test(tui): delivery_tests sandbox case fails when the workspace lives under /tmp (bwrap --tmpfs /tmp shadows it)

Observed (deterministic, isolation)

On the CI lane (x86_64 Linux), the sandbox delivery test fails whenever the test workspace is a tempfile under /tmp:

cargo test -p codewhale-tui --lib --locked \
  tools::subagent::delivery_tests::enforced_readonly_python_queries_sqlite_under_a_live_peer_write_claim -- --exact

panicked: called `Result::unwrap()` on an `Err` value:
  Failed to execute tool: bwrap: Can't chdir to /tmp/.tmpN8FjYQ: No such file or directory

Root cause

crates/tui/src/sandbox/bwrap.rs mounts --tmpfs /tmp and then binds the workspace roots. A workspace that itself lives under /tmp is shadowed by the tmpfs, so the subsequent --chdir <workspace> targets a path that no longer exists inside the sandbox.

Pre-existing?

Yes — it fails identically at the pre-change control commit for the current fleet work, and the code path is untouched by it. It is a test-environment interaction, not a product regression.

Suggested fix

Test-side: create the sandbox fixture workspace outside /tmp on Linux (the crate already knows the sandbox layout). Do not weaken the --tmpfs /tmp isolation, which is deliberate.

Seen during the 2026-09-17 fleet-rework lane runs; reported by the Codewhale night program.