feat: migrate MiniMax provider to AI SDK

[hannesrudolph]

Summary

Migrates the MiniMax provider from raw @anthropic-ai/sdk usage to the AI SDK (@ai-sdk/anthropic with custom baseURL), following the Archetype 3 migration pattern established by the Anthropic handler.

Changes

• Rewrite minimax.ts: Replace raw Anthropic SDK client with createAnthropic() + streamText() / generateText() and shared transform layer (convertToAiSdkMessages, processAiSdkStreamPart, handleAiSdkError)
• BaseURL path fix: Resolve all URLs to end with /anthropic/v1 since @ai-sdk/anthropic appends /messages directly (not /v1/messages like the raw Anthropic SDK)
• Thinking signature capture: Add lastThoughtSignature, getThoughtSignature(), and getRedactedThinkingBlocks() matching the anthropic.ts pattern — critical for MiniMax interleaved thinking round-trip
• Prompt caching: Via providerOptions.anthropic.cacheControl (AI SDK native) instead of manual cache_control blocks
• isAiSdkProvider(): Returns true for proper reasoning block preservation in conversation history
• Preserve mergeEnvironmentDetailsForMiniMax: Applied before convertToAiSdkMessages() to maintain tool result merging behavior
• Rewrite minimax.spec.ts: Full test rewrite with AI SDK mocks — 21/21 tests pass

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Important

Migrates MiniMax provider to AI SDK, refactoring URL handling, message streaming, and error management, with updated tests.

• Migration to AI SDK:
  • Replaces raw Anthropic SDK with AI SDK in minimax.ts using createAnthropic(), streamText(), and generateText().
  • Adjusts baseURL handling to append /anthropic/v1.
• New Methods:
  • Adds getThoughtSignature() and getRedactedThinkingBlocks() for capturing and retrieving thought signatures and redacted thinking blocks.
  • Implements isAiSdkProvider() to return true.
• Error Handling:
  • Utilizes handleAiSdkError() for error management.
• Prompt Caching:
  • Uses AI SDK's native caching via providerOptions.anthropic.cacheControl.
• Tests:
  • Updates minimax.spec.ts to mock AI SDK functions and verify new behavior.
  • Ensures all 21 tests pass with the new implementation.

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[roomote]

Rooviewer   See task

Both previously flagged issues have been addressed. No new issues found.

• Missing convertToolsForOpenAI step (minimax.ts:80): Now calls this.convertToolsForOpenAI(metadata?.tools) before convertToolsForAiSdk(), matching the Anthropic handler pattern.
• Tests only exercise legacy config path (minimax.ts): LegacyApiConfiguration type and getLegacyApiConfiguration() removed. Tests now pass minimaxApiKey/minimaxBaseUrl as top-level properties matching the production ProviderSettings shape.

Previous reviews

• 610bf78: Review #1

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