feat(cli): full command-line interface via clap

Replace the ad-hoc `--serve` arg sniff with a clap-parsed CLI:

- positional <file> to open at startup (also the OS file-association path)
- --new, --read-only, --backend, --safe-mode/--no-gpu
- --serve/--port (headless JSON automation, unchanged behaviour)
- --export IN OUT (headless format convert via the automation load/save infra)
- --script FILE (run command lines at startup)
- --log/RUST_LOG, plus --version/--help for free

GUI-only options pass to app::boot through a OnceLock config; read-only
gates the save paths. The web build skips parsing (no args).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/cli.rs

@@ -0,0 +1,88 @@
+//! Command-line interface.
+//!
+//! Parsing lives here; `main` interprets the result. Three run modes split out
+//! of the parsed args:
+//!   - `--serve`            headless JSON automation server (see `app::serve`)
+//!   - `--export IN OUT`    one-shot headless format conversion, then exit
+//!   - otherwise            launch the GUI editor, configured via [`GuiConfig`]
+//!
+//! GUI-only options (open-file, `--new`, `--read-only`, `--script`) are stashed
+//! in [`GUI_CONFIG`] for `app::boot` to read, since the iced daemon boots with
+//! no arguments of its own.
+
+use std::path::PathBuf;
+use std::sync::OnceLock;
+
+use clap::Parser;
+
+/// Open CAD Studio command-line options.
+#[derive(Parser, Debug, Default)]
+#[command(
+    name = "OpenCADStudio",
+    version,
+    about = "Open CAD Studio — 2D/3D CAD editor",
+    long_about = None,
+)]
+pub struct Cli {
+    /// CAD file to open at startup (.dwg / .dxf). Also used by the OS file
+    /// association when a drawing is double-clicked.
+    pub file: Option<PathBuf>,
+
+    /// Start with a new empty drawing, ignoring any file argument.
+    #[arg(long)]
+    pub new: bool,
+
+    /// Open read-only: editing is allowed but saving is disabled.
+    #[arg(long)]
+    pub read_only: bool,
+
+    /// Restrict the GPU backend (e.g. dx12, vulkan, gl, metal). Sets WGPU_BACKEND.
+    #[arg(long, value_name = "BACKEND")]
+    pub backend: Option<String>,
+
+    /// Safe mode: force the GL backend, for flaky/hybrid GPU drivers.
+    #[arg(long, visible_alias = "no-gpu")]
+    pub safe_mode: bool,
+
+    /// Run the headless JSON automation server (stdin/stdout, or --port).
+    #[arg(long)]
+    pub serve: bool,
+
+    /// TCP port for --serve (defaults to stdin/stdout).
+    #[arg(long, value_name = "PORT")]
+    pub port: Option<u16>,
+
+    /// Headless convert: read IN, write OUT (format from OUT's extension), exit.
+    #[arg(long, num_args = 2, value_names = ["IN", "OUT"])]
+    pub export: Option<Vec<PathBuf>>,
+
+    /// Run a command script at startup: one command line per line of FILE.
+    #[arg(long, value_name = "FILE")]
+    pub script: Option<PathBuf>,
+
+    /// Log level (error|warn|info|debug|trace). Also honours RUST_LOG.
+    #[arg(long, value_name = "LEVEL")]
+    pub log: Option<String>,
+}
+
+/// GUI startup configuration, handed from `main` to `app::boot` out-of-band
+/// because the iced daemon's boot closure takes no arguments.
+#[derive(Debug, Default, Clone)]
+pub struct GuiConfig {
+    /// File to open on launch (`None` for a blank session).
+    pub file: Option<PathBuf>,
+    /// Open a fresh drawing tab on launch instead of the welcome screen.
+    pub new: bool,
+    /// Saving disabled for this session.
+    pub read_only: bool,
+    /// Command lines to run once the editor is up.
+    pub script_lines: Vec<String>,
+}
+
+/// Set once by `main` before the GUI boots; read by `app::boot`.
+pub static GUI_CONFIG: OnceLock<GuiConfig> = OnceLock::new();
+
+/// The GUI config, or a default empty one if `main` never set it (e.g. tests).
+pub fn gui_config() -> GuiConfig {
+    GUI_CONFIG.get().cloned().unwrap_or_default()
+}