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Background
A worker uses apps on a display of its own, off your screen, while you keep using your Mac. The runtime queues desktop access, moves the window to that display, delivers input only to it and reports evidence of each effect.
Desktop access
| Concept | Meaning |
|---|---|
| Worker | A configuration and a conversation. It may be preparing a task, waiting for the computer or holding it. |
| Seat | A virtual display with the adopted window on it, input delivered to that window only, and a fence that keeps your cursor out. The display is 2560x1440 at 60 Hz by default, adjustable under Settings → Computer → Virtual Display; a change applies to the next seat. |
| Broker | Queues the workers’ requests and grants one seat at a time. A waiting worker’s row reads Waiting for the computer, with how many are ahead. |
One seat today: a second one is refused. Workers converse in parallel, but desktop work takes turns. The physical display must be awake for the virtual one to exist.
External MCP clients share the same broker, browser profile pool and passive Watcher. Separate client grants do not mean simultaneous, unrestricted control of the same app, Chrome profile or Watcher run.
Windows and dialogs
open_session adopts the app’s window, launching the app when it is not running, and moves it to the seat’s display. The runtime never raises the app to the front and never posts a global event: your focus and cursor stay yours.
- Use the current window reference and geometry.
- Observe again after a dialog or a pop-up opens: it can be a window of its own.
- Do not assume a child dialog shares its parent’s bounds or process.
On release the window returns to your display, and an app the worker launched is quit.
Delivery and effect
| Reported outcome | Meaning |
|---|---|
| found_acted | The target was found and the effect was confirmed: a structural change in the window, the field holding the typed value, the control showing the new state, or the surface gone. |
| acted_unverified | The gesture went out but no change could be attributed to it. Observe before deciding; it is never repeated blindly. |
| acted_noop | Nothing was done on purpose, and the message says what to do instead: a toggle already in the requested state, for instance. |
| ambiguous | Several elements carry the target’s name. Add a section or the element ID. |
| honest_miss | No matching target in the current Scene. |
| refused | Not allowed here: a destructive target, a disabled row, a refused shortcut. |
An identical scene after a gesture is a ghost; a changed scene with nothing attributable is a repaint. Both answer acted_unverified. A key, a scroll or a drag is verified only by a visible change. Delivery does not establish completion: a closed Save dialog does not prove the file was written.
Waiting and stopping
A worker waiting for the seat leaves the queue when its turn is stopped. After a turn the worker keeps the seat for 30 seconds, then gives it back; it gives it back at once when another worker is waiting, and never inside a turn. Stop Response and Release Computer are in the Workspace guide.
If Mecum exits without shutting down cleanly, the next launch marks the unfinished turn as failed and runs nothing again. A window a seat had adopted stays where the window server leaves it; its original position is not restored. The agent’s own process may keep running briefly until the next launch ends it.
Check a workflow
The seat depends on private macOS primitives, so each macOS build is validated before the seat acts on it. The bundled ledger lists one validated build: macOS 27.0 (26A5425a) on Mac16,1 with Apple M4, checked in September 2026 for display, input, fence and capture. On another build the app shows Seat: Not Validated, still lets workers try, and records that status with every action.
Validation covers the seat, not an app’s workflow. Check a workflow against the app, its version, the window type and the actions, and record the result.
| Check | Why it matters |
|---|---|
| Dialogs and menus | A workflow can enter a different window or input path. |
| Your own input | The test must include the person continuing to use the Mac. |
| Stop and recovery | Interruption must leave enough evidence to decide what happened. |
A working case does not certify every action, plug-in or release of the same app.
Checked against Mecum app source at main 524eb7f on October 1, 2026. UI labels and paths have not yet been checked against the signed release build.