fix(web): make ~/downloads writable from inside a session - #320
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`~/downloads` is a symlink to /var/lib/agent-box-downloads/<user>, so a
write through it resolves outside /home and ProtectSystem=strict denied it
with EROFS. The agent unit's ReadWritePaths named the SITES dir and not the
downloads one — so the hand-off the canonical guide documents ("mv
./report.pdf ~/downloads/", then give out ${AGENT_BOX_URL}downloads/…) has
never worked from a session:
$ touch /var/lib/agent-box-downloads/agent/probe
touch: ... Read-only file system
Same guard as its neighbour: listed only when web.enable is on, since that
is what gates the tmpfiles rule that creates the dir, and an unconditional
entry fails the whole namespace setup with 226/NAMESPACE on a default
web-less box.
The test is the interesting part. web-surface.nix already exercised this
drop — but as `sudo -u agent` from the driver's root shell, which skips
ProtectSystem entirely, so it passed against a read-only directory. Both
documented flows now write through `nsenter -t <MainPID> -m -- runuser -u
agent`, the handle is hoisted so neither can drift back, and each asserts
its own dir is in the unit's ReadWritePaths.
Fixes #316.
lionello
approved these changes
Aug 21, 2026
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Fixes #316.
~/downloadsis a symlink to/var/lib/agent-box-downloads/<user>, so a write through it resolves outside/homeandProtectSystem=strictdenies it. The agent unit'sReadWritePathsnamed the sites dir and not the downloads dir, so the hand-off the canonical guide documents has never worked from inside a session:Found while trying to publish a screenshot for #317 from a session.
The fix
One entry, under the same
web.enableguard as its neighbour — the tmpfiles rule that creates the dir is gated too, and an unconditional entry fails the namespace setup with 226/NAMESPACE on a default web-less box (the failure modememory-protection.nixexists to catch).Why the existing test did not catch it
web-surface.nixalready exercised the drop — but assudo -u agentfrom the driver's root shell, which skipsProtectSystementirely, so it passed against a read-only directory. The~/sitessubtest right below it had already learned this lesson and usednsenter; the downloads one had not.Both documented flows now write through
nsenter -t <MainPID> -m -- runuser -u agent, with the namespace handle hoisted above the subtests so neither can drift back, and each asserts its own directory is in the unit'sReadWritePaths.Checks run
nix run .#assemble+module-generated-up-to-date— oknix run .#update-golden+golden-snapshot— ok. The golden diff is exactly two lines,ReadWritePaths=/var/lib/agent-box-downloads/{agent,robot}, and only undertests/golden/web/— the ungated (web-off) unit is untouched, which is the 226/NAMESPACE guard holding.module-single-file,multi-user— oknix eval .#checks.x86_64-linux.{web-surface,memory-protection}.drvPath— both evaluate (VM tests are x86-only; CI runs them)