diff --git a/gitnexus/src/core/evolver/index.ts b/gitnexus/src/core/evolver/index.ts
index 22af70b5c..7d76650f5 100644
--- a/gitnexus/src/core/evolver/index.ts
+++ b/gitnexus/src/core/evolver/index.ts
@@ -2,3 +2,4 @@ export * from './types.js';
 export * from './metric-evaluator.js';
 export * from './resource-manager.js';
 export * from './variant-generator.js';
+export * from './sandbox-runner.js';
diff --git a/gitnexus/src/core/evolver/sandbox-runner.ts b/gitnexus/src/core/evolver/sandbox-runner.ts
new file mode 100644
index 000000000..dc4e84446
--- /dev/null
+++ b/gitnexus/src/core/evolver/sandbox-runner.ts
@@ -0,0 +1,102 @@
+import type {
+  ErrorEvent,
+  MetricReading,
+  ResourceBudget,
+  ResourceUsage,
+  TrialResult,
+  VariantSpec,
+} from './types.js';
+
+export interface SandboxProtocol {
+  id: string;
+  maxDurationMs: number;
+}
+
+export interface SandboxRunnerResult {
+  metrics: MetricReading[];
+  resourceUsage: ResourceUsage;
+}
+
+export type SandboxRunner = (variant: VariantSpec, protocol: SandboxProtocol) => Promise<SandboxRunnerResult>;
+
+const completedAt = '2026-05-25T00:00:00.000Z';
+
+export async function runSandboxTrial(
+  variant: VariantSpec,
+  protocol: SandboxProtocol,
+  runner: SandboxRunner,
+  budget: ResourceBudget,
+): Promise<TrialResult> {
+  const trialId = buildTrialId(variant, protocol);
+
+  if (protocol.maxDurationMs > budget.maxDurationMs) {
+    return buildFailedTrial(
+      trialId,
+      variant,
+      protocol,
+      'resource-exhaustion',
+      'sandbox protocol duration budget exceeded',
+    );
+  }
+
+  try {
+    const result = await runner(variant, protocol);
+
+    return {
+      id: trialId,
+      variantId: variant.id,
+      protocolId: protocol.id,
+      metrics: result.metrics,
+      resourceUsage: result.resourceUsage,
+      errors: [],
+      completedAt,
+    };
+  } catch (error) {
+    return buildFailedTrial(
+      trialId,
+      variant,
+      protocol,
+      'temporary-failure',
+      error instanceof Error ? error.message : String(error),
+    );
+  }
+}
+
+function buildFailedTrial(
+  trialId: string,
+  variant: VariantSpec,
+  protocol: SandboxProtocol,
+  type: ErrorEvent['type'],
+  message: string,
+): TrialResult {
+  return {
+    id: trialId,
+    variantId: variant.id,
+    protocolId: protocol.id,
+    metrics: [],
+    resourceUsage: emptyResourceUsage(),
+    errors: [
+      {
+        id: `error-${trialId}`,
+        type,
+        message,
+        occurredAt: completedAt,
+        variantId: variant.id,
+      },
+    ],
+    completedAt,
+  };
+}
+
+function buildTrialId(variant: VariantSpec, protocol: SandboxProtocol): string {
+  return `trial-${variant.id}-${protocol.id}`;
+}
+
+function emptyResourceUsage(): ResourceUsage {
+  return {
+    durationMs: 0,
+    computeUnits: 0,
+    apiCostUsd: 0,
+    storageBytes: 0,
+  };
+}
diff --git a/gitnexus/test/unit/evolver/sandbox-runner.test.ts b/gitnexus/test/unit/evolver/sandbox-runner.test.ts
new file mode 100644
index 000000000..a3cad1e6e
--- /dev/null
+++ b/gitnexus/test/unit/evolver/sandbox-runner.test.ts
@@ -0,0 +1,159 @@
+import { describe, expect, it } from 'vitest';
+import { runSandboxTrial } from '../../../src/core/evolver/index.js';
+import type { ResourceBudget, VariantSpec } from '../../../src/core/evolver/index.js';
+
+const capturedAt = '2026-05-25T00:00:00.000Z';
+
+const budget: ResourceBudget = {
+  maxDurationMs: 1000,
+  maxComputeUnits: 10,
+  maxApiCostUsd: 1,
+  maxStorageBytes: 2048,
+  maxConcurrency: 2,
+  maxHighRiskVariants: 1,
+};
+
+const variant: VariantSpec = {
+  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,
+    },
+  ],
+};
+
+describe('runSandboxTrial', () => {
+  it('records a successful sandbox trial from an injected runner', async () => {
+    const result = await runSandboxTrial(
+      variant,
+      { id: 'protocol-1', maxDurationMs: 1000 },
+      async () => ({
+        metrics: [
+          {
+            metricId: 'task_success_rate',
+            value: 0.82,
+            capturedAt,
+          },
+        ],
+        resourceUsage: {
+          durationMs: 120,
+          computeUnits: 1,
+          apiCostUsd: 0,
+          storageBytes: 256,
+        },
+      }),
+      budget,
+    );
+
+    expect(result).toEqual({
+      id: 'trial-variant-parameter-1-protocol-1',
+      variantId: 'variant-parameter-1',
+      protocolId: 'protocol-1',
+      metrics: [
+        {
+          metricId: 'task_success_rate',
+          value: 0.82,
+          capturedAt,
+        },
+      ],
+      resourceUsage: {
+        durationMs: 120,
+        computeUnits: 1,
+        apiCostUsd: 0,
+        storageBytes: 256,
+      },
+      errors: [],
+      completedAt: capturedAt,
+    });
+  });
+
+  it('records runner failures as trial errors without throwing', async () => {
+    const result = await runSandboxTrial(
+      variant,
+      { id: 'protocol-1', maxDurationMs: 1000 },
+      async () => {
+        throw new Error('sandbox failure');
+      },
+      budget,
+    );
+
+    expect(result.variantId).toBe('variant-parameter-1');
+    expect(result.metrics).toEqual([]);
+    expect(result.errors).toEqual([
+      {
+        id: 'error-trial-variant-parameter-1-protocol-1',
+        type: 'temporary-failure',
+        message: 'sandbox failure',
+        occurredAt: capturedAt,
+        variantId: 'variant-parameter-1',
+      },
+    ]);
+  });
+
+  it('rejects a trial before running when protocol duration exceeds budget', async () => {
+    let runnerCalled = false;
+
+    const result = await runSandboxTrial(
+      variant,
+      { id: 'protocol-1', maxDurationMs: 1500 },
+      async () => {
+        runnerCalled = true;
+        return {
+          metrics: [],
+          resourceUsage: {
+            durationMs: 1,
+            computeUnits: 1,
+            apiCostUsd: 0,
+            storageBytes: 0,
+          },
+        };
+      },
+      budget,
+    );
+
+    expect(runnerCalled).toBe(false);
+    expect(result.errors).toEqual([
+      {
+        id: 'error-trial-variant-parameter-1-protocol-1',
+        type: 'resource-exhaustion',
+        message: 'sandbox protocol duration budget exceeded',
+        occurredAt: capturedAt,
+        variantId: 'variant-parameter-1',
+      },
+    ]);
+  });
+});