[BUG] `--dir=/etc/alternatives` mount is not read‑only inside sandbox

[ombagal777]

Description

The isolate invocation includes --dir=/etc/alternatives=/etc/alternatives without the :ro suffix. Isolate’s --dir option supports dest=src:ro to mount directories read‑only, but the current configuration mounts /etc/alternatives as writable from inside the sandbox.

This unnecessarily exposes system alternative configuration to potential modification from sandboxed processes if they manage to bypass other protections.

Impact

• Sandbox processes may be able to write to /etc/alternatives inside the container/host namespace, depending on user and isolation settings.
• Could allow tampering with alternative symlinks or binaries, increasing the blast radius of a sandbox escape.

Expected Behavior

• /etc/alternatives should be mounted read‑only using :ro so sandboxed processes cannot make changes.

Actual Behavior

• /etc/alternatives is mounted without :ro, allowing potential writes from within the sandbox.

Possible Solution

• Update the isolate command in core/sandbox.ts to:
  • --dir=/etc/alternatives=/etc/alternatives:ro
• Re‑run tests to ensure no language runtime relies on write access to /etc/alternatives.