greetd-moongreet/DECISIONS.md

# Decisions

## 2026-04-24 – Cursor theme via config instead of env (v0.9.0)

- **Who**: ClaudeCode, Dom
- **Why**: Cursor theme in the greeter was the default fallback even with `XCURSOR_THEME=Sweet-cursors` in `/etc/greetd/config.toml`'s `env` prefix. Cage forwards the env, but GTK4 does not honour `XCURSOR_THEME` reliably under greetd — it picks up the theme from `gtk-cursor-theme-name` on `GtkSettings`, and without a session-level settings.ini or GSettings override in the greeter user's home, that property stays at the GTK default. Adding an env-var hack worked for the wlroots pointer rendered by cage, but GTK widgets (button hover, text input) used their own wrong cursor.
- **Tradeoffs**: Adds two config fields (`cursor-theme`, `cursor-size`) — symmetric with the existing `gtk-theme` field and justified by the same cause (GTK4 under greetd ignores the usual discovery paths). Alternative would have been a system-wide `/etc/gtk-4.0/settings.ini` with `gtk-cursor-theme-name=`, but that couples moongreet's appearance to the host system's GTK config and affects every GTK4 app running as any user.
- **How**: `config.rs` gains `cursor_theme: Option<String>` and `cursor_size: Option<i32>` (range-validated 1–256). `greeter.rs::create_greeter_window` applies them via `gtk::Settings::set_gtk_cursor_theme_name()` and `set_gtk_cursor_theme_size()` directly after the existing `gtk-theme` handling, reusing `is_valid_gtk_theme()` for name validation. Moonarch's deployed config gains `cursor-theme = "Sweet-cursors"` + `cursor-size = 24`. The env-prefix hack in `/etc/greetd/config.toml` is now redundant.

## 2026-04-23 – Wallpaper-only windows on secondary monitors (v0.8.5)

- **Who**: ClaudeCode, Dom
- **Why**: The v0.8.4 fix (keyboard grab on the built-in panel) only half-worked. The greeter still rejected keystrokes until the user moved the mouse to eDP-1 — Niri scopes layer-shell keyboard routing by active output, so even though the primary window was the sole `KeyboardMode::Exclusive` surface, keys went nowhere when another output was active. Hardcoding a compositor focus call (e.g. `niri msg action focus-monitor`) would tie moongreet to a specific compositor.
- **Tradeoffs**: Reverts part of 2026-04-08: only the built-in panel shows the full greeter UI, other monitors go back to wallpaper-only. Users with multiple monitors lose the symmetric "login widget on every screen" look, but gain a reliable keyboard path regardless of which output the compositor considers active at startup. Compositor-agnostic — no Niri-specific IPC.
- **How**: New `create_wallpaper_window()` in `greeter.rs` builds a minimal `ApplicationWindow` with the shared background `Picture` (same `blur_cache` as the primary) and no login widgets. `main.rs` uses `create_greeter_window()` for the index returned by `pick_primary_monitor_index()` and `create_wallpaper_window()` for the rest. Hotplugged monitors also get wallpaper-only windows. Both variants use `Layer::Top`; only the primary sets `KeyboardMode::Exclusive`.

## 2026-04-23 – Keyboard focus on built-in display, not first enumerated monitor (v0.8.4)

- **Who**: ClaudeCode, Dom
- **Why**: With a DisplayLink dock attached, the greeter showed its UI on all monitors but the password entry accepted no input. `display.monitors()` enumerated evdi phantom connectors (`DVI-I-*`) before the laptop panel (`eDP-1`); the v0.8.0 logic gave `KeyboardMode::Exclusive` to index 0, so the keyboard grab landed on an invisible surface. Symptom showed up on 2026-04-23 after kernel 6.19.11 → 6.19.12 + moongreet 0.8.0 → 0.8.2 changed evdi enumeration timing — previous Thursdays with the same dock worked.
- **Tradeoffs**: Prefers built-in displays by connector-name pattern (`eDP*`/`LVDS*`/`DSI*`) rather than a generic "primary monitor" concept — Wayland has no portable primary signal, and gdk4's `primary_monitor()` was removed. Pattern-matching covers every current Linux laptop, at the cost of a tiny list to maintain if a new form factor ships a new connector type. Fallback is still index 0, so behavior on desktops without a built-in panel is unchanged.
- **How**: New pure function `pick_primary_monitor_index()` in `main.rs` scans connector names and returns the built-in index (or 0). Used during initial enumeration to decide which window gets `KeyboardMode::Exclusive`. Hotplug branch unchanged — new monitors still get keyboard=false so focus never migrates off the panel. Unit-tested against evdi/eDP/LVDS/DSI/HDMI/DP mixes.

## 2026-04-21 – Ship polkit rule in moongreet instead of moonarch (v0.8.3)

- **Who**: ClaudeCode, Dom
- **Why**: Reboot/shutdown from the greeter silently failed on a fresh install. The polkit rule that grants the `greeter` user `org.freedesktop.login1.{reboot,power-off}` lived in the moonarch repo but was never installed by any PKGBUILD. The laptop worked only because the rule had been hand-deployed once.
- **Tradeoffs**: Rule ownership moves from moonarch (system defaults) to moongreet (greeter-specific auth). Cleaner boundary — moonarch no longer needs to know about the greeter's auth requirements — but it means moongreet is now responsible for a system polkit rule that ties it to a fixed username (`greeter`).
- **How**: Source file moved to `moongreet/config/polkit/50-moongreet-power.rules`, installed to `/etc/polkit-1/rules.d/` by `moongreet-git/PKGBUILD`. Old file removed from the moonarch repo.

## 2026-04-09 – Monitor hotplug via ListModel items-changed

- **Who**: ClaudeCode, Dom
- **Why**: Greeter windows were only created at startup. If a monitor was hotplugged (e.g. HDMI reconnect), it would show no greeter UI. Aligned with moonlock's hotplug fix (same day).
- **Tradeoffs**: Hotplugged monitors get greeter windows without keyboard input (keyboard stays on the primary monitor). Acceptable — user can still interact on the primary screen.
- **How**: Connect to `display.monitors().connect_items_changed()` and create new greeter windows for added monitors. Shared state (config, texture, blur_cache) moved to Rc for the closure.

## 2026-04-08 – Show greeter UI on all monitors instead of just one

- **Who**: ClaudeCode, Dom
- **Why**: moonlock showed its UI on all monitors via ext-session-lock-v1, but moongreet only showed the login UI on one monitor (compositor-picked) with wallpaper-only windows on the rest. Inconsistent UX across the ecosystem.
- **Tradeoffs**: Each monitor gets its own full greeter widget tree (slightly more memory), but the UI is lightweight. Screen mirroring (e.g., wl-mirror/screencopy) was considered and rejected — it requires an external process, compositor screencopy support, adds latency, and fights Wayland's per-output model. One-window-per-monitor is the established Wayland pattern (swaylock, hyprlock, moonlock all do this).
- **How**: Create one `create_greeter_window()` per monitor with `set_monitor()`, only the first gets `KeyboardMode::Exclusive`. Removed `create_wallpaper_window()` (no longer needed). No layer shell fallback keeps single-window mode for development.

## 2026-04-06 – Restore explicit gtk-theme in moongreet config

- **Who**: ClaudeCode, Dom
- **Why**: GTK4 under greetd does not reliably read `/etc/xdg/gtk-4.0/settings.ini` — likely requires a settings daemon that doesn't run in the greeter session. moongreet fell back to Adwaita/Colloid-default (blue accent) instead of Colloid-Grey-Dark-Catppuccin.
- **Tradeoffs**: Reverts `094878f` ("Remove gtk-theme from app config, use system-wide GTK settings instead"). Duplicates the theme name between settings.ini and moongreet.toml, but the explicit set via `set_gtk_theme_name()` is the only reliable path in a greetd context.
- **How**: Added `gtk-theme = "Colloid-Grey-Dark-Catppuccin"` to example config and deployed `/etc/moongreet/moongreet.toml`.

## 2026-04-02 – Replace hardcoded CSS colors with GTK theme variables

- **Who**: ClaudeCode, Dom
- **Why**: moongreet used hardcoded colors (#1a1a2e, white, #ff6b6b) while moonset already used @theme_bg_color, @theme_fg_color, @error_color etc. Inconsistent across the ecosystem and broke theme flexibility.
- **Tradeoffs**: Depends on the active GTK theme defining standard color variables. Catppuccin Colloid provides all needed vars (@theme_bg_color, @theme_fg_color, @error_color, @success_color, @theme_selected_bg_color). Fallback behavior if a theme lacks vars is GTK's default colors — acceptable.
- **How**: Replaced all hardcoded hex/named colors with GTK theme variables. Coordinated change across moongreet, moonlock, and moonset (all three now use identical pattern).

## 2026-03-31 – Fourth audit: power timeout, timing mitigation, release profile, GREETD_SOCK caching

- **Who**: ClaudeCode, Dom
- **Why**: Fourth triple audit found moongreet power.rs had no timeout on loginctl (greeter could freeze), username enumeration via timing differential, GREETD_SOCK re-read on every login, missing release profile, and missing GResource compression.
- **Tradeoffs**: 500ms minimum login response time adds slight delay on fast auth but prevents timing-based username enumeration. Power timeout (30s + SIGKILL) matches moonset pattern — aggressive but prevents greeter freeze.
- **How**: (1) power.rs adapted from moonset with 30s timeout + SIGKILL (nix dependency added). (2) 500ms min response floor in attempt_login via Instant + glib::timeout_future. (3) GREETD_SOCK cached in GreeterState at startup. (4) `[profile.release]` with LTO, codegen-units=1, strip. (5) `compressed="true"` on GResource entries. (6) SYNC comments on duplicated blur/background functions.

## 2026-03-30 – Full audit fix: security, quality, performance (v0.6.2)

- **Who**: ClaudeCode, Dom
- **Why**: Three parallel audits (security, code quality, performance) identified 10 actionable findings across the codebase — from world-readable cache dirs to a GPU blur geometry bug to a race condition in fingerprint probing.
- **Tradeoffs**: `too_many_arguments` Clippy warnings suppressed with `#[allow]` rather than introducing a `UiWidgets` struct — GTK's `clone!` macro with `#[weak]` refs requires individual widget parameters, a struct would fight the idiom. Async avatar loading skipped because `Pixbuf` is `!Send`; cache already prevents repeat loads. TOCTOU socket pre-check removed entirely — `connect()` in login_worker already handles errors, the `metadata()` check gave false security guarantees.
- **How**: Cache dirs use `DirBuilder::mode(0o700)` instead of `create_dir_all`. Blur config clamped to `0.0..=200.0` with `is_finite()` guard. Blur texture cached in `Rc<RefCell<Option<gdk::Texture>>>` across monitors. FingerprintProbe device proxy cached in `GreeterState` with generation counter to prevent stale async writes. GPU blur geometry fixed (`-pad` origin shift instead of texture stretching). `is_valid_gtk_theme` extracted as testable function. 9 new tests.

## 2026-03-29 – Fingerprint authentication via greetd multi-stage PAM

- **Who**: ClaudeCode, Dom
- **Why**: moonlock supports fprintd but moongreet rejected multi-stage auth. Users with enrolled fingerprints couldn't use them at the login screen.
- **Tradeoffs**: Direct fprintd D-Bus verification (like moonlock) can't start a greetd session — greetd controls session creation via PAM. Using greetd multi-stage means PAM decides the auth order (fingerprint first, then password fallback), not truly parallel. Acceptable — matches standard pam_fprintd behavior.
- **How**: Replace single-pass auth with a loop over auth_message rounds. Secret prompts get the password, non-secret prompts (fprintd) get None and block until PAM resolves. fprintd D-Bus probe (gio::DBusProxy) only for UI — detecting device availability and enrolled fingers. 60s socket timeout when fingerprint available. Config option `fingerprint-enabled` (default true).

## 2026-03-28 – Remove embedded wallpaper from binary

- **Who**: ClaudeCode, Dom
- **Why**: Wallpaper is installed by moonarch to /usr/share/moonarch/wallpaper.jpg. Embedding a 374K JPEG in the binary is redundant. GTK background color (Catppuccin Mocha base) is a clean fallback.
- **Tradeoffs**: Without moonarch installed AND without config, greeter shows plain dark background instead of wallpaper. Acceptable — that's the expected minimal state.
- **How**: Remove wallpaper.jpg from GResources, return None from resolve_background_path when no file found, skip wallpaper window creation and background picture when no path available.

## 2026-03-28 – GPU blur via GskBlurNode replaces CPU blur

- **Who**: ClaudeCode, Dom
- **Why**: CPU-side Gaussian blur (`image` crate) blocked the GTK main thread for 500ms–2s on 4K wallpapers at cold cache. Disk cache and async orchestration added significant complexity.
- **Tradeoffs**: GPU blur quality is slightly different (box-blur approximation vs true Gaussian), acceptable for wallpaper backgrounds. Removes `image` crate dependency entirely (~15 transitive crates eliminated). No disk cache needed.
- **How**: `Snapshot::push_blur()` + `GskRenderer::render_texture()` on `connect_realize`. Blur happens once on the GPU when the widget gets its renderer, producing a concrete `gdk::Texture`. Zero startup latency. Symmetric with moonlock and moonset.

## 2026-03-28 – Optional background blur via `image` crate (superseded)

- **Who**: ClaudeCode, Dom
- **Why**: Blurred wallpaper as greeter background is a common UX pattern for login screens
- **Tradeoffs**: Adds `image` crate dependency (~15 transitive crates); CPU-side Gaussian blur at load time adds startup latency proportional to image size and sigma. Acceptable because blur runs once and the texture is shared across monitors.
- **How**: `load_background_texture(bg_path, blur_radius)` loads texture, optionally applies `imageops::blur()`, returns blurred `gdk::Texture`. Config option `background-blur: Option<f32>` in `[appearance]` TOML section.

## 2026-03-28 – Audit fixes for shared wallpaper texture (v0.4.1)
- **Who**: ClaudeCode, Dominik
- **Why**: Quality, performance, and security audits flagged issues in `load_background_texture()`, debug logging, and greetd error handling
- **Tradeoffs**: GResource path now requires UTF-8 (returns `None` for non-UTF-8 instead of aborting); 50 MB wallpaper limit is generous but prevents OOM; debug logging off by default trades observability for security
- **How**: GResource branch via `resources_lookup_data()` + `from_bytes()` (no abort), file size limit, error details only at debug level, `MOONGREET_DEBUG` env var for log level, greetd retry path truncation matching `show_greetd_error()`