Patch partner

Partial update following JSON Merge Patch (RFC 7396). Send only the fields to change; omitted fields are left unchanged and an explicit null clears a field. What a clear reaches depends on the resource. Where the value is carried onto an underlying configuration, the field is reset to what a freshly built configuration holds for it rather than to absent, since that configuration has no representation for unset; where the absence cannot be stored at all, the null is accepted and the stored value is kept. A field the resource fills by resolving a reference keeps what is stored whenever the reference cannot be read back, a null being indistinguishable there from a lookup the session was not allowed to make. Requires Content-Type: application/merge-patch+json (sending application/json is rejected with HTTP 415). Control keys steer the merge and are spelled as a namespace prefix, a $ and the marker — the JSON form of the import vocabulary's core:mode. core$mode=overwrite, on the body or on any object inside it, resets the members that object did not send; a read-only member is not reset, since a marker cannot clear what a value could not set. An overwrite therefore has to carry every member the resource requires — its name among them — because omitting one asks for a record the store cannot accept. A reset is bound by the same limits an explicit null has, and those differ by resource: where the value is carried onto an underlying configuration the member goes back to what a freshly built one holds, and where the absence cannot be stored at all the member is kept rather than reset — so an overwrite is not a way to clear what a null could not. Nor does it remove a nested object the resource does not store separately: omitting a profile's inputAgentSettings under an overwrite does not remove the input agent, because a profile without one is not a state the store can hold. Send the nested object to reset inside it. core$mode=noResolve, likewise inherited by everything nested in it, matches nothing against the stored record, so the collections it covers are replaced, and a core$index or core$delete anywhere below it is rejected with 400 rather than passed over. core$index is a zero-based position in the stored list, sent as a number or its string form: the array element carrying it is merged into that stored element instead of replacing the list, and core$delete=true on the same element removes that position instead. Both steer an element of a list and are rejected with 400 anywhere else — on the body root, or on a member that holds a single object rather than a collection. Positions are counted in the list as it stood before the patch, so a core$delete earlier in the same array does not shift the entries a later core$index names, and the order of the elements does not matter. A core$index naming a position the list does not have, or whose stored element is of another type, is not honoured; the array then reads as an ordinary send. An element carrying core$delete=true is the exception: a delete steers the collection whether or not it matched anything, so an unhonoured one leaves the stored list exactly as it was rather than replacing it. An array no element of which carries an honoured marker replaces the stored collection, and [] clears it. An array that mixes steered and unmarked elements keeps the stored collection and adds the unmarked ones, so re-sending such a body adds them again — only an array whose every element is steered is idempotent. Outside a free-form map or property bag, whose keys are the caller's own and are stored verbatim however they are spelled, any other member spelling a $ is rejected with 400 — including a misspelled marker, a core$index that is not a whole number, a core$delete that is not true or false, a core$mode other than overwrite, noResolve or inherited, and any of the three carrying an object or an array as its value.