refactor(agent-core-v2): extract btw into a features/btw Feature unit (#2724)

- move session/btw to features/btw, mirroring the plan feature layout
- contribute ISessionBtwService at Session scope through BtwFeature
  (contributeService) instead of a static registerScopedService call
- keep the package root exports unchanged; move the test to
  test/features/btw

packages/agent-core-v2/src/features/btw/btwFeature.ts

@@ -0,0 +1,26 @@
+/**
+ * `btw` domain — `BtwFeature`: the side-question ("by the way") capability
+ * assembled as one App-scope Feature unit.
+ *
+ * Contributes the per-Session `ISessionBtwService` through the `features`
+ * base-class seams; retracting the unit withdraws it across the scope tree.
+ * Registered into the feature table at import.
+ */
+
+import { LifecycleScope } from '#/app/scopes';
+import { Feature } from '#/features/feature';
+import { registerFeature } from '#/features/featureRegistry';
+
+import { ISessionBtwService } from './btw';
+import { SessionBtwService } from './btwService';
+
+export class BtwFeature extends Feature {
+  static override readonly name = 'btw';
+
+  constructor() {
+    super();
+    this.contributeService(LifecycleScope.Session, ISessionBtwService, SessionBtwService);
+  }
+}
+
+registerFeature(BtwFeature);

packages/agent-core-v2/src/features/btw/btwService.ts

@@ -5,16 +5,14 @@
  * `IAgentLifecycleService.fork`, then disables tool calls via an
  * `onBeforeExecuteTool` veto listener (blocks every tool call with the
  * `toolApproval.formatDenyMessage`-formatted TOOL_CALL_DISABLED_MESSAGE) and
- * appends the side-channel system reminder. Bound at Session scope —
- * `fork('main')` is a session-level operation, so the service injects the
- * session's `IAgentLifecycleService` directly rather than resolving it through
- * the main agent's accessor. Callers materialize the main agent first;
- * forking a missing source throws.
+ * appends the side-channel system reminder. Contributed at Session scope by
+ * `BtwFeature` (`features/btw/btwFeature`) — `fork('main')` is a
+ * session-level operation, so the service injects the session's
+ * `IAgentLifecycleService` directly rather than resolving it through the main
+ * agent's accessor. Callers materialize the main agent first; forking a
+ * missing source throws.
  */
 
-import { LifecycleScope } from '#/app/scopes';
-
-import { ScopeActivation, registerScopedService } from '#/_base/di/scope';
 import { IAgentSystemReminderService } from '#/agent/systemReminder/systemReminder';
 import { IAgentToolApprovalService } from '#/agent/toolApproval/toolApproval';
 import { denyToolExecution } from '#/agent/toolExecutor/beforeToolExecuteEvent';
@@ -50,11 +48,3 @@ export class SessionBtwService implements ISessionBtwService {
     return child.id;
   }
 }
-
-registerScopedService(
-  LifecycleScope.Session,
-  ISessionBtwService,
-  SessionBtwService,
-  ScopeActivation.OnScopeCreated,
-  'session-btw',
-);

packages/agent-core-v2/src/index.ts

@@ -289,6 +289,9 @@ export * from '#/app/flag/flagService';
 
 export * from '#/agent/activityView/activityView';
 import '#/agent/activityView/activityViewService';
+export * from '#/features/btw/btw';
+export * from '#/features/btw/btwService';
+import '#/features/btw/btwFeature';
 import '#/features/plan/profile/plan';
 export * from '#/features/plan/tools/enter-plan-mode/enter-plan-mode';
 import '#/features/plan/tools/enter-plan-mode/enterPlanModeTool';
@@ -625,8 +628,6 @@ export * from '#/agent/rpc/prompt-metadata';
 export * from '#/agent/scopeContext/scopeContext';
 export * from '#/agent/stepRetry/stepRetry';
 export * from '#/agent/stepRetry/stepRetryService';
-export * from '#/session/btw/btw';
-export * from '#/session/btw/btwService';
 export * from '#/session/sessionInit/sessionInit';
 export * from '#/session/sessionInit/sessionInitService';
 export * from '#/session/sessionInit/profile/init';

packages/agent-core-v2/test/features/btw/btw.test.ts

@@ -6,14 +6,14 @@ import { TestInstantiationService } from '#/_base/di/test';
 import { IAgentSystemReminderService } from '#/agent/systemReminder/systemReminder';
 import { IAgentToolApprovalService } from '#/agent/toolApproval/toolApproval';
 import { IAgentToolExecutorService } from '#/agent/toolExecutor/toolExecutor';
-import type { ToolCall } from '#/kosong/contract/message';
-import { IAgentLifecycleService } from '#/session/agentLifecycle/agentLifecycle';
 import {
   ISessionBtwService,
   SIDE_QUESTION_SYSTEM_REMINDER,
   TOOL_CALL_DISABLED_MESSAGE,
-} from '#/session/btw/btw';
-import { SessionBtwService } from '#/session/btw/btwService';
+} from '#/features/btw/btw';
+import { SessionBtwService } from '#/features/btw/btwService';
+import type { ToolCall } from '#/kosong/contract/message';
+import { IAgentLifecycleService } from '#/session/agentLifecycle/agentLifecycle';
 
 import { stubToolExecutorEvents, type ToolExecutorEventStubs } from '../../agent/toolExecutor/stubs';