fix(render): surface structured outcomes (#2153)

packages/core/src/compiler/inlineSubCompositions.ts

@@ -228,13 +228,21 @@ export function inlineSubCompositions(
       continue;
     }
 
-    // Find the inner composition root
+    // Keep structural flattening tied to an exact mount-id match. A template
+    // may intentionally use a different local id (for example, a
+    // `captions-comp` host mounting a `captions` template); flattening that
+    // fallback root changes the compiled DOM and can invalidate selectors and
+    // regression goldens. Discover it separately so script timeline
+    // registration can still map the authored id onto the runtime mount id.
     const innerRoot = compId
       ? queryByAttr(contentDoc, "data-composition-id", compId)
       : contentDoc.querySelector("[data-composition-id]");
-    const inferredCompId = innerRoot?.getAttribute("data-composition-id")?.trim() || "";
+    const authoredCompositionRoot = innerRoot ?? contentDoc.querySelector("[data-composition-id]");
+    const inferredCompId =
+      authoredCompositionRoot?.getAttribute("data-composition-id")?.trim() || "";
     const authoredRootId = innerRoot?.getAttribute("id")?.trim() || null;
     const scopeCompId = compId || inferredCompId;
+    const scriptCompositionId = inferredCompId || scopeCompId;
     const runtimeScope = runtimeCompId ? buildScopeSelector(runtimeCompId) : "";
 
     // Variable merging (bundler feature). Read declared defaults from the
@@ -312,13 +320,13 @@ export function inlineSubCompositions(
         }
         scriptItems.push({ kind: "external", src: externalSrc });
       } else {
-        const wrappedScript = scopeCompId
+        const wrappedScript = scriptCompositionId
           ? wrapScopedCompositionScript(
               s.textContent || "",
-              scopeCompId,
+              scriptCompositionId,
               scriptErrorLabel,
               runtimeScope || undefined,
-              runtimeCompId || scopeCompId,
+              runtimeCompId || scopeCompId || scriptCompositionId,
               authoredRootId,
             )
           : wrapInlineScriptWithErrorBoundary(s.textContent || "", scriptErrorLabel);