diff --git a/frontend/user/modules/opportunity-board.js b/frontend/user/modules/opportunity-board.js
index 85cc9bd..50d1131 100644
--- a/frontend/user/modules/opportunity-board.js
+++ b/frontend/user/modules/opportunity-board.js
@@ -168,22 +168,25 @@ function renderDecisionBadge(brief) {
   return `<span class="atlas-decision-mini" data-decision-stance="${escapeAttr(stance)}" title="${escapeAttr(title)}">${escapeText(label)}</span>`;
 }
 
-function formatValue(value, format, item = {}) {
-  if (value === null || value === undefined || Number.isNaN(value)) return "—";
-  if (format === "pct") return `${Number(value).toFixed(2)}%`;
-  if (format === "years") {
-    const n = Number(value);
-    return n > 0 ? `${n.toFixed(1)} 年` : "—";
-  }
-  if (format === "wan") return Number(value).toLocaleString("en-US");
-  if (format === "int") return String(Math.round(Number(value)));
+export function formatValue(value, format, item = {}) {
   if (format === "sample") {
     const label = item.quality?.label || item.sampleLabel || null;
-    const numeric = Number(value);
+    const missing = value === null || value === undefined || value === "" || Number.isNaN(value);
+    const numeric = missing ? Number.NaN : Number(value);
     if (label && Number.isFinite(numeric)) return `${label} · ${Math.round(numeric)}`;
     if (label) return label;
     return Number.isFinite(numeric) ? `${Math.round(numeric)} 套` : "—";
   }
+
+  if (value === null || value === undefined || value === "" || Number.isNaN(value)) return "—";
+  const numeric = Number(value);
+  if (["pct", "years", "wan", "int"].includes(format) && !Number.isFinite(numeric)) return "—";
+  if (format === "pct") return `${numeric.toFixed(2)}%`;
+  if (format === "years") {
+    return numeric > 0 ? `${numeric.toFixed(1)} 年` : "—";
+  }
+  if (format === "wan") return numeric.toLocaleString("en-US");
+  if (format === "int") return String(Math.round(numeric));
   return String(value);
 }
 
diff --git a/tests/frontend/test_opportunity_board_format.mjs b/tests/frontend/test_opportunity_board_format.mjs
new file mode 100644
index 0000000..0aa7d6a
--- /dev/null
+++ b/tests/frontend/test_opportunity_board_format.mjs
@@ -0,0 +1,92 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { formatValue } from "../../frontend/user/modules/opportunity-board.js";
+
+// Baseline: explicit-zero is a real value, mirroring sortItems' policy.
+test("formatValue pct: explicit 0 renders as 0.00% (not missing)", () => {
+  assert.equal(formatValue(0, "pct"), "0.00%");
+});
+
+test("formatValue pct/wan/int: null and undefined render as —", () => {
+  assert.equal(formatValue(null, "pct"), "—");
+  assert.equal(formatValue(undefined, "pct"), "—");
+  assert.equal(formatValue(null, "wan"), "—");
+  assert.equal(formatValue(undefined, "wan"), "—");
+  assert.equal(formatValue(null, "int"), "—");
+  assert.equal(formatValue(undefined, "int"), "—");
+});
+
+test("formatValue pct/wan/int: literal NaN renders as —", () => {
+  assert.equal(formatValue(Number.NaN, "pct"), "—");
+  assert.equal(formatValue(Number.NaN, "wan"), "—");
+  assert.equal(formatValue(Number.NaN, "int"), "—");
+});
+
+// The bug: Number.isNaN("abc") is false, so non-numeric strings slip past the
+// guard and Number(value) coerces them to NaN, which then renders to the UI as
+// the literal string "NaN%" / "NaN". The renderer must never leak "NaN" into
+// the DOM — fall back to the missing marker like the `sample` branch already
+// does via Number.isFinite.
+test("formatValue pct: non-numeric strings render as — (no leaked 'NaN%')", () => {
+  assert.equal(formatValue("abc", "pct"), "—");
+  assert.equal(formatValue("--", "pct"), "—");
+});
+
+test("formatValue wan: non-numeric strings render as — (no leaked 'NaN')", () => {
+  assert.equal(formatValue("abc", "wan"), "—");
+});
+
+test("formatValue int: non-numeric strings render as — (no leaked 'NaN')", () => {
+  assert.equal(formatValue("abc", "int"), "—");
+});
+
+// Empty string is the upstream "no value" marker (see coerceNumber in
+// comparison-helpers.js). Number("") coerces to 0, so without an early
+// guard pct/wan/int would render "0.00%" / "0" — silently inventing data.
+test("formatValue pct/wan/int: empty string renders as — (not silently 0)", () => {
+  assert.equal(formatValue("", "pct"), "—");
+  assert.equal(formatValue("", "wan"), "—");
+  assert.equal(formatValue("", "int"), "—");
+});
+
+// Infinity slips through Number.isNaN too. Defensive against bad upstream
+// math (e.g. divide-by-zero in a derived metric) — should not render as
+// "Infinity%" or "Infinity".
+test("formatValue pct/wan/int: Infinity renders as —", () => {
+  assert.equal(formatValue(Infinity, "pct"), "—");
+  assert.equal(formatValue(-Infinity, "wan"), "—");
+  assert.equal(formatValue(Infinity, "int"), "—");
+});
+
+// Regression guard for the happy path so the new strictness doesn't break
+// numeric strings that the API legitimately serializes (some endpoints send
+// numeric IDs/values as strings).
+test("formatValue pct/wan/int: numeric strings still format correctly", () => {
+  assert.equal(formatValue("4.25", "pct"), "4.25%");
+  assert.equal(formatValue("1500", "wan"), "1,500");
+  assert.equal(formatValue("88.4", "int"), "88");
+});
+
+// `years` already short-circuits non-positive values to "—" by domain choice
+// (negative payback is meaningless). Lock that in so the refactor doesn't
+// accidentally widen the window.
+test("formatValue years: <= 0 stays as — (domain rule, not just a missing marker)", () => {
+  assert.equal(formatValue(0, "years"), "—");
+  assert.equal(formatValue(-1, "years"), "—");
+  assert.equal(formatValue(7.4, "years"), "7.4 年");
+});
+
+// `sample` already handles non-numeric input via Number.isFinite — pin that
+// behavior so the consolidated guard doesn't regress the label-only path.
+test("formatValue sample: label-only when numeric is missing or non-finite", () => {
+  assert.equal(
+    formatValue(null, "sample", { quality: { label: "可用" } }),
+    "可用",
+  );
+  assert.equal(
+    formatValue("abc", "sample", { quality: { label: "可用" } }),
+    "可用",
+  );
+  assert.equal(formatValue(null, "sample", {}), "—");
+});