What causes "Failed to take child stdout" in BloopAI/vibe-kanban?

Add/restore .stdout(Stdio::piped()) on the command before spawn.

Failed to take child stdout

Error message

Failed to take child stdout

What it means

Same as the stdin variant: after spawning the child, spawn_stdio_session takes the child's stdout handle and fails if it is None. Stdout is None only when the command was not configured with Stdio::piped() for stdout, but the stdio session needs to relay the child's output back over the SSH channel.

Source

Thrown at crates/embedded-ssh/src/handler.rs:102

        for (k, v) in env {
            cmd.env(k, v);
        }
        if let Ok(home) = std::env::var("HOME") {
            cmd.current_dir(home);
        }

        let mut child = cmd
            .spawn()
            .map_err(|e| anyhow::anyhow!("Failed to spawn stdio command: {e}"))?;

        let stdin = child
            .stdin
            .take()
            .ok_or_else(|| anyhow::anyhow!("Failed to take child stdin"))?;
        let stdout = child
            .stdout
            .take()
            .ok_or_else(|| anyhow::anyhow!("Failed to take child stdout"))?;
        let stderr = child
            .stderr
            .take()
            .ok_or_else(|| anyhow::anyhow!("Failed to take child stderr"))?;

        let (writer_tx, mut writer_rx) = mpsc::channel::<Vec<u8>>(64);
        tokio::spawn(async move {
            let mut stdin = stdin;
            while let Some(data) = writer_rx.recv().await {
                if stdin.write_all(&data).await.is_err() {
                    break;
                }
                if stdin.flush().await.is_err() {
                    break;
                }
            }
        });

View on GitHub (pinned to 4deb7eca8f)

Solutions

Add/restore .stdout(Stdio::piped()) on the command before spawn.
Verify no code path replaces stdout with Stdio::inherit or Stdio::null for stdio sessions.
Add a unit/integration test that spawns a trivial command through spawn_stdio_session and asserts output is relayed, catching regressions.

Example fix

// before
cmd.stdout(Stdio::inherit());
// after
cmd.stdout(Stdio::piped());

Defensive patterns

Strategy: validation

Validate before calling

let mut cmd = Command::new(shell);
cmd.stdin(Stdio::piped());
cmd.stdout(Stdio::piped()); // required, otherwise take() -> None
let mut child = cmd.spawn()?;

Prevention

Keep .stdout(Stdio::piped()) on every command spawned for stdio relay.
Cover stdout relay with an integration test (echo output through the SSH channel).
Review any refactor of command construction for dropped Stdio settings.
Treat this error as an internal invariant break; alert rather than retry.

When it happens

Trigger: child.stdout.take() returns None because the spawned command lacks .stdout(Stdio::piped()) — an internal construction bug, not user input.

Common situations: Encountered only after code changes to command construction in the embedded-ssh handler; users cannot cause it remotely.

Related errors

AI-assisted analysis of BloopAI/vibe-kanban@4deb7eca8f (2026-08-29). Data as JSON: /api/errors/0d028e6dcab2f547. Report an issue: GitHub.