feat(topology): LLM-judge scorer + async Scorer trait

Make Scorer async and add JudgeScorer (behind the `provider` feature): asks a
cm-llm model to rate a run's output 0-100 vs the task and normalizes to [0,1],
giving the comparison harness real quality numbers. Robust integer parsing
(handles "Score: 92/100", clamps >100); provider errors score 0.0.

11 tests with --features provider (judge incl. parse + scripted-provider score);
core stays 7. Clippy clean.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

crates/cm-orchestrator/src/judge.rs

@@ -0,0 +1,121 @@
+//! An LLM-judge [`Scorer`]: ask a model to rate how well a run's output
+//! accomplishes the task, on a 0–100 scale, normalized to `[0,1]`.
+//!
+//! Gives the comparison harness real quality numbers (vs the deterministic
+//! scorers used in tests). Behind the `provider` feature.
+
+use std::sync::Arc;
+
+use cm_llm::{ChatMessage, ChatRequest, ChatRole, ContentPart, LlmEvent, LlmProvider};
+use futures::StreamExt;
+
+use crate::{RunRecord, Scorer};
+
+/// Scores run quality with an LLM via any `cm-llm` provider.
+pub struct JudgeScorer {
+    provider: Arc<dyn LlmProvider>,
+    model: String,
+    max_tokens: u32,
+}
+
+impl JudgeScorer {
+    /// Build a judge over a shared provider, model id, and token budget.
+    pub fn new(provider: Arc<dyn LlmProvider>, model: impl Into<String>, max_tokens: u32) -> Self {
+        JudgeScorer {
+            provider,
+            model: model.into(),
+            max_tokens,
+        }
+    }
+}
+
+/// Extract the first integer in the text and map 0..100 → 0.0..1.0.
+/// Returns 0.0 if no integer is present.
+fn parse_score(s: &str) -> f64 {
+    let mut digits = String::new();
+    for c in s.chars() {
+        if c.is_ascii_digit() {
+            digits.push(c);
+        } else if !digits.is_empty() {
+            break;
+        }
+    }
+    digits
+        .parse::<f64>()
+        .ok()
+        .map(|n| (n / 100.0).clamp(0.0, 1.0))
+        .unwrap_or(0.0)
+}
+
+impl Scorer for JudgeScorer {
+    async fn score(&self, task: &str, record: &RunRecord) -> f64 {
+        let request = ChatRequest {
+            system: "You are a strict evaluator. Rate how well RESULT accomplishes TASK on a \
+                     scale from 0 to 100. Reply with ONLY the integer."
+                .to_string(),
+            messages: vec![ChatMessage {
+                role: ChatRole::User,
+                parts: vec![ContentPart::text(format!(
+                    "TASK:\n{task}\n\nRESULT:\n{}",
+                    record.final_output
+                ))],
+            }],
+            tools: vec![],
+            model: self.model.clone(),
+            max_tokens: self.max_tokens,
+        };
+
+        let mut stream = match self.provider.stream(request).await {
+            Ok(s) => s,
+            Err(_) => return 0.0,
+        };
+        let mut text = String::new();
+        while let Some(event) = stream.next().await {
+            if let Ok(LlmEvent::TextDelta(t)) = event {
+                text.push_str(&t);
+            }
+        }
+        parse_score(&text)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{RunMetrics, RunRecord};
+    use cm_topology::TopologyKind;
+
+    fn record(output: &str) -> RunRecord {
+        RunRecord {
+            kind: TopologyKind::Flat,
+            steps: vec![],
+            final_output: output.to_string(),
+            totals: RunMetrics::default(),
+        }
+    }
+
+    #[test]
+    fn parse_score_handles_text_and_garbage() {
+        assert!((parse_score("85") - 0.85).abs() < 1e-9);
+        assert!((parse_score("Score: 92/100") - 0.92).abs() < 1e-9);
+        assert!((parse_score("over") - 0.0).abs() < 1e-9);
+        assert!((parse_score("150") - 1.0).abs() < 1e-9); // clamped
+    }
+
+    #[tokio::test]
+    async fn judge_returns_normalized_score() {
+        // Scenario keyed on "RESULT" (always in the judge prompt) returns "85".
+        let toml = r#"
+            [[scenario]]
+            marker = "RESULT"
+            [[scenario.turns]]
+            [[scenario.turns.events]]
+            type = "text"
+            text = "85"
+        "#;
+        let provider = Arc::new(cm_llm::ScriptedProvider::from_toml(toml).unwrap());
+        let judge = JudgeScorer::new(provider, "test-model", 16);
+        let score = judge.score("write a poem", &record("a fine poem")).await;
+        assert!((score - 0.85).abs() < 1e-9, "got {score}");
+    }
+}