t3 thread start: start a thread on the running server from the CLI, like t3 project add

[TheConnMan]

Problem or use case

I run a job queue on the same machine as my T3 server. It starts unattended threads through a small launcher script so I can watch and steer them in the app. T3 has no CLI command for that, so the launcher has to use the server's internal orchestration protocol: it mints a session with t3 auth session issue, reads the shell snapshot, dispatches thread.create and message.dispatch, and subscribes to the thread to wait for the run. That protocol changes often on nightlies, and the launcher breaks with it. The latest break was the shell snapshot outgrowing Node's 4 MiB WebSocket message limit.

t3 project add already does the same thing for projects: it reads the live orchestration snapshot and dispatches a command to the running server. A thread command shipped in the same binary would never drift from the server.

Proposed solution

1. t3 thread start --project <id|title|path> --prompt <text|-> [--provider <instance>] [--model <slug>] [--effort <level>] [--runtime-mode <mode>] [--title <text>] [--worktree <path> --branch <name>] [--json] prints the new thread's id and URL and exits once the server accepts the turn.
2. --wait [--timeout <duration>] waits for that turn's run to finish and prints its status and final assistant message. A distinct exit code for "timed out, still running" and another for "failed before any thread was created" lets callers decide whether retrying is safe.
3. Optionally, t3 thread read <id> and t3 thread wait <id> for a thread started earlier.

Like t3 project add, it would run with the host's own authority. A person who can run it can already mint an administrative session.

Related

#11722 asks for an interactive terminal client. This asks for one non-interactive subcommand built on the live-server helpers t3 project add already uses. #16133 covers prompt links, which still need a person to press send. #7332 and #17593 cover reading sessions from the CLI.

Drafted with Claude Code from a working launcher I maintain.