test(drivers): pin root rejection for image-mapped policy identities in Docker and Podman #3653

User Story

As a custom-image operator, I want regression tests ensuring image account lookup cannot turn an accepted policy name into a root workload.

Problem Statement

Docker and Podman resolve policy process.run_as_user and process.run_as_group names against the image's passwd/group files. After lookup, ResolvedWorkloadIdentity::new rejects UID/GID 0 (since #2942). #2578 treats image account data as untrusted input. This requests resolver-level regression tests, not new production checks.

The existing tests use OCI USER or policy root, not an accepted policy name resolving to 0 (test citations below). The security identity table attributes the identity change to the supervisor; it is done by the sandbox runtime's launcher (openshell-sandbox), after the driver's lookup and zero check, and the table describes neither.

Impact / Why This Matters

Existing tests could miss a resolver bypassing the constructor or resolving names after the zero check.

Proposed Design

Test image-mapped policy identities in both resolvers and correct the security identity table.

Acceptance Criteria

• Both resolvers reject validator-accepted policy names, including sandbox, mapped to UID 0 or GID 0, with a valid non-root control.
• Security docs credit the sandbox runtime for the identity change and describe image account lookup followed by the driver's numeric zero check.

Alternatives Considered

Shared-constructor tests alone do not cover each resolver's policy-name lookup path.

Agent Investigation

Read policy validation, identity resolution, resolver tests, and security documentation at main a8f98ec; nothing executed.

• crates/openshell-policy/src/lib.rs:853-860: accepts sandbox or an in-range numeric ID, not root.
• crates/openshell-driver-docker/src/lib.rs:621-693, crates/openshell-driver-podman/src/isolation.rs:85-182: image account lookup, then ResolvedWorkloadIdentity::new.
• crates/openshell-isolation-interface/src/contract.rs:212-223: rejects UID/GID 0.
• crates/openshell-driver-podman/src/isolation.rs:442-454: OCI USER test; crates/openshell-driver-docker/src/tests.rs:1515-1526: policy root/root test.
• docs/security/best-practices.mdx:211-212: supervisor attribution; no image-name lookup or post-resolution check. The calls are in crates/openshell-sandbox/src/main.rs:1456-1467.

Checklist

• I've reviewed existing issues and the architecture docs
• This is a design proposal, not a "please build this" request