fix(review): plan dedup keeps a lowered_from that is not a severity, so rule B counts it as blocker

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/validators/plan-gate-diff-mode.test.mjs

@@ -1077,3 +1077,36 @@ test('28: the clauses with short texts (fewer than 6 content words): at its plac
     assert.equal(hit[0].severity, 'major');
   }
 });
+
+// ---- 29 ------------------------------------------------------------------------
+
+test('29: a lowered_from that is not a severity reaches the gate and counts as blocker; a blank one is no lowering', () => {
+  const p0 = buildPlan();
+  const TEXT = 'Run one never states what it prints when the input file is missing';
+  const one = extra => [f('minor', at(p0, S1_CHANGES), TEXT, { caught_by: 'tests/mod1.test.mjs', ...extra })];
+
+  for (const bad of ['high', 'critical', 3, true]) {
+    const d = dd({ pc: one({ lowered_from: bad }) });
+    assert.equal(d.findings.length, 1);
+    assert.equal(d.findings[0].lowered_from, bad, `dedup keeps lowered_from ${JSON.stringify(bad)} as given`);
+    const r1 = rec(p0, d);
+    const v = r1.verdict;
+    const g0 = byText(v, TEXT);
+    assert.equal(g0.severity, 'blocker', `lowered_from ${JSON.stringify(bad)} counts as blocker`);
+    assert.equal(g0.lowering_refused, 'rule B: lowered_from is not a severity; counted as blocker');
+    assert.equal(v.verdict, 'BLOCK');
+    const g = gatePlan(r1.text);
+    assert.equal(g.code, 1);
+    assert.ok(g.reasons.some(x => x.code === 'PLAN_GATE_OPEN_BLOCKER'), JSON.stringify(g.reasons));
+  }
+
+  for (const blank of ['', '  ']) {
+    const d = dd({ pc: one({ lowered_from: blank }) });
+    assert.equal(d.findings.length, 1);
+    assert.equal('lowered_from' in d.findings[0], false, `a blank lowered_from ${JSON.stringify(blank)} leaves no key`);
+    const v = rec(p0, d).verdict;
+    const g0 = byText(v, TEXT);
+    assert.equal(g0.severity, 'minor');
+    assert.equal(g0.lowering_refused, undefined);
+  }
+});