[httpsphl]

Part 5a of the ideas from 2026-10-04 (reactions come next, in 5b).

Daemon

• messages.send takes replyTo (a chat item id). The item must be in that bot's chat (not_found otherwise) and be a reply or an inbound message with text (validation).
• The message keeps replyTo { itemId, text }, the text on one line and cut at 300 characters (migration 0018_message_reply.sql, no foreign key since chat items leave before messages on delete).
• The bot reads Replying to: "<quote>" above the owner's words (spec 9.3).

App

• Hovering a bot's reply or another bot's message shows a reply button in its corner (keyboard: on focus).
• The quote goes over the composer ("Replying to Scout", X, Esc cancels) and the field takes the focus.
• Sent, the quote shows over the owner's bubble (Markdown marks taken off); a click jumps to the quoted item.

Spec 9.3, 11.2, 12 and 15.3 updated.

Test plan

• cargo fmt, clippy -D warnings, cargo test --workspace (new tests/reply_to.rs, envelope and courier render tests)
• pnpm check (new reply.test.tsx)
• Preview: reply to Scout's summary, quote over the bubble
• Real Claude: reply to a bot's answer and check it understands which one you mean