Add shared library for APIs/chunking

lib/scoring.js

@@ -0,0 +1,77 @@
+import { rerank } from "./voyage.js";
+import { judgeEntailment } from "./anthropic.js";
+
+// These bounds are a starting ramp for rerank-2; log raw scores and adjust.
+const RERANK_FLOOR = 0.2;
+const RERANK_CEILING = 0.8;
+const MIN_SENTENCE_LENGTH = 20;
+const MAX_SENTENCES = 12;
+const MAX_CITED_CHUNKS = 5;
+
+function splitIntoSentences(text) {
+    const cleaned = text.replace(/\[\d+\]/g, "").trim();
+    const raw = cleaned.split(/(?<=[.!?])\s+/);
+    return raw
+        .map((s) => s.trim())
+        .filter((s) => s.length >= MIN_SENTENCE_LENGTH)
+        .slice(0, MAX_SENTENCES);
+}
+
+function calibrate(rawScore) {
+    const scaled = (rawScore - RERANK_FLOOR) / (RERANK_CEILING - RERANK_FLOOR);
+    return Math.max(0, Math.min(1, scaled));
+}
+
+function groundednessMode() {
+    const mode = (process.env.GROUNDEDNESS_MODE || "rerank_nli").toLowerCase();
+    return mode === "rerank" ? "rerank" : "rerank_nli";
+}
+
+export async function computeGroundedness(answerText, citedChunkTexts) {
+    if (!citedChunkTexts || citedChunkTexts.length === 0) return 0;
+
+    const sentences = splitIntoSentences(answerText);
+    if (sentences.length === 0) return 0;
+
+    const chunks = citedChunkTexts.filter(Boolean).slice(0, MAX_CITED_CHUNKS);
+    if (chunks.length === 0) return 0;
+
+    const mode = groundednessMode();
+
+    const perSentence = await Promise.all(
+        sentences.map(async (sentence) => {
+            const ranked = await rerank(sentence, chunks);
+            const raw =
+                ranked.length === 0
+                    ? 0
+                    : Math.max(...ranked.map((r) => r.relevanceScore));
+            const calibrated = calibrate(raw);
+
+            let nli = null;
+            if (mode === "rerank_nli") {
+                nli = await judgeEntailment(sentence, chunks);
+            }
+
+            console.log(
+                JSON.stringify({
+                    event: "sentence_groundedness",
+                    sentence: sentence.slice(0, 80),
+                    rawRerank: Number(raw.toFixed(4)),
+                    calibrated: Number(calibrated.toFixed(4)),
+                    nli,
+                    mode,
+                })
+            );
+
+            return { raw, calibrated, nli };
+        })
+    );
+
+    if (perSentence.some((s) => s.nli && s.nli.label === "contradicted")) {
+        console.log(JSON.stringify({ event: "groundedness_floored", reason: "contradicted" }));
+        return 0;
+    }
+
+    const total = perSentence.reduce((sum, s) => sum + s.calibrated, 0);
+    return total / perSentence.length;
+}