Merge remote-tracking branch 'origin/worktree/web-multimodal-image-input' into worktree/web-multimodal-image-input

# Conflicts:
#	.agents/notes/implemented/feature/2026-07-22-web-multimodal-image-input-and-durable-attachments.i18n.yaml
#	apps/web/tests/code-mode-fixture.snapshot.ts
#	apps/web/tests/image-display.snapshot.ts
#	docs/architecture.i18n.yaml
#	docs/module-graph.md
#	packages/client/test-runtime/tests/runtime.spec.tsx
#	packages/client/ui-conversation/src/client/skeleton/ConversationSession.tsx
#	packages/client/ui-conversation/tests/terminal-card.spec.tsx
#	packages/client/ui-trajectory/src/client/layout.ts

packages/client/test-runtime/src/sessions.ts

@@ -1,7 +1,6 @@
 /** Test-owned sessions face: the SlotsService host contract over declarative fixtures. */
 import type { Context } from 'cordis'
 import type { AttachmentIdType } from '@deepseek-ai/dsh-attachment'
-import type { HostDescription } from '@deepseek-ai/dsh-client-connection/client'
 import { createScope, scopeOf, SessionProvideChannel } from '@deepseek-ai/dsh-client-runtime/client'
 import { createSnapshotStore } from '@deepseek-ai/dsh-client-runtime/client'
 import type {
@@ -197,14 +196,6 @@ export class TestSessions implements ISessions {
     this.list.subscribe(() => { this.channel.publishCurrent() })
   }
 
-  /**
-   * Test runtime has no host handshake unless a fixture explicitly supplies one.
-   * @returns undefined.
-   */
-  hostDescription(): HostDescription | undefined {
-    return undefined
-  }
-
   /**
    * Add a session from a fixture and (by default) make it current.
    * @param fixture - identity + snapshot/summary overrides + behavior face.