feat: add backend worker workdir registry

crates/worker-runtime/src/catalog.rs

@@ -117,6 +117,10 @@ pub struct WorkingDirectoryRequest {
     pub materializer: MaterializerKind,
     #[serde(default)]
     pub dirty_state_policy: DirtyStatePolicy,
+    /// Backend-assigned stable Workdir id. Runtimes use this when present so the
+    /// Backend can create canonical registry rows before materialization.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub backend_workdir_id: Option<String>,
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]

crates/worker-runtime/src/worker_backend.rs

@@ -1036,6 +1036,7 @@ mod tests {
             },
             materializer: MaterializerKind::LocalGitWorktree,
             dirty_state_policy: DirtyStatePolicy::CleanPointOnly,
+            backend_workdir_id: None,
         }
     }
 

crates/worker-runtime/src/working_directory.rs

@@ -395,7 +395,10 @@ impl WorkingDirectoryMaterializer for LocalGitWorktreeMaterializer {
         &self,
         request: &WorkingDirectoryRequest,
     ) -> Result<WorkingDirectoryBinding, WorkingDirectoryDiagnostic> {
-        let working_directory_id = next_working_directory_id(&request.repository.id);
+        let working_directory_id = request
+            .backend_workdir_id
+            .clone()
+            .unwrap_or_else(|| next_working_directory_id(&request.repository.id));
         self.materialize_with_working_directory_id(
             working_directory_id,
             request,
@@ -719,6 +722,7 @@ mod tests {
             },
             materializer: MaterializerKind::LocalGitWorktree,
             dirty_state_policy: DirtyStatePolicy::CleanPointOnly,
+            backend_workdir_id: None,
         }
     }