sandbox: native enforcement degrades silently on a manual 'make build' (no warning anywhere)

[FabioLeitao]

Version / branch / commit

main @ f30f550, built manually via go build (not make build-all).

OS and environment

LMDE 7 (gigi) / Linux 6.12 / Go 1.26.6 / amd64

Steps to reproduce

1. Clone the repo, build with go build -o zero ./cmd/zero (or plain make build) instead of
   make build-all.
2. Run zero sandbox policy.
3. Run zero doctor.

Expected behavior

Either the companion zero-linux-sandbox helper is produced by the normal build path too, or the
CLI/TUI actively surfaces that native sandbox enforcement is unavailable — ideally at the start of
a session that will run exec_command/write_file/etc, not only when a user thinks to run
zero doctor explicitly.

Actual behavior

zero sandbox policy reports:

enforcement_level: degraded
backend_native_isolation: false
backend_available: false
downgrade_reason: Linux sandbox helper is not available

bwrap is installed and functional — the missing piece is the zero-linux-sandbox companion
binary (cmd/zero-linux-sandbox/), which is only produced by make build-all, not by
make build/plain go build. Nothing outside of zero doctor (run explicitly) surfaces this —
the TUI and zero exec proceed normally with reduced isolation and no visible indication. A
session can run many tool calls with the native sandbox effectively off and nobody notices.

Root cause detail: selectPlatformBackend (internal/sandbox/manager.go) resolves the helper via
a plain $PATH lookup (lookupExecutable); it does not check the directory next to the running
zero binary (a different lookup path, findLinuxSandboxHelperCommand in
internal/sandbox/linux_helper.go, does check that, but it isn't what backend selection uses).

Relevant logs, screenshots, or error messages

$ zero sandbox policy
mode: enforce
network: deny
backend: unavailable
enforcement_level: degraded
requires_platform_sandbox: true
downgrade_reason: Linux sandbox helper is not available
backend_available: false
backend_native_isolation: false
warning: native process isolation unavailable on linux
warning: shell commands are not wrapped by a native platform sandbox

I have a candidate fix (TUI banner + persistent indicator, structured warning at the start of
zero exec, and producing zero-linux-sandbox from the normal make build target on Linux) on a
personal fork, tested against the full local gate (fmt, vet, full test suite, cross-compiled tests
for darwin/windows, lint, govulncheck — all green) — happy to open a PR against an approved issue
per CONTRIBUTING.md once/if this is triaged as worth fixing.

[Vasanthdev2004]

Two parts here, with different answers.

The missing helper on a plain go build is handled by #946, approved and waiting on merge: when zero-linux-sandbox is neither beside the binary nor on PATH, zero now execs itself as the helper, so a go build -o zero ./cmd/zero binary gets native enforcement as long as bwrap is installed. Once that lands, your first two steps report backend_available: true.

The visibility gap is real on its own and this issue stays open for it: today only zero doctor and zero sandbox policy say enforcement is degraded, and a TUI session or a zero exec run proceeds with reduced isolation and no notice. Approving for that part: a one-line notice at session start in the TUI and on stderr for exec whenever enforcement_level is degraded, naming the downgrade reason, wherever each surface already reports sandbox state.