feat: add interactive Fee Reality widget (#136)

package.json

@@ -5,7 +5,7 @@
   "version": "0.1.0",
   "private": true,
   "scripts": {
-    "fetch": "node scripts/fetch-release.mjs && node scripts/fetch-engine-docs.mjs && node scripts/fetch-discussions.mjs && node scripts/fetch-milestones.mjs",
+    "fetch": "node scripts/fetch-release.mjs && node scripts/fetch-engine-docs.mjs && node scripts/fetch-discussions.mjs && node scripts/fetch-milestones.mjs && node scripts/build-fee-data.mjs",
     "dev": "npm run fetch && astro dev",
     "build": "npm run fetch && astro build",
     "preview": "astro preview",

scripts/build-fee-data.mjs

@@ -0,0 +1,78 @@
+#!/usr/bin/env node
+/**
+ * #136 — Fee Reality experiment data builder.
+ *
+ * Parses recorded experiment numbers from src/content/engine-docs/
+ * (specifically experiment-rule-family-significance.md) and updates
+ * data/fee-reality-experiments.json at build time.
+ *
+ * Every number in the Fee Reality widget is traceable directly to
+ * keel's recorded experiment docs.
+ */
+import { readFileSync, writeFileSync, existsSync } from "node:fs";
+import { join, dirname } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const root = dirname(dirname(fileURLToPath(import.meta.url)));
+const docFile = join(root, "src/content/engine-docs/experiment-rule-family-significance.md");
+const outFile = join(root, "data/fee-reality-experiments.json");
+
+let currentData = null;
+if (existsSync(outFile)) {
+  try {
+    currentData = JSON.parse(readFileSync(outFile, "utf8"));
+  } catch (err) {
+    // fallback
+  }
+}
+
+if (!existsSync(docFile)) {
+  console.log("  fee-data: experiment doc absent, using existing fallback data");
+  process.exit(0);
+}
+
+try {
+  const content = readFileSync(docFile, "utf8");
+  const lines = content.split("\n");
+  const families = currentData?.families || {};
+
+  for (const line of lines) {
+    if (!line.startsWith("|")) continue;
+    const parts = line.split("|").map((p) => p.trim());
+    if (parts.length < 12) continue;
+
+    const familyKey = parts[1];
+    const regime = parts[2];
+    const n = parseInt(parts[3].replace(/,/g, ""), 10);
+    const nEff = parseFloat(parts[4].replace(/,/g, ""));
+    const payoff = parseFloat(parts[5]);
+    const breakEven = parseFloat(parts[6]);
+    const winRate = parseFloat(parts[7]);
+    const edge = parseFloat(parts[8].replace(/\*\*/g, "").replace(/−/g, "-"));
+
+    if (!families[familyKey]) continue;
+
+    const targetKey = regime.includes("outside") ? "outside_allowance_120bp" : "inside_allowance_0bp";
+    families[familyKey][targetKey] = {
+      ...families[familyKey][targetKey],
+      payoff_b: payoff,
+      break_even_win_rate: breakEven,
+      observed_win_rate: winRate,
+      edge: edge,
+    };
+    if (!isNaN(n)) families[familyKey].n_pooled = n;
+    if (!isNaN(nEff)) families[familyKey].n_eff = nEff;
+  }
+
+  const output = {
+    updatedAt: new Date().toISOString(),
+    sourceDoc: "docs/experiments/2026-08-21-rule-family-significance.md",
+    sourceUrl: "https://github.com/CodeGateSoftware/keel/blob/main/docs/experiments/2026-08-21-rule-family-significance.md",
+    families,
+  };
+
+  writeFileSync(outFile, JSON.stringify(output, null, 2) + "\n");
+  console.log("  wrote data/fee-reality-experiments.json (synced from experiment docs)");
+} catch (err) {
+  console.warn("  fee-data warning:", err.message, "— retaining fallback data");
+}