fix(sites): don't list the snippet dir in ReadWritePaths when web.enable is off

[defangdevs]

Master is red and, more importantly, a default (web-less) agent-box no longer starts any agent sessions.

What broke

7b687b9 (the fix for #195, ~/sites being read-only in the agent's own namespace) added /var/lib/agent-box-sites/<user> to the agent unit's ReadWritePaths unconditionally. The tmpfiles rule that creates that directory lives inside mkIf (cfg.enable && cfg.web.enable), and web.enable is a mkEnableOption — default off. With web off the path never exists, and ProtectSystem=strict namespace setup fails hard:

agent-box-agent.service: Failed to set up mount namespacing:
  /var/lib/agent-box-sites/agent: No such file or directory
agent-box-agent.service: Failed at step NAMESPACE ... status=226/NAMESPACE

The unit never starts — no tmux sessions at all — and restart-loops (the counter passed 427 in the CI run). tests/memory-protection.nix, the only test that runs with web off, timed out on wait_for_unit: https://github.com/defangdevs/agent-box/actions/runs/31016454644

The parent commit's reasoning ("tmpfiles-created at sysinit, long before this unit, so no - prefix") is right about ordering — it just doesn't hold when the rule isn't emitted at all.

The fix

Guard the entry on cfg.web.enable, mirroring what gates the tmpfiles rule.

Deliberately still no - prefix: a directory that is genuinely missing while web is on should fail loudly rather than silently reverting to the EROFS that #195 was about.

Verification

Both node configs evaluated directly, no VM boot needed:

config	effective ReadWritePaths
web off (memory-protection)	["/home/agent"]
web on (self-serve-domain)	["/home/agent" "/var/lib/agent-box-sites/agent"]

So the #195 flow keeps working where it applies, and the web-off box boots again.

memory-protection now asserts the entry is absent, so the web-off case has an explicit guard instead of only failing indirectly via wait_for_unit.

Also run natively on aarch64: module-generated-up-to-date (regenerated modules/agent-box.nix from .nix.in), the ty/ruff testScript gate, and a drvPath eval of all seven VM tests.

Note: the deploy-test leg is expected-red on master for unrelated reasons (#186/#190).

Opened from a webhook triage session that picked up the #195 close event.

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https://claude.ai/code/session_014Kq2nqcWR5Y6aryf8WzWbs