fn delete_split_tokens(ns: &str)Expand description
Delete every entry the chunked per-field layout could have written
(FIELD_ACCESS/FIELD_REFRESH/FIELD_ID’s chunks + :count + :gen).
Shared by muxbus_clear (unconditional logout cleanup, any platform) and
the macOS/Linux migration path in muxbus_load_tokens (collapsing a
pre-fix install’s chunked entries into the single-blob format — see
blob_key’s doc comment). Best-effort: secret_store::delete
on a non-existent entry is a no-op success, and a real delete failure here
just leaves an orphaned, unreadable-without-the-others chunk behind rather
than losing anything live.