• POST /db/train: train zstd compression dictionaries for trainable keyspaces such as repos and events (plus feature-gated event/index keyspaces). the crawler, firehose, and backfill worker are paused for the duration and restored on completion. dictionaries are written to disk as dict_<name>.bin in the database folder, but a restart doesn't apply them to an existing database. a keyspace's compression is saved when the keyspace is created and reused on every later open, so a dictionary only gets used by a keyspace created while its file is already in the database folder (see fixed when the database is created).
• POST /db/compact: trigger a full major compaction of all database keyspaces in parallel. the crawler, firehose, and backfill worker are paused for the duration and restored on completion.