refactor(api): converge the Remote failure vocabulary and client surface

Single RemoteError with a merge-extensible, domain-prefixed code map;
owners throw at the failure point; streams surface marked failures;
clients consume ctx.remote directly with isRemoteFailure as the only
discrimination point and construct no failure instances.

packages/api/session-controller/src/index.ts

@@ -6,7 +6,7 @@ import { errorChain } from '@deepseek-ai/dsh-llm'
 import { canOpenNativePath, openNativePath } from '@deepseek-ai/dsh-native-command'
 import type { SessionEvent, SessionHeader, SessionId } from '@deepseek-ai/dsh-session'
 import type { SessionObservation } from '@deepseek-ai/dsh-session-query'
-import { Remote, TypertRemoteFailure, TypertRemoteService } from '@deepseek-ai/dsh-typert-protocol'
+import { Remote, RemoteError, TypertRemoteService } from '@deepseek-ai/dsh-typert-protocol'
 import {
   ApiSessionAgentController,
   inspectApiSession,
@@ -264,7 +264,7 @@ export class SessionController extends TypertRemoteService {
    * @param request - path after best-effort Session workspace resolution.
    * @param signal - caller lifetime; abort terminates the native command.
    * @returns confirmation after the native opener accepts the path.
-   * @throws TypertRemoteFailure when the request is invalid, cancelled, or the opener fails.
+   * @throws RemoteError when the request is invalid, cancelled, or the opener fails.
    */
   @Remote('openWorkspacePath')
   async openWorkspacePath(
@@ -272,27 +272,23 @@ export class SessionController extends TypertRemoteService {
     signal: AbortSignal,
   ): Promise<SessionOpenWorkspacePathValue> {
     if (request.path.length === 0) {
-      throw new TypertRemoteFailure({
-        code: 'bad-request',
-        message: 'session.openWorkspacePath requires a non-empty path',
-        details: {},
-      })
+      throw new RemoteError(
+        'gateway/bad-request',
+        'session.openWorkspacePath requires a non-empty path',
+        {},
+      )
     }
     signal.throwIfAborted()
     try {
       await this.openPath(request.path, signal)
       return { opened: true }
     } catch (error: unknown) {
-      if (signal.aborted) {
-        throw new TypertRemoteFailure({
-          code: 'cancelled', message: 'path open was aborted', details: {},
-        })
-      }
-      throw new TypertRemoteFailure({
-        code: 'internal',
-        message: `path open failed: ${error instanceof Error ? error.message : String(error)}`,
-        details: {},
-      })
+      if (signal.aborted) throw new RemoteError('gateway/cancelled', 'path open was aborted', {})
+      throw new RemoteError(
+        'gateway/internal',
+        `path open failed: ${error instanceof Error ? error.message : String(error)}`,
+        {},
+      )
     }
   }