Addresses Copilot's round-4 review on #2035 — again reported as "no new
comments" while carrying three suppressed ones. All three reproduced.
1. The TUI form still named its fields from the SDK. `uriTemplateToForm`
read `UriTemplate.variableNames`, which mangles a name: `{;id}` yields
";id" and `{id:3}` yields "id:3". The form therefore submitted
`{ ";id": "7" }` while the shared expander looked up `id`, found
nothing, and dropped the expression — the value vanished silently.
This is the finding that mattered most, because it falsified the claim
this change is built on. Moving the expander into core only makes the
clients agree if each client's FORM derives its names from the same
parser: a form submits under the names it rendered. The TUI now reads
`templateVariables`, and the SDK template is constructed only to
validate, preserving the existing malformed-template diagnostic.
Its `required` flag comes from `requiredGroups`, and only a variable
that is the sole member of a non-omittable expression is marked: ink-
form cannot express "any one of these", so marking every member of
`{a,b}` required would refuse input the expander accepts.
2. `encodeURIComponent` is not RFC 3986's unreserved set — it leaves the
sub-delims !'()* bare, which RFC 6570 requires encoded for every
operator except + and #.
Fixing that settled a design question left open in the previous round.
With two encoders, the SAME value encoded differently depending on
whether its expression happened to carry a modifier, since only the
modifier pushed it onto our path. So delegation is gone entirely: one
expander, one set of rules. The SDK's `UriTemplate` is still
constructed, but only to validate a template.
3. The "Any one of: a, b" hint could contradict the disabled submit
button. A name can sit in a singleton required group AND a shared one
(`x://{a}/{a,b}`), where the singleton demands that exact field. The
hint is suppressed in that case.
Signed-off-by: cliffhall <cliff@futurescale.com>