feat(kubernetes): support PVC subPath driver config

[mjamiv]

Summary

Add Kubernetes driver-config support for mounting existing PVCs into the agent container with optional sub_path values. This gives deployments a narrow driver-owned storage topology for durable per-user PVC data without broad PodSpec overrides.

Related Issue

Fixes #2033

Changes

• Adds driver_config.kubernetes.volumes[] for PVC-backed pod volumes.
• Adds driver_config.kubernetes.containers.agent.volume_mounts[] for agent PVC mounts with optional sub_path.
• Defaults user-supplied PVC volumes and mounts to read-only unless read_only: false is explicit.
• Validates duplicate names, unknown volume references, protected mount paths, invalid sub_path values, and attempts to weaken read-only PVC volumes.
• Skips the default /sandbox workspace PVC injection when an explicit Kubernetes driver-config mount targets a path below /sandbox/.
• Documents the schema and a single-PVC multi-subPath example in the Kubernetes driver README and compute-driver reference docs.

Testing

• mise run pre-commit passes
  • Not completed: this environment initially lacked mise; after installing it, mise run pre-commit refused to run until the repo config was trusted. I did not run mise trust because it persistently changes local trust settings.
  • Ran direct underlying checks instead:
    • cargo fmt --all -- --check
    • cargo test -p openshell-driver-kubernetes
    • cargo clippy -p openshell-driver-kubernetes --all-targets -- -D warnings
    • npx --yes markdownlint-cli2@0.22.0 crates/openshell-driver-kubernetes/README.md docs/reference/sandbox-compute-drivers.mdx
    • UV_CACHE_DIR=.cache/uv uv run python scripts/update_license_headers.py --check
• Unit tests added/updated
  • Added positive validation coverage for a read-write PVC with multiple read-write subPath mounts.
• E2E tests added/updated (if applicable)
  • Not run locally; a k3d or Kubernetes cluster proof with a pre-existing PVC should verify actual subPath mounts and pod recreation behavior.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)
  • Published docs and the Kubernetes driver README are updated; no top-level architecture doc was needed for this driver-local config addition.

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[austin-shih]

Thanks for this — the caller-owned-PVC-by-claim_name + subPath model is exactly what disposable-pod / durable-per-user-storage deployments need. A few test-scope observations from the perspective of someone planning to run this pattern:

1. Positive validation coverage. The render test exercises a writable PVC, but it goes through sandbox_to_k8s_spec, which doesn't run validate(). The from_template tests are all rejection cases, so there's no happy-path assertion that a writable config is actually accepted. A test that from_template returns Ok for a read-write PVC with several RW subPath mounts (the real per-user shape: workspace, memory, sessions) would lock that path in.

2. Missing-PVC behavior is untested. When a referenced claim_name doesn't exist, behavior currently falls to the kubelet's FailedMount. Worth covering (ideally in e2e) so the failure surfaces clearly rather than as a stuck pod.

3. E2E is where the core claims live. The unit tests prove the pod template renders; they can't prove that a pre-existing PVC actually mounts at the subPaths, that the agent can read/write, that the default /sandbox injection is correctly skipped, and — most importantly — that data persists across pod recreation against the same PVC. The PR notes e2e wasn't run; a k3d-based e2e (pre-create PVC → create sandbox with this driver_config → verify mounts + RW → recreate referencing the same PVC → data persists) would de-risk the durability story.

Happy to help validate — we're deploying this exact pattern and can share e2e findings.

[mjamiv]

Thanks for the test-scope review. I added positive from_template validation coverage for a read-write PVC with multiple read-write sub_path mounts (workspace, memory, sessions) and also normalized the example names in the docs/tests to keep the contribution generic.

I agree the missing-PVC and durability claims need cluster-level coverage: kubelet FailedMount, actual subPath mount behavior, read/write checks, default /sandbox injection being skipped, and data surviving pod recreation all belong in k3d or Kubernetes e2e rather than unit tests.

[elezar]

Why are we redefining what should be shared across drivers (see driver_mounts::RESERVED_MOUNT_TARGETS)? Note that the openshell_core::driver_utils::SUPERVISOR_CONTAINER_* constants added to the list later would already be covered by /opt/openshell which is included in the shared list.

[elezar]

Review: PVC subPath driver config

Thanks for this — the direction is good and it correctly routes subpath/source/target validation through the shared openshell_core::driver_mounts module. Two themes below: code reuse (so the K8s driver doesn't become a fourth divergent copy of mount logic) and implementation issues (a few I'd gate merge on).

Code reuse / overlap with other drivers

All container drivers already converge on openshell_core::driver_mounts (Docker lib.rs:1779-1909, Podman container.rs:546-688), so subpath rules, NUL/empty checks, .. rejection, and the /sandbox + reserved-target base list are already unified. This PR reuses most of that — good. Remaining duplication worth consolidating:

1. path_is_or_under is an exact copy of the private fn in driver_mounts.rs:99-104. Make the shared one pub and import it instead of re-declaring.
2. default_true() is now defined a third time (already in docker/lib.rs:342 and podman/container.rs:136). Along with the #[serde(default = "default_true")] read_only: bool idiom, this belongs in the shared module.
3. Duplicate mount-target detection is identical in three places — Docker (lib.rs:1857-1917), Podman (container.rs:625-681), and now here. A shared validate_unique_mount_targets(&[...], driver_name) would collapse all three.
4. Protected-path list overlaps and risks drift. KUBERNETES_DRIVER_PROTECTED_MOUNT_PATHS repeats /etc/openshell, /etc/openshell-tls, /run/netns (already in driver_mounts::RESERVED_MOUNT_TARGETS) and redundantly lists SUPERVISOR_CONTAINER_DIR / SUPERVISOR_CONTAINER_BINARY, both already under /opt/openshell which the shared list covers. Since validate_kubernetes_mount_path calls validate_container_mount_target first, keep only the K8s-unique entries (/var/run/secrets/openshell, /spiffe-workload-api) locally and let the shared list cover the rest — otherwise the two lists will silently diverge.
5. Consider promoting the stricter path checks into the shared validator. validate_kubernetes_mount_path adds rejection of internal empty segments (/a//b), . segments, and surrounding whitespace — checks validate_container_mount_target lacks today (Docker/Podman currently accept /a//b). If these are correctness improvements, hoist them so every driver benefits and the K8s wrapper shrinks to just the protected-list check.

Correctly kept driver-local (don't hoist): the reserved volume-name list (PVC names are K8s-only), the PVC config structs, and the SPIFFE runtime-conflict check.

Note for reviewers: subpath support is intentionally inconsistent across drivers — Docker supports it on volume mounts, Podman rejects it (reject_subpath). This PR adding subpath for PVC mounts matches Docker; it's deliberate, not an oversight.

Implementation issues

Gate on these:

1. Validation is split across three sites with inconsistent handling of the same check. validate_kubernetes_mount_path is used in validate() (returns Err), in kubernetes_driver_volume_mount_to_k8s (.expect() — panics), and in has_explicit_sandbox_data_mount (.ok() — silently ignores). In the normal flow create_sandbox validates before rendering, so the panic is currently unreachable — but this PR widens the panic surface, since from_template() now fails on semantic checks (duplicate/reserved names, bad subpath, protected paths, read-only weakening), not just serde errors. Any future render path not preceded by validate_driver_config_for_sandbox will panic the driver instead of returning InvalidArgument. Render functions should take an already-validated, normalized config rather than re-parsing and .expect()-ing.

2. Re-validation at render exists only to recompute the normalized string. kubernetes_driver_volume_mount_to_k8s re-runs validate_kubernetes_mount_path / validate_mount_subpath purely to get the normalized mountPath/subPath. Validate once, store the normalized values on the struct, render from those — removes the redundant work and the panic in (1).

3. Reserved volume-name list duplicates pod-spec string literals. KUBERNETES_DRIVER_RESERVED_VOLUME_NAMES hardcodes "openshell-client-tls" and "openshell-sa-token"; the pod spec hardcodes the same literals (driver.rs:1465,1478). They match today, but if either managed volume is renamed the guard silently stops matching and a user volume could collide. Extract both to named constants used in both places (the other three already use constants).

Design — worth discussing:

4. Any subpath mount under /sandbox disables all default workspace persistence. has_explicit_sandbox_data_mount flips inject_workspace off for any mount at-or-under /sandbox, so the documented example (/sandbox/.openshell/workspace, /sandbox/.openshell/memory) makes /sandbox itself ephemeral image content while only the two leaf subpaths persist. Kubernetes supports nested volumeMounts, so disabling the whole workspace isn't strictly required — it's a coarse simplification that silently drops persistence for everything else under /sandbox. At minimum this needs a prominent warning in the docs/README; better, reconsider whether the default workspace should coexist with narrow user subpath mounts.

5. Double read-only opt-in is easy to trip. Both the PVC volume and the mount default to read_only: true, and the validator rejects a RW mount on a RO volume — so RW requires read_only: false in two places. Consider defaulting the mount's read_only from the volume's value to halve the opt-in.

Minor:

6. validate_kubernetes_reference_name and the claim_name check don't enforce DNS-1123 label syntax, so invalid-but-printable names pass driver validation and fail later at the API server.
7. validate_kubernetes_driver_runtime_mounts re-runs validate_kubernetes_mount_path on every mount already validated by validate() (~3× per create) — folds away once (1)/(2) land.

Checked and not issues: the reserved volume-name list does currently cover all five managed volume names; protected-path coverage of managed mounts (TLS, sa-token, supervisor) is complete via the protected list + shared RESERVED_MOUNT_TARGETS; mount_path_conflicts_with_protected_path correctly also blocks mounting a parent of a reserved path.

Net: approve the direction; I'd like 1–3 (and ideally reuse items 1–4) addressed before merge.

[elezar]

Review: PVC subPath driver config

Thanks for this — the direction is good and it correctly routes subpath/source/target validation through the shared openshell_core::driver_mounts module. Two themes below: code reuse (so the K8s driver doesn't become a fourth divergent copy of mount logic) and implementation issues (a few I'd gate merge on).

Code reuse / overlap with other drivers

All container drivers already converge on openshell_core::driver_mounts (Docker lib.rs:1779-1909, Podman container.rs:546-688), so subpath rules, NUL/empty checks, .. rejection, and the /sandbox + reserved-target base list are already unified. This PR reuses most of that — good. Remaining duplication worth consolidating:

1. path_is_or_under is an exact copy of the private fn in driver_mounts.rs:99-104. Make the shared one pub and import it instead of re-declaring.
2. default_true() is now defined a third time (already in docker/lib.rs:342 and podman/container.rs:136). Along with the #[serde(default = "default_true")] read_only: bool idiom, this belongs in the shared module.
3. Duplicate mount-target detection is identical in three places — Docker (lib.rs:1857-1917), Podman (container.rs:625-681), and now here. A shared validate_unique_mount_targets(&[...], driver_name) would collapse all three.
4. Protected-path list overlaps and risks drift. KUBERNETES_DRIVER_PROTECTED_MOUNT_PATHS repeats /etc/openshell, /etc/openshell-tls, /run/netns (already in driver_mounts::RESERVED_MOUNT_TARGETS) and redundantly lists SUPERVISOR_CONTAINER_DIR / SUPERVISOR_CONTAINER_BINARY, both already under /opt/openshell which the shared list covers. Since validate_kubernetes_mount_path calls validate_container_mount_target first, keep only the K8s-unique entries (/var/run/secrets/openshell, /spiffe-workload-api) locally and let the shared list cover the rest — otherwise the two lists will silently diverge.
5. Consider promoting the stricter path checks into the shared validator. validate_kubernetes_mount_path adds rejection of internal empty segments (/a//b), . segments, and surrounding whitespace — checks validate_container_mount_target lacks today (Docker/Podman currently accept /a//b). If these are correctness improvements, hoist them so every driver benefits and the K8s wrapper shrinks to just the protected-list check.

Correctly kept driver-local (don't hoist): the reserved volume-name list (PVC names are K8s-only), the PVC config structs, and the SPIFFE runtime-conflict check.

Note for reviewers: subpath support is intentionally inconsistent across drivers — Docker supports it on volume mounts, Podman rejects it (reject_subpath). This PR adding subpath for PVC mounts matches Docker; it's deliberate, not an oversight.

Implementation issues

Gate on these:

1. Validation is split across three sites with inconsistent handling of the same check. validate_kubernetes_mount_path is used in validate() (returns Err), in kubernetes_driver_volume_mount_to_k8s (.expect() — panics), and in has_explicit_sandbox_data_mount (.ok() — silently ignores). In the normal flow create_sandbox validates before rendering, so the panic is currently unreachable — but this PR widens the panic surface, since from_template() now fails on semantic checks (duplicate/reserved names, bad subpath, protected paths, read-only weakening), not just serde errors. Any future render path not preceded by validate_driver_config_for_sandbox will panic the driver instead of returning InvalidArgument. Render functions should take an already-validated, normalized config rather than re-parsing and .expect()-ing.

2. Re-validation at render exists only to recompute the normalized string. kubernetes_driver_volume_mount_to_k8s re-runs validate_kubernetes_mount_path / validate_mount_subpath purely to get the normalized mountPath/subPath. Validate once, store the normalized values on the struct, render from those — removes the redundant work and the panic in (1).

3. Reserved volume-name list duplicates pod-spec string literals. KUBERNETES_DRIVER_RESERVED_VOLUME_NAMES hardcodes "openshell-client-tls" and "openshell-sa-token"; the pod spec hardcodes the same literals (driver.rs:1465,1478). They match today, but if either managed volume is renamed the guard silently stops matching and a user volume could collide. Extract both to named constants used in both places (the other three already use constants).

Design — worth discussing:

4. Any subpath mount under /sandbox disables all default workspace persistence. has_explicit_sandbox_data_mount flips inject_workspace off for any mount at-or-under /sandbox, so the documented example (/sandbox/.openshell/workspace, /sandbox/.openshell/memory) makes /sandbox itself ephemeral image content while only the two leaf subpaths persist. Kubernetes supports nested volumeMounts, so disabling the whole workspace isn't strictly required — it's a coarse simplification that silently drops persistence for everything else under /sandbox. At minimum this needs a prominent warning in the docs/README; better, reconsider whether the default workspace should coexist with narrow user subpath mounts.

5. Double read-only opt-in is easy to trip. Both the PVC volume and the mount default to read_only: true, and the validator rejects a RW mount on a RO volume — so RW requires read_only: false in two places. Consider defaulting the mount's read_only from the volume's value to halve the opt-in.

Minor:

6. validate_kubernetes_reference_name and the claim_name check don't enforce DNS-1123 label syntax, so invalid-but-printable names pass driver validation and fail later at the API server.
7. validate_kubernetes_driver_runtime_mounts re-runs validate_kubernetes_mount_path on every mount already validated by validate() (~3× per create) — folds away once (1)/(2) land.

Checked and not issues: the reserved volume-name list does currently cover all five managed volume names; protected-path coverage of managed mounts (TLS, sa-token, supervisor) is complete via the protected list + shared RESERVED_MOUNT_TARGETS; mount_path_conflicts_with_protected_path correctly also blocks mounting a parent of a reserved path.

Net: approve the direction; I'd like 1–3 (and ideally reuse items 1–4) addressed before merge.