diff --git a/assets/__samples__/refused/.gitkeep b/assets/__samples__/refused/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/assets/__samples__/refused/no-provenance.png b/assets/__samples__/refused/no-provenance.png
new file mode 100644
index 0000000..cee3880
Binary files /dev/null and b/assets/__samples__/refused/no-provenance.png differ
diff --git a/scripts/validate-assets.mjs b/scripts/validate-assets.mjs
new file mode 100644
index 0000000..03314c8
--- /dev/null
+++ b/scripts/validate-assets.mjs
@@ -0,0 +1,84 @@
+#!/usr/bin/env node
+// scripts/validate-assets.mjs — Phase 1 asset provenance gate (PIPE-03, AEST-08, AEST-09)
+//
+// Walks /assets/ (or process.env.ASSETS_DIR for tests), requires every non-sidecar
+// non-.gitkeep file to have a sibling <filename>.provenance.json validating against
+// ProvenanceSchema. Excludes /assets/__samples__/refused/ (which intentionally lacks
+// sidecars to prove the gate).
+//
+// Per CONTEXT D-03: minimum-viable. No curator workflow, no two-stage promotion,
+// no pre-commit hook. Sidecar + this script + CI is the entire pipeline.
+//
+// Per CONTEXT D-01: 6 required fields per CLAUDE.md provenance metadata.
+// Per RESEARCH Open Question #2: optional provenance_schema_version for Phase 5 fwd-compat.
+
+import { readdir, readFile } from 'node:fs/promises';
+import { join, basename } from 'node:path';
+import { z } from 'zod';
+
+const ProvenanceSchema = z.object({
+  model_id: z.string().min(1),
+  checkpoint_hash: z.string().min(1),
+  prompt: z.string().min(1),
+  seed: z.union([z.string(), z.number()]),
+  sampler: z.string().min(1),
+  params: z.record(z.string(), z.unknown()),
+  provenance_schema_version: z.number().int().positive().optional(),
+});
+
+const ASSETS_DIR = process.env.ASSETS_DIR ?? 'assets';
+// Refused-sample exclusion is relative to the *real* assets tree; tests pointing
+// ASSETS_DIR at a tmpdir won't have these paths so the exclusion is harmless.
+const REFUSED_PREFIXES = ['assets/__samples__/refused', 'assets/__test_fixtures__/refused'];
+
+async function* walk(dir) {
+  let entries;
+  try {
+    entries = await readdir(dir, { withFileTypes: true });
+  } catch (e) {
+    if (e.code === 'ENOENT') return;
+    throw e;
+  }
+  for (const entry of entries) {
+    const path = join(dir, entry.name);
+    if (entry.isDirectory()) {
+      yield* walk(path);
+    } else {
+      yield path;
+    }
+  }
+}
+
+function normalizePath(p) {
+  return p.replaceAll('\\', '/');
+}
+
+const errors = [];
+let assetCount = 0;
+
+for await (const path of walk(ASSETS_DIR)) {
+  const norm = normalizePath(path);
+  if (REFUSED_PREFIXES.some((r) => norm.startsWith(r))) continue;
+  if (norm.endsWith('.provenance.json')) continue;
+  if (basename(norm) === '.gitkeep') continue;
+  if (basename(norm) === 'README.md') continue;
+
+  assetCount++;
+  const sidecar = path + '.provenance.json';
+  try {
+    const raw = await readFile(sidecar, 'utf8');
+    const parsed = ProvenanceSchema.safeParse(JSON.parse(raw));
+    if (!parsed.success) {
+      errors.push(`${path}: provenance schema validation failed — ${parsed.error.message}`);
+    }
+  } catch (e) {
+    errors.push(`${path}: missing or unreadable provenance sidecar (${sidecar}): ${e.code ?? e.message}`);
+  }
+}
+
+if (errors.length) {
+  console.error('[provenance] validation failed:');
+  for (const err of errors) console.error('  ' + err);
+  process.exit(1);
+}
+console.log(`[provenance] all ${assetCount} assets carry valid provenance.`);
diff --git a/scripts/validate-assets.test.ts b/scripts/validate-assets.test.ts
new file mode 100644
index 0000000..5902f5e
--- /dev/null
+++ b/scripts/validate-assets.test.ts
@@ -0,0 +1,57 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { execFile } from 'node:child_process';
+import { promisify } from 'node:util';
+import { mkdtemp, rm, writeFile } from 'node:fs/promises';
+import { join } from 'node:path';
+import os from 'node:os';
+
+const exec = promisify(execFile);
+const SCRIPT = 'scripts/validate-assets.mjs';
+
+describe('PIPE-03 / AEST-09: asset provenance gate', () => {
+  it('exits 0 against the real /assets/ tree (refused sample excluded)', async () => {
+    const result = await exec('node', [SCRIPT]);
+    expect(result.stdout).toMatch(/all \d+ assets carry valid provenance/);
+  });
+
+  describe('with an isolated tmpdir fixture missing provenance', () => {
+    let tmpDir: string;
+    let fixtureFile: string;
+
+    beforeAll(async () => {
+      // Per-test-run unique tmpdir under os.tmpdir() — isolated from /assets/,
+      // no risk of polluting the real tree even if the runner is killed mid-test.
+      tmpDir = await mkdtemp(join(os.tmpdir(), 'tlg-provenance-test-'));
+      fixtureFile = join(tmpDir, 'orphan.png');
+      // Tiny 1x1 PNG with no sidecar
+      const png = Buffer.from(
+        '89504e470d0a1a0a0000000d49484452000000010000000108060000001f15c4890000000d49444154789c63600100000005000146cd9c5d0000000049454e44ae426082',
+        'hex',
+      );
+      await writeFile(fixtureFile, png);
+    });
+
+    afterAll(async () => {
+      await rm(tmpDir, { recursive: true, force: true });
+    });
+
+    it('exits non-zero with a clear error message when ASSETS_DIR points at the fixture', async () => {
+      // Run the validator against the isolated tmpdir; the script reads ASSETS_DIR
+      // from process.env, so the orphan.png is the only file under inspection.
+      let exitCode = 0;
+      let combinedOutput = '';
+      try {
+        await exec('node', [SCRIPT], { env: { ...process.env, ASSETS_DIR: tmpDir } });
+      } catch (err: any) {
+        exitCode = err.code ?? -1;
+        combinedOutput = (err.stdout ?? '') + (err.stderr ?? '');
+      }
+      expect(exitCode).toBe(1);
+      expect(combinedOutput).toMatch(/validation failed/);
+      expect(combinedOutput).toMatch(/orphan\.png/);
+      expect(combinedOutput).toMatch(/missing.*provenance sidecar/i);
+      // Sanity check: silence the unused-var lint by referencing fixtureFile.
+      expect(fixtureFile).toContain('orphan.png');
+    });
+  });
+});
diff --git a/vitest.config.ts b/vitest.config.ts
index d0bff50..22b35af 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -11,7 +11,7 @@ import { defineConfig } from 'vitest/config';
 export default defineConfig({
   test: {
     environment: 'happy-dom',
-    include: ['src/**/*.test.ts', 'src/**/*.test.tsx', 'scripts/**/*.test.mjs'],
+    include: ['src/**/*.test.ts', 'src/**/*.test.tsx', 'scripts/**/*.test.mjs', 'scripts/**/*.test.ts'],
     passWithNoTests: false,
     globals: false,
   },