refactor(backend): abstraire le sink de stream hors de tauri::ipc::Channel (#13)

Lot B2 du chantier server/client mode : le cœur backend émet désormais ses
flux via une abstraction de sink agnostique, sans dépendre directement de
tauri::ipc::Channel, préalable au futur serveur web + PTY WebSocket.

- crates/backend : abstraction de sink (stream.rs) câblée dans lib.rs.
- crates/app-tauri : implémentation Tauri du sink (stream.rs) et adaptation
  des surfaces lib.rs, pty.rs, chat.rs.
- Nettoyage clippy des 2 warnings B2.

Validé : cargo check --workspace vert, tests backend/app-tauri verts,
cœur agnostique Tauri, clippy B2 propre.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/backend/src/stream.rs

@@ -0,0 +1,216 @@
+use std::collections::HashMap;
+use std::hash::Hash;
+use std::sync::{Arc, Mutex};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum OutputSinkError {
+    Closed,
+    Full,
+    Other(String),
+}
+
+pub trait OutputSink<T>: Send + Sync + 'static {
+    fn send(&self, item: T) -> Result<(), OutputSinkError>;
+}
+
+type SharedOutputSink<T> = Arc<dyn OutputSink<T>>;
+type SinkRegistry<K, T> = HashMap<K, (u64, SharedOutputSink<T>)>;
+
+pub struct OutputBridge<K, T>
+where
+    K: Copy + Eq + Hash,
+{
+    sinks: Mutex<SinkRegistry<K, T>>,
+}
+
+impl<K, T> Default for OutputBridge<K, T>
+where
+    K: Copy + Eq + Hash,
+    T: 'static,
+{
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<K, T> OutputBridge<K, T>
+where
+    K: Copy + Eq + Hash,
+    T: 'static,
+{
+    #[must_use]
+    pub fn new() -> Self {
+        Self {
+            sinks: Mutex::new(HashMap::new()),
+        }
+    }
+
+    pub fn register(&self, key: K, sink: SharedOutputSink<T>) -> u64 {
+        if let Ok(mut map) = self.sinks.lock() {
+            let gen = map.get(&key).map_or(0, |(g, _)| g.wrapping_add(1));
+            map.insert(key, (gen, sink));
+            gen
+        } else {
+            0
+        }
+    }
+
+    pub fn unregister(&self, key: &K) {
+        if let Ok(mut map) = self.sinks.lock() {
+            map.remove(key);
+        }
+    }
+
+    pub fn unregister_if(&self, key: &K, gen: u64) {
+        if let Ok(mut map) = self.sinks.lock() {
+            if matches!(map.get(key), Some((g, _)) if *g == gen) {
+                map.remove(key);
+            }
+        }
+    }
+
+    pub fn try_send_output(&self, key: &K, item: T) -> Result<(), OutputSinkError> {
+        let sink = {
+            let Ok(map) = self.sinks.lock() else {
+                return Err(OutputSinkError::Closed);
+            };
+            map.get(key)
+                .map(|(_, sink)| Arc::clone(sink))
+                .ok_or(OutputSinkError::Closed)?
+        };
+        sink.send(item)
+    }
+
+    pub fn send_output(&self, key: &K, item: T) -> bool {
+        self.try_send_output(key, item).is_ok()
+    }
+
+    #[must_use]
+    pub fn active_sessions(&self) -> usize {
+        self.sinks.lock().map(|m| m.len()).unwrap_or(0)
+    }
+}
+
+struct ReplayEntry<T> {
+    generation: u64,
+    sink: Option<SharedOutputSink<T>>,
+    scrollback: Vec<T>,
+}
+
+pub struct ReplayOutputBridge<K, T>
+where
+    K: Copy + Eq + Hash,
+{
+    entries: Mutex<HashMap<K, ReplayEntry<T>>>,
+    max_chunks: usize,
+    max_bytes: usize,
+    measure: fn(&T) -> usize,
+}
+
+impl<K, T> ReplayOutputBridge<K, T>
+where
+    K: Copy + Eq + Hash,
+    T: Clone + 'static,
+{
+    #[must_use]
+    pub fn new(max_chunks: usize, max_bytes: usize, measure: fn(&T) -> usize) -> Self {
+        Self {
+            entries: Mutex::new(HashMap::new()),
+            max_chunks,
+            max_bytes,
+            measure,
+        }
+    }
+
+    pub fn register(&self, key: K, sink: SharedOutputSink<T>) -> u64 {
+        if let Ok(mut map) = self.entries.lock() {
+            match map.get_mut(&key) {
+                Some(entry) => {
+                    entry.generation = entry.generation.wrapping_add(1);
+                    entry.sink = Some(sink);
+                    entry.generation
+                }
+                None => {
+                    map.insert(
+                        key,
+                        ReplayEntry {
+                            generation: 0,
+                            sink: Some(sink),
+                            scrollback: Vec::new(),
+                        },
+                    );
+                    0
+                }
+            }
+        } else {
+            0
+        }
+    }
+
+    #[must_use]
+    pub fn scrollback(&self, key: &K) -> Vec<T> {
+        self.entries
+            .lock()
+            .ok()
+            .and_then(|m| m.get(key).map(|e| e.scrollback.clone()))
+            .unwrap_or_default()
+    }
+
+    pub fn unregister(&self, key: &K) {
+        if let Ok(mut map) = self.entries.lock() {
+            map.remove(key);
+        }
+    }
+
+    pub fn detach_if(&self, key: &K, gen: u64) {
+        if let Ok(mut map) = self.entries.lock() {
+            if let Some(entry) = map.get_mut(key) {
+                if entry.generation == gen {
+                    entry.sink = None;
+                }
+            }
+        }
+    }
+
+    pub fn try_send_output(&self, key: &K, item: T) -> Result<(), OutputSinkError> {
+        let sink = {
+            let Ok(mut map) = self.entries.lock() else {
+                return Err(OutputSinkError::Closed);
+            };
+            let Some(entry) = map.get_mut(key) else {
+                return Err(OutputSinkError::Closed);
+            };
+            entry.scrollback.push(item.clone());
+            trim_scrollback(entry, self.max_chunks, self.max_bytes, self.measure);
+            entry.sink.as_ref().map(Arc::clone)
+        };
+
+        match sink {
+            Some(sink) => sink.send(item),
+            None => Err(OutputSinkError::Closed),
+        }
+    }
+
+    pub fn send_output(&self, key: &K, item: T) -> bool {
+        self.try_send_output(key, item).is_ok()
+    }
+
+    #[must_use]
+    pub fn active_sessions(&self) -> usize {
+        self.entries.lock().map(|m| m.len()).unwrap_or(0)
+    }
+}
+
+fn trim_scrollback<T>(
+    entry: &mut ReplayEntry<T>,
+    max_chunks: usize,
+    max_bytes: usize,
+    measure: fn(&T) -> usize,
+) {
+    while !entry.scrollback.is_empty()
+        && (entry.scrollback.len() > max_chunks
+            || entry.scrollback.iter().map(measure).sum::<usize>() > max_bytes)
+    {
+        entry.scrollback.remove(0);
+    }
+}