chore: update docs + rename reset to clear

docs/extensions.md

@@ -421,7 +421,7 @@ ACP installs an elicitation-bridged UI context (`createAcpExtensionUiContext` in
 
 For durable extension state:
 
-1. Persist with `pi.appendEntry(customType, data)`.
+1. Persist with `pi.appendEntry("com.example.my-extension.state", data)`. The `customType` namespace is global: use a package- or reverse-domain-qualified value and avoid the core-reserved values in the [`custom` session-entry reference](./session.md#custom).
 2. Rebuild state from `ctx.sessionManager.getBranch()` on `session_start`, `session_branch`, `session_tree`.
 3. Keep tool result `details` structured when state should be visible/reconstructible from tool result history.
 
@@ -431,7 +431,10 @@ Example reconstruction pattern:
 pi.on("session_start", async (_event, ctx) => {
   let latest;
   for (const entry of ctx.sessionManager.getBranch()) {
-    if (entry.type === "custom" && entry.customType === "my-state") {
+    if (
+      entry.type === "custom" &&
+      entry.customType === "com.example.my-extension.state"
+    ) {
       latest = entry.data;
     }
   }