fix(gui): harden multimodal image attachments

packages/client/connection/README.md

@@ -1,6 +1,6 @@
 # @deepseek-ai/dsh-client-connection
 
-Wire consumer layer: the client plugin's apply mounts `ctx.connection` (shared api client + single-consumer stream-loop starter); the export face carries the wire contract types, the `AbstractApiClient` seam, and the loop's sink/config types. The platform subclasses (WebApiClient/FixtureApiClient), the ConnectionController loop, and the fixture data source are package-internal — apply selects and drives them; tests reach them via src. Contract: api-contracts v3 §3.
+Wire consumer layer: the client plugin's apply mounts `ctx.connection` (shared api client + single-consumer stream-loop starter); the export face carries the wire contract types, the `AbstractApiClient` seam, and the loop's sink/config types. Each successful generation publishes its validated `host.describe` value through `onDescription` before `onConnected`; a business-error response fails the generation like a transport error. The platform subclasses (WebApiClient/FixtureApiClient), the ConnectionController loop, and the fixture data source are package-internal — apply selects and drives them; tests reach them via src. Contract: api-contracts v3 §3.
 
 ## Model Experience
 

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'
 

packages/client/connection/tests/connection.spec.ts

@@ -23,9 +23,11 @@ describe('connection lifecycle', () => {
   it('announces connected after describe + both streams open, then pumps frames to sinks', async () => {
     const api = new FakeApiClient()
     const muxSeen: string[] = []
+    const descriptions: string[] = []
     let connected = 0
     const controller = new ConnectionController(api, {
       onMuxEnvelope: envelope => muxSeen.push(envelope.payload.type),
+      onDescription: description => descriptions.push(description.version),
       onConnected: () => { connected++ },
     }, FAST)
     controller.start()
@@ -34,6 +36,7 @@ describe('connection lifecycle', () => {
       api.pushMux(subscribedFrame())
       await vi.waitFor(() => { expect(muxSeen).toEqual(['session/subscribed']) })
       expect(api.callsOf('host.describe')).toHaveLength(1)
+      expect(descriptions).toEqual(['0-fake'])
     } finally {
       controller.stop()
     }
@@ -83,6 +86,35 @@ describe('connection lifecycle', () => {
     }
   })
 
+  it('treats a host.describe business error as generation failure', async () => {
+    const api = new FakeApiClient()
+    let describeCalls = 0
+    api.onDescribe = () => {
+      describeCalls += 1
+      if (describeCalls === 1) {
+        return Promise.resolve({
+          rpcId: 'bad-describe' as never,
+          result: {
+            ok: false as const,
+            error: { code: 'internal' as const, message: 'not ready', details: {} },
+          },
+        })
+      }
+      return Promise.resolve(ok({ version: '0', cwd: '/f', attachedSessions: 0 }))
+    }
+    let connected = 0
+    const warnSpy = vi.spyOn(console, 'warn').mockImplementation(() => undefined)
+    const controller = new ConnectionController(api, { onConnected: () => { connected++ } }, FAST)
+    controller.start()
+    try {
+      await vi.waitFor(() => { expect(describeCalls).toBe(2) })
+      await vi.waitFor(() => { expect(connected).toBe(1) })
+    } finally {
+      controller.stop()
+      warnSpy.mockRestore()
+    }
+  })
+
   it('converges stream/error frames into reconnect instead of dispatching them', async () => {
     const api = new FakeApiClient()
     const muxSeen: string[] = []

packages/client/connection/tests/fixture.spec.ts

@@ -207,6 +207,31 @@ describe('createFixtureApi', () => {
     })
   })
 
+  it('accounts for every base64 padding form and reports a missing fixture attachment', async () => {
+    const api = createFixtureApi()
+    const created = await api.sessions.create(req({}))
+    if (!created.result.ok) throw new Error('create failed')
+    const sessionId = created.result.value.sessionId
+    const prompted = await api.sessions.prompt(req({
+      sessionId,
+      mode: 'queue' as const,
+      content: ['YQ==', 'YWI=', 'YWJj'].map(data => ({
+        type: 'image' as const,
+        mediaType: 'image/png' as const,
+        data,
+      })),
+    }))
+    expect(prompted.result.ok).toBe(true)
+    const missing = await api.sessions.attachment(req({
+      sessionId,
+      attachmentId: 'fixture:missing' as never,
+    }))
+    expect(missing.result).toMatchObject({
+      ok: false, error: { details: { reason: 'ATTACHMENT_NOT_FOUND' } },
+    })
+    await api.sessions.cancel(req({ sessionId }))
+  })
+
   it('gamma interval flip emits host/session-status and a running log-less session subscribes at lastSeq -1', async () => {
     vi.useFakeTimers()
     try {