From 32bbddab1d21276abd4bcc5d3e30ec6674718bee Mon Sep 17 00:00:00 2001
From: Eneko Ruiz <196690101+eneekoruiz@users.noreply.github.com>
Date: Sun, 11 Oct 2026 11:31:21 +0200
Subject: [PATCH] fix: keep unchanged skill rates stable at zero threshold

---
 scripts/lib/skill-evolution/health.js |  3 +++
 tests/lib/skill-evolution.test.js     | 30 +++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/scripts/lib/skill-evolution/health.js b/scripts/lib/skill-evolution/health.js
index c57e23354..34caaf80b 100644
--- a/scripts/lib/skill-evolution/health.js
+++ b/scripts/lib/skill-evolution/health.js
@@ -121,6 +121,9 @@ function getFailureTrend(successRate7d, successRate30d, warnThreshold) {
   }
 
   const delta = roundRate(successRate7d - successRate30d);
+  if (delta === 0) {
+    return 'stable';
+  }
   if (delta <= (-1 * warnThreshold)) {
     return 'worsening';
   }
diff --git a/tests/lib/skill-evolution.test.js b/tests/lib/skill-evolution.test.js
index f2dd4e6ec..db2452023 100644
--- a/tests/lib/skill-evolution.test.js
+++ b/tests/lib/skill-evolution.test.js
@@ -580,6 +580,36 @@ function runTests() {
       );
     })) passed++; else failed++;
 
+    if (test('zero warning threshold distinguishes unchanged rates from actual trends', () => {
+      const recent = '2026-03-14T10:00:00.000Z';
+      const older = '2026-02-24T10:00:00.000Z';
+      const records = [
+        { skill_id: 'unchanged', outcome: 'success', recorded_at: recent },
+        { skill_id: 'improving', outcome: 'failure', recorded_at: older },
+        { skill_id: 'improving', outcome: 'success', recorded_at: recent },
+        { skill_id: 'declining', outcome: 'success', recorded_at: older },
+        { skill_id: 'declining', outcome: 'failure', recorded_at: recent },
+      ];
+      const report = health.collectSkillHealth({
+        repoRoot,
+        homeDir,
+        now,
+        warnThreshold: 0,
+        stateStore: { listSkillExecutionRecords: () => records },
+      });
+
+      assert.strictEqual(report.warn_threshold, 0);
+      for (const [skillId, expectedTrend] of [
+        ['unchanged', 'stable'],
+        ['improving', 'improving'],
+        ['declining', 'worsening'],
+      ]) {
+        const skill = report.skills.find(entry => entry.skill_id === skillId);
+        assert.strictEqual(skill.failure_trend, expectedTrend);
+        assert.strictEqual(skill.declining, expectedTrend === 'worsening');
+      }
+    })) passed++; else failed++;
+
     if (test('does not report unmeasured skills as healthy (#2463)', () => {
       // A runs file that does not exist: skills are still discovered, so this
       // is exactly the "discovered but never executed" state.