fix(mimic): rewrite tool_use names in messages to match renamed tools

[iFwu]

Summary

When claude_code_mimic rewrites tool names in tools[] and tool_choice, it currently leaves messages[].content[].name blocks (type == "tool_use") with their original names. Anthropic validates that every tool referenced by a tool_use block is declared in tools[], so the mismatch produces an error like:

messages.N.content.M: Input tag 'original_name' not found in tools

surfaced as HTTP 400 directly, or wrapped as 424 by upstream proxies (e.g. Bedrock gateways).

Reproduction

1. An account with extra.claude_code_mimic = true
2. A client that sends tools beyond the Claude Code built-in set (e.g. web_search, or any user-defined tool whose name gets rewritten)
3. A multi-turn request where the assistant has previously invoked one of those tools, so the history contains tool_use blocks referencing the original name

The rewrite renames tools[*].name, but the older tool_use blocks in messages still point at the old name → Anthropic rejects the request.

Why Parrot didn't need this

The existing code comment referenced Parrot's behavior:

历史 $.messages[*].content[*].name（tool_use）不在请求侧改写——这与 Parrot 一致；响应侧 bytes.Replace 会连带还原它们。

Parrot only mimics Claude Code's built-in tool set, so by construction messages[].name and tools[].name use the same set of names, and there is no cross-turn mismatch. sub2api is more permissive — clients may send any tools[] — so the assumption no longer holds for historical tool_use blocks, which were named back when the rewrite hadn't been applied yet.

Fix

Apply the same ToolNameRewrite.Forward map to messages[].content[] entries where type == "tool_use", keeping tools[], tool_choice and messages self-consistent before the request hits Anthropic.

• tool_result blocks reference tools via tool_use_id, not name, so they don't need changes.
• Server tools (e.g. web_search_20250305 with non-empty type) are still skipped by shouldMimicToolName, so they aren't touched.
• Response-side bytes.Replace still restores the original names in the final output, so the client sees no difference.

Testing

Added TestApplyToolNameRewriteToBody_RenamesToolUseInMessages to gateway_tool_rewrite_test.go, covering:

• tools[*].name rewritten
• tool_choice.name rewritten
• messages[*].content[*].name (type == "tool_use") rewritten
• Server tools (type != "") untouched
• Text blocks untouched
• tool_result blocks untouched (no name field)

$ go test ./internal/service/ -run TestApplyToolNameRewriteToBody -v
=== RUN   TestApplyToolNameRewriteToBody_RenamesToolsAndToolChoice
--- PASS: TestApplyToolNameRewriteToBody_RenamesToolsAndToolChoice (0.00s)
=== RUN   TestApplyToolNameRewriteToBody_RenamesToolUseInMessages
--- PASS: TestApplyToolNameRewriteToBody_RenamesToolUseInMessages (0.00s)
PASS

Validated in production: previously the affected account hit 424 on every multi-turn request containing web_search tool_use history; after this fix those requests succeed.

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[iFwu]

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