Chat / messaging / customer-support UI message unit. Two variants
via the `side` enum:
- side="left" (default): from-others bubble. Slate-100 fill,
slate-900 text, alignItems=flex-start. Optional `author` text
shown above the bubble (group-chat pattern).
- side="right": from-self bubble. Accent-color fill (customizable
via `accent_color`), white text, alignItems=flex-end. Author
intentionally suppressed on this side — a self-bubble never
carries "You:".
Optional `timestamp` below the bubble on either side.
Max-width mechanic: pen-core has no native max-width primitive, so
`max_width` becomes the bubble's fixed width (clamped 160..480).
Short messages get extra padding on one side — matches every real
chat client (iMessage / WhatsApp / Slack). Message text uses
`textGrowth: 'fixed-width'` + `width: 'fill_container'` to wrap
correctly inside the fixed-width surface.
Full wiring: pen-core builder + pen-mcp handler + schema (into
ext-2, shorter shard — 24 tools vs ext-1's 24 after this) + shim
+ SERVER_BUILDERS + parity CASES + contract allow-list +
elements.md decision tree + triggers + minimal usage for both
sides. Handler test covers 9 cases: registration, left defaults,
left+author, right with self-dropped-author, right+accent_color,
timestamp both sides, max_width clamps (low + high split into
separate tests to avoid cache-interference), textGrowth wiring,
bogus parent_id rejection.
165fb94e44