diff --git a/browse/test/bun-polyfill.test.ts b/browse/test/bun-polyfill.test.ts
new file mode 100644
index 00000000..7ca25dfa
--- /dev/null
+++ b/browse/test/bun-polyfill.test.ts
@@ -0,0 +1,72 @@
+import { describe, test, expect, afterAll } from 'bun:test';
+import * as path from 'path';
+
+// Load the polyfill into a fresh object (don't clobber globalThis.Bun)
+const polyfillPath = path.resolve(import.meta.dir, '../src/bun-polyfill.cjs');
+
+describe('bun-polyfill', () => {
+  // We test the polyfill by requiring it in a subprocess under Node.js
+  // since it's designed for Node, not Bun.
+
+  test('Bun.sleep resolves after delay', async () => {
+    const result = Bun.spawnSync(['node', '-e', `
+      require('${polyfillPath}');
+      (async () => {
+        const start = Date.now();
+        await Bun.sleep(50);
+        const elapsed = Date.now() - start;
+        console.log(elapsed >= 40 ? 'OK' : 'TOO_FAST');
+      })();
+    `], { stdout: 'pipe', stderr: 'pipe' });
+    expect(result.stdout.toString().trim()).toBe('OK');
+    expect(result.exitCode).toBe(0);
+  });
+
+  test('Bun.spawnSync runs a command and returns stdout', () => {
+    const result = Bun.spawnSync(['node', '-e', `
+      require('${polyfillPath}');
+      const r = Bun.spawnSync(['echo', 'hello'], { stdout: 'pipe' });
+      console.log(r.stdout.toString().trim());
+      console.log('exit:' + r.exitCode);
+    `], { stdout: 'pipe', stderr: 'pipe' });
+    const lines = result.stdout.toString().trim().split('\n');
+    expect(lines[0]).toBe('hello');
+    expect(lines[1]).toBe('exit:0');
+  });
+
+  test('Bun.spawn launches a process with pid', async () => {
+    const result = Bun.spawnSync(['node', '-e', `
+      require('${polyfillPath}');
+      const p = Bun.spawn(['echo', 'test'], { stdio: ['pipe', 'pipe', 'pipe'] });
+      console.log(typeof p.pid === 'number' ? 'HAS_PID' : 'NO_PID');
+      console.log(typeof p.kill === 'function' ? 'HAS_KILL' : 'NO_KILL');
+      console.log(typeof p.unref === 'function' ? 'HAS_UNREF' : 'NO_UNREF');
+    `], { stdout: 'pipe', stderr: 'pipe' });
+    const lines = result.stdout.toString().trim().split('\n');
+    expect(lines[0]).toBe('HAS_PID');
+    expect(lines[1]).toBe('HAS_KILL');
+    expect(lines[2]).toBe('HAS_UNREF');
+  });
+
+  test('Bun.serve creates an HTTP server that responds', async () => {
+    const result = Bun.spawnSync(['node', '-e', `
+      require('${polyfillPath}');
+      const server = Bun.serve({
+        port: 0,  // Note: polyfill uses port directly, so we pick one
+        hostname: '127.0.0.1',
+        fetch(req) {
+          return new Response(JSON.stringify({ ok: true }), {
+            headers: { 'Content-Type': 'application/json' },
+          });
+        },
+      });
+      // The polyfill doesn't support port 0, so we test the object shape
+      console.log(typeof server.stop === 'function' ? 'HAS_STOP' : 'NO_STOP');
+      console.log(typeof server.port === 'number' ? 'HAS_PORT' : 'NO_PORT');
+      server.stop();
+    `], { stdout: 'pipe', stderr: 'pipe' });
+    const lines = result.stdout.toString().trim().split('\n');
+    expect(lines[0]).toBe('HAS_STOP');
+    expect(lines[1]).toBe('HAS_PORT');
+  });
+});
diff --git a/browse/test/config.test.ts b/browse/test/config.test.ts
index 12892ce4..0cbe47fa 100644
--- a/browse/test/config.test.ts
+++ b/browse/test/config.test.ts
@@ -197,6 +197,36 @@ describe('resolveServerScript', () => {
   });
 });
 
+describe('resolveNodeServerScript', () => {
+  const { resolveNodeServerScript } = require('../src/cli');
+
+  test('finds server-node.mjs in dist from dev mode', () => {
+    const srcDir = path.resolve(__dirname, '../src');
+    const distFile = path.resolve(srcDir, '..', 'dist', 'server-node.mjs');
+    const fs = require('fs');
+    // Only test if the file exists (it may not be built yet)
+    if (fs.existsSync(distFile)) {
+      const result = resolveNodeServerScript(srcDir, '');
+      expect(result).toBe(distFile);
+    }
+  });
+
+  test('returns null when server-node.mjs does not exist', () => {
+    const result = resolveNodeServerScript('/nonexistent/$bunfs', '/nonexistent/browse');
+    expect(result).toBeNull();
+  });
+
+  test('finds server-node.mjs adjacent to compiled binary', () => {
+    const distDir = path.resolve(__dirname, '../dist');
+    const distFile = path.join(distDir, 'server-node.mjs');
+    const fs = require('fs');
+    if (fs.existsSync(distFile)) {
+      const result = resolveNodeServerScript('/$bunfs/something', path.join(distDir, 'browse'));
+      expect(result).toBe(distFile);
+    }
+  });
+});
+
 describe('version mismatch detection', () => {
   test('detects when versions differ', () => {
     const stateVersion = 'abc123';
diff --git a/browse/test/platform.test.ts b/browse/test/platform.test.ts
new file mode 100644
index 00000000..fb6c64b9
--- /dev/null
+++ b/browse/test/platform.test.ts
@@ -0,0 +1,37 @@
+import { describe, test, expect } from 'bun:test';
+import { TEMP_DIR, isPathWithin, IS_WINDOWS } from '../src/platform';
+
+describe('platform constants', () => {
+  test('TEMP_DIR is /tmp on non-Windows', () => {
+    if (!IS_WINDOWS) {
+      expect(TEMP_DIR).toBe('/tmp');
+    }
+  });
+
+  test('IS_WINDOWS reflects process.platform', () => {
+    expect(IS_WINDOWS).toBe(process.platform === 'win32');
+  });
+});
+
+describe('isPathWithin', () => {
+  test('path inside directory returns true', () => {
+    expect(isPathWithin('/tmp/foo', '/tmp')).toBe(true);
+  });
+
+  test('path outside directory returns false', () => {
+    expect(isPathWithin('/etc/foo', '/tmp')).toBe(false);
+  });
+
+  test('exact match returns true', () => {
+    expect(isPathWithin('/tmp', '/tmp')).toBe(true);
+  });
+
+  test('partial prefix does not match (path traversal)', () => {
+    // /tmp-evil should NOT match /tmp
+    expect(isPathWithin('/tmp-evil/foo', '/tmp')).toBe(false);
+  });
+
+  test('nested path returns true', () => {
+    expect(isPathWithin('/tmp/a/b/c', '/tmp')).toBe(true);
+  });
+});