A component variable `default_value` is untyped in the MCP tool schema, so an
agent can store a bare string where the renderer expects
`{ type: 'dynamic_text', data: { content } }`. Probing that primitive with the
`in` operator threw, `fetchPageByPath` swallowed the error, and every page
using the component fell back to the starter template — both in the builder
preview and on the published site.

Coerce strings to `dynamic_text` at render time so existing bad data recovers
without a migration, and wrap them at the MCP boundary so new writes are
stored in the correct shape.

Co-authored-by: Cursor <cursoragent@cursor.com>

…e-values

fix: guard string component variable values

The design guide sent to agents omitted several properties the schema and
class mapper already support (mixBlendMode, filter, backdropFilter, raw
backgroundImage values), so agents assumed blend-mode overlays required
custom code. Also documents that htmlEmbed renders as a sandboxed iframe
on published sites and the custom_attributes style escape hatch for CSS
with no design field (e.g. pointer-events).

docs: surface undocumented MCP design capabilities in agent instructions

fix: prevent component variables with plain-text values from breaking pages