diff --git a/gitnexus/src/core/evolver/index.ts b/gitnexus/src/core/evolver/index.ts
index 7d76650f5..4343f58d7 100644
--- a/gitnexus/src/core/evolver/index.ts
+++ b/gitnexus/src/core/evolver/index.ts
@@ -3,3 +3,4 @@ export * from './metric-evaluator.js';
 export * from './resource-manager.js';
 export * from './variant-generator.js';
 export * from './sandbox-runner.js';
+export * from './safety-gate.js';
diff --git a/gitnexus/src/core/evolver/safety-gate.ts b/gitnexus/src/core/evolver/safety-gate.ts
new file mode 100644
index 000000000..76b10a4fe
--- /dev/null
+++ b/gitnexus/src/core/evolver/safety-gate.ts
@@ -0,0 +1,80 @@
+import type { EvaluationReport, GateDecision, VariantSpec } from './types.js';
+
+const decidedAt = '2026-05-25T00:00:00.000Z';
+
+export function decidePromotion(variant: VariantSpec, report: EvaluationReport): GateDecision {
+  const gateId = `gate-${variant.id}-${report.id}`;
+
+  if (report.safetyFindings.length > 0) {
+    return reject(gateId, variant, report, ['evaluation report contains safety findings']);
+  }
+
+  if (variant.provenance.length === 0) {
+    return reject(gateId, variant, report, ['variant provenance is required']);
+  }
+
+  if (variant.rollbackPlan.operations.length === 0 && variant.mutationType === 'parameter') {
+    return reject(gateId, variant, report, ['rollback operations are required for automatic promotion']);
+  }
+
+  if (report.verdict === 'reject') {
+    return reject(gateId, variant, report, ['evaluation report rejected variant']);
+  }
+
+  if (variant.mutationType === 'algorithm') {
+    return needsReview(gateId, variant, report, ['algorithm variants require review before promotion']);
+  }
+
+  if (variant.mutationType === 'structure') {
+    return needsReview(gateId, variant, report, ['structure variants require review before promotion']);
+  }
+
+  if (variant.riskLevel !== 'low') {
+    return needsReview(gateId, variant, report, ['non-low-risk variants require review before promotion']);
+  }
+
+  if (report.verdict !== 'promote') {
+    return needsReview(gateId, variant, report, ['evaluation report does not recommend promotion']);
+  }
+
+  return {
+    id: gateId,
+    variantId: variant.id,
+    reportId: report.id,
+    decision: 'allow',
+    reasons: ['parameter variant passed promotion gate'],
+    decidedAt,
+  };
+}
+
+function reject(
+  id: string,
+  variant: VariantSpec,
+  report: EvaluationReport,
+  reasons: string[],
+): GateDecision {
+  return {
+    id,
+    variantId: variant.id,
+    reportId: report.id,
+    decision: 'reject',
+    reasons,
+    decidedAt,
+  };
+}
+
+function needsReview(
+  id: string,
+  variant: VariantSpec,
+  report: EvaluationReport,
+  reasons: string[],
+): GateDecision {
+  return {
+    id,
+    variantId: variant.id,
+    reportId: report.id,
+    decision: 'needs-review',
+    reasons,
+    decidedAt,
+  };
+}
diff --git a/gitnexus/test/unit/evolver/safety-gate.test.ts b/gitnexus/test/unit/evolver/safety-gate.test.ts
new file mode 100644
index 000000000..5ab5e2756
--- /dev/null
+++ b/gitnexus/test/unit/evolver/safety-gate.test.ts
@@ -0,0 +1,201 @@
+import { describe, expect, it } from 'vitest';
+import { decidePromotion } from '../../../src/core/evolver/index.js';
+import type { EvaluationReport, VariantSpec } from '../../../src/core/evolver/index.js';
+
+const capturedAt = '2026-05-25T00:00:00.000Z';
+
+function parameterVariant(overrides: Partial<VariantSpec> = {}): VariantSpec {
+  return {
+    id: 'variant-parameter-1',
+    planId: 'plan-1',
+    mutationType: 'parameter',
+    description: 'Adjust topK',
+    patch: {
+      operations: [
+        {
+          op: 'setParameter',
+          path: 'retrieval.topK',
+          previousValue: 5,
+          nextValue: 8,
+        },
+      ],
+    },
+    expectedGain: [
+      {
+        metricId: 'task_success_rate',
+        expectedDelta: 0.05,
+        direction: 'increase',
+      },
+    ],
+    riskLevel: 'low',
+    rollbackPlan: {
+      strategy: 'restore-previous-parameters',
+      operations: [
+        {
+          op: 'setParameter',
+          path: 'retrieval.topK',
+          previousValue: 8,
+          nextValue: 5,
+        },
+      ],
+    },
+    provenance: [
+      {
+        source: 'synthetic-benchmark',
+        reference: 'run-1',
+        capturedAt,
+      },
+    ],
+    ...overrides,
+  };
+}
+
+function promoteReport(overrides: Partial<EvaluationReport> = {}): EvaluationReport {
+  return {
+    id: 'report-1',
+    variantId: 'variant-parameter-1',
+    baselineId: 'baseline-1',
+    metricDeltas: [
+      {
+        metricId: 'task_success_rate',
+        baselineValue: 0.72,
+        candidateValue: 0.81,
+        delta: 0.09,
+        direction: 'increase',
+        passed: true,
+      },
+    ],
+    regressions: [],
+    resourceCost: {
+      durationMs: 120,
+      computeUnits: 1,
+      apiCostUsd: 0,
+      storageBytes: 256,
+    },
+    safetyFindings: [],
+    verdict: 'promote',
+    ...overrides,
+  };
+}
+
+describe('decidePromotion', () => {
+  it('allows a low-risk parameter variant with valid evaluation, provenance, rollback, and safety checks', () => {
+    const decision = decidePromotion(parameterVariant(), promoteReport());
+
+    expect(decision).toEqual({
+      id: 'gate-variant-parameter-1-report-1',
+      variantId: 'variant-parameter-1',
+      reportId: 'report-1',
+      decision: 'allow',
+      reasons: ['parameter variant passed promotion gate'],
+      decidedAt: capturedAt,
+    });
+  });
+
+  it('marks an algorithm variant as needs-review', () => {
+    const variant = parameterVariant({
+      id: 'variant-algorithm-1',
+      mutationType: 'algorithm',
+      riskLevel: 'medium',
+      patch: {
+        operations: [
+          {
+            op: 'selectAlgorithm',
+            policyId: 'ranking-policy',
+            previousAlgorithm: 'baseline-ranker',
+            nextAlgorithm: 'candidate-ranker',
+          },
+        ],
+      },
+      rollbackPlan: {
+        strategy: 'disable-candidate',
+        operations: [
+          {
+            op: 'selectAlgorithm',
+            policyId: 'ranking-policy',
+            previousAlgorithm: 'candidate-ranker',
+            nextAlgorithm: 'baseline-ranker',
+          },
+        ],
+      },
+    });
+
+    const decision = decidePromotion(
+      variant,
+      promoteReport({ id: 'report-algorithm', variantId: variant.id, verdict: 'needs-review' }),
+    );
+
+    expect(decision.decision).toBe('needs-review');
+    expect(decision.reasons).toEqual(['algorithm variants require review before promotion']);
+  });
+
+  it('marks a structure variant as needs-review', () => {
+    const variant = parameterVariant({
+      id: 'variant-structure-1',
+      mutationType: 'structure',
+      riskLevel: 'high',
+      patch: {
+        operations: [
+          {
+            op: 'proposeStructureChange',
+            planPath: 'docs/aegis/plans/structure-change.md',
+            summary: 'Split evaluator into a plugin pipeline',
+          },
+        ],
+      },
+      rollbackPlan: {
+        strategy: 'manual-review-required',
+        operations: [],
+      },
+    });
+
+    const decision = decidePromotion(
+      variant,
+      promoteReport({ id: 'report-structure', variantId: variant.id, verdict: 'needs-review' }),
+    );
+
+    expect(decision.decision).toBe('needs-review');
+    expect(decision.reasons).toEqual(['structure variants require review before promotion']);
+  });
+
+  it('rejects a variant without provenance', () => {
+    const decision = decidePromotion(parameterVariant({ provenance: [] }), promoteReport());
+
+    expect(decision.decision).toBe('reject');
+    expect(decision.reasons).toEqual(['variant provenance is required']);
+  });
+
+  it('rejects a variant without rollback operations', () => {
+    const decision = decidePromotion(
+      parameterVariant({
+        rollbackPlan: {
+          strategy: 'restore-previous-parameters',
+          operations: [],
+        },
+      }),
+      promoteReport(),
+    );
+
+    expect(decision.decision).toBe('reject');
+    expect(decision.reasons).toEqual(['rollback operations are required for automatic promotion']);
+  });
+
+  it('rejects a variant when the evaluation report contains safety findings', () => {
+    const decision = decidePromotion(
+      parameterVariant(),
+      promoteReport({
+        safetyFindings: [
+          {
+            id: 'safety-1',
+            severity: 'high',
+            message: 'unsafe action attempted',
+          },
+        ],
+        verdict: 'reject',
+      }),
+    );
+
+    expect(decision.decision).toBe('reject');
+    expect(decision.reasons).toEqual(['evaluation report contains safety findings']);
+  });
+});