The structure completion has no caller

trading.v1.ops.complete_structure writes a structure, its members and takes every leg live in one transaction, with two cases proving a refusal leaves every leg a draft and writes no member. Nothing calls it.

The grouping screen's route (POST /api/structures) still writes the structure through the entity write and then each member through the member write, one call at a time, and never executes a leg. The book-a-trade flow adds a leg the same way. So grouped legs stay drafts and a grouping that fails halfway leaves a half-grouped deal standing, which is the state the operation exists to make impossible.

An operation with no caller is not a capability, it is a comment. The arc's own acceptance says a completed structure has every leg live and unauthorised, and nothing in the product completes one.

Wiring it also forces a decision the arc has not taken: grouping and completing are two different acts, and the grouping screen currently does the first while pretending it did the second. Either the grouping screen completes (and a leg can no longer wait as a draft), or the structure page carries a Complete action and the grouping screen keeps making drafts. The prototype drew the structure page's own actions, which is the second.

Not designed here. The pieces that appear necessary:

• Decide where completing happens: the structure page's action, or the grouping screen's confirm step.
• Point the route at the operation: one call carrying the anchor and the legs, in place of the loop of entity writes.
• State what the screen shows when the store refuses one leg: the completion is all-or-nothing, so the message is about the deal rather than about a row.
• A render test, since the screen's submit path is what changes.

Grouping a set of trades, or pressing Complete on a structure, produces one structure whose every leg is live and waiting on Operations, and a refusal leaves the trades as they were.

• trading.v1.ops.complete_structure — the operation, with its four cases.
• POST /api/structures in packages/bff/src/structures.ts — the loop that should become one call.

• Complete a structure in one unit — the task that built the operation.
• Build the structure page — the screen whose actions the prototype draws.