bug: Podman driver picks the wrong host IP for the supervisor callback on multi-homed Linux hosts (regression from #2942)

User Story

As a user running the local Podman driver on a multi-homed Linux laptop (wired dock + Wi-Fi + Tailscale), I want openshell sandbox create to work without hand-editing the gateway config or bringing interfaces down.

Problem Statement

On a host with multiple network interfaces, the Podman driver and Podman disagree on which host IP host.containers.internal points to, so the in-container supervisor can't reach the gateway and provisioning fails.

• The gateway binds its callback listener to the default-route interface plus loopback: 192.168.1.27:17670 and 127.0.0.1:17670.
• The driver tells the supervisor to dial host.containers.internal:17670 and injects --add-host host.containers.internal:host-gateway.
• Podman resolves host-gateway to a different interface — here the Tailscale address 100.64.0.2 (wt0, CGNAT 100.64.0.0/10), where nothing listens. Bringing Wi-Fi down didn't help; Podman then used the Tailscale IP instead of the wired one.
• The supervisor's policy fetch fails, it exits 1, the sandbox container follows, and the sandbox enters Error.

The reported error is also misleading: ContainerExited: Container exited with code 0 refers to the sandbox container reacting to its supervisor dying. The real failure is only in the openshell-supervisor-<id> container logs.

Impact / Why This Matters

• Consequence: sandbox creation fails outright on multi-homed hosts (dock + Wi-Fi + VPN/mesh laptops are common), and the surfaced error points at the wrong container, so it's hard to diagnose.

• Workaround: set host_gateway_ip = "127.0.0.1" under [openshell.drivers.podman] in ~/.config/openshell/gateway.toml, then systemctl --user restart openshell-gateway. This works because the supervisor uses --network host, so loopback reaches the gateway's 127.0.0.1:17670 listener, and both host.containers.internal and 127.0.0.1 are cert SANs. The sandbox then reaches Ready.

  [openshell.drivers.podman]
  host_gateway_ip = "127.0.0.1"
  

• Why insufficient: it relies on an undocumented field and non-obvious reasoning about host-network loopback; it isn't discoverable from the error. The default should just work on multi-homed hosts.

Confirmed Regression (#2942)

Confirmed by version bisection: this is a regression introduced by PR #2942 (RFC 0012 sandbox architecture).

• 0.0.116 (does not contain #2942; tagged 2026-08-28): openshell sandbox create reaches a working sandbox shell with default config (no host_gateway_ip) on this multi-homed host. ✅
• 0.0.117-dev / current main (contains #2942, merged 2026-09-16 as c1f2e7189, first released in v0.1.0-pre.2): the same default config fails with Error, and only the host_gateway_ip = "127.0.0.1" workaround makes it succeed. ❌
• The gateway binds the same two listeners (192.168.1.27 + 127.0.0.1) on both versions, so the DefaultRouteInterface listener is not the trigger — the change is the callback path.

Mechanism:

• #2942 split the sandbox into two containers and moved the gateway callback onto a host-networked supervisor (crates/openshell-driver-podman/src/container.rs: supervisor.netns.nsmode = "host"). Previously a single container made the callback.

• The callback machinery predates #2942 and assumes bridge/pasta semantics: the DefaultRouteInterface listener negotiation is from #2492, and the host-gateway --add-host injection from #1637.

• Under the same --add-host host.containers.internal:host-gateway, the network mode changes what the alias resolves to:

  Network mode	host.containers.internal resolves to
  Bridge (--network openshell) — pre-#2942 style	169.254.1.2 (link-local host-gateway)
  Host netns (--network host) — #2942 supervisor	non-link-local host IP (here, the Tailscale interface)

• The supervisor even warns about this: host.openshell.internal maps to a non-link-local IP; trusted-gateway SSRF exemption disabled. The callback path was designed around a link-local host-gateway (bridge/pasta), which host networking does not provide. On a single-homed host the host-netns resolution still lands on a reachable IP; on a multi-homed host it selects the wrong interface, where nothing listens.

• Note: the host_gateway_ip = "127.0.0.1" workaround only works because the supervisor is now host-networked (an artifact of the #2942 change) and therefore shares the host loopback.

Acceptance Criteria

• A multi-homed Linux host reaches Ready with the Podman driver using default config (no manual host_gateway_ip).
• The supervisor reaches the gateway regardless of which interface Podman picks for host-gateway.
• When the supervisor can't reach the gateway, the phase error reports its failure reason, not ContainerExited: code 0.
• Covered by a test, or the multi-homed host_gateway_ip guidance is documented.

Reproduction Steps

1. On a Linux host whose interfaces differ from Podman's host-gateway resolution (e.g. wired dock + Wi-Fi + Tailscale), configure the Podman driver.
2. Run openshell sandbox create --provider <any>.
3. The sandbox enters Error during provisioning.

Confirm the mismatch:

ss -ltn | grep 17670
#   LISTEN ... 192.168.1.27:17670   (default-route iface)
#   LISTEN ...    127.0.0.1:17670

podman run --rm --network host --add-host host.containers.internal:host-gateway \
  registry.fedoraproject.org/fedora-minimal:latest getent hosts host.containers.internal
#   100.64.0.2  host.containers.internal   <-- Tailscale wt0, nothing listening there

Environment

• OpenShell: 0.0.117-dev.167+g7e7a8d561 (development build; regression absent in 0.0.116), installed with:

  curl -LsSf https://raw.githubusercontent.com/NVIDIA/OpenShell/main/install.sh | OPENSHELL_VERSION=dev sh
  

• OS / kernel: Fedora Linux 44 (Workstation) / 7.2.5-200.fc44.x86_64
• Podman: 5.8.4 (netavark)
• Driver: podman (rootless); gateway runs as the openshell-gateway systemd user service (native install, not containerized)
• Network: multi-homed — wired dock 192.168.1.27, Wi-Fi 192.168.1.75 (same subnet), Tailscale wt0 in 100.64.0.0/10

Related

Related: #2540, #1952, and the macOS cases #1519 / #1634. Distinct from #1909 (containerized gateway on Fedora 44).

Logs

Supervisor container (openshell-supervisor-<id>) — the actual failure:

WARN openshell_supervisor: Policy fetch failed, retrying
Error: × Policy fetch failed after 5 attempts: failed to connect to OpenShell server

Start with crates/openshell-driver-podman/src/container.rs and the supervisor callback path introduced by #2942. Reproduce the failure with the documented Podman host-network command and inspect the supervisor logs alongside the misleading phase error. Done means default configuration reaches Ready on a multi-homed Linux host, reports the supervisor's failure reason when unreachable, and has test coverage or documented guidance.