feat: migrate anthropic provider to AI SDK

[daniel-lxs]

Summary

Migrates the Anthropic provider (src/api/providers/anthropic.ts) from using the raw @anthropic-ai/sdk to @ai-sdk/anthropic with the Vercel AI SDK, following the same pattern already used by Gemini and Vertex providers.

Key Changes

New Files

• src/api/transform/caching/ai-sdk-anthropic.ts — Cache breakpoint utility that adds providerOptions.anthropic.cacheControl to AI SDK messages
• src/api/transform/caching/__tests__/ai-sdk-anthropic.spec.ts — Tests for the cache utility

Modified Files

• src/package.json — Added @ai-sdk/anthropic dependency
• src/api/providers/anthropic.ts — Full rewrite from raw SDK to AI SDK pattern:
  • Uses createAnthropic() + streamText()/generateText() from the AI SDK
  • Cache breakpoints via post-processing utility (consistent with existing caching/ directory pattern)
  • System prompt caching with providerOptions.anthropic.cacheControl
  • Thinking config mapped from budget_tokens → budgetTokens (snake_case → camelCase)
  • All beta headers passed manually via headers option
  • Fixes thought signature capture — previously not implemented (noted at old line 308)
  • Adds redacted thinking support via getRedactedThinkingBlocks()
  • Cache write tokens from providerMetadata.anthropic.cacheCreationInputTokens
• src/api/transform/ai-sdk.ts — Enhanced processAiSdkStreamPart to handle reasoning-end with signatures; convertToAiSdkMessages preserves thinking block signatures and redacted_thinking
• src/api/providers/__tests__/anthropic.spec.ts — Full rewrite: 33 tests
• src/api/transform/__tests__/ai-sdk.spec.ts — Updated for thinking/signature handling

Testing

• 33 tests passing in anthropic.spec.ts
• 60 tests passing in ai-sdk.spec.ts
• 8 tests passing in ai-sdk-anthropic.spec.ts
• All existing provider tests unaffected

Migration Pattern

Follows the established AI SDK migration pattern from Gemini/Vertex:

1. Convert Anthropic messages → AI SDK ModelMessage[] via convertToAiSdkMessages()
2. Post-process with cache breakpoints via addAiSdkAnthropicCacheBreakpoints()
3. Stream via streamText() → result.fullStream → processAiSdkStreamPart()
4. Capture reasoning/signatures from result.reasoning after stream completes

---

Important

Migrates Anthropic provider to AI SDK, adding cache and reasoning support, with extensive testing.

• Behavior:
  • Migrates anthropic.ts to use @ai-sdk/anthropic and ai for message processing.
  • Implements cache breakpoints for Anthropic models in ai-sdk-anthropic.ts.
  • Handles reasoning and tool call stream parts in ai-sdk.ts.
• Testing:
  • Adds ai-sdk-anthropic.spec.ts for cache utility tests.
  • Updates anthropic.spec.ts with 33 tests for new SDK behavior.
  • Updates ai-sdk.spec.ts for reasoning and signature handling.
• Dependencies:
  • Adds @ai-sdk/anthropic to package.json.

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[roomote]

Rooviewer   See task

Reviewed the Anthropic AI SDK migration. One issue flagged:

• Bearer auth token mode sends an empty x-api-key header alongside Authorization: Bearer, which may break custom backends that validate x-api-key (comment)

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[roomote]

When useAuthToken is true, setting apiKey: "" causes @ai-sdk/anthropic to send an x-api-key: "" header on every request, alongside the Authorization: Bearer header added here. The old code used the Anthropic SDK's authToken constructor option, which sent only the Authorization: Bearer header and never set x-api-key. Custom Anthropic-compatible backends that validate x-api-key for non-empty values will reject these requests. This only affects users with a custom anthropicBaseUrl who also enable anthropicUseAuthToken. One possible workaround is to pass apiKey: undefined (if the AI SDK accepts it) or to strip x-api-key from outgoing requests via a custom fetch wrapper.

_{Fix it with Roo Code or mention @roomote and request a fix.}