feat(runtime): add Alibaba native WebSearch for Qwen3.8-Max

[MoonOld]

Problem

Alibaba Cloud Model Studio now documents native Web Search support for qwen3.8-max in the China (Beijing) and Singapore deployment scopes. The same model capability is documented as unsupported in the Frankfurt, Virginia, Tokyo, and Hong Kong global scopes. The Token Plan Harness surface also documents Web Search for qwen3.8-max-preview.

Maka cannot currently expose that provider-native search path:

• providerHostedWebSearchAdapter('alibaba') resolves to openai-responses with implemented: false;
• the Alibaba fallback model rule only recognizes Qwen 3.5 Plus/Flash families;
• routeWebSearchTools() therefore removes WebSearch when model is selected, even for a supported Qwen3.8-Max deployment.

This forces users to configure a separate Tavily credential despite their selected model and deployment already offering native search.

Official references:

• Qwen3.8-Max capabilities and regional availability: https://www.alibabacloud.com/help/en/model-studio/qwen3-8-max
• Model Studio built-in web search and Responses tool shape: https://www.alibabacloud.com/help/en/model-studio/web-search
• Token Plan Harness tools: https://www.alibabacloud.com/help/en/model-studio/token-plan-harness-tool

Desired outcome

Add a production Alibaba Model Studio native-search adapter, with Qwen3.8-Max as the initial supported model family.

• Confirm and implement the official Qwen3.8-Max API wire instead of assuming that generic OpenAI compatibility implies Responses web_search.
• Reuse the active Alibaba connection, endpoint, and credential in the primary model request; do not create a nested model request or store a second search credential.
• Represent supported exact models/deployment scopes through model metadata or narrow fail-closed rules. Unsupported regions and models must not receive the tool.
• Preserve existing providerExecuted call/result events, normalized source rows, opaque provider output for replay, privacy-mode removal, child-tool ceilings, and explicit no-fallback behavior.
• Add capability-resolution, request-wire, result-projection/replay, and production-composition tests. A live smoke against a supported Beijing or Singapore deployment would pin the final contract.

Alternatives or workarounds

Users can select Tavily, but that requires a separate API key and executes as a client tool. Token Plan Harness search is another provider-managed surface, but it does not solve native search for ordinary Maka Alibaba model connections.

[MoonOld]

I will take this. I am starting with the Alibaba Model Studio provider-native WebSearch path for Qwen3.8-Max, including fail-closed capability routing, provider wire/result replay tests, and production-composition coverage. I will link the implementation PR here once it is ready.

[MoonOld]

After inspecting the existing Alibaba Responses work in #3255, I found that #3163 already tracks the broader and more accurate Alibaba Harness-tool integration, including the web_search first slice. Closing this issue as a duplicate of #3163 so implementation and review stay on the established dependency chain.