diff --git a/hydra/cli.py b/hydra/cli.py
index 48d159b..1e593b8 100644
--- a/hydra/cli.py
+++ b/hydra/cli.py
@@ -13,13 +13,30 @@ from .session import launch_session, session_helper, view
 
 
 def parser() -> argparse.ArgumentParser:
-    cli = argparse.ArgumentParser(prog='hydra', description='Independent HydraOS VM manager')
+    cli = argparse.ArgumentParser(prog='hydra', description='Hydra OS independent VM manager')
     cli.add_argument('--config', type=Path, default=Path(os.environ.get('XDG_CONFIG_HOME', Path.home() / '.config')) / 'hydra')
     cli.add_argument('--state', type=Path, default=Path(os.environ.get('XDG_STATE_HOME', Path.home() / '.local/state')) / 'hydra')
     cli.add_argument('--runtime', type=Path, default=Path(os.environ.get('XDG_RUNTIME_DIR', f'/tmp/hydra-{os.getuid()}')) / 'hydra')
     cli.add_argument('--defaults', type=Path, default=Path('/etc/hydra/defaults.toml'),
                      help='Distribution preferences for newly created profiles')
-    commands = cli.add_subparsers(dest='command', required=True)
+    commands = cli.add_subparsers(dest='command')
+    commands.add_parser('menu', help='Open the terminal VM menu')
+    download = commands.add_parser('download', help='Download and validate a direct ISO URL')
+    download.add_argument('url')
+    download.add_argument('--sha256')
+    run = commands.add_parser('run', help='Create, start and display a VM from a local ISO or HTTP(S) URL')
+    run.add_argument('source')
+    run.add_argument('--name', required=True)
+    run.add_argument('--memory', '--ram', type=int, default=4096, help='VM RAM in MiB')
+    run.add_argument('--cpus', type=int, default=2)
+    run.add_argument('--disk-size', default='40G')
+    run.add_argument('--sha256')
+    run.add_argument('--no-view', action='store_true')
+    run.add_argument('--windowed', action='store_true')
+    opener = commands.add_parser('open', help='Start a stopped VM or reconnect a running VM')
+    opener.add_argument('name')
+    opener.add_argument('--no-view', action='store_true')
+    opener.add_argument('--windowed', action='store_true')
     add = commands.add_parser('add', help='Create a VM profile without starting it')
     add.add_argument('name')
     add.add_argument('--iso', type=Path)
@@ -48,7 +65,7 @@ def parser() -> argparse.ArgumentParser:
     viewer = commands.add_parser('view', help='Connect a viewer without changing VM power')
     viewer.add_argument('name')
     viewer.add_argument('--windowed', action='store_true')
-    session = commands.add_parser('session', help='Start the minimal HydraOS labwc session')
+    session = commands.add_parser('session', help='Start the minimal Hydra OS labwc session')
     session.add_argument('--nested', action='store_true')
     helper = commands.add_parser('_session-helper', help=argparse.SUPPRESS)
     helper.add_argument('operation')
@@ -56,10 +73,47 @@ def parser() -> argparse.ArgumentParser:
     return cli
 
 
+def _download_progress():
+    last = None
+    interactive = sys.stderr.isatty()
+    def report(received, total):
+        nonlocal last
+        step = received * 100 // total if total else received // (64 * 1024 * 1024)
+        if last == step:
+            return
+        last = step
+        if not interactive and received and (total is None or received != total):
+            return
+        suffix = f' / {total // (1024 * 1024)} MiB ({step}%)' if total else ' MiB'
+        print(f'Download: {received // (1024 * 1024)}{suffix}', file=sys.stderr)
+    return report
+
+
 def main(argv: list[str] | None = None) -> int:
-    args = parser().parse_args(argv)
+    cli = parser()
+    args = cli.parse_args(argv)
     runtime = Runtime(args.config, args.state, args.runtime)
     try:
+        if args.command is None and not sys.stdin.isatty():
+            cli.print_help()
+            return 0
+        if args.command in (None, 'menu'):
+            from .launch import session_manifest
+            from .menu import run_menu
+            return run_menu(runtime, manifest=session_manifest(runtime))
+        if args.command == 'download':
+            from .media import download_iso
+            print(download_iso(args.url, sha256=args.sha256, progress=_download_progress()))
+            return 0
+        if args.command == 'run':
+            from .launch import run_source
+            return run_source(runtime, args.source, name=args.name, memory=args.memory,
+                              cpus=args.cpus, disk_size=args.disk_size, sha256=args.sha256,
+                              no_view=args.no_view, windowed=args.windowed, defaults=args.defaults,
+                              progress=_download_progress())
+        if args.command == 'open':
+            from .launch import open_vm
+            return open_vm(runtime, args.name, no_view=args.no_view, windowed=args.windowed)
         if args.command == 'view':
             return view(runtime, args.name, windowed=args.windowed)
         elif args.command == 'session':
@@ -87,6 +141,9 @@ def main(argv: list[str] | None = None) -> int:
             result = getattr(runtime, args.command)(args.name)
         print(json.dumps(result, indent=2))
         return 0
+    except KeyboardInterrupt:
+        print('hydra: Cancelled', file=sys.stderr)
+        return 130
     except (RuntimeError, OSError, ValueError, subprocess.TimeoutExpired) as exc:
         print(f'hydra: {exc}', file=sys.stderr)
         return 1
diff --git a/hydra/launch.py b/hydra/launch.py
new file mode 100644
index 0000000..acff051
--- /dev/null
+++ b/hydra/launch.py
@@ -0,0 +1,123 @@
+"""Explicit start-if-stopped and new-ISO launch, preserving runtime authority."""
+
+import json
+import os
+from pathlib import Path
+
+from . import media, session
+from .profiles import Profile, load_defaults, validate_name
+from .runtime import Runtime, RuntimeError
+
+
+HOST_RESERVE_MIB = 768
+
+
+def available_memory_mib() -> int:
+    """Linux MemAvailable accounts for reclaimable host caches."""
+    try:
+        for line in Path('/proc/meminfo').read_text().splitlines():
+            if line.startswith('MemAvailable:'):
+                return int(line.split()[1]) // 1024
+    except (OSError, ValueError, IndexError) as exc:
+        raise RuntimeError('Cannot estimate available RAM from /proc/meminfo') from exc
+    raise RuntimeError('Cannot estimate available RAM: MemAvailable is missing')
+
+
+def _memory_preflight(memory: int) -> None:
+    available = available_memory_mib()
+    if memory + HOST_RESERVE_MIB > available:
+        raise RuntimeError(f'Not enough available RAM: VM needs {memory} MiB plus a {HOST_RESERVE_MIB} MiB host reserve; '
+                           f'{available} MiB available. Choose less --memory or stop another VM')
+
+
+def session_manifest(runtime: Runtime, manifest: Path | None = None) -> Path | None:
+    """Use an inherited session only when it belongs to these runtime roots."""
+    explicit = manifest is not None
+    inherited = os.environ.get('HYDRA_SESSION_MANIFEST')
+    if not explicit and not inherited:
+        return None
+    path = Path(manifest if explicit else inherited).expanduser().absolute()
+    try:
+        data = json.loads(path.read_text(encoding='utf-8'))
+        if (not isinstance(data, dict) or
+                any(not isinstance(data.get(key), str) or not Path(data[key]).is_absolute()
+                    or Path(data[key]) != getattr(runtime, key) for key in ('config', 'state', 'runtime')) or
+                not isinstance(data.get('names'), list) or
+                any(not isinstance(name, str) for name in data['names']) or
+                not isinstance(data.get('terminal'), str) or not Path(data['terminal']).is_absolute() or
+                not isinstance(data.get('directory'), str) or Path(data['directory']) != path.parent):
+            raise ValueError('Invalid session manifest or different runtime roots')
+        for name in data['names']:
+            validate_name(name)
+        return path
+    except (OSError, ValueError) as exc:
+        if explicit:
+            raise session.SessionError('Invalid session manifest; start a fresh Hydra OS session') from exc
+        return None
+
+
+def _view_preflight(runtime: Runtime, *, no_view: bool, manifest: Path | None) -> Path | None:
+    if no_view:
+        return None
+    selected = session_manifest(runtime, manifest)
+    session._display()
+    session._viewer()
+    return selected
+
+
+def _show(runtime: Runtime, name: str, *, no_view: bool, windowed: bool,
+          manifest: Path | None) -> int:
+    if no_view:
+        return 0
+    if manifest is not None:
+        return session.request_refresh(manifest, selected=name)
+    return session.view(runtime, name, windowed=windowed)
+
+
+def open_vm(runtime: Runtime, name: str, *, windowed=False, no_view=False,
+            manifest: Path | None = None) -> int:
+    profile = runtime.profile(name)
+    current = runtime.status(name)
+    status = current['status']
+    if status == 'unknown':
+        raise RuntimeError(f'Cannot open {name}: unknown VM identity; {current.get("error", "inspect its QMP identity before retrying")}')
+    manifest = _view_preflight(runtime, no_view=no_view, manifest=manifest)
+    if status == 'stopped':
+        _memory_preflight(profile.memory)
+        runtime.start(name)
+    # Other verified QEMU states (for example paused) are viewable without a
+    # new process. Runtime.start owns the lock and final identity recheck.
+    return _show(runtime, name, no_view=no_view, windowed=windowed, manifest=manifest)
+
+
+def run_source(runtime: Runtime, source: str | Path, *, name: str, memory=4096,
+               cpus=2, disk_size='40G', sha256: str | None = None, windowed=False,
+               no_view=False, manifest: Path | None = None, defaults: Path | None = None,
+               progress=None) -> int:
+    validate_name(name)
+    profile_path = runtime.config / f'{name}.toml'
+    if profile_path.exists() or profile_path.is_symlink():
+        raise RuntimeError(f'VM {name} already exists; use hydra open {name}')
+    paths = runtime.paths(name)
+    if paths.disk.parent.exists() or paths.disk.parent.is_symlink():
+        raise RuntimeError(f'Existing VM state/disk for {name}; choose a new name and preserve the old disk')
+    if runtime.status(name)['status'] != 'stopped':
+        raise RuntimeError(f'Cannot create {name}: existing or unknown VM identity')
+    preferences = load_defaults(defaults) if defaults is not None else {}
+    # Validate requested allocations before downloading or creating anything.
+    Profile(name, memory=memory, cpus=cpus, disk_size=disk_size, **preferences)
+    manifest = _view_preflight(runtime, no_view=no_view, manifest=manifest)
+    _memory_preflight(memory)
+    source = str(source)
+    if '://' in source:
+        iso = media.download_iso(source, sha256=sha256, progress=progress)
+    else:
+        iso = media.validate_iso(Path(source).expanduser().resolve(), sha256=sha256)
+    # Recheck after a potentially lengthy transfer. Profile publication itself
+    # is exclusive ('x') and Runtime never replaces an existing disk.
+    if paths.disk.parent.exists() or paths.disk.parent.is_symlink():
+        raise RuntimeError(f'Existing VM state/disk for {name}; choose a new name')
+    _memory_preflight(memory)
+    runtime.add(Profile(name, iso, memory, cpus, disk_size, **preferences))
+    runtime.start(name)
+    return _show(runtime, name, no_view=no_view, windowed=windowed, manifest=manifest)
diff --git a/hydra/media.py b/hydra/media.py
new file mode 100644
index 0000000..3bec458
--- /dev/null
+++ b/hydra/media.py
@@ -0,0 +1,164 @@
+"""Private, validated ISO downloads with atomic, non-replacing publication."""
+
+import fcntl
+import hashlib
+import http.client
+import os
+import re
+import shutil
+import stat
+import tempfile
+import urllib.error
+import urllib.parse
+import urllib.request
+from pathlib import Path
+
+from .runtime import _private_dir
+
+
+class MediaError(ValueError):
+    """An actionable image error without remote query strings or credentials."""
+
+
+def _checksum(sha256: str | None) -> str | None:
+    if sha256 is not None and (not isinstance(sha256, str) or not re.fullmatch(r'[a-fA-F0-9]{64}', sha256)):
+        raise MediaError('SHA-256 must contain exactly 64 hexadecimal characters')
+    return sha256.lower() if sha256 else None
+
+
+def _url(url: str) -> urllib.parse.SplitResult:
+    try:
+        parts = urllib.parse.urlsplit(url)
+        port = parts.port
+    except ValueError as exc:
+        raise MediaError('Invalid HTTP(S) image URL') from exc
+    if parts.scheme not in ('http', 'https') or not parts.hostname:
+        raise MediaError('Use a direct HTTP(S) ISO URL, or a local ISO path with hydra run')
+    if parts.username is not None or parts.password is not None:
+        raise MediaError('URL credentials are not supported; use a direct image URL without credentials')
+    if any(ord(char) < 32 or ord(char) == 127 for char in url):
+        raise MediaError('Image URL contains control characters')
+    return parts
+
+
+class _SafeRedirect(urllib.request.HTTPRedirectHandler):
+    def redirect_request(self, req, fp, code, msg, headers, newurl):
+        _url(newurl)
+        return super().redirect_request(req, fp, code, msg, headers, newurl)
+
+
+def validate_iso(path: Path, *, sha256: str | None = None) -> Path:
+    """Recognize ISO9660 or UDF volume descriptors and optional whole-file hash."""
+    wanted = _checksum(sha256)
+    path = Path(path)
+    if not path.is_file():
+        raise MediaError(f'ISO does not exist or is not a file: {path}')
+    found = False
+    with path.open('rb') as stream:
+        stream.seek(16 * 2048)
+        for _ in range(241):
+            sector = stream.read(2048)
+            if len(sector) != 2048:
+                break
+            if ((sector[1:6] == b'CD001' and sector[0] in (0, 1, 2, 3, 255) and sector[6] == 1)
+                    or (sector[1:6] in (b'NSR02', b'NSR03') and sector[6] == 1)):
+                found = True
+                break
+        if not found:
+            raise MediaError('Not an ISO9660/UDF image; use a direct ISO download URL rather than an HTML download page')
+        if wanted:
+            stream.seek(0)
+            digest = hashlib.file_digest(stream, 'sha256').hexdigest()
+            if digest != wanted:
+                raise MediaError('ISO SHA-256 mismatch; image was not accepted')
+    return path
+
+
+def _cached(path: Path, sha256: str | None) -> Path | None:
+    try:
+        info = path.lstat()
+    except FileNotFoundError:
+        return None
+    if not stat.S_ISREG(info.st_mode) or info.st_uid != os.getuid():
+        raise MediaError('Refusing an unsafe ISO cache entry; choose another cache directory')
+    try:
+        return validate_iso(path, sha256=sha256)
+    except MediaError as exc:
+        raise MediaError('Cached ISO failed validation; move it aside or choose another cache directory') from exc
+
+
+def download_iso(url: str, *, sha256: str | None = None, cache: Path | None = None,
+                 progress=None) -> Path:
+    """Download once under a URL lock; publish only complete verified images."""
+    parts = _url(url)
+    wanted = _checksum(sha256)
+    cache = Path(cache) if cache is not None else Path(os.environ.get('XDG_CACHE_HOME', Path.home() / '.cache')) / 'hydra/iso'
+    cache = cache.expanduser().absolute()
+    _private_dir(cache)
+    basename = re.sub(r'[^A-Za-z0-9._-]', '_', urllib.parse.unquote(Path(parts.path).name))[:96].strip('.') or 'image.iso'
+    if not basename.lower().endswith('.iso'):
+        basename += '.iso'
+    key = hashlib.sha256(url.encode()).hexdigest()
+    destination = cache / f'{key}-{basename}'
+    lock = os.open(cache / (key + '.lock'), os.O_RDWR | os.O_CREAT | os.O_NOFOLLOW, 0o600)
+    try:
+        fcntl.flock(lock, fcntl.LOCK_EX)
+        cached = _cached(destination, wanted)
+        if cached:
+            if progress:
+                size = cached.stat().st_size
+                progress(size, size)
+            return cached
+        temporary = None
+        try:
+            opener = urllib.request.build_opener(_SafeRedirect())
+            request = urllib.request.Request(url, headers={'User-Agent': 'Hydra-OS/1', 'Accept-Encoding': 'identity'})
+            with opener.open(request, timeout=30) as response:
+                if response.status != 200:
+                    raise MediaError(f'Image server returned HTTP {response.status}; use a direct ISO URL')
+                if response.headers.get_content_type() in ('text/html', 'application/xhtml+xml'):
+                    raise MediaError('Server returned an HTML download page; use a direct ISO URL')
+                raw_length = response.headers.get('Content-Length')
+                try:
+                    total = int(raw_length) if raw_length is not None else None
+                    if total is not None and total <= 0:
+                        raise ValueError
+                except ValueError as exc:
+                    raise MediaError('Image server supplied an invalid content length') from exc
+                if total is not None and total > shutil.disk_usage(cache)[2]:
+                    raise MediaError('Not enough free disk space for the ISO download')
+                fd, name = tempfile.mkstemp(prefix='.' + key + '-', suffix='.part', dir=cache)
+                temporary = Path(name)
+                received = 0
+                with os.fdopen(fd, 'wb') as output:
+                    if progress:
+                        progress(0, total)
+                    while True:
+                        chunk = response.read(1024 * 1024)
+                        if not chunk:
+                            break
+                        if len(chunk) > shutil.disk_usage(cache)[2]:
+                            raise MediaError('Not enough free disk space for the ISO download')
+                        received += len(chunk)
+                        if total is not None and received > total:
+                            raise MediaError('Image download exceeds its advertised content length')
+                        output.write(chunk)
+                        if progress:
+                            progress(received, total)
+                    output.flush()
+                    os.fsync(output.fileno())
+                if total is not None and received != total:
+                    raise MediaError('Image download was truncated; retry the direct ISO URL')
+            validate_iso(temporary, sha256=wanted)
+            # Linking cannot replace a concurrent or unrelated destination.
+            os.link(temporary, destination)
+            return destination
+        except urllib.error.HTTPError as exc:
+            raise MediaError(f'Image server returned HTTP {exc.code}; use a direct ISO URL') from None
+        except (urllib.error.URLError, http.client.HTTPException, TimeoutError) as exc:
+            raise MediaError('ISO download failed or timed out; check networking and retry the direct URL') from None
+        finally:
+            if temporary is not None:
+                temporary.unlink(missing_ok=True)
+    finally:
+        os.close(lock)
diff --git a/tests/test_cli.py b/tests/test_cli.py
index c78b036..268adc6 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -64,3 +64,51 @@ class CLITests(unittest.TestCase):
             self.assertEqual(result.returncode, 1, result.stderr)
             self.assertNotIn('Traceback', result.stderr)
             self.assertFalse((self.root / 'config/guest.toml').exists())
+
+    def test_plain_noninteractive_invocation_prints_help_without_creating_state(self):
+        result = self.run_cli()
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertIn('Hydra OS', result.stdout)
+        self.assertIn('run', result.stdout)
+        self.assertFalse((self.root / 'state').exists())
+
+    def test_run_and_open_are_headless_and_existing_name_is_never_replaced(self):
+        import os
+        from unittest.mock import patch
+        from test_media import iso_bytes
+        from test_runtime import FAKE_IMG, FAKE_QEMU
+        from hydra.runtime import Runtime
+        iso = self.root / 'installer.iso'
+        iso.write_bytes(iso_bytes())
+        qemu = self.root / 'qemu'
+        qemu.write_text(FAKE_QEMU)
+        qemu.chmod(0o700)
+        img = self.root / 'img'
+        img.write_text(FAKE_IMG)
+        img.chmod(0o700)
+        runtime = Runtime(self.root / 'config', self.root / 'state', self.root / 'run')
+        def cleanup():
+            if runtime.status('guest')['status'] == 'running':
+                runtime.stop('guest', force=True)
+        self.addCleanup(cleanup)
+        with patch.dict(os.environ, {'HYDRA_QEMU': str(qemu), 'HYDRA_QEMU_IMG': str(img),
+                                    'DISPLAY': '', 'WAYLAND_DISPLAY': '', 'HYDRA_SESSION_MANIFEST': '/not/a/manifest'}):
+            started = self.run_cli('run', str(iso), '--name', 'guest', '--memory', '256', '--cpus', '1', '--disk-size', '8M', '--no-view')
+            self.assertEqual(started.returncode, 0, started.stderr)
+            original = (self.root / 'config/guest.toml').read_bytes()
+            pid = runtime.paths('guest').pid.read_bytes()
+            duplicate = self.run_cli('run', str(iso), '--name', 'guest', '--no-view')
+            self.assertEqual(duplicate.returncode, 1, duplicate.stderr)
+            self.assertIn('hydra open guest', duplicate.stderr)
+            iso.unlink()
+            opened = self.run_cli('open', 'guest', '--no-view')
+            self.assertEqual(opened.returncode, 0, opened.stderr)
+            self.assertEqual((self.root / 'config/guest.toml').read_bytes(), original)
+            self.assertEqual(runtime.paths('guest').pid.read_bytes(), pid)
+
+    def test_download_rejects_credential_urls_without_echoing_secrets(self):
+        result = self.run_cli('download', 'https://user:supersecret@example.org/installer.iso?token=private')
+        self.assertEqual(result.returncode, 1, result.stderr)
+        self.assertNotIn('supersecret', result.stderr)
+        self.assertNotIn('private', result.stderr)
+        self.assertNotIn('Traceback', result.stderr)
diff --git a/tests/test_launch.py b/tests/test_launch.py
new file mode 100644
index 0000000..bb5d3be
--- /dev/null
+++ b/tests/test_launch.py
@@ -0,0 +1,176 @@
+import json
+import os
+import tempfile
+import unittest
+from pathlib import Path
+from unittest.mock import patch
+
+from hydra import launch
+from hydra.profiles import Profile
+from hydra.runtime import Runtime, RuntimeError as VMError
+from test_media import iso_bytes
+from test_runtime import FAKE_IMG, FAKE_QEMU
+
+
+class LaunchTests(unittest.TestCase):
+    def setUp(self):
+        self.tmp = tempfile.TemporaryDirectory(prefix='hl-')
+        self.addCleanup(self.tmp.cleanup)
+        self.root = Path(self.tmp.name)
+        self.runtime = Runtime(self.root / 'config', self.root / 'state', self.root / 'run', boot_timeout=1)
+        self.iso = self.root / 'installer.iso'
+        self.iso.write_bytes(iso_bytes())
+        self.qemu = self.root / 'qemu'
+        self.qemu.write_text(FAKE_QEMU)
+        self.qemu.chmod(0o700)
+        self.img = self.root / 'img'
+        self.img.write_text(FAKE_IMG)
+        self.img.chmod(0o700)
+        self.viewer = self.root / 'viewer'
+        self.viewer.write_text('#!/bin/sh\necho --hide-toolbar\n')
+        self.viewer.chmod(0o700)
+        env = patch.dict(os.environ, {'HYDRA_QEMU': str(self.qemu), 'HYDRA_QEMU_IMG': str(self.img), 'HYDRA_VIEWER': str(self.viewer)})
+        env.start()
+        self.addCleanup(env.stop)
+        memory = patch('hydra.launch.available_memory_mib', return_value=16384)
+        memory.start()
+        self.addCleanup(memory.stop)
+        self.addCleanup(self.cleanup_guests)
+
+    def cleanup_guests(self):
+        for name in ('guest', 'other'):
+            if self.runtime.status(name)['status'] == 'running':
+                self.runtime.stop(name, force=True)
+
+    def test_run_creates_and_starts_once_then_open_reconnects_without_memory_or_iso(self):
+        self.assertEqual(launch.run_source(self.runtime, str(self.iso), name='guest', memory=256, cpus=1, disk_size='8M', no_view=True), 0)
+        profile = self.runtime.profile('guest')
+        self.assertEqual((profile.memory, profile.cpus, profile.disk_size), (256, 1, '8M'))
+        pid = self.runtime.paths('guest').pid.read_bytes()
+        disk = self.runtime.paths('guest').disk.read_bytes()
+        self.iso.unlink()
+        with patch('hydra.launch.available_memory_mib', return_value=0):
+            self.assertEqual(launch.open_vm(self.runtime, 'guest', no_view=True), 0)
+        self.assertEqual(self.runtime.paths('guest').pid.read_bytes(), pid)
+        self.assertEqual(self.runtime.paths('guest').disk.read_bytes(), disk)
+
+    def test_existing_profile_or_orphan_disk_refuses_run_without_changes(self):
+        self.runtime.add(Profile('guest', memory=256))
+        original = (self.runtime.config / 'guest.toml').read_bytes()
+        with self.assertRaisesRegex(VMError, 'open guest'):
+            launch.run_source(self.runtime, str(self.iso), name='guest', no_view=True)
+        self.assertEqual((self.runtime.config / 'guest.toml').read_bytes(), original)
+        paths = self.runtime.paths('other')
+        paths.disk.parent.mkdir(parents=True)
+        paths.disk.write_text('valuable old disk')
+        with self.assertRaisesRegex(VMError, 'disk|state'):
+            launch.run_source(self.runtime, str(self.iso), name='other', no_view=True)
+        self.assertEqual(paths.disk.read_text(), 'valuable old disk')
+        self.assertFalse((self.runtime.config / 'other.toml').exists())
+
+    def test_memory_reserve_refuses_before_profile_or_disk_then_allows_boundary(self):
+        with patch('hydra.launch.available_memory_mib', return_value=1023):
+            with self.assertRaisesRegex(VMError, '768'):
+                launch.run_source(self.runtime, str(self.iso), name='guest', memory=256, no_view=True)
+        self.assertFalse(self.runtime.config.exists())
+        with patch('hydra.launch.available_memory_mib', return_value=1024):
+            self.assertEqual(launch.run_source(self.runtime, str(self.iso), name='guest', memory=256, no_view=True), 0)
+
+    def test_open_stopped_preserves_disk_and_checks_memory(self):
+        self.runtime.add(Profile('guest', memory=256))
+        paths = self.runtime.paths('guest')
+        paths.disk.parent.mkdir(parents=True)
+        paths.disk.write_text('installed OS')
+        with patch('hydra.launch.available_memory_mib', return_value=1000):
+            with self.assertRaises(VMError):
+                launch.open_vm(self.runtime, 'guest', no_view=True)
+        self.assertEqual(self.runtime.status('guest')['status'], 'stopped')
+        self.assertEqual(launch.open_vm(self.runtime, 'guest', no_view=True), 0)
+        self.assertEqual(paths.disk.read_text(), 'installed OS')
+
+    def test_missing_display_or_viewer_refuses_before_launch_side_effects(self):
+        with patch.dict(os.environ, {'DISPLAY': '', 'WAYLAND_DISPLAY': ''}):
+            with self.assertRaisesRegex(ValueError, 'display'):
+                launch.run_source(self.runtime, str(self.iso), name='guest', no_view=False)
+        self.assertFalse(self.runtime.config.exists())
+        self.runtime.add(Profile('guest', memory=256))
+        with patch.dict(os.environ, {'DISPLAY': ':1', 'HYDRA_VIEWER': '/does/not/exist'}):
+            with self.assertRaisesRegex(ValueError, 'Missing'):
+                launch.open_vm(self.runtime, 'guest')
+        self.assertFalse(self.runtime.paths('guest').disk.exists())
+        self.assertEqual(self.runtime.status('guest')['status'], 'stopped')
+
+    def test_unknown_identity_never_restarts_or_controls_vm(self):
+        launch.run_source(self.runtime, str(self.iso), name='guest', memory=256, no_view=True)
+        paths = self.runtime.paths('guest')
+        original = paths.metadata.read_text()
+        pid = paths.pid.read_bytes()
+        paths.metadata.write_text(json.dumps({'name': 'foreign', 'uuid': 'foreign'}))
+        try:
+            with self.assertRaisesRegex(VMError, 'unknown|identity'):
+                launch.open_vm(self.runtime, 'guest', no_view=True)
+            self.assertEqual(paths.pid.read_bytes(), pid)
+        finally:
+            paths.metadata.write_text(original)
+
+    def test_invalid_local_iso_never_creates_profile(self):
+        self.iso.write_text('<html>not an ISO</html>')
+        with self.assertRaises(ValueError):
+            launch.run_source(self.runtime, str(self.iso), name='guest', no_view=True)
+        self.assertFalse(self.runtime.config.exists())
+
+    def test_session_open_writes_selected_refresh_and_preserves_other_guest(self):
+        self.runtime.add(Profile('guest', memory=256))
+        self.runtime.add(Profile('other', memory=256))
+        launch.open_vm(self.runtime, 'other', no_view=True)
+        other_pid = self.runtime.paths('other').pid.read_bytes()
+        directory = self.root / 'session'
+        directory.mkdir()
+        manifest = directory / 'session.json'
+        manifest.write_text(json.dumps({'config': str(self.runtime.config), 'state': str(self.runtime.state),
+                                       'runtime': str(self.runtime.runtime), 'terminal': '/bin/sh',
+                                       'directory': str(directory), 'names': ['guest', 'other']}))
+        with patch.dict(os.environ, {'DISPLAY': ':1', 'HYDRA_SESSION_MANIFEST': str(manifest)}):
+            self.assertEqual(launch.open_vm(self.runtime, 'guest'), 0)
+        self.assertEqual(json.loads((directory / 'refresh.request').read_text()), {'selected': 'guest'})
+        self.assertEqual(self.runtime.status('guest')['status'], 'running')
+        self.assertEqual(self.runtime.paths('other').pid.read_bytes(), other_pid)
+
+    def test_invalid_explicit_manifest_refuses_before_new_profile_and_environment_falls_back(self):
+        manifest = self.root / 'bad.json'
+        manifest.write_text('{}')
+        with patch.dict(os.environ, {'DISPLAY': ':1'}):
+            with self.assertRaisesRegex(ValueError, 'manifest'):
+                launch.run_source(self.runtime, str(self.iso), name='guest', manifest=manifest)
+        self.assertFalse(self.runtime.config.exists())
+        with patch.dict(os.environ, {'HYDRA_SESSION_MANIFEST': str(manifest)}):
+            self.assertIsNone(launch.session_manifest(self.runtime))
+
+    def test_remote_run_downloads_then_launches_with_distribution_defaults(self):
+        import http.server
+        import threading
+        owner = self
+        class Handler(http.server.BaseHTTPRequestHandler):
+            def do_GET(self):
+                body = iso_bytes()
+                self.send_response(200)
+                self.send_header('Content-Length', str(len(body)))
+                self.end_headers()
+                self.wfile.write(body)
+            def log_message(self, *args):
+                pass
+        server = http.server.ThreadingHTTPServer(('127.0.0.1', 0), Handler)
+        self.addCleanup(server.server_close)
+        thread = threading.Thread(target=server.serve_forever, daemon=True)
+        thread.start()
+        self.addCleanup(server.shutdown)
+        defaults = self.root / 'defaults.toml'
+        defaults.write_text('network="bridge"\nbridge="testbr0"\nwidth=1600\n')
+        with patch.dict(os.environ, {'XDG_CACHE_HOME': str(self.root / 'cache')}):
+            result = launch.run_source(self.runtime, f'http://127.0.0.1:{server.server_port}/os.iso', name='guest',
+                                       memory=256, no_view=True, defaults=defaults)
+        self.assertEqual(result, 0)
+        profile = self.runtime.profile('guest')
+        self.assertEqual((profile.network, profile.bridge, profile.width), ('bridge', 'testbr0', 1600))
+        self.assertEqual(profile.iso.read_bytes(), iso_bytes())
+        self.assertTrue(profile.iso.is_relative_to(self.root / 'cache/hydra/iso'))
diff --git a/tests/test_media.py b/tests/test_media.py
new file mode 100644
index 0000000..7d46cc6
--- /dev/null
+++ b/tests/test_media.py
@@ -0,0 +1,134 @@
+import hashlib
+import http.server
+import tempfile
+import threading
+import unittest
+from pathlib import Path
+from unittest.mock import patch
+
+from hydra import media
+
+
+def iso_bytes(signature=b'CD001'):
+    data = bytearray(40 * 2048)
+    data[16 * 2048:16 * 2048 + 7] = b'\x01' + signature + b'\x01'
+    return bytes(data)
+
+
+class MediaTests(unittest.TestCase):
+    def setUp(self):
+        self.tmp = tempfile.TemporaryDirectory()
+        self.addCleanup(self.tmp.cleanup)
+        self.cache = Path(self.tmp.name) / 'cache'
+        self.requests = []
+        owner = self
+        class Handler(http.server.BaseHTTPRequestHandler):
+            def do_GET(self):
+                owner.requests.append(self.path)
+                body = b'<html>download here</html>' if self.path.startswith('/html') else iso_bytes()
+                self.send_response(200)
+                self.send_header('Content-Type', 'text/html' if self.path.startswith('/html') else 'application/octet-stream')
+                self.send_header('Content-Length', str(len(body) + (100 if self.path.startswith('/truncated') else 0)))
+                self.end_headers()
+                self.wfile.write(body)
+            def log_message(self, *args):
+                pass
+        self.server = http.server.ThreadingHTTPServer(('127.0.0.1', 0), Handler)
+        self.addCleanup(self.server.server_close)
+        self.thread = threading.Thread(target=self.server.serve_forever, daemon=True)
+        self.thread.start()
+        self.addCleanup(self.server.shutdown)
+        self.url = f'http://127.0.0.1:{self.server.server_port}'
+
+    def test_verified_download_is_reused_and_progress_reports_complete_bytes(self):
+        updates = []
+        url = self.url + '/installer.iso?token=secret'
+        path = media.download_iso(url, cache=self.cache, progress=lambda got, total: updates.append((got, total)))
+        self.assertEqual(path.read_bytes(), iso_bytes())
+        self.assertEqual(path.stat().st_mode & 0o777, 0o600)
+        self.assertNotIn('secret', path.name)
+        self.assertEqual(updates[-1], (81920, 81920))
+        self.assertEqual(media.download_iso(url, cache=self.cache), path)
+        self.assertEqual(len(self.requests), 1)
+
+    def test_html_truncation_and_checksum_do_not_publish_images(self):
+        for endpoint, checksum in (('/html.iso', None), ('/truncated.iso', None), ('/wrong.iso', '0' * 64)):
+            with self.subTest(endpoint=endpoint):
+                with self.assertRaises(ValueError):
+                    media.download_iso(self.url + endpoint, cache=self.cache, sha256=checksum)
+                self.assertFalse(list(self.cache.glob('*.iso')))
+                self.assertFalse(list(self.cache.glob('*.part')))
+
+    def test_cancellation_removes_partial_and_retry_completes(self):
+        def cancel(got, total):
+            if got:
+                raise KeyboardInterrupt
+        with self.assertRaises(KeyboardInterrupt):
+            media.download_iso(self.url + '/cancel.iso', cache=self.cache, progress=cancel)
+        self.assertFalse(list(self.cache.glob('*.iso')))
+        self.assertFalse(list(self.cache.glob('*.part')))
+        self.assertEqual(media.download_iso(self.url + '/cancel.iso', cache=self.cache).read_bytes(), iso_bytes())
+
+    def test_same_basename_different_urls_and_concurrent_downloads_are_safe(self):
+        results = []
+        errors = []
+        def fetch():
+            try:
+                results.append(media.download_iso(self.url + '/one/os.iso', cache=self.cache))
+            except Exception as exc:
+                errors.append(exc)
+        threads = [threading.Thread(target=fetch) for _ in range(2)]
+        for thread in threads:
+            thread.start()
+        for thread in threads:
+            thread.join(5)
+        self.assertEqual(errors, [])
+        self.assertEqual(len(set(results)), 1)
+        self.assertEqual(self.requests, ['/one/os.iso'])
+        second = media.download_iso(self.url + '/two/os.iso', cache=self.cache)
+        self.assertNotEqual(second, results[0])
+
+    def test_corrupt_cache_and_symlink_never_overwrite_unrelated_files(self):
+        url = self.url + '/installer.iso'
+        path = media.download_iso(url, cache=self.cache)
+        path.write_text('valuable unrelated data')
+        with self.assertRaises(ValueError):
+            media.download_iso(url, cache=self.cache)
+        self.assertEqual(path.read_text(), 'valuable unrelated data')
+        path.unlink()
+        target = Path(self.tmp.name) / 'outside'
+        target.write_bytes(iso_bytes())
+        path.symlink_to(target)
+        with self.assertRaises(ValueError):
+            media.download_iso(url, cache=self.cache)
+        self.assertTrue(path.is_symlink())
+        self.assertEqual(target.read_bytes(), iso_bytes())
+
+    def test_unsupported_urls_checksums_and_insufficient_space_fail_before_download(self):
+        for url in ('ftp://example.org/os.iso', 'http://user:secret@example.org/os.iso'):
+            with self.assertRaises(ValueError):
+                media.download_iso(url, cache=self.cache)
+        with self.assertRaises(ValueError):
+            media.download_iso(self.url + '/os.iso', cache=self.cache, sha256='bad')
+        with patch('hydra.media.shutil.disk_usage', return_value=(10, 9, 1)):
+            with self.assertRaisesRegex(ValueError, 'space'):
+                media.download_iso(self.url + '/os.iso', cache=self.cache)
+        self.assertFalse(list(self.cache.glob('*.iso')))
+
+    def test_local_validation_accepts_udf_and_rejects_html_and_bad_checksum(self):
+        path = Path(self.tmp.name) / 'os.iso'
+        path.write_bytes(iso_bytes(b'NSR03'))
+        media.validate_iso(path, sha256=hashlib.sha256(path.read_bytes()).hexdigest())
+        with self.assertRaises(ValueError):
+            media.validate_iso(path, sha256='0' * 64)
+        path.write_text('<html>not an image</html>')
+        with self.assertRaisesRegex(ValueError, 'direct|ISO'):
+            media.validate_iso(path)
+
+    def test_cache_reuse_reports_completed_progress_without_another_request(self):
+        url = self.url + '/cached.iso'
+        path = media.download_iso(url, cache=self.cache)
+        updates = []
+        self.assertEqual(media.download_iso(url, cache=self.cache, progress=lambda got, total: updates.append((got, total))), path)
+        self.assertEqual(updates, [(81920, 81920)])
+        self.assertEqual(self.requests, ['/cached.iso'])