feat(studio): enable SDK cutover by default for every op family

Master flag defaults true; unset family list now means all five families.
VITE_STUDIO_SDK_CUTOVER_ENABLED=false / VITE_STUDIO_SDK_CUTOVER_FAMILIES=...
remain as runtime kill switches via __HF_STUDIO_ENV__. Gate: 0 divergences on
0.8.41-0.8.46 shadow tile, 3455/0 success/failed on dev builds (30d).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

packages/studio/src/components/editor/manualEditingAvailability.test.ts

@@ -1,5 +1,6 @@
 import { afterEach, describe, expect, it, vi } from "vitest";
 import { resolveStudioBooleanEnvFlag } from "./manualEditingAvailability";
+import { STUDIO_SDK_OPERATION_FAMILIES } from "../../utils/sdkCutoverPolicy";
 
 async function loadAvailabilityWithEnv(env: Record<string, string | undefined>) {
   vi.resetModules();
@@ -88,4 +89,22 @@ describe("manual editing availability", () => {
     });
     expect(off.STUDIO_FLAT_INSPECTOR_ENABLED).toBe(false);
   });
+
+  it("defaults SDK cutover on for every family", async () => {
+    const all = await loadAvailabilityWithEnv({});
+    expect(all.STUDIO_SDK_CUTOVER_ENABLED).toBe(true);
+    expect(all.STUDIO_SDK_CUTOVER_FAMILIES).toEqual(new Set(STUDIO_SDK_OPERATION_FAMILIES));
+  });
+
+  it("honors the SDK cutover kill switches", async () => {
+    const off = await loadAvailabilityWithEnv({ VITE_STUDIO_SDK_CUTOVER_ENABLED: "false" });
+    expect(off.STUDIO_SDK_CUTOVER_ENABLED).toBe(false);
+    expect(off.STUDIO_SDK_CUTOVER_FAMILIES.size).toBe(0);
+
+    const subset = await loadAvailabilityWithEnv({
+      VITE_STUDIO_SDK_CUTOVER_FAMILIES: "dom,timing",
+    });
+    expect(subset.STUDIO_SDK_CUTOVER_ENABLED).toBe(true);
+    expect(subset.STUDIO_SDK_CUTOVER_FAMILIES).toEqual(new Set(["dom", "timing"]));
+  });
 });

packages/studio/src/components/editor/manualEditingAvailability.ts

@@ -38,16 +38,20 @@ const runtimeEnv =
     : {};
 const env = { ...(import.meta.env ?? {}), ...runtimeEnv } as StudioFeatureFlagEnv;
 
-// Stage 7 Step 3c: SDK cutover — routes inline-style ops through SDK dispatch
-// instead of the server patch-element API. Default false; enable via
-// VITE_STUDIO_SDK_CUTOVER_ENABLED=true. Requires SDK session to be open.
+// Stage 7 SDK cutover — routes Studio edits through SDK dispatch instead of the
+// server patch/mutation routes. Default TRUE as of the flip release (spec:
+// 2026-09-17-studio-sdk-cutover-flip-design.md). Kill switch:
+// VITE_STUDIO_SDK_CUTOVER_ENABLED=false (works at runtime via __HF_STUDIO_ENV__).
 export const STUDIO_SDK_CUTOVER_ENABLED = resolveStudioBooleanEnvFlag(
   env,
   ["VITE_STUDIO_SDK_CUTOVER_ENABLED"],
-  false,
+  true,
 );
 
-/** Explicit per-operation-family canary selection; the master flag alone enables nothing. */
+/**
+ * Per-family selection. Unset = every family (the master alone enables all).
+ * Set `VITE_STUDIO_SDK_CUTOVER_FAMILIES=dom,timing` to RESTRICT to a subset.
+ */
 export const STUDIO_SDK_CUTOVER_FAMILIES = resolveEnabledSdkFamilies(
   env,
   STUDIO_SDK_CUTOVER_ENABLED,

packages/studio/src/utils/sdkCutover.gate.test.ts

@@ -1,11 +1,12 @@
 import { describe, expect, it, vi } from "vitest";
 
-// Dark-launch contract: with STUDIO_SDK_CUTOVER_ENABLED=false, EVERY cutover
+// Kill-switch contract: with VITE_STUDIO_SDK_CUTOVER_ENABLED=false, EVERY cutover
 // persist chokepoint must explicitly decline so the caller takes the legacy server
 // path — even when a valid SDK session exists (one always does, for
-// shadow/selection). This is the contract the prod flag-flip rests on; a future
-// refactor of the gate guards that silently re-enables cutover on flag-off
-// turns these red. (sdkCutover.test.ts mocks the flag TRUE; this is its sibling.)
+// shadow/selection). Default is ON (manualEditingAvailability.test.ts pins that);
+// this file pins that the env override still turns it fully off. A future
+// refactor of the gate guards that ignores the flag turns these red.
+// (sdkCutover.test.ts mocks the flag TRUE; this is its sibling.)
 vi.mock("../components/editor/manualEditingAvailability", () => ({
   STUDIO_SDK_CUTOVER_ENABLED: false,
   STUDIO_SDK_RESOLVER_SHADOW_ENABLED: false,

packages/studio/src/utils/sdkCutoverPolicy.test.ts

@@ -7,8 +7,17 @@ import {
 } from "./sdkCutoverPolicy";
 
 describe("Studio SDK operation-family policy", () => {
-  it("enables no family from the master switch alone", () => {
-    expect(resolveEnabledSdkFamilies({}, true).size).toBe(0);
+  it("enables every family when the master switch is on and no family list is set", () => {
+    const all = new Set(STUDIO_SDK_OPERATION_FAMILIES);
+    expect(resolveEnabledSdkFamilies({}, true)).toEqual(all);
+    expect(resolveEnabledSdkFamilies({ VITE_STUDIO_SDK_CUTOVER_FAMILIES: "" }, true)).toEqual(all);
+    expect(resolveEnabledSdkFamilies({ VITE_STUDIO_SDK_CUTOVER_FAMILIES: "  " }, true)).toEqual(
+      all,
+    );
+  });
+
+  it("enables no family when the master switch is off, regardless of the family list", () => {
+    expect(resolveEnabledSdkFamilies({}, false).size).toBe(0);
     expect(resolveEnabledSdkFamilies({ VITE_STUDIO_SDK_CUTOVER_FAMILIES: "dom" }, false).size).toBe(
       0,
     );

packages/studio/src/utils/sdkCutoverPolicy.ts

@@ -54,7 +54,8 @@ export function resolveEnabledSdkFamilies(
 ): ReadonlySet<StudioSdkOperationFamily> {
   if (!masterEnabled) return new Set();
   const raw = env["VITE_STUDIO_SDK_CUTOVER_FAMILIES"];
-  if (typeof raw !== "string" || raw.trim() === "") return new Set();
+  // Unset/blank = every family. The list exists to RESTRICT (kill switch per family).
+  if (typeof raw !== "string" || raw.trim() === "") return new Set(STUDIO_SDK_OPERATION_FAMILIES);
   const requested = raw
     .split(",")
     .map((family) => family.trim())
@@ -85,8 +86,9 @@ export function renderStudioSdkCutoverReport(): string {
   return [
     "# Studio SDK cutover report",
     "",
-    "Master flag: `VITE_STUDIO_SDK_CUTOVER_ENABLED=true`",
-    "Family flag: `VITE_STUDIO_SDK_CUTOVER_FAMILIES=dom,timing,...`",
+    "Default: SDK persist ON for every family. Kill switches:",
+    "  `VITE_STUDIO_SDK_CUTOVER_ENABLED=false` (all families → server path)",
+    "  `VITE_STUDIO_SDK_CUTOVER_FAMILIES=dom,timing` (only listed families → SDK; rest → server)",
     "",
     "A family graduates only after zero unexplained resolver/serialization divergences over its agreed corpus and soak window.",
     "",