## Why
Concurrent Linux test spawns can inherit writable descriptors for executable fixtures, preventing those fixtures from being executed even after the writing test closes its descriptor.
## What changed
Replace direct executable fixture writes and copies across the Rust tests with `codex_utils_cargo_bin::write_executable` and `copy_executable`. These existing helpers complete writes and copies in separate processes on Linux.
Remove the empty temporary inode before creating fake bubblewrap executables, and stage tampered bubblewrap bytes in a separate data file before copying them into the executable fixture. Add the required test dependencies.
GitOrigin-RevId: c875c83088731a4933ef1574e8d79d8cecc12f54
## Why
The voice helper previously supported only handshake and shutdown, without
validating that its packaged native runtime could be initialized safely.
## What changed
- Add an `initializeRuntime` protocol exchange that loads GStreamer and the
required plugins from physical package paths without opening audio devices.
- Restrict plugin discovery, registry access, and native library search paths,
and keep loaded libraries alive until the helper exits.
- Give initialization a dedicated deadline and terminate the owned helper when
initialization is cancelled or fails.
- Allow binary-only Rust targets to disable the default Bazel library target.
## Testing
- Cover helper-only packages, cancellation, and environment filtering.
- Add an ignored integration test for initialization from a relocated prepared
runtime and rejection of duplicate initialization.
GitOrigin-RevId: 8fff68fe26e52cb2e0722dc98fb5f124eddb0d4d
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