MCPJVM-371: Public rebuild action support for state-store Artifacts

[nimbly-dev]

Description

Once rebuild capability exists internally, Regression Suite needs a public MCP maintenance action so users and orchestrators can trigger deterministic state-store recovery without introducing a new top-level tool. This story exposes rebuild through artifact_management for public state-store maintenance.

This story should define the public request/response shape, scope selection behavior, summary output, and fail-closed behavior for rebuild.

Scope

In scope:

• Expose public rebuild action support through artifact_management
• Support bounded rebuild scope selection for relevant state surfaces such as run_state, correlation_state, and watcher_state
• Return deterministic summary output rather than unbounded raw scan dumps
• Preserve fail-closed behavior when required canonical Artifact evidence is missing or invalid

Out of scope:

• Storage implementation internals of rebuild logic
• Legacy backfill semantics
• Manual mutation of runtime-owned rows outside controlled maintenance actions

Acceptance Criteria

• Public rebuild action is available through artifact_management
• Rebuild request/response shape is bounded, deterministic, and fail-closed
• Response output provides a usable maintenance summary for agents/users
• The public action does not require a new top-level MCP tool
• Rebuild remains aligned with canonical Artifact-based recovery rather than ad hoc manual mutation

Implementation Notes

• Public rebuild should be a maintenance entrypoint only; actual row population still occurs through runtime execution flow or controlled rebuild logic.
• Keep summary output compact even for large projects.

Testing

• UT for rebuild input validation and scope normalization
• UT for summary response shaping
• IT for public rebuild invocation over existing canonical Artifacts
• IT for fail-closed behavior when required Artifact evidence is missing or invalid