[rlrs]

Plan item P7, worker half: sandbox workers no longer have a Docker image path.

What goes

• build_direct_runtime_service's DockerOverlay2RootfsStore branch, its docker_binary, and the overlay2 rootfs_format in boot_config_sha256. The agent refuses to start without the environment registry and backend socket. serve-direct-node-agent drops --docker-binary (vm_init never rendered it) and its DockerImageRuntime.
• image_eviction.py (LRU Docker image evictor), the provisioner's image_evictor, and the node agent's pre-pull eviction, post-pull note_used and forget_evicted_images.
• DockerOverlay2RootfsStore's worker-only methods: list_image_ids, image_tag_times, image_present, image_content_id, evict_image, _docker_time_seconds.
• Gateway OCI-pull paths: the 2 s create image wait and the 32-pull background cap. Every create now waits up to 30 s for its attach. The gateway imports external images whenever immutable_environments is set.
• immutable_environments.worker_enabled as a switch.

Code −347/+49, tests −210/+53, including image_eviction.py (145) and test_image_eviction.py (129).

Kept

• sandbox.max_concurrent_image_pulls, which bounds environment attaches.
• vm_init is untouched. The sandbox role's Docker setup and docker_quota_image_gb stay, because that quota mount holds UCLOUD_DIRECT_IMAGE_CACHE_ROOT. dockerd and the agent unit's After=/Requires=docker.service also stay: Docker's FORWARD DROP policy must be in place before the agent sets ip_forward=1, and the guest init is docker-init.
• The DockerOverlay2RootfsStore class stays for builders (R6).
• Three paths stay because the LocalFleet harness's default Docker-ABI LocalRootfsStore still uses them: the provisioner's non-idle collect_image path, the agent's image_materializer for a non-materializing runtime, and OverlayRootfsManager's overlay2 bundle branches. They should go with R6 once the harness defaults to environments.

Evidence (2026-10-24, read-only)

• deployment.json has immutable_environments.worker_enabled: true.
• All 6 live sandbox workers (agent 0.10.0) advertise immutable-environment-host-erofs-v1. The agent advertises that capability only when EnvironmentRootfsStore is selected.
• So no removed worker path ran in production.

Compatibility and rollback

• worker_enabled is accepted only as true. A file without the key also loads. Any other value is refused with "delete the key". to_dict writes it as true.
• 0.10.0 reads a missing key as false, so on a rollback keep worker_enabled: true in deployment.json. Then the same deployment.json loads and workers stay on environments.
• A deployment without immutable_environments can no longer start sandbox workers.
• CHANGELOG ## Unreleased has the operator notes.

Checks

• uv run ruff check sandboxes tests scripts: clean.
• scripts/check_test_rules.py: baseline lowered for test_direct_runtime_assembly.py, which lost its private-member Docker fixtures.
• Full suite with PostgreSQL (run_tests.py -j 6): 2446 pass, 26 skip, 0 fail.
• After rebasing onto shared_control: fold the additive DDL into the schema files #40, I re-ran only the affected modules, not the full suite. They pass.
• No Rust changes.
• New test: a worker without immutable environments refuses to start and creates nothing.

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