feat(plugins): agents and workspaces carry plugin metadata

Plugins had nowhere to keep their own data on an agent or workspace, so
Phase 5 and 6 surfaces would each have invented a side store. Both now
hold an opaque Record<string, JsonValue> that Paseo stores, snapshots and
hands to hooks without reading a key.

Set at creation or changed with agent.metadata.update.request /
workspace.metadata.update.request (top-level keys replace, null removes).
Persisted on the agent and workspace records, so it survives a restart.
Reaches agent.create.before (which may add to it), agent.open.before
(read-only), agent.create.after and workspace.create.before/after.

Gated once on server_info.features.entityMetadata; the client throws
"Update the host" instead of sending to a host without it.

packages/protocol/src/messages.ts

@@ -303,6 +303,9 @@ import type {
 // unknown avoids zod-aot's recursive z.json() object-codegen regression.
 const JsonWireValueSchema = z.unknown() as z.ZodType<JsonValue>;
 
+/** Plugin-owned data on an agent or workspace. Paseo stores it and never reads a key. */
+const EntityMetadataSchema = z.record(z.string(), JsonWireValueSchema);
+
 export const AgentStatusSchema = z.enum(AGENT_LIFECYCLE_STATUSES);
 
 const AgentModeSchema: z.ZodType<AgentMode> = z.object({
@@ -922,6 +925,7 @@ export const AgentSnapshotPayloadSchema = z.object({
   lastError: z.string().optional(),
   title: z.string().nullable(),
   labels: z.record(z.string(), z.string()).default({}),
+  metadata: EntityMetadataSchema.optional(),
   requiresAttention: z.boolean().optional(),
   attentionReason: z.enum(["finished", "error", "permission"]).nullable().optional(),
   attentionTimestamp: z.string().nullable().optional(),
@@ -1071,6 +1075,22 @@ export const WorkspaceTitleSetRequestSchema = z.object({
   requestId: z.string(),
 });
 
+export const AgentMetadataUpdateRequestSchema = z.object({
+  type: z.literal("agent.metadata.update.request"),
+  agentId: z.string(),
+  // Top-level keys replace; null removes the key.
+  patch: EntityMetadataSchema,
+  requestId: z.string(),
+});
+
+export const WorkspaceMetadataUpdateRequestSchema = z.object({
+  type: z.literal("workspace.metadata.update.request"),
+  workspaceId: z.string(),
+  // Top-level keys replace; null removes the key.
+  patch: EntityMetadataSchema,
+  requestId: z.string(),
+});
+
 export const WorkspacePinSetRequestSchema = z.object({
   type: z.literal("workspace.pin.set.request"),
   workspaceId: z.string(),
@@ -1847,6 +1867,7 @@ export const CreateAgentRequestMessageSchema = z.object({
   // Omitted on agent-scoped creation, the caller agent's own value applies.
   background: z.boolean().optional(),
   labels: z.record(z.string(), z.string()).default({}),
+  metadata: EntityMetadataSchema.optional(),
   requestId: z.string(),
 });
 
@@ -2225,6 +2246,28 @@ export const WorkspaceTitleSetResponseSchema = z.object({
   payload: WorkspaceTitleSetResponsePayloadSchema,
 });
 
+export const AgentMetadataUpdateResponseSchema = z.object({
+  type: z.literal("agent.metadata.update.response"),
+  payload: z.object({
+    requestId: z.string(),
+    agentId: z.string(),
+    accepted: z.boolean(),
+    metadata: EntityMetadataSchema.nullable(),
+    error: z.string().nullable(),
+  }),
+});
+
+export const WorkspaceMetadataUpdateResponseSchema = z.object({
+  type: z.literal("workspace.metadata.update.response"),
+  payload: z.object({
+    requestId: z.string(),
+    workspaceId: z.string(),
+    accepted: z.boolean(),
+    metadata: EntityMetadataSchema.nullable(),
+    error: z.string().nullable(),
+  }),
+});
+
 export const WorkspacePinSetResponsePayloadSchema = z.object({
   requestId: z.string(),
   workspaceId: z.string(),
@@ -2780,6 +2823,7 @@ export const WorkspaceCreateRequestSchema = z.object({
   idempotencyKey: z.string().min(1).max(512).optional(),
   // Optional user-set title applied to the created workspace.
   title: z.string().optional(),
+  metadata: EntityMetadataSchema.optional(),
   // Optional prompt context for workspace-level name/branch generation.
   firstAgentContext: FirstAgentContextSchema.optional(),
   // Retained for wire parsing; public internal creation is no longer supported.
@@ -3377,6 +3421,8 @@ export const SessionInboundMessageSchema = z.discriminatedUnion("type", [
   ProjectIconSetRequestSchema,
   ProjectRemoveRequestSchema,
   WorkspaceTitleSetRequestSchema,
+  AgentMetadataUpdateRequestSchema,
+  WorkspaceMetadataUpdateRequestSchema,
   WorkspacePinSetRequestSchema,
   WorkspaceLabelListRequestSchema,
   WorkspaceLabelAssignmentSetRequestSchema,
@@ -3917,6 +3963,7 @@ export const ServerInfoStatusPayloadSchema = z
         explicitEventSubscriptions: z.boolean().optional(),
         ownedSubscriptions: z.boolean().optional(),
         providerOptionControls: z.boolean().optional(),
+        entityMetadata: z.boolean().optional(),
         binaryChunkingV1: z.boolean().optional(),
         workspaceSetupObservation: z.boolean().optional(),
         workspaceSortTimes: z.boolean().optional(),
@@ -4251,6 +4298,7 @@ export const WorkspaceDescriptorPayloadSchema = z
     pinnedAt: z.string().nullable().optional(),
     // COMPAT(workspaceLabels): added in v0.5.0, remove optional after 2027-08-14.
     labels: z.array(z.string()).optional(),
+    metadata: EntityMetadataSchema.optional(),
     // Retained for wire parsing of older daemon descriptors.
     internal: z.boolean().optional(),
     background: z.boolean().optional(),
@@ -7267,6 +7315,8 @@ export const SessionOutboundMessageSchema = z.discriminatedUnion("type", [
   ProjectIconSetResponseSchema,
   ProjectRemoveResponseSchema,
   WorkspaceTitleSetResponseSchema,
+  AgentMetadataUpdateResponseSchema,
+  WorkspaceMetadataUpdateResponseSchema,
   WorkspacePinSetResponseSchema,
   WorkspaceRecoveryInspectResponseSchema,
   WorkspaceRecoveryRestoreResponseSchema,
@@ -7636,6 +7686,10 @@ export type ProjectIconSetRequest = z.infer<typeof ProjectIconSetRequestSchema>;
 export type ProjectRemoveRequest = z.infer<typeof ProjectRemoveRequestSchema>;
 export type WorkspaceTitleSetRequest = z.infer<typeof WorkspaceTitleSetRequestSchema>;
 export type WorkspacePinSetRequest = z.infer<typeof WorkspacePinSetRequestSchema>;
+export type AgentMetadataUpdateRequest = z.infer<typeof AgentMetadataUpdateRequestSchema>;
+export type WorkspaceMetadataUpdateRequest = z.infer<typeof WorkspaceMetadataUpdateRequestSchema>;
+export type AgentMetadataUpdateResponse = z.infer<typeof AgentMetadataUpdateResponseSchema>;
+export type WorkspaceMetadataUpdateResponse = z.infer<typeof WorkspaceMetadataUpdateResponseSchema>;
 export type WorkspaceRecoveryInspectRequest = z.infer<typeof WorkspaceRecoveryInspectRequestSchema>;
 export type WorkspaceRecoveryRestoreRequest = z.infer<typeof WorkspaceRecoveryRestoreRequestSchema>;
 export type SetAgentModeRequestMessage = z.infer<typeof SetAgentModeRequestMessageSchema>;