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crates/modules/README.md

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+# modules
+
+Bar modules. Each module renders a piece of the bar (or its popup) and is
+object-safe behind `common::BarModule`, so core holds them as
+`Box<dyn BarModule>` and never knows their message types — everything crosses
+the `common::Wire` boundary.
+
+Message types are shared, so they live in the `common` crate, under
+`common/src/messages/modules/`. That is what lets a module and core name the
+same payload without either depending on the other.
+
+## Getting started: add a module
+
+1. Declare the module's messages in `crates/common/src/messages/modules/greeter.rs`:
+
+```rust
+//! Greeter module messages.
+
+#[derive(Clone)]
+pub enum GreeterMsg {
+    Poke,
+}
+```
+
+2. Re-export them from `crates/common/src/messages/modules/mod.rs`:
+
+```rust
+mod clock;
+mod greeter;
+
+pub use clock::ClockMsg;
+pub use greeter::GreeterMsg;
+```
+
+3. Create `crates/modules/src/greeter.rs`:
+
+```rust
+use std::error::Error;
+
+use iced::widget::text;
+use iced::{Element, Task};
+
+use common::{BarModule, Endpoint, GreeterMsg, ModuleEffect, Service, Wire};
+
+pub struct Greeter {
+    text: String,
+}
+
+impl Default for Greeter {
+    fn default() -> Self {
+        Self { text: "hi".into() }
+    }
+}
+
+impl BarModule for Greeter {
+    fn id(&self) -> &'static str {
+        "greeter"
+    }
+
+    fn view(&self, _window_id: Option<iced::window::Id>) -> Element<'_, Wire> {
+        text(&self.text).into()
+    }
+
+    fn update(&mut self, msg: Wire) -> Task<ModuleEffect> {
+        match msg.downcast::<GreeterMsg>() {
+            Some(GreeterMsg::Poke) => {
+                self.text = "poked".into();
+                Task::none()
+            }
+            None => Task::none(),
+        }
+    }
+
+    /// Route keys this module subscribes to.
+    fn services(&self) -> Vec<Service> {
+        Vec::new(
+    }
+
+    /// Optional: read `module.greeter` from the config table.
+    fn config(&mut self, _config: toml::Table) -> Result<(), Box<dyn Error>> {
+        Ok(())
+    }
+}
+```
+
+4. Register it in `crates/modules/src/lib.rs`'s `all()` and re-export it:
+
+```rust
+mod greeter;
+pub use greeter::Greeter;
+
+pub fn all(module_config: toml::Table) -> Vec<Box<dyn BarModule>> {
+    vec![
+        Box::new(clock::Clock::new(Some(module_config.clone()))),
+        Box::new(greeter::Greeter::default()),
+    ]
+}
+```
+
+That's it — core picks it up by `id()`. Use `wire` targeting:
+
+```rust
+// Module-local message back to yourself:
+Wire::module(Endpoint::module(self.id()), self.id(), GreeterMsg::Poke)
+```
+
+To talk to a service, add it to `services()` and send via
+`Wire::service(...)`; service ticks arrive in `update()` and you `downcast`
+to the payload type (e.g. `common::ClockPayload`). See `src/clock.rs` for a
+full example.