Validate safeWriteJson replacement and recovery with native Windows file handles #2178

The JSON persistence caller audit identified a Windows validation gap.

Source: src/utils/safeWriteJson.ts.

The writer commits with one rename and enters a two-rename fallback only for EPERM. Fault-injection tests exercise that branch. They do not establish the error codes or replacement behavior produced by real Windows file handles.

Proposed scope:

• Run native Windows tests with a reader that has explicit handle-sharing flags.
• Record OS and Node versions and the observed rename errors.
• Check both direct replacement and the fallback.
• Check interruption between fallback renames, backup restoration, and lock handling.
• Decide whether EBUSY or EACCES require changes only after collecting platform evidence.

Acceptance:

• Previously committed content remains readable or recoverable after each injected interruption.
• Failed restoration preserves committed backups.
• Tests identify when Windows permits or rejects replacement.
• The documented fallback matches observed platform behavior.
• CI or an equivalent reproducible Windows run records the result.

This is a validation gap, not a claim that an additional error code must trigger the fallback.