3.9 Answers

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3.9.1 Shape #

A surface answers the outstanding turn with Answer:

values MUST name only enabled input elements of the turn named by seq; a value for an unknown ref, a disabled element, an output element or an action is a protocol error. A value's JSON type must match the element type's answer encoding (§3.B).

3.9.2 Actions #

If the turn has any enabled action, the answer MUST name exactly one of them; if it has none, the answer MUST omit action — the implicit submit. Naming anything that is not an enabled action of the turn is a protocol error.

What an action means — next, back, cancel, begin — is the daemon's business alone. A surface presents actions and reports which was pressed; it MUST NOT ascribe navigation semantics of its own.

3.9.3 Validation #

An answer validates unless the action it names carries validate: false (§3.B) — the escape that lets Back and Cancel leave a half-filled page. When an answer validates:

• every enabled, required input element MUST have a value in values;
• an omitted optional input with a default is treated as answering with that default.

The daemon then applies its own domain validation — is that disk still present, is that name well-formed — which this chapter does not constrain.

3.9.4 The three fates #

An answer is exactly one of:

• Stale — seq is not the outstanding turn. Ignored silently (§3.3).
• Applied — structurally sound and valid. The acknowledgement is whatever the daemon broadcasts next: the following turn, or END. The winning answer itself is never echoed to anyone.
• Failed validation — structurally sound, but required values are missing or domain validation failed. The daemon broadcasts an UPDATE setting error on the offending elements; the turn stays open for every surface (§3.3).

A structurally unsound answer — the protocol errors above — is none of these: it is answered by Error on the offending connection only (§3.11), and the turn is unaffected.

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