[bobleer]

ComputerUse already exposed clipboard_get and clipboard_set, but Windows passed writes through a line-oriented PowerShell pipeline, reads ignored the advertised max_output_bytes, and clipboard helpers could wait indefinitely. This change makes plain-text reads/writes preserve Unicode, empty strings, and LF/CRLF on Windows, macOS, and Linux.

• Use an STA Windows Forms helper with raw UTF-8 IO, explicit AppKit string types on macOS, and the selected Linux display server's text clipboard (wl-clipboard for Wayland; xclip/xsel for X11).
• Bound helper IO and cleanup; never retry a potentially completed write through another helper. Keep clipboard contents out of command arguments and diagnostics.
• Honor max_output_bytes while retaining the old max_bytes alias and result fields. Require the control owner lease for reads and deny global clipboard access during window-only sharing.
• Document the existing actions and Linux dependencies; add native round trips to the three-OS CI matrix, with isolated Xvfb and headless Sway seats on Linux.

Validation completed locally: Services Core 20 tests including real macOS AppKit round trips on a private named pasteboard; 59 focused Core tool tests; five control contract tests; 11 Desktop admission tests; full Desktop build; Windows and Linux service/test cross-checks; repository hygiene and GitHub configuration checks; shell syntax and diff checks.

Native CI evidence on the final commit: Windows system clipboard round trip passed (one test, zero ignored); macOS clipboard suite passed including the real named AppKit pasteboard (20 tests, zero ignored); isolated Linux X11 and Wayland round trips each passed (one test, zero ignored per display server). All 14 PR checks passed, including the three OS Rust jobs, three CLI jobs, frontend, Linux x64/ARM64 release validation, and the final Rust/CLI result. CI run.

Remote coverage: tool fixtures reject clipboard actions for SSH workspaces and headless hosts before native IO. Relay remote control, Peer Device Mode, and live Detached Dispatch were not exercised end to end. Clipboard operations remain on the executing desktop host; no controller-local fallback is introduced. No persisted shape is changed.