A lookup binds in the availability check, never in a read

Status: accepted, 2026-10-03; supersedes Lookups satisfy root fields from cached entities. Serves The store is the UI's state. Reopen if a lens must render a root field that no availability check has walked, such as a lens built over the root by hand outside an operation.

Context#

baton.json names root fields that return an entity by one of their arguments, and the plan carries each lookup. Until now two places bound a lookup: the availability check, before a handle is ready, and the lens read of a missing root link, which resolved the entity and wrote the link. The second is a write inside a view body: the body that reads the field writes the slot it is reading and notifies the channel it has just registered on, while it renders. The check writes the link too, outside any commit, but before the handle it serves is ready, so no body has read the slot yet.

Decision#

Only the availability check binds a lookup. A handle is ready only after the check has walked the operation's selection, so by the time a body reads a root field the check has either written the link to the cached entity or reported the data incomplete, and the fetch writes the link from the response. A lens read of a missing link reads nil and reports missing data, as for any other field. The generated accessors take no lookup; the lookup: parameters of linked, requiredLinked and throwingLinked and Store.resolveLookup are gone.

The configuration, the plan's lookups, the rule for a lookup without a type (one live record among the field's possible types) and the image's part (an entity only the image holds satisfies a lookup that names its type) are as the superseded record says.

Evidence#

• The spine's first-body test is unchanged: a detail whose root field was never fetched is .ready on creation, rendering the entity the list fetched, because the handle's check binds the link.
• A new spine test reads the root field before any check: nil, with the miss reported, and the link still missing; after the check the same lens reads the entity.
• The two other tests that relied on the read-side write, each a lens built over the root by hand, now run the check first, as a handle does.

Not chosen#

• Keeping the read-side binding: a write and a notification during rendering, with no undo and no commit, for a case a handle never reaches.
• Turning the binding into a commit through the store's transaction: the link needs no undo and no row in the image, and a commit from a read is still a write from a read.