Task: Factor out the shared planner loop

One planner states its family's facts and nothing the families share. Every planner builds its slots from one helper, the netting set scan exists once, and the bond, commodity and interest rate populations are unchanged down to their identifiers.

• One helper states the envelope every family shares: the book, the counterparty, the trader, the identifiers, the trade date and the netting set.
• The bond, commodity and interest rate planners call it, and none of them scans the netting sets itself.
• The three suites pass unchanged, and a plan of each family is identical to the plan the same scope produced before the change.

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

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.

The bond, commodity and interest rate planners state the envelope of a slot once. common_slot sets the book, the counterparty, the trader, the two identifiers, the trade date and the netting set, and slot_count states how many slots a scope holds, so each planner now says only what its family adds: the trade type, the notional and the terms. The netting set scan exists once instead of three times, and the planner file is twenty-five lines shorter.

The extraction is known to be inert by measurement. A digest of a bond plan's envelope, hashed, was recorded from the planner as it stood before the change; the refactored planner produces the same value and a case asserts it. That case also pins the determinism the interface promises, so a later edit that moves a slot field fails a test rather than quietly changing a population.

What this does not do: the dispatch on trade_type_code still appears in the planner, in the writer and in the routing table. Collapsing it needs the payload to state the product, which touches both sides of the rate family, so it stays its own change.