feat(console-web): add bounded iframe keep-alive

- opt service and settings pages into document retention
- preserve iframe identity and local Solid state across navigation
- cap retained documents with deterministic LRU eviction
- deliver activate, deactivate, and dispose lifecycle messages
- reject commands emitted by inactive page documents
- expose page activity as a Solid accessor
- test retention, recreation, eviction, and invalid limits

crates/wasmeld-console/web/src/sdk/protocol.ts

@@ -14,6 +14,7 @@ export const SDK_VERSION = 1;
 
 export type RuntimeAction = "start" | "stop" | "restart";
 export type ServiceAction = "start" | "stop" | "restart";
+export type PageLifecyclePhase = "activate" | "deactivate" | "dispose";
 
 export type HostSharedState = {
   // This is a serializable snapshot, never a Solid signal crossing realms.
@@ -67,7 +68,8 @@ export type HostMessage =
       channel: typeof SDK_CHANNEL;
       version: typeof SDK_VERSION;
       source: "host";
-      type: "dispose";
+      type: "lifecycle";
+      phase: PageLifecyclePhase;
     };
 
 export function isPageMessage(value: unknown): value is PageMessage {
@@ -82,12 +84,15 @@ export function isPageMessage(value: unknown): value is PageMessage {
 
 export function isHostMessage(value: unknown): value is HostMessage {
   if (!isRecord(value)) return false;
-  return (
-    value.channel === SDK_CHANNEL &&
-    value.version === SDK_VERSION &&
-    value.source === "host" &&
-    (value.type === "state" || value.type === "dispose")
-  );
+  if (value.channel !== SDK_CHANNEL || value.version !== SDK_VERSION || value.source !== "host") {
+    return false;
+  }
+  if (value.type === "state") return isRecord(value.state);
+  return value.type === "lifecycle" && isPageLifecyclePhase(value.phase);
+}
+
+function isPageLifecyclePhase(value: unknown): value is PageLifecyclePhase {
+  return value === "activate" || value === "deactivate" || value === "dispose";
 }
 
 function isRecord(value: unknown): value is Record<string, unknown> {