[antonreshetov]

Notes, snippets, HTTP requests, folder .meta.yaml, state.json / .state.yaml and doctor id fixes were written with fs.writeFileSync over the existing file. It truncates first, so ENOSPC/EIO in the middle of a write left a cut-off file on disk even though the runtime rolled back.

• Add writeFileAtomicSync in runtime/shared/atomicWrite.ts: write a hidden .<name>.<hex>.tmp next to the target, then renameSync over it. Preserves the file mode, writes through symlinks, removes the temp file on failure, falls back to an in-place write on Windows when the target is locked by another process.
• Use it in all vault writers listed above.
• Tests: unit tests for the helper, partial-write and failed-rename cases for notes and snippets; path-keyed write mocks moved to renameSync.

Checked on a real iCloud Drive vault with the dev build: repeated saves, rename/move, external edits picked up by the watcher, upload without conflicts, content verified after eviction, edits blocked until a dataless note is downloaded.