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nodes/implement/prompt.md

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+Goal: # Plan: Support Anthropic fast mode (`speed: fast`) — Issue #120
+
+## Context
+
+Anthropic's API supports [fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) (beta) for Claude Opus 4.6 — up to 2.5x faster output at 6x pricing ($30/$150 per MTok vs $5/$25 standard). The API requires:
+- `"speed": "fast"` top-level field in request body
+- `anthropic-beta: fast-mode-2026-02-01` header
+- Response includes `usage.speed` confirming actual speed used
+
+This follows the same pattern as `reasoning_effort`, which is already implemented end-to-end.
+
+## Implementation
+
+### 1. Foundation: `lib/crates/fabro-llm/src/types.rs`
+
+- Add `speed: Option<String>` to `Request` (after `reasoning_effort`, line ~454)
+- Add `speed: Option<String>` to `Usage` (before `raw`, line ~372)
+- In `Usage::Add` impl (line ~389): propagate `speed` from `self` (left-hand side wins, since all requests in a session use the same speed)
+
+### 2. Graph layer: `lib/crates/fabro-graphviz/src/graph/types.rs`
+
+Add after `reasoning_effort()` (~line 211):
+```rust
+#[must_use]
+pub fn speed(&self) -> Option<&str> {
+    self.str_attr("speed")
+}
+```
+Returns `Option` (no default) — unlike `reasoning_effort` which defaults to "high", speed defaults to None (standard) since fast mode is 6x cost.
+
+### 3. Stylesheet: `lib/crates/fabro-workflows/src/stylesheet.rs`
+
+Add `"speed"` to `STYLESHEET_PROPERTIES` array (line 5):
+```rust
+const STYLESHEET_PROPERTIES: &[&str] = &["model", "provider", "reasoning_effort", "speed", "backend"];
+```
+
+### 4. Agent config: `lib/crates/fabro-agent/src/config.rs`
+
+- Add `pub speed: Option<String>` field to `SessionConfig` (line ~66)
+- Add `speed: None` to `Default` impl (line ~135)
+
+### 5. Session wiring: `lib/crates/fabro-agent/src/session.rs`
+
+- Add `speed: self.config.speed.clone()` to Request construction (~line 908)
+- Add `set_speed()` method analogous to `set_reasoning_effort()` (~line 458)
+
+### 6. Anthropic provider: `lib/crates/fabro-llm/src/providers/anthropic.rs`
+
+**6a. `ApiRequest` struct** (~line 87): Add `speed: Option<String>` field
+
+**6b. Beta header constant** (~line 510):
+```rust
+const FAST_MODE_BETA_HEADER: &str = "fast-mode-2026-02-01";
+```
+
+**6c. `build_beta_header()`** (~line 582): Add `include_fast_mode_header: bool` parameter. Inject fast-mode header (same pattern as cache header).
+
+**6d. `build_api_request()`** (~line 1082):
+- Set `speed: request.speed.clone()` on `ApiRequest`
+- Compute `let is_fast = request.speed.as_deref() == Some("fast")`
+- Pass `is_fast` to `build_beta_header()`
+
+**6e. `ApiUsage`** (~line 160): Add `speed: Option<String>` field
+
+**6f. Response parsing**: Map `api_resp.usage.speed` → `Usage.speed` in both:
+- Non-streaming path (~line 1192)
+- Streaming `message_start` handler (~line 690)
+
+### 7. Usage tracking: `lib/crates/fabro-workflows/src/outcome.rs`
+
+- Add `speed: Option<String>` to `StageUsage` (with `serde(default, skip_serializing_if)`)
+- Update `From<&StageUsage> for Usage` to include `speed`
+
+### 8. Cost multiplier: `lib/crates/fabro-workflows/src/cost.rs`
+
+Apply 6x multiplier when `speed == "fast"`:
+```rust
+let multiplier = if usage.speed.as_deref() == Some("fast") { 6.0 } else { 1.0 };
+// Apply multiplier to final cost
+```
+
+### 9. Backend wiring: `lib/crates/fabro-workflows/src/backend/api.rs`
+
+- SessionConfig construction (~line 195): add `speed: node.speed().map(String::from)`
+- Prompt-mode Request construction (~line 285): add `speed: node.speed().map(String::from)`
+- Both StageUsage constructions (~lines 389, 589): add `speed: response.usage.speed.clone()` / `total_usage.speed.clone()`
+
+### 10. Tests
+
+- `anthropic.rs`: `build_api_request_sets_speed`, `build_api_request_injects_fast_mode_beta_header`, `beta_header_includes_both_cache_and_fast_mode`
+- `cost.rs`: `compute_stage_cost_fast_mode_6x_multiplier`
+- `stylesheet.rs`: `apply_speed_property`
+- `session.rs`: `set_speed_mid_session`
+- Update all existing struct literals (`Request`, `Usage`, `SessionConfig`, `StageUsage`, `ApiRequest`, `ApiUsage`) in tests to include `speed: None`
+
+## Implementation order
+
+1. `types.rs` (Request + Usage) — everything depends on this
+2. `graph/types.rs` + `stylesheet.rs` — graph layer
+3. `config.rs` + `session.rs` — agent layer
+4. `anthropic.rs` — provider (ApiRequest, beta header, response parsing)
+5. `outcome.rs` + `cost.rs` — usage tracking
+6. `backend/api.rs` — final wiring
+7. Tests throughout
+
+## Verification
+
+```
+cargo build --workspace
+cargo test --workspace
+cargo fmt --check --all
+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.

nodes/implement/provider_used.json

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+{
+  "mode": "agent",
+  "provider": "anthropic",
+  "model": "claude-opus-4-6"
+}

nodes/implement/response.md

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+All verification passes. Let me summarize all the changes made:
+
+## Summary of Changes
+
+### 1. Foundation: `lib/crates/fabro-llm/src/types.rs`
+- Added `speed: Option<String>` to `Request` struct (after `reasoning_effort`)
+- Added `speed: Option<String>` to `Usage` struct (with `serde(default, skip_serializing_if)`, before `raw`)
+- Added `speed: self.speed` to `Usage::Add` impl (left-hand side wins)
+- Updated all test struct literals to include `speed: None`
+
+### 2. Graph layer: `lib/crates/fabro-graphviz/src/graph/types.rs`
+- Added `speed()` method to `Node` returning `Option<&str>` (no default, unlike `reasoning_effort` which defaults to "high")
+- Added `assert_eq!(node.speed(), None)` to `node_defaults` test
+
+### 3. Stylesheet: `lib/crates/fabro-workflows/src/stylesheet.rs`
+- Added `"speed"` to `STYLESHEET_PROPERTIES` array
+- Added `apply_speed_property` test
+
+### 4. Agent config: `lib/crates/fabro-agent/src/config.rs`
+- Added `pub speed: Option<String>` to `SessionConfig`
+- Added `speed: None` to `Default` impl
+
+### 5. Session wiring: `lib/crates/fabro-agent/src/session.rs`
+- Added `speed: self.config.speed.clone()` to Request construction
+- Added `set_speed()` method
+
+### 6. Anthropic provider: `lib/crates/fabro-llm/src/providers/anthropic.rs`
+- **6a.** Added `speed: Option<String>` to `ApiRequest` struct
+- **6b.** Added `FAST_MODE_BETA_HEADER` constant (`"fast-mode-2026-02-01"`)
+- **6c.** Extended `build_beta_header()` with `include_fast_mode_header: bool` parameter
+- **6d.** In `build_api_request()`: set `speed` on ApiRequest, compute `is_fast`, pass to `build_beta_header()`
+- **6e.** Added `speed: Option<String>` to `ApiUsage` struct
+- **6f.** Map `api_resp.usage.speed` → `Usage.speed` in both non-streaming and streaming paths
+- Added 3 new tests: `build_api_request_sets_speed`, `build_api_request_injects_fast_mode_beta_header`, `beta_header_includes_both_cache_and_fast_mode`
+
+### 7. Usage tracking: `lib/crates/fabro-workflows/src/outcome.rs`
+- Added `speed: Option<String>` to `StageUsage` (with `serde(default, skip_serializing_if)`)
+- Updated `From<&StageUsage> for Usage` to include `speed`
+
+### 8. Cost multiplier: `lib/crates/fabro-workflows/src/cost.rs`
+- Applied 6x multiplier when `speed == "fast"`
+- Added `compute_stage_cost_fast_mode_6x_multiplier` test
+
+### 9. Backend wiring: `lib/crates/fabro-workflows/src/backend/api.rs`
+- SessionConfig construction: added `speed: node.speed().map(String::from)`
+- Prompt-mode Request construction: added `speed: node.speed().map(String::from)`
+- Both StageUsage constructions: added `speed: response.usage.speed.clone()` / `total_usage.speed.clone()`
+
+### 10. Other files updated with `speed: None` in struct literals:
+- `fabro-agent/src/compaction.rs`, `fabro-agent/src/tools.rs`, `fabro-agent/src/types.rs`
+- `fabro-hooks/src/executor.rs`
+- `fabro-api/src/server.rs`
+- `fabro-cli/src/doctor.rs`
+- `fabro-llm/src/generate.rs` (also added `speed` to `GenerateParams`)
+- `fabro-llm/src/client.rs`, `fabro-llm/src/providers/fabro_server.rs`, `fabro-llm/src/providers/gemini.rs`, `fabro-llm/src/providers/openai.rs`, `fabro-llm/src/providers/openai_compatible.rs`
+- `fabro-workflows/src/backend/cli.rs`, `fabro-workflows/src/event.rs`, `fabro-workflows/src/preamble.rs`
+- `fabro-llm/tests/integration.rs`, `fabro-workflows/tests/integration.rs`

nodes/implement/status.json

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+{
+  "status": "success",
+  "notes": "Stage completed: implement",
+  "failure_reason": null,
+  "timestamp": "2026-03-20T22:20:17.081529+00:00"
+}