun turbo typecheck	35/35 tasks pass

Screenshots / recordings

N/A — provider wire-format change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

🤖 Generated with Claude Code

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

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1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Found one related PR:

• PR fix(llm): round-trip Anthropic tool_search_tool_result blocks #48466: fix(llm): round-trip Anthropic tool_search_tool_result blocks — fix(llm): round-trip Anthropic tool_search_tool_result blocks #48466

This is not a duplicate of the current PR (#48485). According to the PR description, #48466 is the companion fix against the dev branch (in packages/llm), while #48485 is the same fix against the beta branch (in packages/ai). These are parallel changes to address the same underlying issue in two different code locations.