a flow-context explicit key leaks an excluded field and wants the same fix as the compact block-sequence mapping

a flow-context explicit key leaks an excluded field and wants the same fix as the compact block-sequence mapping

Found by the round-9 adversarial RUTHLESS review of build/itd-183. PRE-EXISTING on the branch -- leaks on HEAD and on the parent alike, and named in no residue list or record before now.

meta: {? origin : <value>} and meta: {? "origin" : <value>} are a valid YAML origin key. questionLineRe is anchored to line start; flowKeyRe requires [{,] immediately before the name; excludedKeyLineRe reads only meta. So the key travels.

THE POINT OF THIS RECORD, in the reviewer's words: this is the same class as the compact block-sequence mapping (items: / - origin: <value>) already recorded in iss-2608301237450573, and the two want one fix, not two. Both are a real YAML key that the line-anchored and delimiter-anchored patterns cannot see because it is nested. Fixing them one at a time is how this floor has spent nine rounds.

Per the facilitator's ruling of 2026-08-30, this is seed material for the exclusion-floor intent rather than another round on this branch: a spelling arms race needs a design, not more patterns.

Grounds

• pursued: we expect refusing the construction rather than learning the key's spelling to end the arms race this record names, because the refusal does not depend on which name is hidden; an explicit flow key still assembling, or an ordinary flow sequence being refused, would show it wrong