diff --git a/src/crates/assembly/core/src/service/workspace/service.rs b/src/crates/assembly/core/src/service/workspace/service.rs
index 61bd993e49..9dd4e505ed 100644
--- a/src/crates/assembly/core/src/service/workspace/service.rs
+++ b/src/crates/assembly/core/src/service/workspace/service.rs
@@ -2138,7 +2138,26 @@ impl WorkspaceService {
 
         let assistant_root = self.path_manager.assistant_workspace_base_dir(None);
         if path.parent()? != assistant_root {
-            return None;
+            // BitFun → OpenBitFun rebranding left pre-migration assistant
+            // workspaces rooted at the legacy hidden directory. Keep them
+            // recognizable so delete/reset commands can still operate on them.
+            let legacy_root = self
+                .path_manager
+                .product_home_dir()
+                .parent()
+                .map(|home| home.join(".bitfun").join("personal_assistant"))?;
+            if path.parent()? != legacy_root {
+                return None;
+            }
+            // The pre-rebranding default assistant workspace (no id suffix)
+            // is also recognizable so it can be deleted/reset like named ones.
+            if path == legacy_root.join("workspace") {
+                return Some(AssistantWorkspaceDescriptor {
+                    path: path.to_path_buf(),
+                    assistant_id: None,
+                    display_name: Self::assistant_display_name(None),
+                });
+            }
         }
 
         let file_name = path.file_name()?.to_string_lossy();
@@ -3789,6 +3808,30 @@ mod tests {
             Some("Legacy TypeScript implementation".to_string())
         );
     }
+
+    #[tokio::test]
+    async fn legacy_bitfun_assistant_workspace_paths_are_still_recognized() {
+        let env = TestEnvironment::new();
+        let service = build_test_workspace_service(env.path_manager.clone()).await;
+
+        // New-brand assistant root remains recognized.
+        let new_root = env.path_manager.assistant_workspace_base_dir(None);
+        assert!(service.is_assistant_workspace_path(&new_root.join("workspace-abc")));
+        assert!(service.is_assistant_workspace_path(&new_root.join("workspace")));
+
+        // Pre-rebranding assistant workspaces rooted at ~/.bitfun are recognized
+        // so delete/reset commands can still operate on them.
+        let product_home = env.path_manager.product_home_dir();
+        let home = product_home.parent().unwrap();
+        let legacy_root = home.join(".bitfun").join("personal_assistant");
+        assert!(service.is_assistant_workspace_path(&legacy_root.join("workspace-44e0e781")));
+        assert!(service.is_assistant_workspace_path(&legacy_root.join("workspace")));
+
+        // Unrelated paths are still rejected.
+        assert!(!service.is_assistant_workspace_path(&home.join("personal_assistant").join("workspace-xyz")));
+        assert!(!service.is_assistant_workspace_path(&home.join(".bitfun").join("workspace-xyz")));
+        assert!(!service.is_assistant_workspace_path(&home.join(".bitfun").join("personal_assistant").join("other")));
+    }
 }
 
 fn workspace_catalog_revision() -> &'static tokio::sync::watch::Sender<u64> {
diff --git a/src/web-ui/src/flow_chat/store/FlowChatStore.test.ts b/src/web-ui/src/flow_chat/store/FlowChatStore.test.ts
index 5860f7ed50..c96ad9de1e 100644
--- a/src/web-ui/src/flow_chat/store/FlowChatStore.test.ts
+++ b/src/web-ui/src/flow_chat/store/FlowChatStore.test.ts
@@ -986,6 +986,20 @@ describe('FlowChatStore session removal active selection', () => {
     expect(flowChatStore.getState().activeSessionId).toBeNull();
     expect(Array.from(flowChatStore.getState().sessions.keys())).toEqual(['session-keep']);
   });
+
+  it('deletes a session whose workspace directory is unavailable (ID-first backend)', async () => {
+    const session = createSession({
+      sessionId: 'session-legacy',
+      title: 'Legacy assistant session',
+      workspacePath: undefined,
+      projectWorkspacePath: undefined,
+    });
+    flowChatStore.setState(() => ({ sessions: new Map([[session.sessionId, session]]), activeSessionId: session.sessionId }));
+    await flowChatStore.deleteSession(session.sessionId, { nextActiveSessionId: null });
+    expect(apiMocks.deleteSession).toHaveBeenCalledExactlyOnceWith(session.sessionId, session.workspaceId);
+    expect(flowChatStore.getState().sessions.has(session.sessionId)).toBe(false);
+    expect(flowChatStore.getState().activeSessionId).toBeNull();
+  });
 });
 
 describe('FlowChatStore token usage', () => {
diff --git a/src/web-ui/src/flow_chat/store/FlowChatStore.ts b/src/web-ui/src/flow_chat/store/FlowChatStore.ts
index fcab35017c..0a402e6cf6 100644
--- a/src/web-ui/src/flow_chat/store/FlowChatStore.ts
+++ b/src/web-ui/src/flow_chat/store/FlowChatStore.ts
@@ -5379,9 +5379,9 @@ export class FlowChatStore {
         scope.assertCurrent('delete session');
         const sess = this.state.sessions.get(id);
         if (sess?.draft?.phase !== 'editing') {
-          if (!sess || !sessionProjectWorkspacePath(sess)) {
-            throw new Error(`Workspace path not found for session ${id}`);
-          }
+          // The backend resolves session storage by workspace ID, not by path,
+          // so deletion must still be attempted when the workspace directory is
+          // unavailable (e.g. pre-migration assistant workspaces under ~/.bitfun).
           await agentAPI.deleteSession(id, this.sessionHistoryWorkspaceId(id));
           scope.assertCurrent('complete session deletion');
         }