Add per-output palettes and window-scoped theme binding

Each Hyprland/GDK connector can have its own palette and stylesheet
under $XDG_RUNTIME_DIR/bread/{palettes,themes}/. GTK apps bind a
widget-level provider so two windows in one process can follow
different wallpapers. Bump workspace version to 0.7.4 for the tag.

bread-theme/src/bin/bread-theme.rs

@@ -9,6 +9,8 @@
 //!                           # signal every running bread GUI to recolour
 //!   bread-theme path       # print the stylesheet path
 //!   bread-theme print      # render to stdout (no write)
+//!   bread-theme generate-output <OUTPUT> --image <PATH> [--shared]
+//!   bread-theme generate-output <OUTPUT> --from-json <PATH> [--shared]
 
 use std::process::ExitCode;
 
@@ -25,6 +27,149 @@ fn write_and_report(verb: &str) -> ExitCode {
     }
 }
 
+fn print_help() {
+    eprintln!(
+        "bread-theme — shared stylesheet generator\n\n\
+         USAGE:\n\
+         \x20 bread-theme [generate|reload|path|print]\n\
+         \x20 bread-theme generate-output <OUTPUT> --image <PATH> [--shared]\n\
+         \x20 bread-theme generate-output <OUTPUT> --from-json <WAL-OR-PALETTE.json> [--shared]\n\n\
+         generate          render the pywal palette to the shared stylesheet (default)\n\
+         reload            re-render and signal running bread GUIs to recolour live\n\
+         path              print the stylesheet path ({})\n\
+         print             render to stdout without writing\n\
+         generate-output   write palettes/<OUTPUT>.json and themes/<OUTPUT>.css\n\
+         \x20                --image      isolated `wal -i` (does not touch ~/.cache/wal)\n\
+         \x20                --from-json  wal colors.json or a color1-6 object\n\
+         \x20                --shared     also write the session-global theme.css",
+        bread_theme::shared_css_path().display()
+    );
+}
+
+fn generate_output_cmd() -> ExitCode {
+    let args: Vec<String> = std::env::args().skip(2).collect();
+    if args.is_empty()
+        || args
+            .iter()
+            .any(|a| matches!(a.as_str(), "-h" | "--help" | "help"))
+    {
+        print_help();
+        return if args.is_empty() {
+            ExitCode::FAILURE
+        } else {
+            ExitCode::SUCCESS
+        };
+    }
+
+    let output = args[0].as_str();
+    if output.starts_with('-') {
+        eprintln!("bread-theme: generate-output requires an OUTPUT name (got '{output}')");
+        return ExitCode::FAILURE;
+    }
+
+    let mut image: Option<&str> = None;
+    let mut from_json: Option<&str> = None;
+    let mut shared = false;
+    let mut i = 1;
+    while i < args.len() {
+        match args[i].as_str() {
+            "--shared" => shared = true,
+            "--image" => {
+                i += 1;
+                match args.get(i) {
+                    Some(p) => image = Some(p.as_str()),
+                    None => {
+                        eprintln!("bread-theme: --image requires a path");
+                        return ExitCode::FAILURE;
+                    }
+                }
+            }
+            "--from-json" => {
+                i += 1;
+                match args.get(i) {
+                    Some(p) => from_json = Some(p.as_str()),
+                    None => {
+                        eprintln!("bread-theme: --from-json requires a path");
+                        return ExitCode::FAILURE;
+                    }
+                }
+            }
+            other => {
+                eprintln!("bread-theme: unknown generate-output flag '{other}'");
+                return ExitCode::FAILURE;
+            }
+        }
+        i += 1;
+    }
+
+    match (image, from_json) {
+        (Some(_), Some(_)) => {
+            eprintln!("bread-theme: pass only one of --image or --from-json");
+            ExitCode::FAILURE
+        }
+        (None, None) => {
+            eprintln!("bread-theme: generate-output needs --image <PATH> or --from-json <PATH>");
+            ExitCode::FAILURE
+        }
+        (Some(path), None) => {
+            match bread_theme::generate_output(output, std::path::Path::new(path)) {
+                Ok(css) => finish_generate_output(output, css, shared),
+                Err(e) => {
+                    eprintln!("bread-theme: generate-output failed: {e}");
+                    ExitCode::FAILURE
+                }
+            }
+        }
+        (None, Some(path)) => match write_output_from_json(output, path, shared) {
+            Ok(()) => ExitCode::SUCCESS,
+            Err(e) => {
+                eprintln!("bread-theme: generate-output failed: {e}");
+                ExitCode::FAILURE
+            }
+        },
+    }
+}
+
+fn write_output_from_json(output: &str, json_path: &str, shared: bool) -> std::io::Result<()> {
+    let json = std::fs::read_to_string(json_path)?;
+    let palette = bread_theme::palette_from_json(&json).ok_or_else(|| {
+        std::io::Error::new(
+            std::io::ErrorKind::InvalidData,
+            format!("could not parse palette JSON: {json_path}"),
+        )
+    })?;
+    let pal_path = bread_theme::write_output_palette(output, &palette)?;
+    let css_path = bread_theme::write_output_css(output, &palette)?;
+    eprintln!(
+        "bread-theme: wrote {} and {}",
+        pal_path.display(),
+        css_path.display()
+    );
+    if shared {
+        let shared_path = bread_theme::write_shared_css_from(&palette)?;
+        eprintln!("bread-theme: wrote shared {}", shared_path.display());
+    }
+    Ok(())
+}
+
+fn finish_generate_output(output: &str, css: std::path::PathBuf, shared: bool) -> ExitCode {
+    eprintln!("bread-theme: wrote {}", css.display());
+    if shared {
+        match bread_theme::write_shared_css_from(&bread_theme::load_palette_for(output)) {
+            Ok(path) => {
+                eprintln!("bread-theme: wrote shared {}", path.display());
+                ExitCode::SUCCESS
+            }
+            Err(e) => {
+                eprintln!("bread-theme: failed to write shared stylesheet: {e}");
+                ExitCode::FAILURE
+            }
+        }
+    } else {
+        ExitCode::SUCCESS
+    }
+}
+
 fn main() -> ExitCode {
     let cmd = std::env::args().nth(1).unwrap_or_else(|| "generate".into());
     match cmd.as_str() {
@@ -42,20 +187,15 @@ fn main() -> ExitCode {
         // the file monitor in every running bread GUI, so they all re-read the
         // palette and recolour live — shared widgets *and* each app's own rules.
         "reload" => write_and_report("reloaded"),
+        "generate-output" => generate_output_cmd(),
         "-h" | "--help" | "help" => {
-            eprintln!(
-                "bread-theme — shared stylesheet generator\n\n\
-                 USAGE:\n  bread-theme [generate|reload|path|print]\n\n\
-                 generate  render the pywal palette to the shared stylesheet (default)\n\
-                 reload    re-render and signal running bread GUIs to recolour live\n\
-                 path      print the stylesheet path ({})\n\
-                 print     render to stdout without writing",
-                bread_theme::shared_css_path().display()
-            );
+            print_help();
             ExitCode::SUCCESS
         }
         other => {
-            eprintln!("bread-theme: unknown command '{other}' (try generate|reload|path|print)");
+            eprintln!(
+                "bread-theme: unknown command '{other}' (try generate|reload|path|print|generate-output)"
+            );
             ExitCode::FAILURE
         }
     }