0243 — topic_id joins the keys of cursor/deliveries/binding; lease gets the column only

Context. With each topic owning its own id sequence, a bare message_id can refer to completely different messages in two topics’ tables, and a group’s claimed/committed are meaningless without knowing which message_log_<topic_id> sequence they count against.

Decision. cursor’s PK became (consumer_group, topic_id), deliveries’ PK became (consumer_group, topic_id, message_id), and binding gained topic_id alongside consumer_group/pattern with its index widened — each folded into that table’s original migration. lease gained the topic_id column without a key change, because the lease token is already a unique random id that disambiguates a row on its own; the column is there only to make what the lease tracks unambiguous.

Consequences. Every table that references message ids or per-log positions names its topic explicitly. Key width is paid only where identity actually requires it — lease shows the rule: a column for clarity is not the same decision as a column in the key.