feat(app): introduce MessageState trait and handler for AppMessage dispatch

- Add `MessageState` trait defining UI reaction callbacks for generation lifecycle, model updates, provider status, resize, and tick events.
- Implement `App::handle_message` to route `AppMessage` variants to the provided `MessageState` and determine exit condition.
- Add `handler.rs` module with the trait and dispatch logic; re-export `MessageState` in `app/mod.rs`.
- Extend `ActiveGeneration` with a public `request_id` getter and clean up dead code annotations.
- Implement empty `MessageState` for `ChatApp` to integrate UI handling.
- Add `log` crate dependency for warning messages.

crates/owlen-tui/Cargo.toml

@@ -42,6 +42,7 @@ uuid = { workspace = true }
 serde_json.workspace = true
 serde.workspace = true
 chrono = { workspace = true }
+log = { workspace = true }
 
 [dev-dependencies]
 tokio-test = { workspace = true }

crates/owlen-tui/src/app/handler.rs

@@ -0,0 +1,135 @@
+use super::{App, messages::AppMessage};
+use log::warn;
+use owlen_core::{
+    provider::{GenerateChunk, GenerateRequest, ProviderStatus},
+    state::AppState,
+};
+use uuid::Uuid;
+
+/// Trait implemented by UI state containers to react to [`AppMessage`] events.
+pub trait MessageState {
+    /// Called when a generation request is about to start.
+    #[allow(unused_variables)]
+    fn start_generation(
+        &mut self,
+        request_id: Uuid,
+        provider_id: &str,
+        request: &GenerateRequest,
+    ) -> AppState {
+        AppState::Running
+    }
+
+    /// Called for every streamed generation chunk.
+    #[allow(unused_variables)]
+    fn append_chunk(&mut self, request_id: Uuid, chunk: &GenerateChunk) -> AppState {
+        AppState::Running
+    }
+
+    /// Called when a generation finishes successfully.
+    #[allow(unused_variables)]
+    fn generation_complete(&mut self, request_id: Uuid) -> AppState {
+        AppState::Running
+    }
+
+    /// Called when a generation fails.
+    #[allow(unused_variables)]
+    fn generation_failed(&mut self, request_id: Option<Uuid>, message: &str) -> AppState {
+        AppState::Running
+    }
+
+    /// Called when refreshed model metadata is available.
+    fn update_model_list(&mut self) -> AppState {
+        AppState::Running
+    }
+
+    /// Called when a models refresh has been requested.
+    fn refresh_model_list(&mut self) -> AppState {
+        AppState::Running
+    }
+
+    /// Called when provider status updates arrive.
+    #[allow(unused_variables)]
+    fn update_provider_status(&mut self, provider_id: &str, status: ProviderStatus) -> AppState {
+        AppState::Running
+    }
+
+    /// Called when a resize event occurs.
+    #[allow(unused_variables)]
+    fn handle_resize(&mut self, width: u16, height: u16) -> AppState {
+        AppState::Running
+    }
+
+    /// Called on periodic ticks.
+    fn handle_tick(&mut self) -> AppState {
+        AppState::Running
+    }
+}
+
+impl App {
+    /// Dispatch a message to the provided [`MessageState`]. Returns `true` when the
+    /// state indicates the UI should exit.
+    pub fn handle_message<State>(&mut self, state: &mut State, message: AppMessage) -> bool
+    where
+        State: MessageState,
+    {
+        use AppMessage::*;
+
+        let outcome = match message {
+            KeyPress(_) => AppState::Running,
+            Resize { width, height } => state.handle_resize(width, height),
+            Tick => state.handle_tick(),
+            GenerateStart {
+                request_id,
+                provider_id,
+                request,
+            } => state.start_generation(request_id, &provider_id, &request),
+            GenerateChunk { request_id, chunk } => state.append_chunk(request_id, &chunk),
+            GenerateComplete { request_id } => {
+                self.clear_active_generation(request_id);
+                state.generation_complete(request_id)
+            }
+            GenerateError {
+                request_id,
+                message,
+            } => {
+                self.clear_active_generation_optional(request_id);
+                state.generation_failed(request_id, &message)
+            }
+            ModelsRefresh => state.refresh_model_list(),
+            ModelsUpdated => state.update_model_list(),
+            ProviderStatus {
+                provider_id,
+                status,
+            } => state.update_provider_status(&provider_id, status),
+        };
+
+        matches!(outcome, AppState::Quit)
+    }
+
+    fn clear_active_generation(&mut self, request_id: Uuid) {
+        if self
+            .active_generation
+            .as_ref()
+            .map(|active| active.request_id() == request_id)
+            .unwrap_or(false)
+        {
+            self.active_generation = None;
+        } else {
+            warn!(
+                "received completion for unknown request {}, ignoring",
+                request_id
+            );
+        }
+    }
+
+    fn clear_active_generation_optional(&mut self, request_id: Option<Uuid>) {
+        match request_id {
+            Some(id) => self.clear_active_generation(id),
+            None => {
+                if self.active_generation.is_some() {
+                    self.active_generation = None;
+                }
+            }
+        }
+    }
+}

crates/owlen-tui/src/app/mod.rs

@@ -1,4 +1,5 @@
 mod generation;
+mod handler;
 mod worker;
 
 pub mod messages;
@@ -12,6 +13,7 @@ use tokio::{
 };
 use uuid::Uuid;
 
+pub use handler::MessageState;
 pub use messages::AppMessage;
 
 /// High-level application state driving the non-blocking TUI.
@@ -65,7 +67,6 @@ impl App {
 }
 
 struct ActiveGeneration {
-    #[allow(dead_code)]
     request_id: Uuid,
     #[allow(dead_code)]
     provider_id: String,
@@ -88,4 +89,8 @@ impl ActiveGeneration {
     fn abort(self) {
         self.abort_handle.abort();
     }
+
+    fn request_id(&self) -> Uuid {
+        self.request_id
+    }
 }

crates/owlen-tui/src/chat_app.rs

@@ -11200,3 +11200,5 @@ fn configure_textarea_defaults(textarea: &mut TextArea<'static>) {
     textarea.set_cursor_style(Style::default());
     textarea.set_cursor_line_style(Style::default());
 }
+
+impl crate::app::MessageState for ChatApp {}