Task: Record each business event as a trade activity

Every business event on a trade is one append-only trade_activity row, and booking writes it in the same transaction.

• trade_activity is append-only: type, actor, time, comment and an operational-error flag; an update or delete is refused.
• The booking operation writes the activity with the anchor, booking and state, and returns its id.
• A null amend is recorded as an activity and versions nothing.

• trade_activity is an immutable entity, like the trade: id, party, activity type, actor, the time the event occurred, a comment and an operational-error flag. It takes the read-only profile, so its handler serves reads only and every write goes through an operation.
• RLS: tenant isolation and strict party isolation, as on the trade. The purge loop already covers it, through the immutable purge switch.
• ores_trading_book_trade_fn writes the trade first, so a refused second booking writes nothing, then the activity, the booking and the state, and returns the activity id instead of a boolean. The service reads an empty result as the conflict and returns the id in book_trade_response.
• A null amend is an activity whose type is not real: recorded, and versioning nothing.
• The component versions still carry the activity type code; the next task replaces it with a foreign key to this row.

Every number this task claims about a tree, with the command that produced it and the commit it was measured at. A number without both is not a measurement, because a clean-up record describes a tree and trunk moves under a branch: a consumer count, a gate's component count and a suite's size all change with no code changing, and the reader of a bare number cannot tell which tree it came from. Where the raw output matters, put it in an evidence/ file beside the task and name that file in the Command column.

Manual QA scenarios (scaffolded via compass add test_scenario) that verify this task. Link new ones here as they're created; the scenario doc itself links back via its "Verifies task" field.

trade_activity records each business event once: type, actor, when it happened, a comment and an operational-error flag, under tenant and party isolation, and refuses any update or delete. Booking a trade writes its activity in the same transaction and returns the activity id; a refused second booking writes none. A null amend is recorded as an activity and versions nothing. The ACME import now leaves one new_booking activity per trade, and the round trip is unchanged.