hardening: namespace snapshot cache keys to avoid sentinel collisions

Use 'page' and 'locator:' prefixed keys instead of raw '__page__' sentinel,
preventing theoretical collision if a CSS selector equals '__page__'.

playwriter/src/clean-html.ts

@@ -26,9 +26,9 @@ function isRegExp(value: any): value is RegExp {
 
 function getSnapshotKey(locator: Locator | Page): string {
   if (isPage(locator)) {
-    return '__page__'
+    return 'page'
   }
-  return locator.selector()
+  return `locator:${locator.selector()}`
 }
 
 export async function getCleanHTML(options: GetCleanHTMLOptions): Promise<string> {

playwriter/src/executor.ts

@@ -790,7 +790,7 @@ export class PlaywrightExecutor {
         const shouldCacheSnapshot = !frame
         // Cache keyed by locator selector so full-page and locator-scoped snapshots
         // don't pollute each other's diff baselines
-        const snapshotKey = locator ? locator.selector() : '__page__'
+        const snapshotKey = locator ? `locator:${locator.selector()}` : 'page'
         let pageSnapshots = this.lastSnapshots.get(resolvedPage)
         if (!pageSnapshots) {
           pageSnapshots = new Map()