diff --git a/test/gstack-upgrade-migration-v1_78_0_0.test.ts b/test/gstack-upgrade-migration-v1_78_0_0.test.ts
new file mode 100644
index 000000000..d7bcb4904
--- /dev/null
+++ b/test/gstack-upgrade-migration-v1_78_0_0.test.ts
@@ -0,0 +1,117 @@
+/**
+ * v1.78.0.0 migration — carry feature-discovery acknowledgement markers
+ * (.feature-prompted-continuous-checkpoint, .feature-prompted-model-overlay)
+ * from the gstack install dir to GSTACK_HOME (#2728 absorption).
+ *
+ * Exercises the script in hermetic mkdtemp roots via GSTACK_INSTALL_DIR /
+ * GSTACK_HOME overrides. Covers: copy-when-absent, destination-wins,
+ * clean no-op, and idempotent re-run.
+ */
+
+import { describe, test, expect, beforeEach, afterAll } from 'bun:test';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import { spawnSync } from 'child_process';
+
+const ROOT = path.resolve(import.meta.dir, '..');
+const MIGRATION = path.join(ROOT, 'gstack-upgrade', 'migrations', 'v1.78.0.0.sh');
+
+const MARKERS = [
+  '.feature-prompted-continuous-checkpoint',
+  '.feature-prompted-model-overlay',
+] as const;
+
+const tmpRoots: string[] = [];
+let tmpHome: string;
+let installDir: string;
+let gstackHome: string;
+
+beforeEach(() => {
+  tmpHome = fs.mkdtempSync(path.join(os.tmpdir(), 'mig-v1.78-'));
+  tmpRoots.push(tmpHome);
+  installDir = path.join(tmpHome, 'install');
+  gstackHome = path.join(tmpHome, '.gstack');
+  fs.mkdirSync(installDir, { recursive: true });
+  // gstackHome deliberately NOT pre-created: the script's own `mkdir -p` is
+  // part of the contract (fresh installs have no ~/.gstack yet).
+});
+
+afterAll(() => {
+  for (const dir of tmpRoots) fs.rmSync(dir, { recursive: true, force: true });
+});
+
+function run(): { code: number; stdout: string; stderr: string } {
+  const r = spawnSync('bash', [MIGRATION], {
+    env: {
+      PATH: '/usr/bin:/bin',
+      HOME: tmpHome,
+      GSTACK_INSTALL_DIR: installDir,
+      GSTACK_HOME: gstackHome,
+    },
+    encoding: 'utf-8',
+    cwd: tmpHome,
+    timeout: 30_000,
+  });
+  return { code: r.status ?? -1, stdout: r.stdout || '', stderr: r.stderr || '' };
+}
+
+describe('v1.78.0.0 migration — feature markers → GSTACK_HOME', () => {
+  test('markers in INSTALL_DIR, absent in GSTACK_HOME → created in GSTACK_HOME, source untouched', () => {
+    for (const m of MARKERS) fs.writeFileSync(path.join(installDir, m), 'source-content\n');
+
+    const r = run();
+    expect(r.code).toBe(0);
+    for (const m of MARKERS) {
+      expect(fs.existsSync(path.join(gstackHome, m))).toBe(true);
+      expect(r.stdout).toContain(`migrated: ${m}`);
+      // Copy, not move: the install-dir marker stays, content intact.
+      expect(fs.readFileSync(path.join(installDir, m), 'utf-8')).toBe('source-content\n');
+    }
+  });
+
+  test('marker already in GSTACK_HOME → NOT overwritten (destination wins); missing sibling still migrates', () => {
+    fs.mkdirSync(gstackHome, { recursive: true });
+    const [checkpoint, overlay] = MARKERS;
+    fs.writeFileSync(path.join(installDir, checkpoint), 'install-side\n');
+    fs.writeFileSync(path.join(gstackHome, checkpoint), 'dest-side\n');
+    fs.writeFileSync(path.join(installDir, overlay), '');
+
+    const r = run();
+    expect(r.code).toBe(0);
+    expect(fs.readFileSync(path.join(gstackHome, checkpoint), 'utf-8')).toBe('dest-side\n');
+    expect(r.stdout).not.toContain(`migrated: ${checkpoint}`);
+    expect(fs.existsSync(path.join(gstackHome, overlay))).toBe(true);
+    expect(r.stdout).toContain(`migrated: ${overlay}`);
+  });
+
+  test('no markers anywhere → clean no-op, exit 0, nothing created', () => {
+    const r = run();
+    expect(r.code).toBe(0);
+    expect(r.stdout).toBe('');
+    expect(r.stderr).toBe('');
+    for (const m of MARKERS) {
+      expect(fs.existsSync(path.join(gstackHome, m))).toBe(false);
+    }
+  });
+
+  test('idempotent: second run exits 0, migrates nothing new, end state unchanged', () => {
+    for (const m of MARKERS) fs.writeFileSync(path.join(installDir, m), '');
+
+    const r1 = run();
+    expect(r1.code).toBe(0);
+    const stateAfterFirst = MARKERS.map((m) => [
+      fs.existsSync(path.join(gstackHome, m)),
+      fs.readFileSync(path.join(gstackHome, m), 'utf-8'),
+    ]);
+
+    const r2 = run();
+    expect(r2.code).toBe(0);
+    expect(r2.stdout).toBe(''); // destinations exist now — no "migrated:" lines
+    const stateAfterSecond = MARKERS.map((m) => [
+      fs.existsSync(path.join(gstackHome, m)),
+      fs.readFileSync(path.join(gstackHome, m), 'utf-8'),
+    ]);
+    expect(stateAfterSecond).toEqual(stateAfterFirst);
+  });
+});