diff --git a/codex-rs/voice-host/README.md b/codex-rs/voice-host/README.md
index ad8780dd37..17d0f3e130 100644
--- a/codex-rs/voice-host/README.md
+++ b/codex-rs/voice-host/README.md
@@ -24,5 +24,16 @@ an existing validated package into a fresh output and adds the helper. Supply
 Linux MUSL apps require same-architecture GNU helpers; other targets must match.
 The package version must end in `+<build-commit>`. The manifest records declared
 build provenance and file hashes, not authentication or binary architecture proof.
-Native loading, media/privacy controls and actual audio proof remain subsequent
-integration stages; this assembler does not add native runtime libraries.
+Add `--runtime <prepared-runtime>` to include the platform preparer's selected
+libraries and `runtime.json` beside the helper. The assembler checks the target,
+pinned source manifest, plugin list, relative paths and file hashes, then checks
+the copied hashes again. It preserves `lib/` and `plugins/` on macOS, `lib/` and
+`lib/gstreamer-1.0/` on Linux, and the shared `bin/` on Windows. Unlisted files are
+not copied. The package manifest records every included runtime file and the
+unchanged runtime receipt.
+Omitting `--runtime` retains helper-only assembly.
+
+This accepts a development runtime receipt, not an authenticated release. It
+does not repeat native loader inspection or establish trust in the build inputs.
+The helper still does not load these files; native loading, media/privacy controls,
+linking against the prepared SDK and actual audio proof remain integration stages.
diff --git a/third_party/voice/BUILD.bazel b/third_party/voice/BUILD.bazel
index c0d0e7d64e..345480c33b 100644
--- a/third_party/voice/BUILD.bazel
+++ b/third_party/voice/BUILD.bazel
@@ -35,6 +35,7 @@ filegroup(
         "build_native.py",
         "linux_runtime.py",
         "macos_runtime.py",
+        "package_runtime.py",
         "runtime.py",
         "windows_runtime.py",
         ":source_inputs",
diff --git a/third_party/voice/assemble_package.py b/third_party/voice/assemble_package.py
index 74a4908552..7397f651ac 100644
--- a/third_party/voice/assemble_package.py
+++ b/third_party/voice/assemble_package.py
@@ -1,4 +1,4 @@
-"""Add a lifecycle-only helper to a fresh private copy of a canonical Codex package."""
+"""Add a helper and optional prepared runtime to a fresh private Codex package."""
 
 import argparse
 import hashlib
@@ -6,9 +6,23 @@ import json
 from pathlib import Path
 import re
 import shutil
+import sys
+
+# Import only this script's siblings, including under PYTHONSAFEPATH.
+sys.path.insert(0, str(Path(__file__).resolve().parent))
+from package_runtime import runtime_files
+from runtime import digest
 
 
-def assemble(package: Path, helper: Path, voice_target: str, commit: str, output: Path):
+def assemble(
+    package: Path,
+    helper: Path,
+    voice_target: str,
+    commit: str,
+    output: Path,
+    *,
+    runtime: Path | None = None,
+):
     package, helper = package.resolve(strict=True), helper.resolve(strict=True)
     output = output.absolute()
     if (
@@ -57,6 +71,17 @@ def assemble(package: Path, helper: Path, voice_target: str, commit: str, output
         raise ValueError("helper and app entrypoint must be regular files")
     if not suffix and not helper.stat().st_mode & 0o111:
         raise ValueError("helper is not executable")
+    inputs = {}
+    if runtime is not None:
+        runtime = runtime.resolve(strict=True)
+        if any(parent.samefile(package) for parent in (runtime, *runtime.parents)):
+            raise ValueError("runtime must be outside the input package")
+        if any(
+            parent.exists() and parent.samefile(runtime)
+            for parent in output.resolve().parents
+        ):
+            raise ValueError("output must be outside the runtime input")
+        inputs = runtime_files(runtime, voice_target)
     output.mkdir()  # Exclusive creation: never clean or overwrite a pre-existing output.
     try:
         shutil.copytree(package, output, dirs_exist_ok=True)
@@ -64,10 +89,19 @@ def assemble(package: Path, helper: Path, voice_target: str, commit: str, output
         destination = output / relative_helper
         destination.parent.mkdir(parents=True)
         shutil.copy2(helper, destination)
+        for relative, expected_digest in inputs.items():
+            copied = output / "codex-resources/voice" / relative
+            copied.parent.mkdir(parents=True, exist_ok=True)
+            shutil.copy2(runtime / relative, copied)
+            if digest(copied) != expected_digest:
+                raise ValueError("runtime file changed during copying")
         digests = {}
         for relative in (entrypoint, relative_helper):
             with (output / relative).open("rb") as source:
                 digests[relative] = hashlib.file_digest(source, "sha256").hexdigest()
+        digests.update(
+            {f"codex-resources/voice/{name}": value for name, value in inputs.items()}
+        )
         manifest = {
             "schemaVersion": 1,
             "buildCommit": commit,
@@ -91,7 +125,15 @@ if __name__ == "__main__":
     parser.add_argument("--voice-target", required=True)
     parser.add_argument("--build-commit", required=True)
     parser.add_argument("--output", type=Path, required=True)
+    parser.add_argument(
+        "--runtime", type=Path, help="prepared development runtime to include unchanged"
+    )
     args = parser.parse_args()
     assemble(
-        args.package, args.helper, args.voice_target, args.build_commit, args.output
+        args.package,
+        args.helper,
+        args.voice_target,
+        args.build_commit,
+        args.output,
+        runtime=args.runtime,
     )
diff --git a/third_party/voice/package_runtime.py b/third_party/voice/package_runtime.py
new file mode 100644
index 0000000000..73bdc02dff
--- /dev/null
+++ b/third_party/voice/package_runtime.py
@@ -0,0 +1,75 @@
+"""Validate prepared runtime files before copying them into a private package.
+
+The runtime receipt records preparation, not authenticity. Preserve its bytes and
+layout; native loader inspection remains the platform preparer's responsibility.
+"""
+
+import hashlib
+import json
+from pathlib import Path
+import re
+
+from runtime import PLUGINS, digest
+
+
+def runtime_files(root: Path, target: str) -> dict[str, str]:
+    manifest_path = root / "runtime.json"
+    if manifest_path.is_symlink() or not manifest_path.is_file():
+        raise ValueError("runtime manifest must be a regular file")
+    with manifest_path.open("rb") as source:
+        data = source.read(1024 * 1024 + 1)
+    if len(data) > 1024 * 1024:
+        raise ValueError("runtime manifest exceeds limit")
+    manifest = json.loads(data)
+    if (
+        manifest.get("schemaVersion") != 1
+        or manifest.get("developmentOnly") is not True
+        or manifest.get("target") != target
+        or manifest.get("sourceManifestSha256")
+        != digest(Path(__file__).with_name("sources.json"))
+        or not re.fullmatch(r"[0-9a-f]{40}", manifest.get("sourceCommit", ""))
+    ):
+        raise ValueError(
+            "runtime receipt does not match the source inputs and helper target"
+        )
+    if target.endswith("-apple-darwin"):
+        pattern, plugin = (
+            r"(?:lib|plugins)/[A-Za-z0-9_+.-]+\.dylib",
+            "plugins/libgst{}.dylib",
+        )
+    elif target.endswith("-unknown-linux-gnu"):
+        pattern, plugin = (
+            r"lib/(?:gstreamer-1\.0/)?[A-Za-z0-9_+.-]+\.so(?:\.[0-9]+)*",
+            "lib/gstreamer-1.0/libgst{}.so",
+        )
+    elif target.endswith("-pc-windows-msvc"):
+        pattern, plugin = r"bin/[A-Za-z0-9_+.-]+\.[dD][lL][lL]", "bin/gst{}.dll"
+    else:
+        raise ValueError("unsupported native runtime target")
+    libraries = manifest.get("libraries", [])
+    if not 1 <= len(libraries) <= 128:
+        raise ValueError("unexpected runtime inventory size")
+    files, names = {}, set()
+    for record in libraries:
+        name, expected = record["path"], record["sha256"]
+        if not re.fullmatch(pattern, name) or name.casefold() in names:
+            raise ValueError("invalid or colliding runtime path")
+        path = root / name
+        if (
+            path.parent.is_symlink()
+            or path.is_symlink()
+            or not path.is_file()
+            or not path.resolve().is_relative_to(root)
+        ):
+            raise ValueError("runtime entries must be regular files inside the input")
+        if not re.fullmatch(r"[0-9a-f]{64}", expected) or digest(path) != expected:
+            raise ValueError("runtime file digest mismatch")
+        names.add(name.casefold())
+        files[name] = expected
+    plugins = sorted(plugin.format(name) for name in PLUGINS)
+    if sorted(manifest.get("plugins", [])) != plugins or not set(plugins).issubset(
+        files
+    ):
+        raise ValueError("runtime must include exactly the selected plugins")
+    files["runtime.json"] = hashlib.sha256(data).hexdigest()
+    return files
diff --git a/third_party/voice/test_assemble_package.py b/third_party/voice/test_assemble_package.py
index 149a2138b6..862db02694 100644
--- a/third_party/voice/test_assemble_package.py
+++ b/third_party/voice/test_assemble_package.py
@@ -2,12 +2,17 @@
 
 import hashlib
 import json
+import os
 from pathlib import Path
+import shutil
+import subprocess
+import sys
 import tempfile
 import unittest
 from unittest.mock import patch
 
 from assemble_package import assemble
+from runtime import PLUGINS, digest
 
 
 class AssembleTests(unittest.TestCase):
@@ -36,6 +41,230 @@ class AssembleTests(unittest.TestCase):
         self.helper.chmod(0o755)
         self.output = self.root / "installed copy"
 
+    def make_runtime(
+        self, target="aarch64-unknown-linux-gnu", plugin="lib/gstreamer-1.0/libgst{}.so"
+    ):
+        root = self.root / target
+        root.mkdir()
+        libraries = []
+        for name in PLUGINS:
+            path = root / plugin.format(name)
+            path.parent.mkdir(parents=True, exist_ok=True)
+            path.write_bytes(f"prepared {name}".encode())
+            libraries.append(
+                {"path": path.relative_to(root).as_posix(), "sha256": digest(path)}
+            )
+        manifest = {
+            "schemaVersion": 1,
+            "developmentOnly": True,
+            "target": target,
+            "sourceCommit": "b" * 40,
+            "sourceManifestSha256": digest(Path(__file__).with_name("sources.json")),
+            "plugins": [record["path"] for record in libraries],
+            "libraries": libraries,
+        }
+        (root / "runtime.json").write_text(json.dumps(manifest))
+        return root, manifest
+
+    def test_cli_packages_each_runtime_layout_without_changing_bytes(self):
+        for target, plugin in (
+            ("aarch64-unknown-linux-gnu", "lib/gstreamer-1.0/libgst{}.so"),
+            ("aarch64-apple-darwin", "plugins/libgst{}.dylib"),
+            ("aarch64-pc-windows-msvc", "bin/gst{}.dll"),
+        ):
+            with self.subTest(target=target):
+                runtime, receipt = self.make_runtime(target, plugin)
+                (runtime / "unlisted-file").write_bytes(b"must not ship")
+                windows = target.endswith("windows-msvc")
+                entrypoint = "bin/codex.exe" if windows else "bin/codex"
+                self.metadata.update(target=target, entrypoint=entrypoint)
+                (self.package / entrypoint).write_bytes(b"unchanged app")
+                (self.package / "codex-package.json").write_text(
+                    json.dumps(self.metadata)
+                )
+                output = self.root / (target + " packaged")
+                subprocess.run(
+                    [
+                        sys.executable,
+                        str(Path(__file__).with_name("assemble_package.py").resolve()),
+                        "--package",
+                        str(self.package),
+                        "--helper",
+                        str(self.helper),
+                        "--voice-target",
+                        target,
+                        "--build-commit",
+                        self.commit,
+                        "--output",
+                        str(output),
+                        "--runtime",
+                        str(runtime),
+                    ],
+                    check=True,
+                    capture_output=True,
+                    cwd=self.root,
+                    env={**os.environ, "PYTHONSAFEPATH": "1"},
+                )
+                voice = output / "codex-resources/voice"
+                self.assertFalse((voice / "unlisted-file").exists())
+                expected = {r["path"]: r["sha256"] for r in receipt["libraries"]}
+                expected["runtime.json"] = digest(runtime / "runtime.json")
+                self.assertEqual(
+                    {name: digest(voice / name) for name in expected}, expected
+                )
+                self.assertEqual(
+                    {name: digest(runtime / name) for name in expected}, expected
+                )
+                manifest = json.loads((voice / "manifest.json").read_text())
+                helper_name = "codex-voice-host.exe" if windows else "codex-voice-host"
+                self.assertEqual(
+                    manifest["sha256"],
+                    {
+                        entrypoint: digest(self.package / entrypoint),
+                        f"codex-resources/voice/bin/{helper_name}": digest(self.helper),
+                        **{
+                            f"codex-resources/voice/{name}": value
+                            for name, value in expected.items()
+                        },
+                    },
+                )
+
+    def test_rejects_invalid_runtime_receipts_before_creating_package(self):
+        runtime, original = self.make_runtime()
+        changes = [
+            {"target": "x86_64-unknown-linux-gnu"},
+            {"developmentOnly": False},
+            {"sourceManifestSha256": "0" * 64},
+            {"sourceCommit": "dev"},
+            {"plugins": original["plugins"][:-1]},
+            {"libraries": []},
+            {"libraries": original["libraries"] * 20},
+            {"libraries": original["libraries"] + [original["libraries"][0]]},
+        ]
+        for name in (
+            "../outside.so",
+            "lib/../outside.so",
+            "bin/codex-voice-host",
+            "lib/evil:stream.so",
+        ):
+            changes.append({"libraries": [{**original["libraries"][0], "path": name}]})
+        for change in changes:
+            with self.subTest(change=change), self.assertRaises(ValueError):
+                (runtime / "runtime.json").write_text(
+                    json.dumps({**original, **change})
+                )
+                assemble(
+                    self.package,
+                    self.helper,
+                    original["target"],
+                    self.commit,
+                    self.output,
+                    runtime=runtime,
+                )
+            self.assertFalse(self.output.exists())
+
+    def test_rejects_runtime_digest_changes_and_nested_output(self):
+        runtime, receipt = self.make_runtime()
+        nested = runtime / "new package"
+        with self.assertRaisesRegex(ValueError, "outside the runtime"):
+            assemble(
+                self.package,
+                self.helper,
+                receipt["target"],
+                self.commit,
+                nested,
+                runtime=runtime,
+            )
+        self.assertFalse(nested.exists())
+        (runtime / receipt["plugins"][0]).write_bytes(b"changed")
+        with self.assertRaisesRegex(ValueError, "digest mismatch"):
+            assemble(
+                self.package,
+                self.helper,
+                receipt["target"],
+                self.commit,
+                self.output,
+                runtime=runtime,
+            )
+        self.assertFalse(self.output.exists())
+
+    def test_rejects_runtime_inside_input_package(self):
+        runtime, receipt = self.make_runtime()
+        nested = self.package / "runtime-staging"
+        runtime.rename(nested)
+        (nested / "unlisted-file").write_bytes(b"must not ship")
+        sources = [nested, self.package]
+        alias = self.package.with_name("APP") / "runtime-staging"
+        if alias.exists():
+            sources.append(alias)
+        for source in sources:
+            with (
+                self.subTest(source=source),
+                self.assertRaisesRegex(ValueError, "outside the input package"),
+            ):
+                assemble(
+                    self.package,
+                    self.helper,
+                    receipt["target"],
+                    self.commit,
+                    self.output,
+                    runtime=source,
+                )
+            self.assertFalse(self.output.exists())
+
+    def test_rejects_symlinked_runtime_library_directories(self):
+        runtime, receipt = self.make_runtime()
+        outside = self.root / "outside"
+        (runtime / "lib/gstreamer-1.0").rename(outside)
+        try:
+            (runtime / "lib/gstreamer-1.0").symlink_to(
+                outside, target_is_directory=True
+            )
+        except OSError as error:
+            self.skipTest(f"symlink creation unavailable: {error}")
+        with self.assertRaisesRegex(ValueError, "regular files"):
+            assemble(
+                self.package,
+                self.helper,
+                receipt["target"],
+                self.commit,
+                self.output,
+                runtime=runtime,
+            )
+        self.assertFalse(self.output.exists())
+
+    def test_copy_revalidation_removes_only_new_output(self):
+        runtime, receipt = self.make_runtime()
+        original_copy = shutil.copy2
+        for changed_name in (receipt["plugins"][0], "runtime.json"):
+
+            def changed_copy(source, destination, **kwargs):
+                result = original_copy(source, destination, **kwargs)
+                if source == runtime.resolve() / changed_name:
+                    Path(destination).write_bytes(b"changed after validation")
+                return result
+
+            with (
+                self.subTest(changed_name=changed_name),
+                patch("assemble_package.shutil.copy2", changed_copy),
+            ):
+                with self.assertRaisesRegex(ValueError, "changed during copying"):
+                    assemble(
+                        self.package,
+                        self.helper,
+                        receipt["target"],
+                        self.commit,
+                        self.output,
+                        runtime=runtime,
+                    )
+            self.assertFalse(self.output.exists())
+            self.assertEqual(
+                json.loads((runtime / "runtime.json").read_text()), receipt
+            )
+            self.assertEqual(
+                (self.package / "bin/codex").read_bytes(), b"unchanged app"
+            )
+
     def test_copies_app_unchanged_and_records_distinct_linux_targets(self):
         assemble(
             self.package,