Make sure no checkpoint will be generated in read-only mode

[zhanglei1949]

Including auto checkpoint and manual checkpoint.

[github-actions]

🤖 Auto-triage: linked as sub-issue of #272 — Refine checkpoint mechanism (confidence: high).

Reason: The issue is about preventing checkpoint generation (auto and manual) in read-only mode, which falls squarely under the checkpoint mechanism refinement tracked by #272.

Auto-applied: labels → store

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