Struct Inner 

struct Inner {
    watched_paths: HashMap<PathBuf, HashSet<String>>,
    pool_subs: HashMap<PathBuf, Subscription>,
}

Fields

watched_paths: HashMap<PathBuf, HashSet<String>>

Canonicalized file path -> block ids with a tab open on it.

pool_subs: HashMap<PathBuf, Subscription>

One pool subscription per watched path — held so it can be handed back to pool.unsubscribe once the last block id for that path unsubscribes. The pool does its own OS-level refcounting internally; this is a different refcount (by block id, which the pool has no concept of), so both layers of bookkeeping are genuinely needed.