feat(model): add MiniMax OpenAI-compatible provider

[Sparkle6979]

What does this PR do?

Closes #2214.

This PR adds MiniMax support to the OpenAI-compatible model extension.

• Registers a minimax: ModelProvider through Java SPI.
• Adds MiniMax chat and multi-agent formatters.
• Sets MiniMax's default base URL to https://api.minimaxi.com/v1.
• Resolves API keys from ModelCreationContext.apiKey or MINIMAX_API_KEY.
• Maps deprecated max_tokens usage to max_completion_tokens.
• Enables reasoning_split by default so MiniMax reasoning fields can be parsed as ThinkingBlock.
• Disables native structured output by default so AgentScope uses the synthetic-tool fallback path.

Why?

MiniMax provides an OpenAI-compatible Chat Completions endpoint:

https://platform.minimaxi.com/docs/api-reference/text-chat-openai

The MiniMax formatter keeps provider-specific behavior small and explicit. reasoning_split is enabled before the base formatter applies options so users can still override it with GenerateOptions.additionalBodyParam.

nativeStructuredOutput is disabled by default because local real-API probing showed that MiniMax accepts OpenAI-compatible requests, but response_format=json_schema strict=true does not behave as a reliable native structured-output contract across MiniMax-M3 and M2.x models. Users can still opt in through ModelCreationContext.option("nativeStructuredOutput", true) for experimentation.

Tests

• mvn -pl agentscope-extensions/agentscope-extensions-model/agentscope-extensions-model-openai test

Additional local real-API smoke/probe coverage was run against:

• MiniMax-M3
• MiniMax-M2.7-highspeed
• MiniMax-M2
• MiniMax-M2.7
• MiniMax-M2.5-highspeed
• MiniMax-M2.5
• MiniMax-M2.1-highspeed
• MiniMax-M2.1

[codecov]

Codecov Report

❌ Patch coverage is 90.16393% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../io/agentscope/core/model/ModelContextWindows.java	0.00%	11 Missing ⚠️
.../extensions/model/openai/ModelProviderSupport.java	96.22%	1 Missing and 1 partial ⚠️
...el/openai/compat/minimax/MiniMaxModelProvider.java	93.93%	2 Missing ⚠️
...nai/compat/minimax/MiniMaxMultiAgentFormatter.java	86.66%	2 Missing ⚠️
...e/extensions/model/openai/OpenAIModelProvider.java	90.00%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[AgentScopeJavaBot]

🤖 AI Review

This PR adds MiniMax as an OpenAI-compatible provider with two well-designed formatters (MiniMaxFormatter for single-agent, MiniMaxMultiAgentFormatter for multi-agent) and a ModelProvider SPI implementation. The formatters correctly override applyOptions (for reasoning_split), applyMaxTokens (for MiniMax's max_tokens deprecation), and supportsStrict. The MiniMaxModelProvider follows the established OpenAIModelProvider pattern with proper ModelCreationContext integration and advanced option support. Test coverage is comprehensive — unit tests for both formatters and the provider, plus an E2E smoke test gated by MINIMAX_API_KEY. No logic bugs, concurrency issues, or architectural violations were found.

[AgentScopeJavaBot]

🤖 AI Review

This PR adds MiniMax as an OpenAI-compatible provider with two well-designed formatters (MiniMaxFormatter for single-agent, MiniMaxMultiAgentFormatter for multi-agent) and a ModelProvider SPI implementation. The formatters correctly override applyOptions (for reasoning_split), applyMaxTokens (for MiniMax's max_tokens deprecation), and supportsStrict. The MiniMaxModelProvider follows the established OpenAIModelProvider pattern with proper ModelCreationContext integration and advanced option support. Test coverage is comprehensive — unit tests for both formatters and the provider, plus an E2E smoke test gated by MINIMAX_API_KEY. No logic bugs, concurrency issues, or architectural violations were found.

[oss-maintainer]

Summary

This PR contains 867 lines of changes. Review in progress.

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