[idea] Make session attach enforce that the session exists and not auto create

[Raynos]

idea / problem

I keep typoing my session names home vs house or games vs game or game-demos vs games-demo

And creating brand new session instead of getting a Not Found message. I'd like to be able to only attach to session that exist and have a manual herdr session create [name] command to create new ones as a one time.

requested change

Give me a config setting to make session attach not auto create sessions.

why you want this

To avoid typos creating brand new blank sessions.

[Lawgk]

Strongly agree with this. Adding some prior-art context and two failure modes beyond plain typos.

attach that creates is the exception, not the norm. In tmux the two operations are deliberately separate commands: tmux attach-session fails with "no such session", and tmux new-session is what creates one. That split isn't a tmux quirk — it's the dominant convention among CLIs that expose an attach verb. docker attach, kubectl attach, gdb attach all mean "connect to something that already exists; error if it doesn't." Herdr's session attach is the outlier, and the docs lean into it by presenting herdr session attach side-project as the way to create a named session.

I understand the appeal of collapsing both into one command — fewer concepts to learn, and the common case just works. But it also removes any way to express "I want the existing one, and only the existing one," and that ambiguity has real costs.

Two ways it bites:

1. Returning to an earlier session with a mistyped name. Instead of an error you get a brand-new empty session whose name is one character off from the real one. The failure is silent: Herdr starts normally and looks correct, so you only notice when you wonder where your panes went.

2. Shell completion that stops at a common prefix. With sessions proj-api and proj-web, completing proj stops at the shared prefix proj-; submitting there creates a third session named literally proj-. (Herdr's shipped zsh completion currently uses _default for the session attach <name> argument, so completing session names needs a custom compdef today — but that's a natural thing for users to wire up, and the more sessions share a prefix, the more often this lands.)

Both leave clutter that has to be noticed and cleaned up later. #3220 is the same root cause seen from the far end: a session created by a typo that then couldn't be deleted from the CLI at all.

Possible directions, in increasing order of invasiveness:

• Keep the default, add an opt-out. A config key (e.g. [session] auto_create = false, default true) for people who want tmux semantics.
• Or a per-invocation flag. herdr session attach <name> --no-create, erroring when the session doesn't exist.
• Longer term, flipping the default seems worth considering, with an explicit herdr session create <name> (or attach --create) for the create path. Two things make the cost look smaller than it first appears: the convention argument above, and the fact that workspaces are now the recommended primary unit. Named sessions remain irreplaceable when you genuinely want independent servers, and I expect they'll stay in wide use for that — but precisely because they're the deliberate, lower-frequency operation, an explicit create verb costs very little, while a silent mis-create costs the most.

If one of these directions looks right, I'd be glad to implement it and open a PR — on a maintainer's go-ahead, not before.

[Raynos]

I created https://github.com/Raynos/dotfiles/blob/master/bin/herdr-attach

So that I can run herdr-attach [sessionName] with tab completion.

I created a bash alias ( https://github.com/Raynos/dotfiles/blob/master/.bashrc#L111-L137 ) that gaurds against auto creation or basically just bans using the herdr cli and forcing the usage of herdr-attach instead.