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/client/contract/result.ts

@@ -1,29 +0,0 @@
-/** Client operation results spanning the Session and subagent Remote calls. */
-
-import type { RpcError } from '@deepseek-ai/dsh-client-connection/client'
-import type { SubagentControlError } from '@deepseek-ai/dsh-subagent/client'
-import type { SessionError } from '../../types.ts'
-
-/** Failure surfaced by the Client Session object layer. */
-export type ClientFailure = RpcError | SessionError | SubagentControlError
-
-/** Success or failure returned by a Client Session operation. */
-export type ClientResult<T> =
-  | { readonly ok: true; readonly value: T }
-  | { readonly ok: false; readonly error: ClientFailure }
-
-/**
- * Fold a rejected carrier operation into the Client Session failure vocabulary.
- * @param error - rejection from a Remote or local carrier call.
- * @returns the failure branch of a Client Session result.
- */
-export function transportResult<T>(error: unknown): ClientResult<T> {
-  return {
-    ok: false,
-    error: {
-      code: 'internal',
-      message: error instanceof Error ? error.message : String(error),
-      details: {},
-    },
-  }
-}

packages/api/session-controller/src/client/contract/session.ts

@@ -13,7 +13,6 @@ import type { SessionId } from '@deepseek-ai/dsh-session/types'
 import type { RemoteResult } from '@deepseek-ai/dsh-typert-protocol'
 import type { ObservableSnapshot } from '@deepseek-ai/dsh-client-store'
 import type { PromptContentPart, QueueAction, SessionRequestId } from '../../types.ts'
-import type { ClientResult } from './result.ts'
 import type { PendingSubmissionImage, SessionSnapshot } from './snapshot.ts'
 
 /**
@@ -84,7 +83,7 @@ export interface ISession {
     mode: 'queue' | 'steer',
     signal?: AbortSignal,
     requestId?: SessionRequestId,
-  ): Promise<ClientResult<{ accepted: true }>>
+  ): Promise<RemoteResult<{ accepted: true }>>
   /**
    * Resolve one durable image referenced by this session.
    * @param attachmentId - opaque id found in the folded session log.
@@ -92,27 +91,27 @@ export interface ISession {
    */
   readAttachment(
     attachmentId: AttachmentIdType,
-  ): Promise<ClientResult<{ attachment: ImageAttachmentRef; data: Uint8Array }>>
+  ): Promise<RemoteResult<{ attachment: ImageAttachmentRef; data: Uint8Array }>>
   /**
    * Apply one edit, remove, or strict steer action to a still-pending queue occurrence.
    * @param itemId - agent-owned inbox occurrence identity.
    * @param action - requested queue operation.
    * @returns acceptance, or a business/transport error.
    */
-  updateQueue(itemId: MessageId, action: QueueAction): Promise<ClientResult<{ accepted: true }>>
+  updateQueue(itemId: MessageId, action: QueueAction): Promise<RemoteResult<{ accepted: true }>>
   /**
    * Cancel the running turn. Pending queued work remains and resumes in FIFO
    * order after the Host reaches cancellation quiescence.
    * @returns acceptance, or the business error.
    */
-  cancel(): Promise<ClientResult<{ accepted: true }>>
+  cancel(): Promise<RemoteResult<{ accepted: true }>>
   /**
    * Rename this session (explicit user title; pins it against automatic
    * regeneration).
    * @param title - raw title text (the host normalizes acceptance).
    * @returns the normalized accepted title and its event seq, or the business error.
    */
-  rename(title: string): Promise<ClientResult<{ title: string; seq: number }>>
+  rename(title: string): Promise<RemoteResult<{ title: string; seq: number }>>
   /**
    * Extend the history window backwards (older messages pagination).
    * @returns completion; failures land in snapshot.openState/loadingOlder.

packages/api/session-controller/src/client/contract/sessions.ts

@@ -8,10 +8,10 @@ import type { Context } from '@deepseek-ai/cordis'
 import type { SubagentAddress } from '@deepseek-ai/dsh-subagent/client'
 import type { SessionId } from '@deepseek-ai/dsh-session/types'
 import type { WorkspaceId } from '@deepseek-ai/dsh-workspace/types'
+import type { RemoteResult } from '@deepseek-ai/dsh-typert-protocol'
 import type { AgentContext } from '../scope.ts'
 import type { SessionSearchResultItem } from '../sessions/manager.ts'
 import type { SessionBinding, SessionListState } from '../sessions/service.ts'
-import type { ClientResult } from './result.ts'
 import type { SessionFace } from './session.ts'
 import type { ObservableSnapshot } from '@deepseek-ai/dsh-client-store'
 
@@ -83,7 +83,7 @@ export interface ISessions {
   search(
     query: string,
     signal: AbortSignal,
-  ): Promise<ClientResult<{ items: SessionSearchResultItem[]; hasMore: boolean }>>
+  ): Promise<RemoteResult<{ items: SessionSearchResultItem[]; hasMore: boolean }>>
   /**
    * Fork a session from a completed-turn prefix of the source; on resolution
    * the child is in the list store and `open()` can target it.

packages/api/session-controller/src/client/contract/snapshot.ts

@@ -3,8 +3,8 @@ import type { ContentBlock } from '@deepseek-ai/dsh-llm/types'
 import type { MessageId } from '@deepseek-ai/dsh-llm/brand'
 import type { SessionId } from '@deepseek-ai/dsh-session/types'
 import type { SubagentAddress } from '@deepseek-ai/dsh-subagent/client'
+import type { RemoteFailure } from '@deepseek-ai/dsh-typert-protocol'
 import type { SessionRequestId } from '../../types.ts'
-import type { ClientFailure } from './result.ts'
 
 /** One transient inbox occurrence from the authoritative queue snapshot. */
 export interface QueuedMessage {
@@ -53,7 +53,7 @@ export type OpenState = 'cold' | 'loading' | 'open' | 'error'
 /** Send/stop failure surfaced by Session consumers. */
 export interface PromptError {
   readonly op: 'send' | 'stop'
-  readonly error: ClientFailure
+  readonly error: RemoteFailure
 }
 
 /** Immutable Session lifecycle and control snapshot. */
@@ -70,7 +70,7 @@ export interface SessionSnapshot {
   } | null
   readonly removed: boolean
   readonly openState: OpenState
-  readonly openError: ClientFailure | null
+  readonly openError: RemoteFailure | null
   readonly hasMore: boolean
   readonly loadingOlder: boolean
   readonly promptError: PromptError | null