* feat(computer-use): support macOS middle click and gate the AX click path
`--mouse-button middle` already validated end-to-end through the CLI, the
zod schema, and the provider validator, and both the Windows and Linux
providers honored it. Only the macOS provider rejected it outright with
"middle-click is not yet supported", so the flag was a dead end on the one
platform that has no fallback.
Two changes:
- Add `.middle` to the macOS button mapping. macOS has no dedicated middle
event family, so it rides `otherMouseDown`/`otherMouseUp` with the button
number carried by `mouseButton: .center`; that constructor argument is
honored for exactly the `otherMouse*` types, so no extra field write is
needed.
- Validate the requested button before the accessibility fast path, and skip
that path for buttons it cannot express. Previously the raw string was read
unvalidated, and `performClickAction` only special-cased `right`, so
`click --mouse-button middle --element-index N` (no modifiers, count 1) fell
through to `AXPress` — a left click — and reported success with
`path: "accessibility"`. Any unrecognized button string did the same. This
matches guards the Windows and Linux providers already had.
The button enum moves into `OrcaComputerUseMacOSCore` so it is unit-testable;
`main.swift` keeps only the CoreGraphics mapping.
Also documents `--mouse-button` in the computer-use skill guide, which never
mentioned the flag, so agents on Windows and Linux had no way to discover it.
* test(computer-use): cover macOS middle click in the real-desktop e2e suite
* test(computer-use): prove macOS middle-click delivery
Brennan Benson
Jinwoo HongandOrca