FIFA 17 sends two different operations to `PUT …/squad/<id>` and distinguishes
them only by body shape. Across 73 captured squad PUTs in five captures there
are exactly two:
* 68x with `players` -- a full replacement (also carrying squadName,
formation, squadType, manager, chemistry/rating, and redundantly
captain/kicktakers);
* 5x without `players` -- `{id, custom, captain, kicktakers}`, emitted by the
captain/kick-taker screen.
`players` has `#[serde(default)]`, so an absent key and an explicit `[]`
collapsed to the same empty vec and every partial update was handed to Core as
a replacement with zero slots. Core's empty-replacement guard refused it (400)
and the host reported 502, losing the user's captain/kick-taker change.
`classify_squad_put` now tests key PRESENCE on the raw JSON before
deserialising, so absence ("the squad was not part of this edit") stays
distinct from an explicit empty array ("replace with nothing"). An explicit
`"players": []` still classifies as a replacement and still meets the guard --
the patch path is not a way around it.
The patch path carries the contract correction: omitted `players`, `manager`
and actives mean UNCHANGED, never cleared. That is structural --
`CoreRolePatchRequest` has no field able to express them. The extension is
MERGED rather than overwritten, because the partial body carries only `custom`
and `kicktakers`; overwriting would drop every kit number in the squad.
`custom` IS taken from the patch, since the role screen writes per-slot values
into it and the two shapes genuinely differ there.
Also fixes the error mapping on this route: a Core 400 means the REQUEST was
invalid, so it is reported as 400, not as a 502 that blames the server and
hides a client error behind "upstream unavailable".
Tests use the real captured body and assert it takes the patch path
(`replace_squad` call count unchanged), that the manager survives, that kit
numbers survive the merge, that an explicit empty `players` still reaches the
replacement path, and that an unresolvable captain refuses the whole patch
rather than half-applying the kick-takers.
funman300
e7893a0162