bread-theme: validate surfaces.*.anchor like its width/layer siblings

anchor was the one enum-shaped schema field taken via
unwrap_or_default() with no manifest-time validation, while width and
layer both bail! on an unrecognized value (as does bar.window.anchors).
A typo'd anchor silently fell through to breadbar's own runtime
eprintln + unanchored-window fallback instead of the load-time hard
error every other typo'd key gets. Validate against the three shapes
breadbar/src/surface.rs actually implements.

bread-theme/src/shell/manifest.rs

@@ -414,6 +414,18 @@ fn resolve_surfaces(
     let mut out = BTreeMap::new();
     let Some(raw) = raw else { return Ok(out) };
     for (namespace, s) in raw {
+        let anchor = match s.anchor.as_deref() {
+            Some(a @ ("top_right" | "bottom_centre" | "fill")) => a.to_string(),
+            Some(other) => bail!(
+                "theme '{theme_id}': surfaces.{namespace}.anchor = \"{other}\" is not \
+                 top_right|bottom_centre|fill (the only shapes breadbar's satellite \
+                 windows implement — see breadbar/src/surface.rs)"
+            ),
+            None => bail!(
+                "theme '{theme_id}': surfaces.{namespace} has no anchor set \
+                 (expected one of top_right|bottom_centre|fill)"
+            ),
+        };
         let offset = match &s.offset {
             None => vec![],
             Some(RawOffset::Single(v)) => vec![*v],
@@ -439,7 +451,7 @@ fn resolve_surfaces(
         out.insert(
             namespace.clone(),
             Surface {
-                anchor: s.anchor.clone().unwrap_or_default(),
+                anchor,
                 offset,
                 width,
                 layer,

bread-theme/src/shell/mod.rs

@@ -1035,6 +1035,67 @@ mod tests {
         assert!(format!("{err:#}").contains("hexagon"));
     }
 
+    #[test]
+    fn unknown_surface_anchor_is_a_hard_error_not_a_silent_default() {
+        // Before the fix, `surfaces.*.anchor` was the one enum-shaped
+        // field in the whole schema that skipped manifest-time validation
+        // entirely (`unwrap_or_default()`), unlike its siblings `width` and
+        // `layer` which both `bail!`. A typo here must fail exactly like
+        // any other typo'd enum value.
+        let xdg = isolated_xdg();
+        write_theme(
+            &xdg,
+            "badanchor",
+            r#"
+                id = "badanchor"
+                [surfaces."breadbar-notif"]
+                anchor = "top_lft"
+                width  = 320
+                layer  = "overlay"
+            "#,
+        );
+        let err = load_named("badanchor").expect_err("unknown anchor must be a hard error");
+        assert!(format!("{err:#}").contains("top_lft"));
+    }
+
+    #[test]
+    fn missing_surface_anchor_is_a_hard_error() {
+        let xdg = isolated_xdg();
+        write_theme(
+            &xdg,
+            "noanchor",
+            r#"
+                id = "noanchor"
+                [surfaces."breadbar-notif"]
+                width  = 320
+                layer  = "overlay"
+            "#,
+        );
+        let err = load_named("noanchor").expect_err("missing anchor must be a hard error");
+        assert!(format!("{err:#}").contains("no anchor set"));
+    }
+
+    #[test]
+    fn every_known_surface_anchor_shape_resolves() {
+        for anchor in ["top_right", "bottom_centre", "fill"] {
+            let xdg = isolated_xdg();
+            write_theme(
+                &xdg,
+                "okanchor",
+                &format!(
+                    r#"
+                        id = "okanchor"
+                        [surfaces."breadbar-notif"]
+                        anchor = "{anchor}"
+                    "#
+                ),
+            );
+            let theme = load_named("okanchor")
+                .unwrap_or_else(|e| panic!("anchor {anchor} should resolve: {e:#}"));
+            assert_eq!(theme.surfaces()["breadbar-notif"].anchor, anchor);
+        }
+    }
+
     // ---- fallback on broken theme -----------------------------------------
 
     #[test]

bread-theme/src/shell/types.rs

@@ -200,6 +200,13 @@ pub struct Launcher {
 /// one lookup.
 #[derive(Debug, Clone, PartialEq)]
 pub struct Surface {
+    /// One of `top_right`/`bottom_centre`/`fill` — validated in
+    /// `manifest.rs::resolve_surfaces` against the shapes
+    /// `breadbar/src/surface.rs::apply` actually implements, the same
+    /// "typo'd key is a hard error" policy this field's siblings
+    /// (`width`, `layer`) already got. Required, not defaulted: a surface
+    /// entry with no anchor at all is as much a hard `theme.toml` error as
+    /// an unrecognized one.
     pub anchor: String,
     pub offset: Vec<f64>,
     pub width: SurfaceWidth,