feat(charts): mount rootfs diff for PageBroker

[dfeigin-nv]

Adds the optional rootfs-diff mount used by the PageBroker-enabled agent image.

Validation: Helm lint and render.

Summary by CodeRabbit

• New Features
  • Added an optional setting to configure the host directory for container runtime snapshots and overlay upper directories.
  • When omitted, the appropriate default directory is selected automatically based on the container runtime.

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📥 Commits

Reviewing files that changed from the base of the PR and between 3342f11 and 6cf0834.

📒 Files selected for processing (2)

• charts/snapshot/templates/_helpers.tpl
• charts/snapshot/values.yaml

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Walkthrough

The snapshot chart now accepts runtime.storageDir. The helper uses this value when set and retains runtime-specific defaults when it is empty.

Changes

Runtime storage configuration

Layer / File(s)	Summary
Storage directory override charts/snapshot/values.yaml, charts/snapshot/templates/_helpers.tpl	The chart adds runtime.storageDir and resolves it before the existing CRI-O or containerd defaults.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to 6cf08

This change adds an optional rootfs-diff mount for the PageBroker-enabled agent image; no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 7

✅ Passed checks (7 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title uses the valid feat Conventional Commit prefix, stays under 72 characters, and describes the rootfs-diff mount change.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (2 skipped: 2 unsupported.)
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Breaking Api Changes	✅ Passed	The topic diff changes no API fields, Go field types, JSON tags, or PodSnapshot immutability markers; its only api/** change adds two constants.
Rbac Least Privilege	✅ Passed	The pull-request patch changes only runtime storageDir Helm values and helper logic; it adds no RBAC marker or Helm RBAC wildcard grant.

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[dfeigin-nv]

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