Hmbown/CodeWhale · error · ExecError

cursor position does not exist on touch devices

Error message

cursor position does not exist on touch devices

What it means

The HarmonyOS computer-use backend throws this from `cursor_position` because hdc-controlled HarmonyOS devices are touch devices with no mouse cursor; the backend fails closed instead of returning a fake coordinate. There is no way to query a pointer position on this platform, so the operation is intentionally unsupported.

Solutions

  1. Wrap cursor_position in a try/catch and treat 'not supported on touch devices' as 'no cursor' in your UI.
  2. Skip cursor-position logic entirely when the selected backend is HarmonyOS (touch-only).
  3. Use an element target with click/longClick instead of cursor-relative positioning for HarmonyOS automation.

Example fix

// before
const pos = await backend.cursor_position();
// after
let pos = null;
try { pos = await backend.cursor_position(); }
catch (e) { /* touch device: no cursor concept */ }
Defensive patterns

Strategy: try-catch

Validate before calling

const isTouchBackend = backendName === "harmonyos";

Type guard

const cursorSupported = typeof backend?.cursor_position === "function" && backendName !== "harmonyos";

Try / catch

let pos;
try { pos = await backend.cursor_position(); }
catch (e) { if (String(e.message).includes("touch devices")) pos = null; else throw e; }

Prevention

When it happens

Trigger: Calling `backend.cursor_position()` on a backend created via `create()` in harmonyos.mjs (backends/harmonyos.mjs:271).

Common situations: Generic computer-use automation code that queries cursor position across platforms; porting macOS/Windows-style mouse-based workflows to a HarmonyOS phone/tablet; implementing a UI status bar that shows cursor coordinates.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of Hmbown/CodeWhale@73e0f67d83 (2026-09-22). Data as JSON: /api/errors/7873fd69d0e72400. Report an issue: GitHub.

Appendix: source

Thrown at crates/tui/plugins/computer-use/src/backends/harmonyos.mjs:271

      const d = Math.max(1, Math.min(5, Number(duration) || 1));
      return uiInput(["longClick", "300", "300"]);
    },
    set_value: async ({ target, value }) => {
      const b = await centerOf(target);
      await uiInput(["click", String(b.cx), String(b.cy)]);
      await new Promise((r) => setTimeout(r, 300));
      await uiInput(["inputText", String(b.cx), String(b.cy), escDeviceText(String(value))]);
      return { action_sent: true, strategy: "uitest-element" };
    },
    select_text: async () => { throw new ExecError("select_text is not exposed by uitest dumpLayout/uiInput on the harmony backend"); },
    perform_action: async ({ target, action }) => {
      const b = await centerOf(target);
      if (action === "longClick") return uiInput(["longClick", String(b.cx), String(b.cy)]);
      return uiInput(["click", String(b.cx), String(b.cy)]);
    },
    read_clipboard: async () => { throw new ExecError("clipboard read is not exposed by hdc on current HarmonyOS builds"); },
    write_clipboard: async () => { throw new ExecError("clipboard write is not exposed by hdc on current HarmonyOS builds"); },
    cursor_position: async () => { throw new ExecError("cursor position does not exist on touch devices"); },
    recordingStart: async ({ intervalMs = 400 } = {}) => {
      if (recording) throw new ExecError(`recording ${recording.id} already running`);
      if (!(await have("ffmpeg"))) throw new ExecError("ffmpeg is required on the host to mux harmony snapshot-series recordings");
      const id = crypto.randomBytes(4).toString("hex");
      const dir = fs.mkdtempSync(path.join(os.tmpdir(), `cu-rec-${id}-`));
      const startedAt = new Date().toISOString();
      const rec = recording = { id, dir, startedAt, intervalMs, seq: 0, controller: new AbortController() };
      const tick = () => {
        if (rec.stopped || rec.pending) return rec.pending;
        rec.pending = (async () => {
          const opts = { timeoutMs: 15_000, signal: rec.controller.signal };
          const remote = `${DEVICE_TMP}-rec-${id}-${String(rec.seq).padStart(5, "0")}.jpeg`;
          try {
            await deviceOut(["snapshot_display", "-f", remote], opts);
            await exec.pullFile(remote, path.join(dir, `f${String(rec.seq).padStart(5, "0")}.jpeg`), opts);
            rec.seq++;
          } finally { await shell(["rm", "-f", remote], opts).catch(() => {}); }
        })().catch(() => {}).finally(() => { rec.pending = null; });

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