Emit bread.paper.changed after a successful set

Link bread-utils v0.7.1 (bread-client) and publish
{ "path": "<wallpaper>" } once awww + wal + bread-theme reload
all succeed. Silent no-op if breadd is down. breadpaper is
CLI-only — no watch subscriber; modules should bread.exec
("breadpaper set …"). See EVENTS.md.

src/lib.rs

@@ -4,7 +4,12 @@ mod wallpaper;
 
 use std::path::{Path, PathBuf};
 
-use anyhow::{Context, Result, bail};
+use anyhow::{bail, Context, Result};
+use bread_utils::bread_client::BreadClient;
+
+/// App id in bread's sibling-app registry (`KNOWN_APPS`). Events publish as
+/// `bread.paper.*`. See `EVENTS.md`.
+const APP_ID: &str = "paper";
 
 const IMAGE_EXTENSIONS: &[&str] = &["png", "jpg", "jpeg", "webp", "gif", "bmp"];
 
@@ -13,9 +18,19 @@ pub fn set(path: &Path) -> Result<()> {
     apply_wallpaper(&path)?;
     generate_palette(&path)?;
     reload_theme()?;
+    emit_changed(&path);
     Ok(())
 }
 
+/// Fire-and-forget `bread.paper.changed`. Silent no-op if breadd is down
+/// (`BreadClient::emit` never blocks or errors the caller).
+fn emit_changed(path: &Path) {
+    BreadClient::connect(APP_ID).emit(
+        "bread.paper.changed",
+        serde_json::json!({ "path": path.to_string_lossy() }),
+    );
+}
+
 pub fn get() -> Result<PathBuf> {
     let home = std::env::var("HOME").context("HOME not set")?;
     let wal_file = PathBuf::from(home).join(".cache/wal/wal");
@@ -59,3 +74,15 @@ fn validate(path: &Path) -> Result<PathBuf> {
 
     Ok(canonical)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn emit_changed_is_silent_without_breadd() {
+        // BreadClient::emit must never panic or error just because the
+        // socket is missing — this is the fail-silent contract.
+        emit_changed(Path::new("/tmp/wallpaper.png"));
+    }
+}