feat(cli): worker start -a|--attach — foreground view, detach with Ctrl-D

[ralyodio]

What

Adds c0mpute worker start -a|--attach: run the worker attached in the foreground watching its log, then press Ctrl-D (or Ctrl-C) to detach and leave it running in the background. Follow-up to #11 (the -d daemon).

The design decision (important)

The naive ask — "run in the foreground, then on Ctrl-D convert this process into a daemon" — isn't sound. Once worker start is up, the Tokio runtime is multi-threaded with live libp2p sockets, and fork() on a multi-threaded process is UB (it copies only the calling thread, leaving a dead runtime + half-held locks). That's exactly why -d daemonizes before the runtime starts.

So -a uses the tmux / docker attach model: the worker is a standalone background daemon the whole time, and -a attaches a live log viewer to your terminal. Detaching (Ctrl-D / Ctrl-C) just stops the viewer — it never touches the worker. Same UX as asked, but robust: nothing is lost on detach, and there's never a duplicate or momentarily-forked worker.

Behavior

• worker start -a → launches the daemon (via the existing -d path, so the fork-before-runtime happens in that child), then streams the log.
• If a worker is already running, -a re-attaches to it instead of spawning a second one.
• Ctrl-D (stdin EOF) or Ctrl-C / SIGTERM → detach; prints detached — worker still running (pid N).
• -a conflicts with -d (clap enforces).
• The attach process never builds the async runtime — it's just a subprocess supervisor + file tail — so it returns your shell cleanly.

Testing (Linux, verified end-to-end)

• Help shows -a; -a -d errors with a clap conflict.
• -a spawns a separate daemon and tails its log; SIGINT detaches the viewer, daemon keeps running; worker stop cleans up.
• Already-running case: -a prints worker already running (pid N); attaching, no duplicate spawned.
• Ctrl-D over a real PTY: sending 0x04 detaches the viewer (worker still running (pid N)), viewer exits, daemon survives.
• cargo build (debug) and cargo build --release both clean.

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