--resume/--session-id needs a session id, but got an empty…

Error message

--resume/--session-id needs a session id, but got an empty value (an unset shell variable?). Use `codewhale --continue` to resume the most recent session.

What it means

The resume path trims the supplied `--resume`/`--session-id` value and bails if it is empty. The guard exists because a shell expanding an unset variable (`codewhale --resume "$SESSION_ID"`) would otherwise quietly start a fresh session, and the loss of intended history is invisible until it is too late. The error suggests `--continue` to resume the most recent session.

Solutions

Provide the actual session id: `codewhale --resume <real-session-id>`.
If you just want the latest session, use `codewhale --continue` instead.
Guard shell scripts: `: "${SESSION_ID:?SESSION_ID is not set}"` before invoking.
List available sessions (`codewhale sessions` or the session store) to find the correct id.

Example fix

// before
codewhale --resume "$SESSION_ID"   # unset
// error: --resume/--session-id needs a session id, but got an empty value...

// after
codewhale --resume 3f9c1a2e-... 
// or: codewhale --continue

Defensive patterns

Strategy: fallback

Validate before calling

# shell guard
if [ -z "${SESSION_ID:-}" ]; then
  echo "SESSION_ID empty; falling back to --continue" >&2
  exec codewhale --continue
fi
codewhale --resume "$SESSION_ID"

Try / catch

match run(args) {
    Err(e) if e.to_string().contains("got an empty value") => {
        eprintln!("empty session id; use `codewhale --continue` for the latest session");
    }
    r => r?,
}

Prevention

Guard interpolated ids with ${VAR:?msg} in scripts.
Use --continue when you do not have a concrete id.
Capture the session id from the command that created the session, not from memory.

When it happens

Trigger: Passing `--resume ""`, `--session-id " "`, or `--resume "$SESSION_ID"` / `--session-id "$ID"` where the shell variable is unset or empty.

Common situations: CI scripts or shell aliases with unset environment variables, sourcing order mistakes where SESSION_ID is defined in a different shell, or users forgetting to paste the id.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of Hmbown/CodeWhale@73e0f67d83 (2026-09-22). Data as JSON: /api/errors/fe916ba52e97d523. Report an issue: GitHub.

Appendix: source

Thrown at crates/cli/src/lib.rs:2339

    }
}

fn root_tui_passthrough(cli: &Cli) -> Result<Vec<String>> {
    let mut forwarded = Vec::new();
    if cli.continue_session {
        forwarded.push("--continue".to_string());
    }
    let resume_session_id = cli
        .resume
        .as_deref()
        .or(cli.session_id.as_deref())
        .map(str::trim);
    if resume_session_id.is_some_and(str::is_empty) {
        // A shell expanding an unset variable -- `codewhale --resume
        // "$SESSION_ID"` -- must not quietly become a fresh session. The user
        // asked to resume; starting new loses the session they meant, and the
        // mistake is invisible until the history is gone.
        bail!(
            "--resume/--session-id needs a session id, but got an empty value \
             (an unset shell variable?). Use `codewhale --continue` to resume \
             the most recent session."
        );
    }
    if let Some(session_id) = resume_session_id {
        forwarded.push("--resume".to_string());
        forwarded.push(session_id.to_string());
    }

    let prompt =
        cli.prompt_flag
            .iter()
            .chain(cli.prompt.iter())
            .fold(String::new(), |mut acc, part| {
                if !acc.is_empty() {
                    acc.push(' ');
                }

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