fix(gui): harden multimodal image attachments

packages/client/connection/src/client/api.ts

@@ -8,6 +8,7 @@
 export type {
   ApiProxy, SessionsApi, SessionSummary, PromptContentPart, HostApi, EventsApi, MuxFrame, HostFrame,
   ApprovalResponsePayload, QuestionResponsePayload, HistoryEntry, ToolEventView,
+  ResponseValue,
 } from '@deepseek-ai/dsh-host-apiproxy/api'
 export type { ToolCallView, ToolResultView } from '@deepseek-ai/dsh-tools/presentation'
 export type {
@@ -20,6 +21,9 @@ export type { IApiClient } from '@deepseek-ai/dsh-host-apiproxy/client'
 export type { SessionId, SessionEvent } from '@deepseek-ai/dsh-session/types'
 export type { ContentBlock, StreamChunk } from '@deepseek-ai/dsh-llm/types'
 
+/** Successful value returned by the connection-generation host handshake. */
+export type HostDescription = import('@deepseek-ai/dsh-host-apiproxy/api').ResponseValue<'host.describe'>
+
 import type { RpcResponse, RpcResult } from '@deepseek-ai/dsh-host-apiproxy/api'
 
 /**

packages/client/connection/src/client/connection.ts

@@ -1,4 +1,4 @@
-import type { IApiClient, HostFrame, MuxFrame, RpcRequest } from './api.ts'
+import type { HostDescription, IApiClient, HostFrame, MuxFrame, RpcRequest } from './api.ts'
 
 /** Reconnect/backoff tunables (deployment-varying — no hardcoded tunables; web-cordis §B.1 lists
  *  these as the future `ctx.connection` plugin Config). All fields optional; defaults below. */
@@ -44,6 +44,8 @@ export type ConnectionState = 'connected' | 'reconnecting'
 export interface ConnectionSinks {
   onMuxEnvelope?: (envelope: RpcRequest<MuxFrame>) => void
   onHostEnvelope?: (envelope: RpcRequest<HostFrame>) => void
+  /** Latest successful host capability snapshot for this connection generation. */
+  onDescription?: (description: HostDescription) => void
   /** After each connection generation is established (both streams open + describe succeeded), first connect included. */
   onConnected?: () => void
   /** Coarse state transitions (deduplicated: fires only on change). The initial pre-connect
@@ -131,13 +133,18 @@ export class ConnectionController {
         // subscribed baseline. The timeout guards against a carrier that never fires onOpen
         // (see ConnectionConfig.streamOpenTimeoutMs).
         const timeout = new AbortController()
-        await Promise.all([
+        const [description] = await Promise.all([
           this.api.host.describe({}),
           Promise.race([streamsOpen, sleep(this.config.streamOpenTimeoutMs, timeout.signal)]),
         ])
         timeout.abort()
+        const descriptionResult = description.result
+        if (!descriptionResult.ok) {
+          throw new Error(`host.describe failed: ${descriptionResult.error.code}: ${descriptionResult.error.message}`)
+        }
         if (ac.signal.aborted) throw new Error('generation aborted during readiness handshake')
         this.attempt = 0
+        this.callSink(() => { this.sinks.onDescription?.(descriptionResult.value) })
         this.emitState('connected')
         this.callSink(this.sinks.onConnected)
       } catch {

packages/client/connection/src/client/index.ts

@@ -19,7 +19,7 @@ export type {
   ToolCallView, ToolResultView,
   RpcRequest, RpcResponse, RpcResult, RpcError, RpcErrorCode,
   ClientRequest, ServerResponse, ServerRequest, ClientResponse, RpcMessage, RpcReceipt,
-  IApiClient, SessionId, SessionEvent, ContentBlock, StreamChunk,
+  HostDescription, IApiClient, SessionId, SessionEvent, ContentBlock, StreamChunk,
 } from './api.ts'
 export { RpcId, AbstractApiClient, transportError } from './api.ts'