sandbox: auto-injected system paths incomplete for common dev workflows

[eliothedeman]

Problem

When default=deny sandboxes auto-inject system read paths (via _SYSTEM_READ_PATHS in std.star), the list is missing paths needed for common developer workflows:

• /var/folders / /private/var/folders — macOS per-user temp directories
• /private/var/db/timezone — timezone data (git, curl need this)
• ~/.gitconfig — any git operation reads this
• ~/.ssh — git SSH signing and remote operations

Users end up manually adding these paths through trial and error, leading to messy policies.

Proposal

Consider a tiered approach:

1. Always inject: paths needed for any process to run (dyld, system libs, timezone, var/folders)
2. Inject when net=allow: DNS-related paths
3. Document per-tool: which paths git, cargo, node, python need so stdlib presets cover them