diff --git a/packages/loopover-engine/src/opportunity-freshness.ts b/packages/loopover-engine/src/opportunity-freshness.ts
index 0c4743f25..8816c2f36 100644
--- a/packages/loopover-engine/src/opportunity-freshness.ts
+++ b/packages/loopover-engine/src/opportunity-freshness.ts
@@ -45,15 +45,18 @@ export const opportunityFreshnessInternals = {
 /* v8 ignore stop */
 
 /**
- * Compute a [0.05, 1] freshness factor from open issue timestamps, mirroring
- * `opportunityFreshnessFactor` in `src/signals/reward-risk.ts` with an injected clock so the miner engine
- * stays pure and testable.
+ * Compute an open-issue freshness factor from issue timestamps, with an injected clock so the miner engine
+ * stays pure and testable. Returns `0` as a sentinel for "no measurable freshness signal" — either there are
+ * no open issues, or `nowMs` is non-finite — and otherwise a value in `[0.05, 1]`. `0` is meaningfully distinct
+ * from `0.05` (measured but maximally stale): in the multiplicative ranker score they differ 20x, so a caller
+ * must not treat a `0` as merely "very stale". `opportunityFreshnessFactor` in
+ * `packages/loopover-engine/src/reward-risk.ts` delegates to this function (#8011) — this module is the
+ * canonical implementation, not a mirror of it.
  */
 export function computeOpportunityFreshness(
   issues: readonly FreshnessIssue[],
   nowMs: number,
 ): number {
-  /* v8 ignore next -- Caller supplies a finite epoch; non-finite clocks degrade to zero freshness. */
   if (!Number.isFinite(nowMs)) return 0;
   const openIssues = issues.filter(isOpenIssue);
   if (openIssues.length === 0) return 0;
diff --git a/packages/loopover-engine/test/opportunity-freshness.test.ts b/packages/loopover-engine/test/opportunity-freshness.test.ts
index 6e0172391..09d78ced2 100644
--- a/packages/loopover-engine/test/opportunity-freshness.test.ts
+++ b/packages/loopover-engine/test/opportunity-freshness.test.ts
@@ -78,3 +78,19 @@ test("computeOpportunityFreshness handles large open-issue lists without spreadi
   const score = computeOpportunityFreshness(issues, nowMs);
   assert.ok(score > 0.7);
 });
+
+test("#9618: a non-finite clock returns the 0 no-signal sentinel", () => {
+  assert.equal(computeOpportunityFreshness([{ state: "open", updatedAt: "2026-07-01T00:00:00.000Z" }], Number.NaN), 0);
+  assert.equal(computeOpportunityFreshness([{ state: "open", updatedAt: "2026-07-01T00:00:00.000Z" }], Number.POSITIVE_INFINITY), 0);
+});
+
+test("#9618: no open issues returns the 0 no-signal sentinel", () => {
+  assert.equal(computeOpportunityFreshness([], 1_700_000_000_000), 0);
+  assert.equal(computeOpportunityFreshness([{ state: "closed", updatedAt: "2023-11-14T00:00:00.000Z" }], 1_700_000_000_000), 0);
+});
+
+test("#9618: the measured range floor and ceiling are exactly 0.05 and 1", () => {
+  // ~5 years old -> exp(-age/20) underflows the clamp to the 0.05 floor; same-day (age 0) -> exp(0) = 1.
+  assert.equal(computeOpportunityFreshness([{ state: "open", updatedAt: "2018-11-14T00:00:00.000Z" }], 1_700_000_000_000), 0.05);
+  assert.equal(computeOpportunityFreshness([{ state: "open", updatedAt: "2023-11-14T00:00:00.000Z" }], 1_700_000_000_000), 1);
+});