F4b-Anthropic — native structured output via forced tool_use#107
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Third and final slice of the F4b family (#102 OpenAI, #103 Gemini, this PR Anthropic). When SendArgs.jsonSchema is set, the Anthropic adapter forces the model to emit its result through a tool_use block — closing the universal defense-in-depth coverage. What lands src/providers/anthropic.ts: Request wiring (build): - AnthropicRequestBody gains optional tools[] and tool_choice fields. Tools is a single-element array; tool_choice pins the model to call exactly that tool. - NEW exported constant ANTHROPIC_STRUCTURED_TOOL_NAME = "structured_output". Same name on both sides of the wire so the parser can match deterministically. - buildAnthropicRequest accepts opts.jsonSchema. When set, the body grows a tools entry with the schema as input_schema and a tool_choice forcing that tool. Anthropic accepts JSON Schema directly, so unlike Gemini there is NO translation layer — the schema flows through verbatim. Response wiring (parse): - parseAnthropicResponse now distinguishes block types in the content array. tool_use blocks whose name matches ANTHROPIC_STRUCTURED_TOOL_NAME have their `input` field captured separately from text blocks. - When a matching tool_use block is present, its JSON-stringified input replaces the concatenated text payload. This keeps the downstream extractJson + validateSchema path entirely unaware of which transport carried the structured value — same parse → same validation → same envelope shape. - Non-matching tool_use blocks (e.g. worker_tools' fetch/verify in a different ReAct context) flow through untouched; only the structured_output tool name triggers the surface change. - Plain text responses keep working unchanged — baseline regression guard tested. src/providers/anthropic.ts (sendAnthropic): Threads args.jsonSchema into the builder. Tests (+9) test/providers/anthropic-native-json.test.ts: build (4): tools + tool_choice attached on jsonSchema; omitted otherwise; no schema translation (rich JSON Schema flows verbatim into input_schema, including $schema and additionalProperties:false); JSON-serializable round trip. parse (5): tool_use input → JSON-stringified text; tool_use trumps prose text block (forced-tool semantics); only the structured_output tool name is captured (other tool names fall through); plain text still works; array values JSON-stringify correctly. Scoreboard TS: 1,325 / 1,325 (+9 over #103's 1,316) typecheck + build: clean F4b coverage complete OpenAI response_format: {type: "json_schema", strict: true} PR #102 Gemini generationConfig.{responseSchema, responseMimeType} PR #103 Anthropic tools[] + tool_choice: forced tool_use THIS PR Universal schema-in-prompt + tolerant parser (F4c) main Every supported provider now has a native channel for structured output. SendArgs.jsonSchema is the single switch the caller flips; each adapter normalises to its own native shape and the universal parse path catches any miss. Schema-in-prompt + F4c's tolerant parser remain the safety net for providers we don't yet have native mode wired for (xai/mistral/groq/deepseek under openai-compat). Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
Re-opened after #104 auto-closed when its base branch (#103/#106's Gemini branch) was deleted. Same diff as #104, rebased onto current main (which now has F4b OpenAI + F4b Gemini squashed in).
Third and final slice of the F4b family. When `SendArgs.jsonSchema` is set, the Anthropic adapter forces the model to emit its result through a `tool_use` block.
What lands
Build side
Parse side
Tests (+9)
Scoreboard
F4b coverage complete
🤖 Generated with Claude Code