Let a command plugin read what was piped into jp

Todo2026-10-29jp

domain: pluginspackage: jp_cli, jp_pluginrelevant-rfd: 116type: enhancement

A command plugin's stdin is the protocol channel to the host, so it can never see what was piped into jp. JP's justfile keeps ticket-add and ticket-comment only to read piped text and pass it to jp ticket as --body.

Proposal

• read_stdin host request (protocol 14). The plugin asks, and jp answers with the piped text, or with nothing when stdin is a terminal.
  • Read on request, so a command that doesn't ask never waits on stdin.
  • Stdin is read once; a second request gets nothing.
• jp ticket add and comment ask for it when no --body is given, and use the piped text as the body, as jp query does. Like jp query, a pipe that never closes makes the command wait.
• jp ticket comment T-02wt0kx#1 replies to comment 1, as the ticket-comment recipe accepts today.
• Drop just ticket-add and just ticket-comment. just ticket-add bug "Title" becomes jp ticket add "Title" --label type=bug.
• A jp older than protocol 14 isn't asked, so piped text is ignored there. The plugins are installed with jp, so that's acceptable.

Piping doesn't take away the prompts: jp decides it can prompt from stdout (crates/jp_cli/src/ctx.rs), and the prompt widgets read keys through crossterm, which opens /dev/tty when stdin isn't a terminal. So pbpaste | jp ticket add should still ask for the title. Confirm that by running it as part of this work.