SEA binary resolution uses an expired importlib.resources temporary path #354

Description

_resource_binary_path() returns the path yielded by importlib.resources.as_file() after leaving the context manager. For resources backed by a ZIP importer, that path is a temporary extraction which is deleted when the context exits. resolve_binary_path() then passes the expired path to _copy_to_cache(), where read_bytes() fails.

The cache copy appears to be the intended mechanism for non-filesystem package resources, but it currently happens too late.

Reproduction

The lifetime problem can be reproduced with any ZIP-backed package resource:

import importlib
import sys
import tempfile
import zipfile
from pathlib import Path
import importlib.resources as resources

with tempfile.TemporaryDirectory() as directory:
    archive = Path(directory) / "package.zip"
    with zipfile.ZipFile(archive, "w") as output:
        output.writestr("example_package/__init__.py", "")
        output.writestr("example_package/binary", b"binary")

    sys.path.insert(0, str(archive))
    importlib.invalidate_caches()

    resource = resources.files("example_package").joinpath("binary")
    with resources.as_file(resource) as extracted:
        returned = extracted
        print(returned.exists())  # True

    print(returned.exists())      # False

Stagehand follows this exact pattern at src/stagehand/_custom/sea_binary.py:60-61, then attempts to read the returned path at line 73.

Expected behavior

The packaged binary should be copied into Stagehand's persistent cache while the as_file() context is still active, or the context lifetime should otherwise cover the copy.

Actual behavior

For a ZIP-backed Traversable, _resource_binary_path() returns a deleted temporary path and local-mode resolution fails before startup.

Why this matters

Normal wheel installs are usually unpacked, which hides the defect. ZIP imports, zipapps, and packaging/deployment systems that expose resources through a non-filesystem loader exercise the temporary-resource path that this code is intended to support.

Prior-art check

I searched open/closed issues and PRs for zipimport, importlib.resources.as_file, packaged resource lifetime, and _resource_binary_path and found no existing report.