Inserts or replaces a key/value pair and updates LRU ordering. This resets TTL to `None` and triggers eviction when over budget.

Looks up a key, updates LRU, and returns its value if present. Expired entries are removed on access to keep memory usage stable.

Sets a TTL for an existing key. Missing or expired keys return `HkvError::NotFound`.

Attempts to parse a single command from the buffer. Returns `Ok(None)` if more data is required.

Removes a node by index and returns its byte size. This updates the map, LRU links, and free list.

Reads one RESP value from the buffered reader.

Records the start of a request. Call this when a request is accepted to increment totals and in-flight.

Starts a background thread that periodically removes expired entries. The returned handle must be stopped to avoid leaking the thread.

Stops the sweeper and waits for the thread to finish. Use this in tests or shutdown hooks to avoid leaking threads.

Returns a snapshot of all counters and histogram buckets.

Returns true when the entry has expired at `now`. Used on access to keep the hot path simple and predictable.

Removes expired entries across all shards. This walks only per-shard TTL heap heads plus any stale heap entries.

Serves accepted TCP connections until shutdown is triggered. The shutdown signal stops new accepts immediately, then drains active connections for a

Returns the shard responsible for a given key.

Returns the histogram upper bound that satisfies the requested percentile.

Records the end of a request. Call this on completion to decrement in-flight and capture latency.

Returns a fresh token for TTL heap scheduling.