ENG-1756: Preserve existing feature flag block-prop values during legacy migration

readAllLegacyFeatureFlags only sources Enable left sidebar from legacy
config. The migration wrote the full FeatureFlags object (with Zod defaults
filling the unsourced keys as false) via setBlockProps, which clobbered any
pre-existing true values for Duplicate node alert enabled and Suggestive
mode overlay enabled.

Expose LEGACY_SOURCED_FEATURE_FLAG_KEYS to identify which keys the legacy
reader actually sources. The migration now overlays only those keys onto the
existing block-prop values, leaving everything else untouched.

Author: sid597

apps/roam/src/components/settings/utils/accessors.ts

@@ -716,6 +716,10 @@ export const isNewSettingsStoreEnabled = (): boolean => {
   return getFeatureFlag("Use new settings store");
 };
 
+export const LEGACY_SOURCED_FEATURE_FLAG_KEYS = Object.keys(
+  FEATURE_FLAG_LEGACY_MAP,
+) as Array<keyof FeatureFlags>;
+
 export const readAllLegacyFeatureFlags = (): Partial<FeatureFlags> => {
   const flags: Partial<FeatureFlags> = {};
   for (const [key, reader] of Object.entries(FEATURE_FLAG_LEGACY_MAP)) {

apps/roam/src/components/settings/utils/migrateLegacyToBlockProps.ts

@@ -6,6 +6,7 @@ import { createBlock } from "roamjs-components/writes";
 import { getSetting, setSetting } from "~/utils/extensionSettings";
 import internalError from "~/utils/internalError";
 import {
+  LEGACY_SOURCED_FEATURE_FLAG_KEYS,
   readAllLegacyFeatureFlags,
   readAllLegacyGlobalSettings,
   readAllLegacyPersonalSettings,
@@ -199,12 +200,21 @@ export const migrateGraphLevel = async (
     failures++;
   } else {
     const legacyFlags = readAllLegacyFeatureFlags();
+    const mergedFlags: Record<string, json> = {
+      ...getBlockProps(featureFlagUid),
+    };
+    for (const key of LEGACY_SOURCED_FEATURE_FLAG_KEYS) {
+      const value = legacyFlags[key];
+      if (value !== undefined) {
+        mergedFlags[key] = value;
+      }
+    }
     if (
       !migrateSection({
         label: "Feature Flags",
         blockUid: featureFlagUid,
         schema: FeatureFlagsSchema,
-        legacyData: legacyFlags as Record<string, unknown>,
+        legacyData: mergedFlags,
       })
     ) {
       failures++;