Copilot round 4: no new visible comments, two in the suppressed block. Both
valid.
1. The `type: [T, "null"]` encoding keeps its keywords at the top level, so a
nullable enum written that way carries the null *inside* the list:
`{ type: ["string", "null"], enum: ["envio", "recebimento", null] }`. The
collapse left it there, which broke both renderers in different ways — the
web dispatcher handed `null` to Mantine as option data, and the TUI's
all-strings check rejected the whole enum and fell back to a plain text
field. Neither is the dropdown the schema asks for.
The collapse now strips a `null` member whenever it flattens, since that
fact has already moved onto `nullable`. An enum of nothing but `null`
drops out entirely: it offers no value a dropdown could show, so the plain
widget serves the field better than an empty select. Covered in core and
end-to-end in both dispatchers.
2. The new integration test claimed in its own header to pin the registry and
config wiring, then called `createNullableFieldsTool()` directly — so a
misspelt preset case or a config naming a dead preset would have left it
green. A fair "this does not test what it says" catch. It now resolves the
checked-in `nullable-fields-http.json` through `loadConfig` →
`resolveConfig`, matching `duplicate-tool-names.test.ts`, and asserts the
resolved tool names before booting the server.
Signed-off-by: cliffhall <cliff@futurescale.com>