fix: preserve unknown fields in Anthropic schemas (restores prompt caching)#74
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sgasser merged 3 commits intosgasser:mainfrom Feb 27, 2026
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- Add biome-ignore comments to suppress noExplicitAny in tests (required for testing unknown field preservation) - Add .passthrough() to OpenAI schemas for consistency (OpenAIMessageSchema, OpenAIContentPartSchema) - Format Anthropic schemas to match project style
- Schema tests for name, tool_calls, audio content, unknown fields - Extractor tests for field preservation through applyMasked
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Problem
Clients that rely on prompt caching experienced dramatically higher token usage when routing through PasteGuard. Every request was billed as if the full system prompt and tool definitions were new input, rather than being served from cache.
Root Cause
PasteGuard validates incoming requests using Zod schemas. Only the top-level
AnthropicRequestSchemaused.passthrough(), but all nested schemas —TextBlockSchema,AnthropicMessageSchema,ToolSchema, and others — did not.Zod strips unknown fields by default. This silently removed
cache_control: { "type": "ephemeral" }from content blocks, system prompt blocks, tool definitions, and messages before they were forwarded upstream. Without these fields, the API receives no cache breakpoints and prompt caching is disabled entirely.The OpenAI schemas already handled this correctly via
OpenAIMessageSchema.passthrough().Fix
Add
.passthrough()to all nestedz.object()schemas insrc/providers/anthropic/types.ts, matching the OpenAI implementation. This ensures any fields PasteGuard does not explicitly declare are passed through unchanged.Tests
Added regression tests covering:
cache_controlpreservation through Zod parsing on text blocks, system blocks, tools, and messagescache_controlsurvival through the fullapplyMaskedround-trip in the extractor