diff --git a/src/bar/mod.rs b/src/bar/mod.rs
index e006a63..0d20edc 100644
--- a/src/bar/mod.rs
+++ b/src/bar/mod.rs
@@ -2,6 +2,7 @@ pub mod bluetooth;
 pub mod clock;
 pub mod control;
 pub mod media;
+pub mod slots;
 pub mod stats;
 pub mod tray;
 pub mod wifi;
diff --git a/src/bar/slots.rs b/src/bar/slots.rs
new file mode 100644
index 0000000..cb4d359
--- /dev/null
+++ b/src/bar/slots.rs
@@ -0,0 +1,53 @@
+//! Module registry for the theme manifest's `[bar.slots]` (plan Phase 3a).
+//!
+//! Each bar module (`workspaces`, `media`, `clock`, `volume`, `wifi`,
+//! `battery`, `control`, …) is still built exactly where it always was in
+//! `main.rs` — this registry only decouples the ORDER in which those
+//! already-constructed widgets get appended into the left/centre/right
+//! containers from the fixed source-code order they were built in. main.rs
+//! registers each widget by its manifest module name once construction is
+//! done, then walks `ShellTheme::slots()` to append them in the theme's
+//! order instead of a hardcoded sequence.
+//!
+//! The Lua-declared `widget_*` containers (`WidgetPlacement`) are NOT part
+//! of this registry — their fixed interleave (right-of-workspaces,
+//! left/right-of-clock, left-of-stats) stays exactly as it is today.
+//! Generalizing their placement is Phase 3b, not this task.
+
+use gtk4::prelude::*;
+use std::collections::HashMap;
+
+/// Maps a `[bar.slots]` module name to its already-built widget.
+#[derive(Default)]
+pub struct ModuleRegistry(HashMap<&'static str, gtk4::Widget>);
+
+impl ModuleRegistry {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Registers `widget` under `name` (a `[bar.slots]` module name, e.g.
+    /// `"workspaces"` or `"clock"`).
+    pub fn register(&mut self, name: &'static str, widget: &impl IsA<gtk4::Widget>) {
+        self.0.insert(name, widget.clone().upcast());
+    }
+
+    /// Appends every module named in `names` (a manifest slot list, in
+    /// theme order) into `container` via `on_widget`, which lets the
+    /// caller interleave fixed Lua widget containers around specific
+    /// modules (e.g. the clock). A name with no registered widget is
+    /// logged and skipped — an unrecognized or unmapped module in a theme
+    /// manifest must never crash the bar.
+    pub fn for_each_in_slot(
+        &self,
+        names: &[String],
+        mut on_widget: impl FnMut(&str, &gtk4::Widget),
+    ) {
+        for name in names {
+            match self.0.get(name.as_str()) {
+                Some(widget) => on_widget(name, widget),
+                None => eprintln!("breadbar: [bar.slots] names unknown module '{name}' — skipping"),
+            }
+        }
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index cf9a5c1..6bf0c6d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -233,7 +233,8 @@ impl SimpleComponent for App {
         workspace_row.set_margin_start(8);
         workspace_row.set_valign(gtk4::Align::Center);
         workspace_row.set_vexpand(false);
-        workspace_row.append(&workspace_trail.overlay);
+        // `workspace_trail.overlay` is appended in the "Assemble" section
+        // below, in the order `[bar.slots].left` names it — not here.
 
         // ── Lua-declared widget containers ──────────────────────────────
         // One per WidgetPlacement; positioned into the layout below as each
@@ -243,7 +244,9 @@ impl SimpleComponent for App {
         use bread_shared::widget::WidgetPlacement;
         let widget_right_of_workspaces = gtk4::Box::new(gtk4::Orientation::Horizontal, 6);
         widget_right_of_workspaces.add_css_class("bread-widget-slot");
-        workspace_row.append(&widget_right_of_workspaces);
+        // Also appended in "Assemble" — after the left slot's modules, so
+        // its fixed position (right of the workspace modules) is preserved
+        // whatever `[bar.slots].left` contains.
 
         let widget_left_of_clock = gtk4::Box::new(gtk4::Orientation::Horizontal, 6);
         widget_left_of_clock.add_css_class("bread-widget-slot");
@@ -396,10 +399,9 @@ impl SimpleComponent for App {
         center_area.add_css_class("center-area");
         center_area.set_valign(gtk4::Align::Center);
         center_area.set_vexpand(false);
-        center_area.append(&media_widget);
-        center_area.append(&widget_left_of_clock);
-        center_area.append(&clock_box);
-        center_area.append(&widget_right_of_clock);
+        // `media_widget`/`clock_box` and the `widget_left_of_clock`/
+        // `widget_right_of_clock` interleave around the clock module are
+        // both appended in "Assemble" below, per `[bar.slots].centre`.
 
         // ── Stats box (right side) ───────────────────────────────────────
         // Demo order: [vol 64] [wifi] [bat 83] [☰]
@@ -408,7 +410,9 @@ impl SimpleComponent for App {
         stats_box.set_margin_end(2);
         stats_box.set_valign(gtk4::Align::Center);
         stats_box.set_vexpand(false);
-        stats_box.append(&widget_left_of_stats);
+        // Also appended in "Assemble" — before the right slot's modules,
+        // preserving its fixed position (left of the stats modules)
+        // whatever `[bar.slots].right` contains.
 
         // CPU/RAM/power draw stay built (control panel + screenshots still
         // read the labels) but never mount on the island — the demo bar
@@ -442,7 +446,7 @@ impl SimpleComponent for App {
         vol_lbl.add_css_class("stat-label");
         vol_box.append(&vol_img);
         vol_box.append(&vol_lbl);
-        stats_box.append(&vol_box);
+        // Appended in "Assemble" below, per `[bar.slots].right`.
 
         let bat_box = gtk4::Box::new(gtk4::Orientation::Horizontal, 0);
         bat_box.add_css_class("stat-pair");
@@ -530,8 +534,8 @@ impl SimpleComponent for App {
         wifi_img.set_halign(gtk4::Align::Center);
         wifi_img.set_hexpand(false);
         connectivity_pair.append(&wifi_img);
-        stats_box.append(&connectivity_pair);
-        stats_box.append(&bat_box);
+        // `connectivity_pair` and `bat_box` are appended in "Assemble"
+        // below, per `[bar.slots].right`.
 
         // ── Control panel popover ────────────────────────────────────────
         // Liquid Motion chrome: CONTROL / vol / bl / lock·sleep·off.
@@ -652,7 +656,8 @@ impl SimpleComponent for App {
             bar::control::spawn_set_brightness(s.value());
         });
 
-        stats_box.append(&hamburger_btn);
+        // `hamburger_btn` is appended in "Assemble" below, per
+        // `[bar.slots].right`.
 
         // Standalone layer windows — below the island, slid in by Hyprland.
         let panels = panel::PanelSet::new(
@@ -707,6 +712,40 @@ impl SimpleComponent for App {
             media_widget.add_controller(mgesture);
         }
 
+        // ── Assemble: slot-driven module order (plan §11 Phase 3a) ───────
+        // Every module widget above is already fully built; only the ORDER
+        // it lands in its container, and which of left/centre/right it
+        // lands in, comes from the theme manifest's `[bar.slots]` now.
+        // The `widget_*` Lua containers keep today's fixed interleave
+        // (right-of-workspaces, left/right-of-clock, left-of-stats) —
+        // generalizing their placement is Phase 3b, not this task.
+        let bar_shell_theme = theme::shell_theme();
+        let bar_slots = bar_shell_theme.slots();
+        let mut bar_modules = bar::slots::ModuleRegistry::new();
+        bar_modules.register("workspaces", &workspace_trail.overlay);
+        bar_modules.register("media", &media_widget);
+        bar_modules.register("clock", &clock_box);
+        bar_modules.register("volume", &vol_box);
+        bar_modules.register("wifi", &connectivity_pair);
+        bar_modules.register("battery", &bat_box);
+        bar_modules.register("control", &hamburger_btn);
+
+        bar_modules.for_each_in_slot(&bar_slots.left, |_, widget| workspace_row.append(widget));
+        workspace_row.append(&widget_right_of_workspaces);
+
+        bar_modules.for_each_in_slot(&bar_slots.centre, |name, widget| {
+            if name == "clock" {
+                center_area.append(&widget_left_of_clock);
+            }
+            center_area.append(widget);
+            if name == "clock" {
+                center_area.append(&widget_right_of_clock);
+            }
+        });
+
+        stats_box.append(&widget_left_of_stats);
+        bar_modules.for_each_in_slot(&bar_slots.right, |_, widget| stats_box.append(widget));
+
         let widget_containers = std::collections::HashMap::from([
             (
                 WidgetPlacement::RightOfWorkspaces,