Hmbown/CodeWhale · error · ExecError

no display ; have [ ] — screenshot takes the display index…

Error message

no display ${disp}; have [${displays.map((x) => x.index).join(", ")}] — screenshot takes the display index from list_displays, not its id

What it means

The darwin computer-use screenshot action validates the requested display against the index field of entries returned by list_displays/displayInfo. Callers that pass a display `id` (a macOS CGDisplay UUID) instead of the numeric `index` fail this check. The library throws early so a wrong display value cannot silently produce points/scale that mis-target all later coordinate actions.

Solutions

1. Re-run list_displays and pass the `index` field (not `id`) as the screenshot display argument.
2. If you don't need a specific display, omit `display` entirely or pass "all" to capture everything.
3. After a monitor connect/disconnect, refresh the display list before retrying.
4. Note that window captures ignore `display` entirely — use window_id instead if you meant to capture a window.

Example fix

// before
await screenshot({ display: displays[0].id });
// after
await screenshot({ display: displays[0].index });

const displays = await list_displays();
if (display != null && display !== "all" && !displays.some(d => d.index === display))
  throw new Error(`use display index from list_displays, not id: ${display}`);

const isDisplayIndex = (v, displays) => v === "all" || displays.some(d => d.index === v);

try { await screenshot({ display }) } catch (e) {
  if (String(e.message).startsWith("no display")) {
    const displays = await list_displays();
    await screenshot({ display: displays[0].index });
  } else throw e;
}

When it happens

Trigger: Calling screenshot({ display: <display id> }) where the value came from the `id` field of list_displays output rather than its numeric `index`; also triggered by a stale index after displays were plugged/unplugged, or by any non-'all' value not found in displays[].index.

Common situations: Copy-pasting a display id from list_displays JSON into the screenshot call; an LLM agent confusing `id` with `index`; hardware display changes making a previously valid index disappear; passing a 0-based index to a 1-based list.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• region must be [x, y, w, h] in screen points
• application not found — call list_apps for exact names/pids
• attempt finalization requires a terminal worker event
• background preview capture failed
• cannot install a bundle from inside the user plugins…

AI-assisted analysis of Hmbown/CodeWhale@73e0f67d83 (2026-09-22). Data as JSON: /api/errors/7a20d38f407d5983. Report an issue: GitHub.

Appendix: source

Thrown at crates/tui/plugins/computer-use/src/backends/darwin.mjs:535

    // `.png` path, which is what a pixel-exact comparison wants.
    const file = outPath || path.join(dir, `shot-${new Date().toISOString().replace(/[:.]/g, "-")}-${crypto.randomBytes(3).toString("hex")}.jpg`);
    if (!/\.(png|jpe?g)$/i.test(file)) throw new ExecError("screenshot path must end in .png, .jpg or .jpeg");
    const args = ["-x", "-t", /\.png$/i.test(file) ? "png" : "jpg"];
    const disp = display ?? state.activeDisplay;
    // An explicit app reference resolves first and alone: nothing may run
    // before it and redirect the capture to another target.
    const window = app_ref !== undefined ? await native("window_info", { app_ref, window_id }) : null;
    if (window && region) throw new ExecError("choose app_ref or region, not both");
    // On the display path, resolve displays before capturing so an unknown
    // index is a clean error instead of a raster silently labelled with another
    // display's geometry — list_displays reports `index` and `id` separately,
    // and a caller passing the id would otherwise get points and scale that
    // mis-target every later coordinate. A window capture ignores `display`.
    let displays = null;
    if (!window) {
      displays = await displayInfo();
      if (disp != null && disp !== "all" && !displays.some((x) => x.index === disp)) {
        throw new ExecError(`no display ${disp}; have [${displays.map((x) => x.index).join(", ")}] — screenshot takes the display index from list_displays, not its id`);
      }
    }
    if (window) args.push("-o", "-l", String(window.window_id));
    else if (disp && disp !== "all") args.push("-D", String(disp));
    if (region) {
      if (!region.every((n) => Number.isFinite(n) && n >= 0) || region.length !== 4) {
        throw new ExecError("region must be [x, y, w, h] in screen points");
      }
      args.push("-R", region.join(","));
    }
    args.push(file);
    const r = await runL("screencapture", args, { timeoutMs: 20_000 });
    if (r.code !== 0) throw new ExecError(`screencapture exited ${r.code}: ${r.stderr.trim().slice(0, 300)}`, r);
    await fitRasterToBudget(file);
    const stat = fs.statSync(file);
    displays ??= await displayInfo();
    const d = displays.find((x) => x.index === (disp === "all" ? 1 : disp)) ?? displays[0];
    const scale = d?.scale ?? 1;

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