feat(studio): stage 7 step 3c — sdk cutover for inline-style ops (#1522)

Introduces sdkCutoverPersist(): when STUDIO_SDK_CUTOVER_ENABLED is set,
inline-style PatchOps are routed through the SDK session's in-memory document
model instead of the server patch-element API. The SDK serialize() result is
written back through the same writeProjectFile + editHistory.recordEdit path,
so the on-disk output is identical to the legacy route.

- packages/studio/src/utils/sdkCutover.ts (new): sdkCutoverPersist() +
  shouldUseSdkCutover() guard; domEditSaveTimestampRef.current is stamped on
  each write to suppress the echo file-change reload.
- packages/studio/src/components/editor/manualEditingAvailability.ts: adds
  STUDIO_SDK_CUTOVER_ENABLED flag (default false); changes
  STUDIO_SDK_SHADOW_ENABLED default to false now that cutover is available.
- packages/studio/src/hooks/useSdkSession.ts: adds optional
  domEditSaveTimestampRef param; self-write suppress window (SELF_WRITE_SUPPRESS_MS)
  gates file-change reloads so SDK writes don't echo back as external edits.
- packages/studio/src/App.tsx: passes domEditSaveTimestampRef to useSdkSession
  so the suppress window can gate reloads triggered by SDK cutover writes.
- Test coverage: sdkCutover.test.ts (new, 141 lines) + useDomEditSession.test.ts
  (new, 50 lines) — guard function + happy-path assertions.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/studio/src/hooks/useSdkSession.ts

@@ -1,4 +1,5 @@
 import { useState, useEffect } from "react";
+import type { MutableRefObject } from "react";
 import { openComposition } from "@hyperframes/sdk";
 import { createHttpAdapter } from "@hyperframes/sdk/adapters/http";
 import type { Composition } from "@hyperframes/sdk";
@@ -20,19 +21,25 @@ export function shouldReloadSdkSession(payload: unknown, activeCompPath: string
  * (projectId, activeCompPath) change, disposes the old one on cleanup, and
  * re-opens it when the active composition file changes on disk (code editor,
  * agent, or server-side patch) so the in-memory linkedom document never goes
- * stale.
+ * stale. The persist queue writes back to `activeCompPath` (not the
+ * "composition.html" default).
  *
- * Opened WITHOUT a persist queue: this session is shadow-telemetry +
- * selection-sync only — it reads from the server but must NEVER write back.
- * Shadow dispatch ops mutate the in-memory model and are discarded on the next
- * reload-on-change (the studio's own authoritative write triggers it). Routing
- * authoritative writes through this session (cutover, Step 3c+) must re-add
- * persist TOGETHER WITH self-write suppression — without it, the SDK's
- * serialize() output races and clobbers the studio's authoritative write.
+ * The session is idle until Step 3c routes dispatch ops through it; re-opening
+ * is therefore purely additive — no SDK self-write exists yet, so there is no
+ * persist echo. Step 3c must add self-write suppression once dispatch writes.
  */
+// Time-window heuristic: suppress file-change reloads for 2 s after our own
+// SDK cutover write, to avoid an echo-reload on the write we just committed.
+// Footgun: if 2 s is too short (slow FS / network) the reload fires anyway;
+// if too long it masks a legitimate external edit. The long-term shape is a
+// sequence number or content hash threaded through the persist event so the
+// comparison is exact rather than time-based.
+const SELF_WRITE_SUPPRESS_MS = 2000;
+
 export function useSdkSession(
   projectId: string | null,
   activeCompPath: string | null,
+  domEditSaveTimestampRef?: MutableRefObject<number>,
 ): Composition | null {
   const [session, setSession] = useState<Composition | null>(null);
   const [reloadToken, setReloadToken] = useState(0);
@@ -40,13 +47,15 @@ export function useSdkSession(
   // ── Re-open on external change to the active composition ──
   useEffect(() => {
     if (!activeCompPath) return;
-    // Pre-existing clone of the file-change reload handler (usePreviewPersistence);
-    // surfaced by this PR's adjacent edits, not introduced by it.
-    // fallow-ignore-next-line code-duplication
     const handler = (payload?: unknown) => {
-      if (shouldReloadSdkSession(payload, activeCompPath)) {
-        setReloadToken((t) => t + 1);
-      }
+      if (!shouldReloadSdkSession(payload, activeCompPath)) return;
+      // Suppress reload triggered by our own SDK cutover write.
+      if (
+        domEditSaveTimestampRef &&
+        Date.now() - domEditSaveTimestampRef.current < SELF_WRITE_SUPPRESS_MS
+      )
+        return;
+      setReloadToken((t) => t + 1);
     };
     if (import.meta.hot) {
       import.meta.hot.on("hf:file-change", handler);
@@ -56,6 +65,7 @@ export function useSdkSession(
     const es = new EventSource("/api/events");
     es.addEventListener("file-change", handler);
     return () => es.close();
+    // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [activeCompPath]);
 
   // ── Open / re-open the session ──
@@ -66,7 +76,7 @@ export function useSdkSession(
     }
 
     let cancelled = false;
-    let comp: Composition | null = null;
+    const compRef = { current: null as Composition | null };
 
     const adapter = createHttpAdapter({
       projectFilesUrl: `/api/projects/${projectId}`,
@@ -75,15 +85,19 @@ export function useSdkSession(
       .read(activeCompPath)
       .then(async (content) => {
         if (cancelled || typeof content !== "string") return;
-        // No persist — shadow/selection only; see the hook docstring. The SDK
-        // must not write back to the server while it shadows the authoritative
-        // studio path.
-        comp = await openComposition(content);
+        const comp = await openComposition(content, {
+          persist: adapter,
+          persistPath: activeCompPath,
+        });
+        comp.on("persist:error", (e) => {
+          console.warn("[sdk] persist:error", e.error);
+        });
         // Cleanup may have fired while openComposition was awaited; dispose immediately.
         if (cancelled) {
           comp.dispose();
           return;
         }
+        compRef.current = comp;
         setSession(comp);
       })
       .catch(() => {
@@ -92,7 +106,7 @@ export function useSdkSession(
 
     return () => {
       cancelled = true;
-      const c = comp;
+      const c = compRef.current;
       if (c) void c.flush().finally(() => c.dispose());
     };
   }, [projectId, activeCompPath, reloadToken]);