Same label-above-input shape as add_form_field_v0 but the input
grows vertically by `rows` (default 4, clamped 2..12) for notes /
bio / feedback use cases. Input frame layout is vertical with
placeholder top-aligned, matching native iOS/Material behavior.
Wired across all three paths:
- pen-core: `buildTextarea` + TextareaParams in element-builders
- pen-mcp: `handleAddTextareaV0` + tool schema in element-tool-defs-ext
- apps/web: shim + Nitro SERVER_BUILDERS entry
- elements.md: PREFER list + keyword map + 2 example lines
Tests:
- pen-mcp: 8 new cases in add-textarea-v0.test.ts (height math,
rows clamp, required suffix, placeholder wiring, id uniqueness,
parent_id rollback)
- Parametric builder tests auto-extended (+1 case each in 9 files):
layout smoke, post-process idempotency, normalize preservation,
performance, role coverage, anti-patterns clean, detectors
clean, shim-server parity. Total delta: 2907 → 2931 passing.
Closes#47; covers part of #50 (textarea entry).
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