fix(pm): make the staged agent-browser binary executable

The npm tarball ships every bin/agent-browser-* as 0644; agent-browser's
own postinstall sets the exec bit, and pm runs no postinstall. The first
browser_navigate auto-installs agent-browser and then fails with
PermissionError.

pm/packages.py

@@ -872,6 +872,10 @@ class AgentBrowser(BinaryPackage):
         for item in bin_dir.iterdir():
             if item.is_file() and item.name.startswith("agent-browser-") and item.name != keep:
                 item.unlink()
+        # The npm tarball ships every native binary as 0644; agent-browser's
+        # own postinstall sets the exec bit, and pm runs no postinstall.
+        kept = bin_dir / keep
+        kept.chmod(kept.stat().st_mode | 0o111)
 
 
 @register

tests/pm/test_agent_browser_package.py

@@ -0,0 +1,48 @@
+"""agent-browser staging leaves the kept native binary executable.
+
+The npm tarball stores every ``bin/agent-browser-*`` as 0644; agent-browser's own
+postinstall sets the exec bit, and pm runs no postinstall.
+"""
+
+import io
+import os
+import stat
+import tarfile
+
+import pytest
+
+from pm import Store, get_package
+
+
+def _npm_tarball(path, names):
+    with tarfile.open(path, "w:gz") as tar:
+        for name in names:
+            data = f"{name} fixture".encode()
+            info = tarfile.TarInfo(f"package/{name}")
+            info.size = len(data)
+            info.mode = 0o755 if name.endswith(".js") else 0o644
+            tar.addfile(info, io.BytesIO(data))
+
+
+@pytest.mark.skipif(os.name == "nt", reason="POSIX exec bit")
+@pytest.mark.parametrize("target", ["linux-arm64", "linux-x64", "darwin-arm64"])
+def test_staged_native_binary_is_executable(tmp_path, target):
+    package = get_package("agent-browser")
+    archive = tmp_path / "agent-browser.tgz"
+    _npm_tarball(archive, [
+        "package.json",
+        "bin/agent-browser.js",
+        "bin/agent-browser-linux-arm64",
+        "bin/agent-browser-linux-x64",
+        "bin/agent-browser-darwin-arm64",
+    ])
+    staged = tmp_path / "staged"
+    package.unpack(archive, staged, target)
+    package.stage(Store(tmp_path / "store"), staged, "fixture", target)
+
+    binary = package.binary(staged, target)
+    assert binary == staged / "bin" / f"agent-browser-{target}"
+    mode = binary.stat().st_mode
+    assert mode & stat.S_IXUSR and mode & stat.S_IXGRP and mode & stat.S_IXOTH
+    assert sorted(p.name for p in (staged / "bin").iterdir()) == sorted(
+        ["agent-browser.js", f"agent-browser-{target}"])