Propose the value one field of a store should have, as its single owner.

Creates an approval card and answers 202 with status: "proposed", plan_action_id, where and approve_url; nothing is declared until the merchant approves it in Magistry, whatever the connection's auto-apply setting. The checks below then run at approval. A field has at most one owner, enforced by a unique index. The merchant grants this app a field in Settings → API & MCP → Connected apps; without that grant the answer is 409 no_policy, and while another owner holds the field it is 409 held_by_other with held_by; a field whose outside change the merchant kept is 409 merchant_kept until a store rule allows declaring it again. Declaring reaches nothing outside Magistry: a reconciler reads the row and is the only code that writes to the platform, and it may still refuse the value (a price under the margin floor), which the declaration's status then reports. Declarable fields: variant: price, compare_at_price (needs catalog:write); campaign: status, daily_budget, bidding (needs ads:write). A declaration always expires, at most 30 days out.