msg type -> wire::push() -> update handle wire into module/service/ect

Cargo.lock

@@ -1831,7 +1831,6 @@ dependencies = [
  "common",
  "iced",
  "serde",
- "services",
  "thiserror 2.0.20",
  "toml",
 ]

crates/common/src/effect.rs

@@ -1,5 +1,7 @@
 use iced::{window, Rectangle};
 
+use crate::Wire;
+
 /// What a module asks the app to do — the single effect vocabulary shared by
 /// modules and app, so mapping module output into a `Message` is a plain
 /// `.map(Message::Effect)` with no mirror enum.
@@ -12,4 +14,6 @@ pub enum ModuleEffect {
     BoundsFound(String, Rectangle),
     /// Request removal of the popup surface.
     ClosePopup(window::Id),
+    /// Route a wire to its target (a module, a service inbox, or a topic).
+    Send(Wire),
 }

crates/common/src/lib.rs

@@ -6,10 +6,14 @@
 
 mod config;
 mod effect;
+mod messages;
 mod module;
 mod service;
+mod wire;
 
 pub use config::BarbarConfig;
 pub use effect::ModuleEffect;
-pub use module::{BarModule, ModuleMsg};
+pub use messages::{ClockKind, ClockMsg, ClockPayload};
-pub use service::{Service, ServiceEvent};
+pub use module::BarModule;
+pub use service::Service;
+pub use wire::{Endpoint, Inbox, Namespace, Target, Wire};

crates/common/src/messages/mod.rs

@@ -0,0 +1,13 @@
+//! Wire vocabulary: every message type that crosses a crate boundary.
+//!
+//! Laid out to mirror the crate that owns the behavior: `modules/*` are
+//! messages a bar module sends or receives, `services/*` are messages a
+//! service produces or accepts. Types live here so either side can name a
+//! payload without depending on the other's crate; only the types are
+//! shared, the behavior stays in the owning crate.
+
+pub mod modules;
+pub mod services;
+
+pub use modules::*;
+pub use services::*;

crates/common/src/messages/modules/clock.rs

@@ -0,0 +1,10 @@
+//! Clock module messages.
+
+/// A module-local message for the clock (bar/popup interactions).
+#[derive(Clone)]
+pub enum ClockMsg {
+    /// Toggle the seconds suffix.
+    ToggleSeconds,
+    /// Open the big-time popup.
+    OpenPopup,
+}

crates/common/src/messages/modules/mod.rs

@@ -0,0 +1,5 @@
+//! Messages owned by bar modules.
+
+mod clock;
+
+pub use clock::ClockMsg;

crates/common/src/messages/services/datetime.rs

@@ -0,0 +1,27 @@
+//! Clock service messages.
+
+use crate::Service;
+
+/// What a clock subscription wants: the tick interval and payload selector.
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+pub enum ClockKind {
+    Mins,
+    Seconds,
+}
+
+impl ClockKind {
+    /// Route key a module subscribes under to receive this kind's ticks.
+    pub fn key(self) -> Service {
+        Service(match self {
+            Self::Mins => "clock.mins",
+            Self::Seconds => "clock.seconds",
+        })
+    }
+}
+
+/// Clock tick payload: the value plus the kind that produced it.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct ClockPayload {
+    pub kind: ClockKind,
+    pub value: String,
+}

crates/common/src/messages/services/mod.rs

@@ -0,0 +1,5 @@
+//! Messages owned by services.
+
+mod datetime;
+
+pub use datetime::{ClockKind, ClockPayload};

crates/common/src/module.rs

@@ -1,56 +1,22 @@
-use std::any::Any;
 use std::error::Error;
-use std::fmt;
-use std::sync::Arc;
 
 use iced::window;
 use iced::{Element, Task};
 
-use crate::ModuleEffect;
+use crate::{ModuleEffect, Wire};
-
-/// A module-local message, boxed with its owner's `id`. The app routes by
-/// `id` and never names a module's message type; the module downcasts.
-#[derive(Clone)]
-pub struct ModuleMsg {
-    pub id: &'static str,
-    pub payload: Arc<dyn Any + Send + Sync>,
-}
-
-impl ModuleMsg {
-    /// Wraps a module's own message; `id` must match its `BarModule::id`.
-    pub fn new<T: Any + Send + Sync>(id: &'static str, msg: T) -> Self {
-        Self {
-            id,
-            payload: Arc::new(msg),
-        }
-    }
-
-    /// Downcasts to the module's own message type.
-    pub fn downcast<T: Any + Send + Sync>(&self) -> Option<&T> {
-        self.payload.downcast_ref()
-    }
-}
-
-impl fmt::Debug for ModuleMsg {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("ModuleMsg")
-            .field("id", &self.id)
-            .field("payload", &self.payload.type_id())
-            .finish()
-    }
-}
 
 /// A bar module. Object-safe; modules live in a `BTreeMap` keyed by id. The
-/// `ModuleMsg` boundary keeps the app ignorant of each module's message enum.
+/// `Wire` boundary keeps the app ignorant of each module's message enum —
+/// the module downcasts whatever arrives.
 pub trait BarModule: Send {
     fn id(&self) -> &'static str;
 
     /// Bar contents. When `window_id` is `Some`, this is the module's popup
     /// surface and the module returns its popup contents instead.
-    fn view(&self, window_id: Option<window::Id>) -> Element<'_, ModuleMsg>;
+    fn view(&self, window_id: Option<window::Id>) -> Element<'_, Wire>;
 
     /// Handles a routed message; may return app-level tasks (e.g. popups).
-    fn update(&mut self, msg: ModuleMsg) -> Task<ModuleEffect>;
+    fn update(&mut self, msg: Wire) -> Task<ModuleEffect>;
 
     /// What services this module wants.
     fn services(&self) -> Vec<crate::Service>;

crates/common/src/service.rs

@@ -1,16 +1,5 @@
-use std::any::Any;
-use std::sync::Arc;
-
 /// Opaque route key identifying a service subscription. Services name their
 /// own keys, so `common` never enumerates them and adding a service never
 /// edits this crate.
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 pub struct Service(pub &'static str);
-
-/// A service event: the route key plus an erased typed payload. The app reads
-/// `key` for fan-out; the consuming module downcasts `payload`.
-#[derive(Clone, Debug)]
-pub struct ServiceEvent {
-    pub key: Service,
-    pub payload: Arc<dyn Any + Send + Sync>,
-}

crates/common/src/wire.rs

@@ -0,0 +1,151 @@
+use std::any::Any;
+use std::fmt;
+use std::hash::{Hash, Hasher};
+use std::sync::{Arc, Mutex};
+
+use iced::futures::channel::mpsc;
+
+/// Which namespace an endpoint lives in. Module ids and service route keys
+/// are separate namespaces, so a module and a service may share a name.
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+pub enum Namespace {
+    Module,
+    Service,
+}
+
+/// A wire's sender: a module id or a service route key.
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+pub struct Endpoint {
+    pub ns: Namespace,
+    pub name: &'static str,
+}
+
+impl Endpoint {
+    pub const fn module(name: &'static str) -> Self {
+        Self {
+            ns: Namespace::Module,
+            name,
+        }
+    }
+
+    pub const fn service(name: &'static str) -> Self {
+        Self {
+            ns: Namespace::Service,
+            name,
+        }
+    }
+}
+
+/// Where a wire goes. Core owns the routing rule for each variant.
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+pub enum Target {
+    /// One module, by id.
+    Module(&'static str),
+    /// One running service's inbox, by route key.
+    Service(&'static str),
+    /// Every module subscribed to a route key (a service's fan-out).
+    Topic(&'static str),
+}
+
+/// One typed message on the wire. Core routes by `to`; the receiver
+/// downcasts `payload` to one of *its own* types. Sender and receiver keep
+/// their own concrete types — nothing here enumerates them.
+#[derive(Clone)]
+pub struct Wire {
+    pub from: Endpoint,
+    pub to: Target,
+    pub payload: Arc<dyn Any + Send + Sync>,
+}
+
+impl Wire {
+    /// A module-local message: addressed straight back to one module.
+    pub fn module<T: Any + Send + Sync>(from: Endpoint, id: &'static str, msg: T) -> Self {
+        Self {
+            from,
+            to: Target::Module(id),
+            payload: Arc::new(msg),
+        }
+    }
+
+    /// Sent into a service's inbox.
+    pub fn service<T: Any + Send + Sync>(from: Endpoint, key: &'static str, msg: T) -> Self {
+        Self {
+            from,
+            to: Target::Service(key),
+            payload: Arc::new(msg),
+        }
+    }
+
+    /// Published by a service to every module subscribed to `key`.
+    pub fn topic<T: Any + Send + Sync>(from: Endpoint, key: &'static str, msg: T) -> Self {
+        Self {
+            from,
+            to: Target::Topic(key),
+            payload: Arc::new(msg),
+        }
+    }
+
+    /// Downcasts to the receiver's own message type.
+    pub fn downcast<T: Any + Send + Sync>(&self) -> Option<&T> {
+        self.payload.downcast_ref()
+    }
+}
+
+impl fmt::Debug for Wire {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Wire")
+            .field("from", &self.from)
+            .field("to", &self.to)
+            .field("payload", &self.payload.type_id())
+            .finish()
+    }
+}
+
+/// A service's inbound mailbox: modules send `Wire`s here, the service's
+/// subscription task reads them. Cloneable; the receiver is taken once.
+///
+/// The `Arc<Mutex<Option<..>>>` lets `Bar` keep a clone and hand the same
+/// value to `Subscription::run_with` on every rebuild without moving the
+/// single-consumer receiver out of its reach.
+#[derive(Clone)]
+pub struct Inbox {
+    key: &'static str,
+    tx: mpsc::UnboundedSender<Wire>,
+    rx: Arc<Mutex<Option<mpsc::UnboundedReceiver<Wire>>>>,
+}
+
+impl Inbox {
+    /// Creates the channel backing a service's inbox.
+    pub fn new(key: &'static str) -> Self {
+        let (tx, rx) = mpsc::unbounded();
+        Self {
+            key,
+            tx,
+            rx: Arc::new(Mutex::new(Some(rx))),
+        }
+    }
+
+    /// The service's route key, used as the `Topic` it publishes under.
+    pub fn key(&self) -> &'static str {
+        self.key
+    }
+
+    /// Sends a wire into the service; `false` if the service is gone.
+    pub fn send(&self, wire: Wire) -> bool {
+        self.tx.unbounded_send(wire).is_ok()
+    }
+
+    /// Takes the receiver; the service stream calls this once, when iced
+    /// first starts it.
+    pub fn take(&self) -> Option<mpsc::UnboundedReceiver<Wire>> {
+        self.rx.lock().unwrap().take()
+    }
+}
+
+impl Hash for Inbox {
+    /// Identity for `Subscription::run_with`: the route key, so returning
+    /// the same service subscription each pass does not restart its stream.
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.key.hash(state);
+    }
+}

crates/core/src/app.rs

@@ -1,10 +1,11 @@
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, BTreeSet};
 
 use iced::window;
 
-use common::{BarModule, Service};
+use common::{BarModule, Inbox, Service};
+use toml::Table;
 
-/// Application state: module registry + popup bookkeeping.
+/// Application state: module registry, routing, popup bookkeeping.
 pub(crate) struct Bar {
     /// Module whose popup is open; None = closed.
     pub(crate) active_popup: Option<String>,
@@ -14,22 +15,35 @@ pub(crate) struct Bar {
     pub(crate) popup_id: Option<window::Id>,
     /// Fan-out routing table: module id -> services it wants.
     pub(crate) routes: BTreeMap<&'static str, Vec<Service>>,
+    /// One inbound mailbox per running service, keyed by route key. Modules
+    /// send here (`Target::Service`) to talk to a running service.
+    pub(crate) inputs: BTreeMap<&'static str, Inbox>,
 }
 
 impl Bar {
-    pub(crate) fn new() -> Self {
+    pub(crate) fn new(modules_config_table: &Table) -> Self {
         // Registry owns construction: adding a module never edits this file.
         let modules: BTreeMap<&'static str, Box<dyn BarModule>> =
-            modules::all().into_iter().map(|m| (m.id(), m)).collect();
+            modules::all(modules_config_table.clone())
-        let routes = modules
+                .into_iter()
+                .map(|m| (m.id(), m))
+                .collect();
+        let routes: BTreeMap<&'static str, Vec<Service>> = modules
             .iter()
             .map(|(id, module)| (*id, module.services()))
             .collect();
+        // One inbox per distinct service any module wants.
+        let wanted: BTreeSet<&'static str> = routes.values().flatten().map(|s| s.0).collect();
+        let inputs = wanted
+            .into_iter()
+            .map(|key| (key, Inbox::new(key)))
+            .collect();
         Self {
             active_popup: None,
             modules,
             popup_id: None,
             routes,
+            inputs,
         }
     }
 }

crates/core/src/main.rs

@@ -46,8 +46,10 @@ fn main() -> Result<(), iced_layershell::Error> {
         None => StartMode::Active,
     };
 
+    let modules = config.modules.clone().unwrap_or_default();
+
     daemon(
-        app::Bar::new,
+        move || Bar::new(&modules),
         subscription::namespace,
         update::update,
         view::view,

crates/core/src/msg.rs

@@ -1,15 +1,13 @@
 use iced::window;
 use iced_layershell::to_layer_message;
 
-use common::{ModuleEffect, ModuleMsg, ServiceEvent};
+use common::{ModuleEffect, Wire};
 
-/// Synchronous input: module traffic, subscription payloads, window events.
+/// Synchronous input: wires plus window events.
 #[derive(Debug, Clone)]
 pub(crate) enum Msg {
-    /// Routed module message; dispatch by `id`, module downcasts.
+    /// One wire; core dispatches by its `to` target.
-    Module(ModuleMsg),
+    Wire(Wire),
-    /// Service event; fan out by route key.
-    Subscription(ServiceEvent),
     /// The compositor confirmed a window closed. The popup is really gone.
     WindowClosed(window::Id),
 }

crates/core/src/popup.rs

@@ -110,7 +110,7 @@ pub fn view(bar: &Bar) -> Element<'_, Message> {
         .map(|module| {
             module
                 .view(Some(popup_id))
-                .map(|m| Message::Event(Msg::Module(m)))
+                .map(|w| Message::Event(Msg::Wire(w)))
         })
         .unwrap_or_else(|| text("unknown module").into());
 

crates/core/src/subscription.rs

@@ -1,5 +1,6 @@
 use iced::{window, Subscription};
 
+use common::Service;
 use services::IntoSubscription;
 
 use crate::app::Bar;
@@ -10,17 +11,15 @@ pub(crate) fn namespace() -> String {
 }
 
 /// Route subscriptions + window-close events (popup really destroyed).
-/// Each module's wants go through the services registry, so adding a
+/// One subscription per service inbox, so adding a service never edits this.
-/// service never edits this file.
 pub(crate) fn gather_subscriptions(bar: &Bar) -> Subscription<Message> {
     let route_sub = Subscription::batch(
-        bar.routes
+        bar.inputs
-            .values()
+            .iter()
-            .flat_map(|wants| wants.iter())
+            .map(|(&key, inbox)| {
-            .map(|&service| {
+                Service(key)
-                service
+                    .into_subscription(inbox.clone())
-                    .into_subscription()
+                    .map(|wire| Message::Event(Msg::Wire(wire)))
-                    .map(|event| Message::Event(Msg::Subscription(event)))
             })
             .collect::<Vec<_>>(),
     );

crates/core/src/update.rs

@@ -1,6 +1,6 @@
 use iced::Task;
 
-use common::{ModuleEffect, ModuleMsg};
+use common::{ModuleEffect, Service, Target, Wire};
 
 use crate::app::Bar;
 use crate::msg::{Message, Msg};
@@ -18,34 +18,7 @@ pub(crate) fn update(bar: &mut Bar, msg: Message) -> Task<Message> {
 /// Applies an input event to state; effects come back as `Task`s.
 fn handle_event(bar: &mut Bar, event: Msg) -> Task<Message> {
     match event {
-        Msg::Module(m) => match bar.modules.get_mut(m.id) {
+        Msg::Wire(wire) => route(bar, wire),
-            // Modules return protocol tasks; wrap effects into messages.
-            Some(module) => module.update(m).map(Message::Effect),
-            None => Task::none(),
-        },
-
-        Msg::Subscription(event) => {
-            // Fan out by route key; the payload is opaque here, the module
-            // downcasts it. New services never touch this file.
-            let key = event.key;
-            let payload = event.payload;
-            bar.modules
-                .iter_mut()
-                .filter(|(id, _)| {
-                    bar.routes
-                        .get(*id)
-                        .is_some_and(|kinds| kinds.contains(&key))
-                })
-                .map(|(_, module)| {
-                    module
-                        .update(ModuleMsg {
-                            id: module.id(),
-                            payload: payload.clone(),
-                        })
-                        .map(Message::Effect)
-                })
-                .fold(Task::none(), |acc, t| acc.chain(t))
-        }
 
         Msg::WindowClosed(id) => {
             // Popup gone; forget it. `popup_id` stays set until this event
@@ -59,6 +32,38 @@ fn handle_event(bar: &mut Bar, event: Msg) -> Task<Message> {
     }
 }
 
+/// Delivers a wire by its target — the only place routing lives.
+fn route(bar: &mut Bar, wire: Wire) -> Task<Message> {
+    match wire.to {
+        Target::Module(id) => match bar.modules.get_mut(id) {
+            Some(module) => module.update(wire).map(Message::Effect),
+            None => Task::none(),
+        },
+
+        Target::Service(key) => {
+            if let Some(inbox) = bar.inputs.get(key) {
+                inbox.send(wire);
+            }
+            Task::none()
+        }
+
+        Target::Topic(key) => {
+            // Fan out by route key; the payload is opaque here, each module
+            // downcasts it. New services never touch this file.
+            let topic = Service(key);
+            bar.modules
+                .iter_mut()
+                .filter(|(id, _)| {
+                    bar.routes
+                        .get(*id)
+                        .is_some_and(|keys| keys.contains(&topic))
+                })
+                .map(|(_, module)| module.update(wire.clone()).map(Message::Effect))
+                .fold(Task::none(), |acc, t| acc.chain(t))
+        }
+    }
+}
+
 /// Runs an effect; may set up bar state for it (e.g. which popup is open).
 fn handle_effect(bar: &mut Bar, effect: ModuleEffect) -> Task<Message> {
     match effect {
@@ -78,5 +83,7 @@ fn handle_effect(bar: &mut Bar, effect: ModuleEffect) -> Task<Message> {
             // renders until `WindowClosed` confirms it's gone.
             Task::done(Message::RemoveWindow(id))
         }
+
+        ModuleEffect::Send(wire) => route(bar, wire),
     }
 }

crates/core/src/view.rs

@@ -18,7 +18,7 @@ fn bar_view(bar: &Bar) -> Element<'_, Message> {
     let mut children: Vec<Element<Message>> = Vec::new();
 
     for (i, (_, module)) in bar.modules.iter().enumerate() {
-        children.push(module.view(None).map(|m| Message::Event(Msg::Module(m))));
+        children.push(module.view(None).map(|w| Message::Event(Msg::Wire(w))));
         if i < bar.modules.len() - 1 {
             children.push(text("|").size(14).into());
         }

crates/modules/Cargo.toml

@@ -9,7 +9,6 @@ path = "src/lib.rs"
 
 [dependencies]
 common = { path = "../common" }
-services = { path = "../services" }
 iced = { workspace = true }
 thiserror = { workspace = true }
 toml = { workspace = true }

crates/modules/src/clock.rs

@@ -1,13 +1,14 @@
-//! Clock module: subscribes to second ticks, renders the time in the bar.
+//! Clock module: subscribes to the clock service, renders the time in the
-//! Left-click toggles the seconds suffix; right-click opens a popup with
+//! bar. Left-click toggles the seconds suffix — and pokes the running clock
-//! the current time in large text.
+//! service to switch which kind it publishes; right-click opens a popup.
 
 use iced::widget::{container, mouse_area, text};
 use iced::{Element, Task};
 
-use common::{BarModule, ModuleEffect, ModuleMsg, Service};
+use common::{
+    BarModule, ClockKind, ClockMsg, ClockPayload, Endpoint, ModuleEffect, Service, Wire,
+};
 use serde::Deserialize;
-use services::datetime::{ClockKind, ClockPayload};
 use toml::Table;
 
 /// Big-text popup size (logical px).
@@ -22,15 +23,6 @@ pub enum ClockError {
     NotBool(&'static str),
 }
 
-/// A module-local message for the clock.
-#[derive(Clone)]
-pub enum ClockMsg {
-    /// Toggle the seconds suffix.
-    ToggleSeconds,
-    /// Open the big-time popup.
-    OpenPopup,
-}
-
 pub struct Clock {
     value: String,
     show_seconds: bool,
@@ -44,11 +36,10 @@ struct ClockConfig {
 
 impl Clock {
     pub fn new(config: Option<Table>) -> Self {
-        let module_config = config_clock(config);
+        match config_clock(config) {
-        match module_config {
             Some(x) => Self {
                 value: "--:--:--".to_string(),
-                show_seconds: { x.format },
+                show_seconds: x.format,
             },
             None => Self::default(),
         }
@@ -70,7 +61,10 @@ impl Clock {
 
 impl Default for Clock {
     fn default() -> Self {
-        Self::new(None)
+        Self {
+            value: "--:--:--".to_string(),
+            show_seconds: false,
+        }
     }
 }
 
@@ -84,7 +78,8 @@ impl BarModule for Clock {
         "clock"
     }
 
-    fn view(&self, window_id: Option<iced::window::Id>) -> Element<'_, ModuleMsg> {
+    fn view(&self, window_id: Option<iced::window::Id>) -> Element<'_, Wire> {
+        let me = Endpoint::module(self.id());
         match window_id {
             // Popup surface: current time in large text.
             Some(_) => container(text(&self.value).size(56)).padding(20).into(),
@@ -92,16 +87,16 @@ impl BarModule for Clock {
             // so the popup can anchor to these bounds.
             None => container(
                 mouse_area(text(self.shown()).size(16))
-                    .on_press(ModuleMsg::new(self.id(), ClockMsg::ToggleSeconds))
+                    .on_press(Wire::module(me, self.id(), ClockMsg::ToggleSeconds))
-                    .on_right_press(ModuleMsg::new(self.id(), ClockMsg::OpenPopup)),
+                    .on_right_press(Wire::module(me, self.id(), ClockMsg::OpenPopup)),
             )
             .id(iced::widget::Id::from(self.id()))
             .into(),
         }
     }
 
-    fn update(&mut self, msg: ModuleMsg) -> Task<ModuleEffect> {
+    fn update(&mut self, msg: Wire) -> Task<ModuleEffect> {
-        // Subscription fan-out delivers a raw `ClockPayload`, not `ClockMsg`.
+        // The service publishes a raw `ClockPayload`; UI sends `ClockMsg`.
         if let Some(payload) = msg.downcast::<ClockPayload>() {
             self.value = payload.value.clone();
             return Task::none();
@@ -109,7 +104,17 @@ impl BarModule for Clock {
         match msg.downcast::<ClockMsg>() {
             Some(ClockMsg::ToggleSeconds) => {
                 self.show_seconds = !self.show_seconds;
-                Task::none()
+                let want = if self.show_seconds {
+                    ClockKind::Seconds
+                } else {
+                    ClockKind::Mins
+                };
+                // Poke the running clock service: tell it which kind to publish.
+                Task::done(ModuleEffect::Send(Wire::service(
+                    Endpoint::module(self.id()),
+                    ClockKind::Seconds.key().0,
+                    want,
+                )))
             }
             Some(ClockMsg::OpenPopup) => Task::done(ModuleEffect::RequestPopup(
                 self.id().to_string(),
@@ -127,3 +132,17 @@ impl BarModule for Clock {
         Some((POPUP_W, POPUP_H))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Regression: `new(None)` used to call `default()`, which called
+    /// `new(None)` — infinite recursion (hard stack overflow) whenever the
+    /// clock config was absent or failed to parse.
+    #[test]
+    fn no_config_terminates() {
+        assert!(!Clock::new(None).show_seconds);
+        assert!(!Clock::default().show_seconds);
+    }
+}

crates/modules/src/lib.rs

@@ -3,7 +3,7 @@
 
 mod clock;
 
-pub use clock::{Clock, ClockError, ClockMsg};
+pub use clock::{Clock, ClockError};
 use common::BarModule;
 use toml::Table;
 

crates/services/src/datetime.rs

@@ -1,48 +1,33 @@
-//! Clock service: emits a `ServiceEvent` whenever a clock kind's displayed
+//! Clock service: publishes a `Wire` on every change of the displayed
-//! value changes (minute or second rollover).
+//! value, and accepts `ClockKind` wires from modules that want it to switch
+//! which kind it publishes.
 //!
 //! The ticker knows nothing about the app's `Message` type; it produces
-//! protocol events from `common` that core routes to subscribed modules.
+//! protocol wires from `common` that core routes to subscribers.
 
 use std::collections::HashMap;
-use std::sync::Arc;
 
-use iced::{futures::SinkExt, Subscription};
+use iced::futures::{channel::mpsc, SinkExt, StreamExt};
+use iced::Subscription;
 
-use common::{Service, ServiceEvent};
+use common::{ClockKind, ClockPayload, Endpoint, Inbox, Wire};
 
 /// Route-key namespace owned by this service; keys are `"clock.<kind>"`.
 pub const NAMESPACE: &str = "clock.";
 
-/// What a clock subscription wants: the tick interval and payload selector.
+/// Drives the clock, publishing only the kind modules last asked for.
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
-pub enum ClockKind {
-    Mins,
-    Seconds,
-}
-
-impl ClockKind {
-    /// Route key a module subscribes under to receive this kind's ticks.
-    pub fn key(self) -> Service {
-        Service(match self {
-            Self::Mins => "clock.mins",
-            Self::Seconds => "clock.seconds",
-        })
-    }
-}
-
-/// Clock tick payload: the value plus the kind that produced it.
-#[derive(Clone, PartialEq, Eq, Debug)]
-pub struct ClockPayload {
-    pub kind: ClockKind,
-    pub value: String,
-}
-
-/// Emits a payload only when a kind's displayed value changes (minute or
-/// second rollover). Drive `tick` once per second.
-#[derive(Default)]
 pub struct ClockTicker {
     last: HashMap<ClockKind, String>,
+    want: ClockKind,
+}
+
+impl Default for ClockTicker {
+    fn default() -> Self {
+        Self {
+            last: HashMap::new(),
+            want: ClockKind::Seconds,
+        }
+    }
 }
 
 impl ClockTicker {
@@ -50,52 +35,63 @@ impl ClockTicker {
         Self::default()
     }
 
-    /// Subscription that emits a `ServiceEvent` on every change.
+    /// Subscription that reads inbound wires from `inbox` and publishes
-    pub fn run() -> Subscription<ServiceEvent> {
+    /// changes to every module subscribed to this service's route key.
-        Subscription::run_with((), |_| {
+    pub fn run(inbox: Inbox) -> Subscription<Wire> {
+        Subscription::run_with(inbox, |inbox| {
+            let key = inbox.key();
+            // ponytail: the builder runs once (identity is stable, see `Inbox`
+            // hashing). If a module ever makes `services()` dynamic and a key
+            // is dropped then recreated, `take()` returns None and this panics
+            // — make `Bar` rebuild the inbox per start instead.
+            let mut rx = inbox.take().expect("inbox receiver is taken once");
             iced::stream::channel(
                 0,
-                |mut sender: iced::futures::channel::mpsc::Sender<ServiceEvent>| async move {
+                move |mut sender: mpsc::Sender<Wire>| async move {
                     let mut clock = ClockTicker::new();
                     let mut interval = tokio::time::interval(std::time::Duration::from_secs(1));
                     loop {
-                        interval.tick().await;
+                        tokio::select! {
-                        for payload in clock.tick() {
+                            _ = interval.tick() => {
-                            let event = ServiceEvent {
+                                if let Some(payload) = clock.tick() {
-                                key: payload.kind.key(),
+                                    let wire = Wire::topic(Endpoint::service(key), key, payload);
-                                payload: Arc::new(payload),
+                                    if sender.send(wire).await.is_err() {
-                            };
-                            if sender.send(event).await.is_err() {
                                         return;
                                     }
                                 }
                             }
+                            msg = rx.next() => match msg {
+                                Some(wire) => {
+                                    // A module poking us: switch published kind.
+                                    if let Some(kind) = wire.downcast::<ClockKind>() {
+                                        clock.want = *kind;
+                                        clock.last.clear();
+                                    }
+                                }
+                                None => return,
+                            },
+                        }
+                    }
                 },
             )
         })
     }
 
-    /// Returns a payload per kind whose value changed since the last tick.
+    /// Latest value for the wanted kind, or `None` if unchanged.
-    /// The second that rolls into a new minute yields `[Seconds, Mins]`.
+    pub fn tick(&mut self) -> Option<ClockPayload> {
-    pub fn tick(&mut self) -> Vec<ClockPayload> {
+        let value = chrono::Local::now()
-        let now = chrono::Local::now();
+            .format(match self.want {
-        [ClockKind::Seconds, ClockKind::Mins]
-            .into_iter()
-            .filter_map(|kind| {
-                let value = now
-                    .format(match kind {
                 ClockKind::Mins => "%H:%M",
                 ClockKind::Seconds => "%H:%M:%S",
             })
             .to_string();
-                match self.last.get(&kind) {
+        if self.last.get(&self.want) == Some(&value) {
-                    Some(prev) if *prev == value => None,
+            return None;
-                    _ => {
-                        self.last.insert(kind, value.clone());
-                        Some(ClockPayload { kind, value })
-                    }
         }
+        self.last.insert(self.want, value.clone());
+        Some(ClockPayload {
+            kind: self.want,
+            value,
         })
-            .collect()
     }
 }

crates/services/src/lib.rs

@@ -4,23 +4,23 @@
 
 use iced::Subscription;
 
-use common::{Service, ServiceEvent};
+use common::{Inbox, Service, Wire};
 
 pub mod datetime;
 
-/// Conversion from a route key to the subscription backing it.
+/// Conversion from a route key + its inbox to the subscription backing it.
 ///
 /// An extension trait (not `impl From<Service> for Subscription<...>`) because
 /// both `Service` and `Subscription` are foreign to this crate — the orphan
 /// rule blocks a foreign trait (`From`) on a foreign type (`Subscription`).
 pub trait IntoSubscription {
-    fn into_subscription(self) -> Subscription<ServiceEvent>;
+    fn into_subscription(self, inbox: Inbox) -> Subscription<Wire>;
 }
 
 impl IntoSubscription for Service {
-    fn into_subscription(self) -> Subscription<ServiceEvent> {
+    fn into_subscription(self, inbox: Inbox) -> Subscription<Wire> {
         match self.0 {
-            key if key.starts_with(datetime::NAMESPACE) => datetime::ClockTicker::run(),
+            key if key.starts_with(datetime::NAMESPACE) => datetime::ClockTicker::run(inbox),
             _ => Subscription::none(),
         }
     }

test.toml

@@ -1,4 +1,4 @@
 monitor = "DP-2"
 
 [modules.clock]
-format = "meow"
+format = true