feat(plugin): observe terminals across connected hosts

Share host-wide terminal observations across plugin surfaces and gate them on terminalCollection. Keep directory observations compatible, and carry creation time in worker v6 state so v5 terminals can drain with an unknown timestamp.

packages/client/src/daemon-client.ts

@@ -6506,10 +6506,16 @@ export class DaemonClient {
   // ============================================================================
 
   observeTerminals(input: {
-    cwd: string;
+    cwd?: string;
     workspaceId?: string;
     signal?: AbortSignal;
   }): OwnedSubscription<CorrelatedResponsePayload<"terminals_changed">> {
+    // COMPAT(terminalCollection): added in v0.16, remove after 2027-06.
+    if (
+      input.cwd === undefined &&
+      this.getLastServerInfoMessage()?.features?.terminalCollection !== true
+    )
+      throw new Error("Update the host to list terminals across workspaces.");
     const { signal, ...query } = input;
     return this.observe(
       "terminals_changed",