breadhelp: add --screenshot CLI mode for automated capture

Three views ("home", "learn", "ask") — one per tab in the Home/Learn/Ask
Stack, switched via the same set_visible_child_name the tab switcher
itself uses, then captured as a full known-size canvas (the window is a
plain top-level, not layer-shell).

Plumbed through breadhelp's own cli::Action/parse() (three more fields,
same shape as force_onboard/autostart/suggest) rather than clap, matching
the app's existing non-clap idiom.

The HANDLES_COMMAND_LINE + thread_local HANDLE singleton architecture
needed one addition beyond the usual NON_UNIQUE-flag fix: every
invocation (including a --screenshot one) normally forwards to the
already-built window over D-Bus and reuses it — worse than the plain
GApplication case in the other apps, since here it's not just "message
the existing instance" but literally switching tabs on and re-capturing
the operator's real, live help-center window. NON_UNIQUE is now set
whenever --screenshot is present in argv (checked before the
Application is even built, since cli::parse() only runs per-invocation
inside connect_command_line).

src/cli.rs

@@ -25,10 +25,39 @@ pub struct Action {
     /// Only acted on if a tour is currently waiting for this exact id —
     /// see the crash-safety note on `ui::tour`.
     pub tour_event: Option<String>,
+    /// Render the named tab, capture it, then exit instead of running
+    /// normally. Known views: "home", "learn", "ask". See `crate::screenshot`.
+    pub screenshot: Option<String>,
+    /// PNG path to write the capture to. Required together with `screenshot`.
+    pub output: Option<String>,
+    /// Capture canvas width — matches the isolated compositor's output
+    /// width (`bread-capture --isolate-width`).
+    pub width: u32,
+    /// Capture canvas height — see `width`.
+    pub height: u32,
+}
+
+impl Action {
+    /// `None` for a normal run. Exits the process with an error if
+    /// `--screenshot` was given without `--output`, before any GTK setup
+    /// happens.
+    pub fn screenshot_request(&self) -> Option<crate::screenshot::ScreenshotRequest> {
+        let view = self.screenshot.clone()?;
+        let Some(output) = self.output.clone() else {
+            eprintln!("breadhelp: --screenshot requires --output");
+            std::process::exit(1);
+        };
+        Some(crate::screenshot::ScreenshotRequest {
+            view,
+            output: output.into(),
+            width: self.width,
+            height: self.height,
+        })
+    }
 }
 
 pub fn parse(args: &[std::ffi::OsString]) -> Action {
-    let mut action = Action::default();
+    let mut action = Action { width: 1920, height: 1080, ..Action::default() };
     let mut it = args.iter().skip(1);
     while let Some(arg) = it.next() {
         if arg == "--onboard" {
@@ -39,6 +68,18 @@ pub fn parse(args: &[std::ffi::OsString]) -> Action {
             action.suggest = it.next().and_then(|s| s.to_str()).map(str::to_string);
         } else if arg == "--tour-event" {
             action.tour_event = it.next().and_then(|s| s.to_str()).map(str::to_string);
+        } else if arg == "--screenshot" {
+            action.screenshot = it.next().and_then(|s| s.to_str()).map(str::to_string);
+        } else if arg == "--output" {
+            action.output = it.next().and_then(|s| s.to_str()).map(str::to_string);
+        } else if arg == "--width" {
+            if let Some(v) = it.next().and_then(|s| s.to_str()).and_then(|s| s.parse().ok()) {
+                action.width = v;
+            }
+        } else if arg == "--height" {
+            if let Some(v) = it.next().and_then(|s| s.to_str()).and_then(|s| s.parse().ok()) {
+                action.height = v;
+            }
         }
     }
     action

src/main.rs

@@ -1,6 +1,7 @@
 mod cli;
 mod config;
 mod content;
+mod screenshot;
 mod services;
 mod theme;
 mod ui;
@@ -19,9 +20,17 @@ fn main() {
     // reach the running (primary) instance's argv, not just re-activate it
     // with no arguments — that's what lets a second launch re-trigger the
     // onboarding tour instead of only focusing the window.
+    let mut flags = ApplicationFlags::HANDLES_COMMAND_LINE;
+    if std::env::args().any(|a| a == "--screenshot") {
+        // Without this, a screenshot run would be forwarded over D-Bus to
+        // the real, already-running breadhelp instead of starting a fresh
+        // one — reusing (and mutating the tab of) the operator's actual
+        // help-center window instead of a disposable one.
+        flags |= ApplicationFlags::NON_UNIQUE;
+    }
     let app = gtk4::Application::builder()
         .application_id("com.breadway.breadhelp")
-        .flags(ApplicationFlags::HANDLES_COMMAND_LINE)
+        .flags(flags)
         .build();
 
     app.connect_command_line(|app, cmdline| {

src/screenshot.rs

@@ -0,0 +1,67 @@
+//! `--screenshot` CLI mode: switch to the named tab, capture it via
+//! `bread-screenshots`, then exit — driven by `bread-ecosystem`'s
+//! `bread-capture` orchestrator, or run standalone for one-off captures.
+//!
+//! breadhelp has three tabs worth capturing (Home/Learn/Ask), switched via
+//! the same `Stack::set_visible_child_name` the tab switcher itself uses —
+//! see `ui::tabs`. The window is a plain top-level (not layer-shell), so a
+//! full known-size canvas capture is enough, same reasoning as breadpad's
+//! popup view.
+
+use gtk4::prelude::*;
+use std::path::PathBuf;
+use std::time::Duration;
+
+/// Extra settle time after `map` for the first frame to actually paint
+/// before grim runs — `map` fires once the surface exists, not once
+/// anything has been drawn into it.
+const SETTLE_DELAY: Duration = Duration::from_millis(300);
+
+const KNOWN_VIEWS: &[&str] = &["home", "learn", "ask"];
+
+#[derive(Clone)]
+pub struct ScreenshotRequest {
+    pub view: String,
+    pub output: PathBuf,
+    pub width: u32,
+    pub height: u32,
+}
+
+/// Wire up the given view's screenshot sequence against an already-built
+/// window and its tab `Stack`. Every path here ends by exiting the process
+/// — it never returns control to the normal help-center UI.
+pub fn dispatch(window: &gtk4::ApplicationWindow, stack: &gtk4::Stack, req: ScreenshotRequest) {
+    if !KNOWN_VIEWS.contains(&req.view.as_str()) {
+        eprintln!(
+            "breadhelp: unknown screenshot view '{}' (known: {})",
+            req.view,
+            KNOWN_VIEWS.join(", ")
+        );
+        std::process::exit(1);
+    }
+    stack.set_visible_child_name(&req.view);
+
+    let output = req.output;
+    let (width, height) = (req.width as i32, req.height as i32);
+    window.connect_map(move |_| {
+        let output = output.clone();
+        gtk4::glib::timeout_add_local_once(SETTLE_DELAY, move || {
+            finish(bread_screenshots::capture_region(0, 0, width, height, &output));
+        });
+    });
+    // The caller (`ui::window::present`) returns immediately after this for
+    // the screenshot path, skipping its own normal `window.present()` call
+    // — trigger it here instead, so `connect_map` above actually has
+    // something to fire for.
+    window.present();
+}
+
+fn finish(result: anyhow::Result<()>) {
+    match result {
+        Ok(()) => std::process::exit(0),
+        Err(e) => {
+            eprintln!("breadhelp: screenshot capture failed: {e}");
+            std::process::exit(1);
+        }
+    }
+}

src/ui/window.rs

@@ -16,6 +16,7 @@ const DEFAULT_TAB: &str = "home";
 struct Handle {
     window: ApplicationWindow,
     home: Home,
+    stack: Stack,
 }
 
 thread_local! {
@@ -39,6 +40,11 @@ pub fn present(app: &Application, action: Action) {
         let handle = cell_ref.as_ref().unwrap();
         let display = WidgetExt::display(&handle.window);
 
+        if let Some(req) = action.screenshot_request() {
+            crate::screenshot::dispatch(&handle.window, &handle.stack, req);
+            return;
+        }
+
         if action.force_onboard {
             tour::restart(&display);
             return;
@@ -131,5 +137,5 @@ fn build(app: &Application) -> Handle {
     // independently of this window (see `tour::start`) — it never needs to
     // be shown at all until the user explicitly opens it later.
 
-    Handle { window, home }
+    Handle { window, home, stack }
 }