move-in's refusal "the vault already holds another value for ..." was an error's text, which the node-engine and the
controller could only quote. It is now an answer: `refused` with the reason holds-another-value and the held value's
record (generation, changed by, changed at, origin; never the value), `why` in words, and no read-back, so an
engine that does not read `refused` still fails as before ("answered with no read-back"). keepLocked's refusal is a
typed error (HeldAnother) whose text is unchanged for every other path.
Quick fix: a stable prefix in the text. Thorough fix: the fields. Chose thorough, as asked; mesh-host's
moveIntoTheVault has to read `refused` to use them.
jschoubben
f3b13de20d