feat(linux): launch_at_login + input device access permission check

[cserby]

Summary

• launch_at_login on Linux — writes/removes a systemd user unit at $XDG_CONFIG_HOME/systemd/user/openlogi-agent.service. Mirrors the macOS LaunchAgent behaviour exactly: Restart=on-failure (crash respawns; clean exit(0) stays stopped), WantedBy=graphical-session.target (takes effect at next login). Unit content is compared before writing (idempotent). systemctl --user enable/disable is best-effort — failures are logged, not propagated.
• Input device access permission check on Linux — Settings → Permissions now shows a Linux-specific row ("Input device access") backed by probes of /dev/uinput (write) and /dev/hidraw* (read/write, Logitech vendor verified numerically from sysfs HID_ID). Returns Granted / Denied / Unknown (unknown = uinput accessible but no Logitech device connected yet). Description is shown only when access is not yet granted.
• macOS-only UI hidden on Linux — accessibility footer, permission "Open" button, and "log in to macOS" copy are all gated to macOS.

Test plan

• cargo test -p openlogi-agent -p openlogi-gui passes on Linux (7 new unit tests in launch_agent.rs, 4 in permissions.rs)
• cargo clippy --workspace --all-targets -- -D warnings clean
• cargo fmt --check clean
• Toggle "Launch at login" → ~/.config/systemd/user/openlogi-agent.service appears; systemctl --user is-enabled openlogi-agent reports enabled; toggle off → file removed, disabled
• Settings → Permissions shows "Granted" with udev rules installed; "Not granted" without
• No macOS-specific text or buttons visible in Linux GUI build

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR adds Linux support for two features: launch_at_login (via a systemd user unit at $XDG_CONFIG_HOME/systemd/user/openlogi-agent.service) and an input-device access permission check (probing /dev/uinput write access and Logitech /dev/hidraw* read/write access via sysfs vendor ID). macOS-only UI elements (accessibility footer, permission "Open" button, login copy) are correctly gated behind #[cfg(target_os = "macos")].

• launch_agent.rs: Adds reconcile_linux that writes/removes the unit file and calls systemctl --user enable/disable; includes escape_systemd_exec for %/$/space/quote handling and 7 unit tests.
• permissions.rs: Adds probe_uinput, probe_logitech_hidraw, and a pure classify function with 4 unit tests; input_device_access() is the new Linux-facing API.
• settings.rs / app.rs: Refactors the permissions page to build platform-specific groups at compile time; Linux shows a single "Input device access" row with contextual hint text.

Confidence Score: 4/5

Safe to merge for new installs; existing Linux users who have manually run systemctl disable may find the launch-at-login setting silently ineffective after restart.

The reconcile_linux function is called at agent startup (main.rs:92) as well as on setting change. When the unit file already has the correct content, it skips both daemon-reload and systemctl enable. On Linux a service file's presence alone does not mean the unit is enabled — the wants/ symlink must also exist. A user who manually disables the unit (without deleting the file) will have the app setting silently ignored on every subsequent restart until they toggle the setting off and on in the UI.

crates/openlogi-agent/src/launch_agent.rs — the want == have arm of reconcile_linux and the backslash handling in escape_systemd_exec

Important Files Changed

Filename	Overview
crates/openlogi-agent/src/launch_agent.rs	Adds Linux systemd user-unit reconcile with write/remove, daemon-reload, and enable/disable. The content-match shortcut skips systemctl enable, which can leave the unit disabled after a manual systemctl disable since reconcile is also called at startup. Also missing backslash escaping in the quoted ExecStart path.
crates/openlogi-core/src/paths.rs	Extracts xdg_config_home() from the existing xdg_base logic; refactors config_dir() to call it. Functionally equivalent to the previous implementation and correctly rejects relative XDG_CONFIG_HOME values per spec.
crates/openlogi-gui/src/platform/permissions.rs	Adds Linux permission probes for /dev/uinput and /dev/hidraw* with Logitech VID sysfs check. Logic is clean and well-tested; classify is correctly exhaustive. Minor: input_device_access() is called per render frame in settings.rs.
crates/openlogi-gui/src/windows/settings.rs	Gates macOS-only UI (permission items, "Open" button, accessibility footer) behind #[cfg(target_os = "macos")]; adds Linux input-device-access row with inline hint text. The permission probe runs on every render pass rather than being cached.
crates/openlogi-gui/src/app.rs	Gates accessibility_status function and its call site behind #[cfg(target_os = "macos")]; non-macOS builds render an empty div instead. Clean and straightforward platform guard.
crates/openlogi-gui/locales/en.yml	Adds "Input device access" translation key for the new Linux permissions row.

Sequence Diagram

sequenceDiagram
    participant Agent as openlogi-agent (startup)
    participant RL as reconcile_linux(enabled)
    participant FS as Filesystem
    participant SC as systemctl --user

    Agent->>RL: reconcile(launch_at_login)
    RL->>FS: read unit file (current)
    RL->>RL: render_unit(current_exe)

    alt content differs or file absent
        RL->>FS: create_dir_all + write unit file
        RL->>SC: daemon-reload
        RL->>SC: enable openlogi-agent.service
    else content matches (idempotent skip)
        RL-->>Agent: no-op (unit may still be disabled!)
    end

    Note over RL,SC: disable path
    alt "enabled=false, file exists"
        RL->>SC: disable openlogi-agent.service
        RL->>FS: remove unit file
        RL->>SC: daemon-reload
    end

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