feat(Select): add renderTrigger for custom trigger elements

[blvdmitry]

Summary

Adds a renderTrigger prop to the custom Select, letting consumers replace the built-in trigger while keeping value resolution, type-ahead, keyboard handling and form submission.

<Select
  name="animal"
  placeholder="Select an animal"
  renderTrigger={(attributes, { active }) => (
    <Actionable attributes={attributes}>
      <Text color="neutral-faded">{attributes.children}</Text>
      <Icon svg={active ? IconChevronUp : IconChevronDown} size={4} />
    </Actionable>
  )}
>
  <Select.Option value="dog">Dog</Select.Option>
</Select>

The plumbing already existed one level down — DropdownMenu.Trigger is Flyout.Trigger, which hands out TriggerAttributes. SelectCustomControlled just hard-coded SelectTrigger as their only consumer, so this forwards that function outward.

API shape follows the existing convention for render props that carry both attributes and state — spreadable attributes as the first positional argument, state as a second argument named props, matching Accordion.Trigger and Resizable.Handle. The wrapped (args: {...}) form used by renderValue/renderDateValue is for value formatters where nothing is spreadable. The resolved value node goes in attributes.children (falling back to placeholder), mirroring how Actionable.render includes children so a bare spread works.

A Select.Trigger compound child was considered and rejected: children is exclusively the option list that traverseOptionList walks, and hoisting a trigger out of it would reintroduce the child scanning that #608 deliberately removed.

Changes:

• Select.types.ts — TriggerRenderAttributes plus renderTrigger on the four custom fragment members. Placed alongside renderValue so value narrows to string vs string[] off the multiple discriminant; typed never on the native fragments.
• SelectHiddenInput.tsx (new) — extracted from SelectTrigger so both paths share one place for the value serialization. Without it, a custom trigger would silently break form submission.
• SelectCustomControlled.tsx — the wiring. onClick is composed manually (Actionable was merging Select's onClick with the flyout's for free) and guarded on disabled.
• Type exports through Select/index.ts and src/index.ts.
• Removed the unused RootProps type — a vestigial render-prop sketch of this same feature, superseded here.

Related Issue

Screenshots / Recordings

Covered by the new renderTrigger story (Components/Select), which renders an Actionable with neutral-faded text and a chevron driven by active.

Notes for Reviewers

Worth a look:

• attributes.children placement. Great for a raw {...attributes} DOM spread, slightly odd when spreading into a Reshaped component's attributes prop — Actionable overrides it with its own children, so consumers read attributes.children and place it themselves, as the story does. Moving it to the second argument is the alternative.
• Placeholder styling. The fallback is passed as a raw string rather than the <Text color="disabled"> the default trigger uses, so custom triggers aren't forced into a look. Consumers distinguish value from placeholder via the value in the second argument.
• width="trigger" and focus return both key off whatever element receives attributes.ref — spreading onto an inner node gives a wrong dropdown width and breaks focus-on-close. Worth calling out in docs, with positionRef as the escape hatch.
• Labelling. id still lands on the hidden input, so a FormControl label's htmlFor points at something unfocusable. Pre-existing, but more visible with a custom trigger — passing id/aria-labelledby through the render arguments would be a follow-up.
• size, variant, icon and startSlot are silently ignored with a custom trigger, matching how Popover treats its trigger.

Verification: tsc --noEmit clean; vitest --project=storybook passes 581/582, the one failure being a pre-existing Image.stories load assertion that also fails on a clean checkout here.

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Generated by Claude Code

[github-actions]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
Library / JS	49.31 KB (+0.34% 🔺)	987 ms (+0.34% 🔺)	876 ms (+2.58% 🔺)	1.9 s
Library / CSS	23.06 KB (0%)	462 ms (0%)	0 ms (+100% 🔺)	462 ms
Theming / JS	7.79 KB (0%)	156 ms (0%)	64 ms (-6.54% 🔽)	219 ms
Theming with a default theme definition / JS	8.67 KB (0%)	174 ms (0%)	65 ms (-22.08% 🔽)	239 ms