test(checkpoint): cover baseline guard edge cases

[fennoai]

Requested by @Yumiue

Summary

• add runtime tests for baseline restore session mismatch, missing code snapshot, and guard creation cleanup
• add a frontend vitest localStorage fallback so FileChangePanel and eventBridge tests run reliably in this environment
• validate with go test on internal checkpoint/runtime packages and targeted web vitest suites

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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