fix(node-client-sdk): better handling for bad filesystem states

[joker23]

• make sdk refuse to load persistent cache from symlinks (as a security measure)
• fallsback to inmemory store if filesystem loading fails (instead of throwing)
• additionally, exposing ConnectionMode type for downstream reference

---

Note

Medium Risk
Changes filesystem trust boundaries and persistence behavior for the local flag cache; misconfigured hosts may silently lose cross-restart persistence, but runtime flag access should remain available.

Overview
Hardens NodeStorage local flag cache initialization so unsafe or broken filesystem layouts no longer redirect reads/writes or leave the SDK unusable.

If the storage directory is a symlink, the cache file is not a regular file, or init otherwise fails (including when fixing a malformed cache cannot be written), persistence is disabled and the SDK warns once and keeps serving flags from an in-memory map. get/set/clear no longer log errors on init failure; disk flushes are skipped when persistence is off. Symlinked ldcache.json paths are treated as malformed and discarded without loading symlink targets.

Also re-exports ConnectionMode from LDCommon for downstream typing. Tests were expanded for symlink, file-at-path, and fallback scenarios; platform tests expect the init-fallback warn instead of storage errors.

^{Reviewed by Cursor Bugbot for commit ced01fd. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 26365 bytes
Compressed size limit: 29000
Uncompressed size: 129044 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 32027 bytes
Compressed size limit: 34000
Uncompressed size: 114248 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 38747 bytes
Compressed size limit: 39000
Uncompressed size: 212249 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 179504 bytes
Compressed size limit: 200000
Uncompressed size: 831427 bytes

[joker23]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit ced01fd. Configure here.}

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.