feat(host-proxy): add targetClientId support to HostFileProxy and HostProxyBase

assistant/src/daemon/host-cu-proxy.ts

@@ -120,6 +120,7 @@ export class HostCuProxy extends HostProxyBase<
     stepNumber: number,
     reasoning?: string,
     signal?: AbortSignal,
+    targetClientId?: string,
   ): Promise<ToolExecutionResult> {
     if (signal?.aborted) {
       return Promise.resolve({
@@ -139,7 +140,7 @@ export class HostCuProxy extends HostProxyBase<
     return this.dispatchRequest(toolName, input, conversationId, signal, {
       stepNumber,
       reasoning,
-    })
+    }, targetClientId)
       .then((observation) => {
         // Capture pre-update state so formatObservation sees the correct
         // previous AX tree.

assistant/src/daemon/host-file-proxy.ts

@@ -31,6 +31,7 @@
   operation: HostFileInput["operation"];
   path: string;
   conversationId: string;
+  targetClientId?: string;
   /** Detach the abort listener from the caller's signal. No-op when no signal was passed. */
   detachAbort: () => void;
 }
@@ -85,6 +86,21 @@
       return Promise.resolve({ content: "Aborted", isError: true });
     }
 
+    const capableClients = assistantEventHub.listClientsByCapability("host_file");
+    let resolvedTargetClientId: string | undefined;
+    if (input.targetClientId) {
+      const target = assistantEventHub.getClientById(input.targetClientId);
+      if (!target || !target.capabilities.includes("host_file")) {
+        return Promise.resolve({
+          content: `Error: client "${input.targetClientId}" is not connected or does not support host_file. Run \`assistant clients list --capability host_file\` to see available clients.`,
+          isError: true,
+        });
+      }
+      resolvedTargetClientId = input.targetClientId;
+    } else if (capableClients.length === 1) {
+      resolvedTargetClientId = capableClients[0].clientId;
+    }
+
     const requestId = uuid();
 
     return new Promise<ToolExecutionResult>((resolve, reject) => {
@@ -101,8 +117,11 @@
           { requestId, operation: input.operation },
           "Host file proxy request timed out",
         );
+        const timeoutMessage = resolvedTargetClientId
+          ? `Host file proxy timed out waiting for response from client ${resolvedTargetClientId}`
+          : "Host file proxy timed out waiting for client response";
         resolve({
-          content: "Host file proxy timed out waiting for client response",
+          content: timeoutMessage,
           isError: true,
         });
       }, timeoutSec * 1000);
@@ -115,11 +134,16 @@
             detachAbort();
             pendingInteractions.resolve(requestId);
             try {
-              broadcastMessage({
-                type: "host_file_cancel",
-                requestId,
+              broadcastMessage(
+                {
+                  type: "host_file_cancel",
+                  requestId,
+                  conversationId,
+                  targetClientId: resolvedTargetClientId,
+                },
                 conversationId,
-              });
+                { targetClientId: resolvedTargetClientId },
+              );
             } catch {
               // Best-effort cancel notification — connection may already be closed.
             }
@@ -137,16 +161,22 @@
         operation: input.operation,
         path: input.path,
         conversationId,
+        targetClientId: resolvedTargetClientId,
         detachAbort,
       });
 
       try {
-        broadcastMessage({
-          ...input,
-          type: "host_file_request",
-          requestId,
+        broadcastMessage(
+          {
+            ...input,
+            type: "host_file_request",
+            requestId,
+            conversationId,
+            targetClientId: resolvedTargetClientId,
+          },
           conversationId,
-        });
+          { targetClientId: resolvedTargetClientId },
+        );
       } catch (err) {
         clearTimeout(timer);
         this.pending.delete(requestId);
@@ -195,11 +225,16 @@
       entry.detachAbort();
       pendingInteractions.resolve(requestId);
       try {
-        broadcastMessage({
-          type: "host_file_cancel",
-          requestId,
-          conversationId: entry.conversationId,
-        });
+        broadcastMessage(
+          {
+            type: "host_file_cancel",
+            requestId,
+            conversationId: entry.conversationId,
+            targetClientId: entry.targetClientId,
+          },
+          entry.conversationId,
+          { targetClientId: entry.targetClientId },
+        );
       } catch {
         // Best-effort cancel notification — connection may already be closed.
       }

assistant/src/daemon/host-proxy-base.ts

@@ -34,8 +34,12 @@ const log = getLogger("host-proxy-base");
  * narrowing is impossible — subclasses are responsible for passing event
  * names that match a real `ServerMessage` variant.
  */
-function broadcastDynamic(envelope: Record<string, unknown>): void {
-  broadcastMessage(envelope as unknown as ServerMessage);
+function broadcastDynamic(envelope: Record<string, unknown>, targetClientId?: string): void {
+  broadcastMessage(
+    envelope as unknown as ServerMessage,
+    undefined,
+    targetClientId ? { targetClientId } : undefined,
+  );
 }
 
 const DEFAULT_TIMEOUT_MS = 60_000;
@@ -63,6 +67,7 @@ interface PendingEntry<TResultPayload> {
   reject: (err: Error) => void;
   timer: ReturnType<typeof setTimeout>;
   conversationId: string;
+  targetClientId?: string;
   /** Detach the abort listener from the caller's signal. No-op when no signal was passed. */
   detachAbort: () => void;
 }
@@ -131,6 +136,7 @@ export abstract class HostProxyBase<TRequest, TResultPayload> {
     conversationId: string,
     signal?: AbortSignal,
     extraFields?: Record<string, unknown>,
+    targetClientId?: string,
   ): Promise<TResultPayload> {
     const requestId = uuid();
 
@@ -162,7 +168,8 @@ export abstract class HostProxyBase<TRequest, TResultPayload> {
                 type: this.cancelEventName,
                 requestId,
                 conversationId,
-              });
+                targetClientId,
+              }, targetClientId);
             } catch {
               // Best-effort cancel notification — connection may already be closed.
             }
@@ -178,6 +185,7 @@ export abstract class HostProxyBase<TRequest, TResultPayload> {
         reject,
         timer,
         conversationId,
+        targetClientId,
         detachAbort,
       });
 
@@ -188,8 +196,9 @@ export abstract class HostProxyBase<TRequest, TResultPayload> {
           conversationId,
           toolName,
           input,
+          targetClientId,
           ...(extraFields ?? {}),
-        });
+        }, targetClientId);
       } catch (err) {
         clearTimeout(timer);
         this.pending.delete(requestId);
@@ -246,7 +255,8 @@ export abstract class HostProxyBase<TRequest, TResultPayload> {
           type: this.cancelEventName,
           requestId,
           conversationId: entry.conversationId,
-        });
+          targetClientId: entry.targetClientId,
+        }, entry.targetClientId);
       } catch {
         // Best-effort cancel notification — connection may already be closed.
       }

assistant/src/daemon/message-types/host-cu.ts

@@ -8,6 +8,7 @@ export interface HostCuRequest {
   type: "host_cu_request";
   requestId: string;
   conversationId: string;
+  targetClientId?: string;
   toolName: string; // "computer_use_click", "computer_use_type_text", etc.
   input: Record<string, unknown>;
   stepNumber: number;
@@ -18,6 +19,7 @@ export interface HostCuCancelRequest {
   type: "host_cu_cancel";
   requestId: string;
   conversationId: string;
+  targetClientId?: string;
 }
 
 // --- Domain-level union aliases (consumed by the barrel file) ---

assistant/src/daemon/message-types/host-file.ts

@@ -8,6 +8,7 @@ export interface HostFileReadRequest {
   type: "host_file_request";
   requestId: string;
   conversationId: string;
+  targetClientId?: string;
   operation: "read";
   path: string;
   offset?: number;
@@ -18,6 +19,7 @@ export interface HostFileWriteRequest {
   type: "host_file_request";
   requestId: string;
   conversationId: string;
+  targetClientId?: string;
   operation: "write";
   path: string;
   content: string;
@@ -27,6 +29,7 @@ export interface HostFileEditRequest {
   type: "host_file_request";
   requestId: string;
   conversationId: string;
+  targetClientId?: string;
   operation: "edit";
   path: string;
   old_string: string;
@@ -43,6 +46,7 @@ export interface HostFileCancelRequest {
   type: "host_file_cancel";
   requestId: string;
   conversationId: string;
+  targetClientId?: string;
 }
 
 // --- Domain-level union aliases (consumed by the barrel file) ---

assistant/src/runtime/assistant-event-hub.ts

@@ -627,11 +627,13 @@ function registerPendingInteraction(
     pendingInteractions.register(msg.requestId, {
       conversationId,
       kind: "host_file",
+      targetClientId,
     });
   } else if (msg.type === "host_cu_request") {
     pendingInteractions.register(msg.requestId, {
       conversationId,
       kind: "host_cu",
+      targetClientId,
     });
   } else if (msg.type === "host_app_control_request") {
     pendingInteractions.register(msg.requestId, {