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Trigger only when coordination can affect a decision
A document does not have one global proposal lock. Each candidate is translated into coordination keys that describe the territory it may affect: its exact target, section UUID or section number, declared basis sections, formatting scope and any explicit parent proposal. A document-wide formatting operation uses a document key because it can affect every target; an ordinary clause edit does not.
Those keys create small target heads. A target head is a revisioned fence for one piece of legal territory on one exact document snapshot. Agents working on different keys advance different heads, so an edit to a payment clause does not wait behind an unrelated edit to a notices clause. The system serializes competing admissions only where their declared territory intersects.
The trade-off is deliberate. An agent may spend one drafting invocation before discovering a collision at staging. In return, every disjoint or abandoned line of work avoids a continuous coordination tax. Earlier advisory target-intent signals could reduce that wasted collision draft in future, but the transactional staging check must remain the final write boundary.