React Strict Mode disposed the memoized content-cache owner while the provider kept reusing it, so validateContextFileOpen threw before any /api/fs/read and toasted "Failed to open file" for notes.txt. Binaries still opened because they skip the pre-read. Serve uncached reads from disposed owners, clear cache on runtime switch without deactivating, and own the cache lifecycle in an effect. Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>