[abhinavrastogi2627]

Problem

Settings persistence currently truncates settings.json before writing it. Another CLI process can read an empty or partial document, and a serialization error can erase the previous valid configuration.

Change

Write to a mode-0600 temporary file in the destination directory, sync and close it, then replace the settings file by rename. Preserve a configured symlink by replacing its target, and remove temporary files on failure. Record the resolved configuration path after initial loading/creation so the first save also uses this path.

Validation

• Two new regressions failed on the original implementation: an already-open reader saw the replacement contents, and a serialization failure left an empty configuration.
• All five settings tests pass with go test -race ./internal/settings -count=10, including original permissions coverage, symlink preservation and failed-replacement cleanup.
• On macOS, go test ./... has one failure, TestGetReservedBytes (12 versus expected 0); the same test fails identically on unchanged upstream cc95e98. The complete suite passes when that known baseline failure is skipped.
• go vet ./..., go build ./..., Staticcheck 2025.1.1, the workflow's pinned sqlclosecheck, and git diff --check pass. go mod tidy produces no dependency changes.

Limits

Atomic replacement prevents torn reads; this does not merge concurrent writers' independent updates. Rename atomicity depends on the operating system/filesystem, and this change does not claim power-loss durability of the parent directory or Windows validation. Initial configuration creation and explicit --reset-config retain their existing behavior.

Fixes #911