fix(client): keep daemon connections lean by default (#4470)

Move supported protocol capabilities into client defaults and make session traffic subscription-driven. Preserve timeline readiness and reconnect recovery across SDK, CLI, and plugin consumers.

packages/protocol/src/client-capabilities.ts

@@ -1,5 +1,7 @@
 export const CLIENT_CAPS = {
   // Clients outside the Paseo app version series can explicitly accept provider IDs.
+  // COMPAT(explicitEventSubscriptions): added in v0.8.0, remove legacy broadcasts after 2027-03-08.
+  explicitEventSubscriptions: "explicit_event_subscriptions",
   allProviders: "all_providers",
   // COMPAT(selectiveAgentTimeline): added in v0.1.106. Capable clients receive
   // agent streams only for their explicit viewed set. Remove after 2027-01-12

packages/protocol/src/messages.ts

@@ -3040,7 +3040,27 @@ export const HubExecutionControlRequestSchema = z.object({
 
 export type HubExecutionControlRequest = z.infer<typeof HubExecutionControlRequestSchema>;
 
+// These connection event streams have no directory bootstrap or timeline membership.
+export const SessionEventSubscriptionSchema = z.enum([
+  "project.update",
+  "providers_snapshot_update",
+  "agent_attention_required",
+  "agent_permission_request",
+  "agent_permission_resolved",
+]);
+export type SessionEventSubscription = z.infer<typeof SessionEventSubscriptionSchema>;
+export const SessionEventsSetSubscriptionRequestSchema = z.object({
+  type: z.literal("session.events.set_subscription.request"),
+  requestId: z.string(),
+  events: z.array(SessionEventSubscriptionSchema),
+});
+export const SessionEventsSetSubscriptionResponseSchema = z.object({
+  type: z.literal("session.events.set_subscription.response"),
+  payload: z.object({ requestId: z.string() }),
+});
+
 export const SessionInboundMessageSchema = z.discriminatedUnion("type", [
+  SessionEventsSetSubscriptionRequestSchema,
   HubExecutionAgentCreateRequestSchema,
   HubExecutionAgentValidateRequestSchema,
   HubExecutionControlRequestSchema,
@@ -3536,6 +3556,7 @@ export const ServerInfoStatusPayloadSchema = z
         forgeProviders: z.boolean().optional(),
         // COMPAT(selectiveAgentTimeline): added in v0.1.106, remove after 2027-01-12.
         selectiveAgentTimeline: z.boolean().optional(),
+        explicitEventSubscriptions: z.boolean().optional(),
         // COMPAT(canonicalSubmittedPrompts): added in v0.2.6, remove gate after 2027-01-30.
         canonicalSubmittedPrompts: z.boolean().optional(),
         // COMPAT(agentTurnIdentity): accept peers that observed pre-release v0.2.6 through 2027-01-31.
@@ -6418,6 +6439,7 @@ export const AgentSkillsImportLegacySelectionResponseSchema = z.object({
 });
 
 export const SessionOutboundMessageSchema = z.discriminatedUnion("type", [
+  SessionEventsSetSubscriptionResponseSchema,
   HubExecutionAgentCreateResponseSchema,
   HubExecutionAgentValidateResponseSchema,
   HubExecutionControlResponseSchema,
@@ -7098,6 +7120,7 @@ export const WSHelloMessageSchema = z.object({
     .object({
       voice: z.boolean().optional(),
       pushNotifications: z.boolean().optional(),
+      [CLIENT_CAPS.explicitEventSubscriptions]: z.boolean().optional(),
       [CLIENT_CAPS.allProviders]: z.boolean().optional(),
       [CLIENT_CAPS.reasoningMergeEnum]: z.boolean().optional(),
       [CLIENT_CAPS.selectiveAgentTimeline]: z.boolean().optional(),