fix(cua-driver-rs): proxy MCP through daemon on Windows/Linux when one is up

[f-trycua]

Summary

`cua-driver mcp` is the entrypoint Claude Code (and every other MCP client) spawns. On macOS it can optionally proxy through a LaunchServices-attributed daemon so TCC bundle-id grants apply. On Windows and Linux the proxy was a no-op — `should_use_daemon_proxy` hard-coded `false` — which meant the in-process MCP server always ran in the calling session.

Concretely on Windows: an `cua-driver mcp` spawned by Claude Code over SSH lands in Session 0 (the sshd service session). Session 0 has no desktop attached, so the window/UIA/screen tools return empty regardless of whether a daemon is up in the user's Session 1+. The `cua-driver call` CLI did not have this problem because `run_call` already had its own `is_daemon_listening` shortcut, but `mcp` (the path Claude Code actually uses) didn't.

Repro live on the Windows VM today

```

Daemon running in Session 2 (RDP user's interactive session)

$ ssh winvm 'cua-driver call list_apps' | head
{ "apps": [ {"pid": 3040, "name": "cua-driver.exe", "running": true},
{"pid": 11552, "name": "WindowsTerminal.exe", "running": true},
{"pid": 9956, "name": "Windows PowerShell ISE (x86)", "running": true},
{"pid": 10516, "name": "Microsoft Edge", "running": true},
{"pid": 2748, "name": "explorer.exe", "running": true} ] }

Claude Code, via the SAME stdio MCP transport:

$ ssh winvm 'claude --print "List running apps via cua-driver"'
"No apps have running:true in the listing."
```

Before this fix: claude's spawned `cua-driver mcp` ran in-process in Session 0 → saw no desktop apps. After: it proxies through the Session-2 daemon → sees what `call` already sees.

What changed

• `crates/cua-driver/src/cli.rs` `should_use_daemon_proxy` non-macOS branch: returns `true` when `is_daemon_listening` finds a daemon on the default socket. Same opt-out knobs as macOS (`--no-daemon-relaunch`, `CUA_DRIVER_RS_MCP_NO_RELAUNCH`); plus `CUA_DRIVER_RS_MCP_FORCE_PROXY` for test harnesses.
• `crates/cua-driver/src/cli.rs` `run_mcp_via_daemon_proxy`: drop the `#[cfg(target_os = "macos")]` gate. The macOS-only auto-launch step (`launch_daemon_and_wait` → `open -n -g -a CuaDriver`) stays macOS-only. On Linux/Windows, when no daemon is up, we bail with an actionable error pointing at `cua-driver autostart enable && kick` rather than silently falling through to a Session-0-attributed in-process server.
• `crates/cua-driver/src/main.rs` non-macOS Mcp arm: now calls the proxy router (mirroring the macOS arm).

Test plan

• macOS `cargo check -p cua-driver` — clean
• Windows PR pre-release-binaries CI builds the artifact (this PR is the test)
• Install the resulting binary on the Windows VM, daemon already in Session 2 via `autostart kick`, run `claude --print "List running apps via cua-driver"` from SSH — should now see real GUI apps
• `cua-driver mcp --no-daemon-relaunch` opt-out still runs in-process

Related

• Built on top of fix(cua-driver-rs): re-exec daemon to refresh TCC trust cache (macOS) #1567 (TCC cache re-exec) and the macOS daemon-proxy infrastructure from PRs cua-driver-rs: missing TCC auto-relaunch (#1479 equivalent) — mcp from IDE terminals fails #1525/cua-driver: auto-delegate mcp to daemon for correct TCC context #1479-equivalent.
• The Windows SSH workflow we verified end-to-end today depends on this fix to be useful for actual Claude Code usage.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Improved MCP daemon-proxy initialization with platform-specific handling
  • macOS now automatically launches the daemon service when required
  • Non-macOS platforms display detailed error messages with instructions when daemon is unavailable
  • Daemon proxy behavior can be controlled via environment variables and command-line flags

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Ignored		May 19, 2026 3:54pm

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 5b5f728f-ab4a-4f8b-ac14-89f4a363bab6

📥 Commits

Reviewing files that changed from the base of the PR and between 0f834c6 and da059cd.

📒 Files selected for processing (2)

• libs/cua-driver-rs/crates/cua-driver/src/cli.rs
• libs/cua-driver-rs/crates/cua-driver/src/main.rs

---

📝 Walkthrough

Walkthrough

This PR modifies the MCP command handling on non-macOS platforms to intelligently route requests through an optional daemon proxy. should_use_daemon_proxy replaces a hardcoded false with environment-variable-driven and socket-availability-based logic. run_mcp_via_daemon_proxy gains platform-specific fallback behavior when no daemon listens. The MCP dispatcher conditionally invokes the proxy path on non-macOS based on the decision function.

Changes

MCP daemon proxy routing on non-macOS

Layer / File(s)	Summary
Daemon proxy decision logic libs/cua-driver-rs/crates/cua-driver/src/cli.rs	should_use_daemon_proxy replaces non-macOS hardcoded false with conditional logic: respects opt-out via --no-daemon-relaunch and CUA_DRIVER_RS_MCP_NO_RELAUNCH, forces proxy when CUA_DRIVER_RS_MCP_FORCE_PROXY=1, and otherwise probes daemon availability on the default socket.
Daemon proxy startup with platform-specific fallback libs/cua-driver-rs/crates/cua-driver/src/cli.rs	run_mcp_via_daemon_proxy gains explicit handling when no daemon is listening: fails immediately with setup instructions under forced proxy, auto-launches daemon with user message on macOS, and bails with actionable guidance on non-macOS.
MCP command routing through proxy libs/cua-driver-rs/crates/cua-driver/src/main.rs	Non-macOS MCP dispatcher now calls should_use_daemon_proxy, conditionally executes run_mcp_via_daemon_proxy with error logging and exit(1) on failure, and falls through to in-process server if proxy is not used.

Sequence Diagram

flowchart TD
  Start["User runs: cua-driver mcp"] --> Decision{"should_use_daemon_proxy<br/>checks: opt-out flags,<br/>force proxy, daemon availability"}
  Decision -->|"no_daemon_relaunch=true<br/>or env var set"| InProcess["Run in-process<br/>MCP server"]
  Decision -->|"CUA_DRIVER_RS_MCP_FORCE_PROXY=1"| ProxyForced["Attempt daemon proxy"]
  Decision -->|"daemon socket listening"| ProxyNormal["Attempt daemon proxy"]
  Decision -->|"no opt-out, no force,<br/>no daemon listening"| ProxyFail
  ProxyForced --> DaemonCheck{"Daemon listening?"}
  ProxyNormal --> DaemonCheck
  DaemonCheck -->|"yes"| ProxyExec["Execute proxy request"]
  DaemonCheck -->|"no + forced"| ErrorFast["Fail: instruct to run<br/>cua-driver serve"]
  DaemonCheck -->|"no + non-macOS"| ErrorUser["Fail: instruct to start<br/>daemon in interactive session"]
  DaemonCheck -->|"no + macOS"| AutoLaunch["Auto-launch daemon<br/>via launch_daemon_and_wait"]
  AutoLaunch --> ProxyExec
  ProxyExec --> Success["Return Ok<br/>and exit"]
  ErrorFast --> Exit1["stderr log error<br/>exit status 1"]
  ErrorUser --> Exit1
  InProcess --> Success

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• trycua/cua#1479: Implements auto-delegation of the mcp command to the serve daemon over Unix socket with matching opt-out behavior (--no-daemon-relaunch, CUA_DRIVER_RS_MCP_NO_RELAUNCH), daemon probing, and proxy fallback logic.

Poem

🐰 A proxy path blooms on non-macOS ground,
Where daemons listen on sockets profound,
Smart routing and fallback, with flags set just right,
Auto-launch on Mac makes everything bright! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: enabling MCP proxy through daemon on Windows/Linux when a daemon is listening, matching the core objective to route requests through the daemon on non-macOS platforms.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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• Create PR with unit tests
• Commit unit tests in branch fix/cua-driver-rs-mcp-proxy-windows

---

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