fabro/nodes/implement/prompt.md

Goal: # Plan: Map reasoning_effort to Anthropic output_config.effort

Context

The Anthropic Messages API now supports output_config: { effort: "low" | "medium" | "high" | "max" } as the recommended way to control thinking depth for Claude Opus 4.6 and Sonnet 4.6 (replacing deprecated budget_tokens). Fabro's unified Request already carries reasoning_effort: Option<String> and workflow nodes default it to "high", but the Anthropic provider silently drops this field — it never appears in the API request. The OpenAI provider correctly maps it to reasoning: { effort }, but the Anthropic provider has no equivalent.

Single file to modify

lib/crates/fabro-llm/src/providers/anthropic.rs

Step 1: Add failing tests

Add tests at the end of the #[cfg(test)] mod tests block (before line 2043's }). These tests reference a new output_config field on ApiRequest that doesn't exist yet, so they won't compile until Step 2.

Test A — build_api_request_maps_reasoning_effort_to_output_config: Build a Request with reasoning_effort: Some("medium"), call build_api_request, assert api_request.output_config == Some(json!({"effort": "medium"})). Pattern: follows existing build_api_request_omits_whitespace_only_system_prompt test (line 1592).

Test B — build_api_request_omits_output_config_when_no_reasoning_effort: Same but with reasoning_effort: None, assert api_request.output_config.is_none().

Step 2: Add output_config field to ApiRequest struct

At line 108 (after thinking), add:

#[serde(skip_serializing_if = "Option::is_none")]
output_config: Option<serde_json::Value>,

Update every existing ApiRequest construction to include output_config: None:

• line 1566 (serialization test)
• line 1962 (merge_provider_options test)
• line 1993 (merge_provider_options test)

At this point: code compiles, Test B passes, Test A fails (proving the bug exists).

Step 3: Map reasoning_effort → output_config in build_api_request

At line 1073 (next to the thinking extraction), add:

let output_config = request
    .reasoning_effort
    .as_ref()
    .map(|effort| serde_json::json!({"effort": effort}));

Add output_config, to the ApiRequest construction at line 1075.

This mirrors the OpenAI provider pattern at openai.rs:385-388.

All tests pass.

Verification

cargo test -p fabro-llm -- anthropic::tests::build_api_request_maps_reasoning_effort
cargo test -p fabro-llm -- anthropic::tests::build_api_request_omits_output_config
cargo test -p fabro-llm  # all provider tests still pass
cargo clippy --workspace -- -D warnings

Completed stages

• toolchain: success
  • Script: command -v cargo >/dev/null || { curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y && sudo ln -sf $HOME/.cargo/bin/* /usr/local/bin/; }; cargo --version 2>&1
  • Stdout:

    cargo 1.94.0 (85eff7c80 2026-01-15)
    

  • Stderr: (empty)
• preflight_compile: success
  • Script: cargo check -q --workspace 2>&1
  • Stdout: (empty)
  • Stderr: (empty)
• preflight_lint: success
  • Script: cargo clippy -q --workspace -- -D warnings 2>&1
  • Stdout: (empty)
  • Stderr: (empty)

Read the plan file referenced in the goal and implement every step. Make all the code changes described in the plan. Use red/green TDD.