fix(layout): auto-réparer l'onglet actif

stale

Le backend renvoie l'id actif autoritaire et le
    frontend l'adopte pour éviter de rejouer un layout
    disparu après overwrite externe.

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

crates/application/src/layout/management.rs

@@ -297,6 +297,15 @@ pub struct SetActiveLayoutInput {
     pub layout_id: LayoutId,
 }
 
+/// Output of [`SetActiveLayout::execute`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct SetActiveLayoutOutput {
+    /// The id of the layout that was **actually** made active. Equals the
+    /// requested id when it exists; otherwise the unchanged current active id
+    /// (self-healing fallback). Authoritative for the frontend (invariant I4).
+    pub active_id: LayoutId,
+}
+
 /// Switches the active layout of a project.
 pub struct SetActiveLayout {
     store: Arc<dyn ProjectStore>,
@@ -317,20 +326,30 @@ impl SetActiveLayout {
 
     /// Sets the active layout.
     ///
+    /// A stale requested id (e.g. an `activeId` left over after git overwrote
+    /// `layouts.json`) must **not** freeze the workspace: instead of hard-
+    /// erroring, it degrades silently to the current active layout (invariant
+    /// I3). The returned [`SetActiveLayoutOutput::active_id`] is the id that was
+    /// actually activated and is authoritative for the frontend (invariant I4).
+    ///
     /// # Errors
-    /// [`AppError::NotFound`] if the project or layout is unknown.
-    pub async fn execute(&self, input: SetActiveLayoutInput) -> Result<(), AppError> {
+    /// - [`AppError::FileSystem`] on persistence failure,
+    /// - [`AppError::Store`] on registry I/O failure.
+    pub async fn execute(
+        &self,
+        input: SetActiveLayoutInput,
+    ) -> Result<SetActiveLayoutOutput, AppError> {
         let project = self.store.load_project(input.project_id).await?;
         let mut doc = resolve_doc(self.fs.as_ref(), &project).await?;
-        if doc.find(input.layout_id).is_none() {
-            return Err(AppError::NotFound(format!("layout {}", input.layout_id)));
-        }
-        doc.active_id = input.layout_id;
+        // Self-heal: keep the requested id when valid, else fall back to the
+        // (always-valid, I2) current active id rather than erroring.
+        let active_id = doc.resolve_existing_id(Some(input.layout_id));
+        doc.active_id = active_id;
 
         persist_doc(self.fs.as_ref(), &project, &doc).await?;
         self.events.publish(DomainEvent::LayoutChanged {
             project_id: input.project_id,
         });
-        Ok(())
+        Ok(SetActiveLayoutOutput { active_id })
     }
 }

crates/application/src/layout/mod.rs

@@ -29,7 +29,7 @@ mod usecases;
 pub use management::{
     CreateLayout, CreateLayoutInput, CreateLayoutOutput, DeleteLayout, DeleteLayoutInput,
     DeleteLayoutOutput, LayoutInfo, ListLayouts, ListLayoutsInput, ListLayoutsOutput, RenameLayout,
-    RenameLayoutInput, SetActiveLayout, SetActiveLayoutInput,
+    RenameLayoutInput, SetActiveLayout, SetActiveLayoutInput, SetActiveLayoutOutput,
 };
 pub use reconcile::{ReconcileLayouts, ReconcileLayoutsInput, ReconcileLayoutsOutput};
 pub use snapshot::{

crates/application/src/layout/store.rs

@@ -77,6 +77,22 @@ impl LayoutsDoc {
         id.unwrap_or(self.active_id)
     }
 
+    /// Resolves a requested view id to a **valid** layout id, never failing.
+    ///
+    /// Returns `id` when it is present in `layouts`; otherwise falls back to
+    /// `active_id` (guaranteed valid by invariant I2 / [`Self::is_valid`]).
+    /// A `None` request (the current view) also resolves to `active_id`. This
+    /// is the self-healing path: a stale `active_id` written by an external tool
+    /// (e.g. git overwriting `layouts.json`) degrades silently instead of
+    /// hard-erroring and freezing the workspace (invariant I3).
+    #[must_use]
+    pub fn resolve_existing_id(&self, id: Option<LayoutId>) -> LayoutId {
+        match id {
+            Some(id) if self.find(id).is_some() => id,
+            _ => self.active_id,
+        }
+    }
+
     /// Finds a layout by id.
     #[must_use]
     pub fn find(&self, id: LayoutId) -> Option<&NamedLayout> {
@@ -177,3 +193,55 @@ pub async fn resolve_doc(fs: &dyn FileSystem, project: &Project) -> Result<Layou
     persist_doc(fs, project, &doc).await?;
     Ok(doc)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Builds a doc with two layouts; the first one is active.
+    fn two_layout_doc() -> (LayoutsDoc, LayoutId, LayoutId) {
+        let active = LayoutId::new_random();
+        let other = LayoutId::new_random();
+        let doc = LayoutsDoc {
+            version: LAYOUTS_VERSION,
+            active_id: active,
+            layouts: vec![
+                NamedLayout {
+                    id: active,
+                    name: "Default".to_owned(),
+                    kind: LayoutKind::Terminal,
+                    tree: default_tree(),
+                },
+                NamedLayout {
+                    id: other,
+                    name: "Second".to_owned(),
+                    kind: LayoutKind::Terminal,
+                    tree: default_tree(),
+                },
+            ],
+        };
+        (doc, active, other)
+    }
+
+    #[test]
+    fn resolve_existing_id_returns_present_id() {
+        let (doc, _active, other) = two_layout_doc();
+        // A present, non-active id is returned verbatim.
+        assert_eq!(doc.resolve_existing_id(Some(other)), other);
+    }
+
+    #[test]
+    fn resolve_existing_id_falls_back_to_active_when_absent() {
+        let (doc, active, _other) = two_layout_doc();
+        // A stale id absent from `layouts` degrades to the valid active id.
+        let stale = LayoutId::new_random();
+        assert_eq!(doc.resolve_existing_id(Some(stale)), active);
+    }
+
+    #[test]
+    fn resolve_existing_id_none_resolves_to_active() {
+        let (doc, active, _other) = two_layout_doc();
+        // The "current view" request resolves to the active id.
+        assert_eq!(doc.resolve_existing_id(None), active);
+    }
+}

crates/application/src/layout/usecases.rs

@@ -169,7 +169,10 @@ impl LoadLayout {
     pub async fn execute(&self, input: LoadLayoutInput) -> Result<LoadLayoutOutput, AppError> {
         let project = self.store.load_project(input.project_id).await?;
         let doc = resolve_doc(self.fs.as_ref(), &project).await?;
-        let id = doc.resolve_id(input.layout_id);
+        // Self-healing (I3): a stale requested id degrades to the valid active
+        // id instead of hard-erroring. `find` is now infallible in practice;
+        // the `ok_or` is kept as a purely defensive guard.
+        let id = doc.resolve_existing_id(input.layout_id);
         let named = doc
             .find(id)
             .ok_or_else(|| AppError::NotFound(format!("layout {id}")))?;
@@ -229,7 +232,10 @@ impl MutateLayout {
     pub async fn execute(&self, input: MutateLayoutInput) -> Result<MutateLayoutOutput, AppError> {
         let project = self.store.load_project(input.project_id).await?;
         let mut doc = resolve_doc(self.fs.as_ref(), &project).await?;
-        let id = doc.resolve_id(input.layout_id);
+        // Self-healing (I3): a stale requested id degrades to the valid active
+        // id instead of hard-erroring. `find_mut` is now infallible in
+        // practice; the `ok_or` is kept as a purely defensive guard.
+        let id = doc.resolve_existing_id(input.layout_id);
 
         let named = doc
             .find_mut(id)