Add `SelectableRichText`, a custom iced widget that mirrors `rich_text`
(linkified spans + A13 link clicks) and adds per-message drag selection,
Ctrl/Cmd+C copy, and Ctrl/Cmd+A select-all. Swap it in for the chat body
element; the chat row and attachment layout are unchanged.
Selection offsets are paragraph-global byte offsets (matching cosmic-text's
hit_test), which equals a single global range because sanitize_chat keeps
every message on one logical line. Pure seam `selected_substring` /
`select_all` is unit-tested incl. unicode/emoji byte boundaries. Highlight
quads are computed from public Paragraph primitives, falling back to a
whole-message span_bounds union if sub-range rects can't be derived.
Only one message holds a selection at a time: each widget clears its own
selection on a left-press that lands outside its bounds. Right-click menu
(Part B) intentionally deferred — native Ctrl/Cmd+C/A is the path.
Implemented by Codex on branch, reviewed/committed by Claude.
464 lib tests, clippy --all-targets clean, release green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
molluskandClaude Opus 4.8
32ee00178e