fix(webapp): gate runTableV2 on native realtime and drop the Electric shape merge

The Electric dual-shape merge was a bridge to let the Electric backend observe
v2 runs during the cutover, but Electric is short-lived and the merge taxed
every tag/batch realtime feed with a second long-poll the moment it deployed.
Gate the v2 run table on the native realtime backend instead (the native client
is table-agnostic and observes v2 runs directly), so a run only routes to
task_run_v2 once its org is on native. Remove the merge module and restore the
single-table Electric proxy.

The cross-table correctness work stays: a v2 run can still have a cross-table
parent or child once an org flips, so the cancelRun cascade, metadata
parent/root routing, the one-time-token claim, and the findRuns guard all still
apply regardless of realtime backend.

Author: d-cs

apps/webapp/app/runEngine/concerns/idempotencyKeys.server.ts

@@ -247,7 +247,11 @@ export class IdempotencyKeyConcern {
             | Record<string, unknown>
             | null
             | undefined) ?? null;
-        if (shouldUseV2RunTable(orgFeatureFlags)) {
+        if (
+          shouldUseV2RunTable(orgFeatureFlags, {
+            nativeRealtimeEnabled: env.REALTIME_BACKEND_NATIVE_ENABLED === "1",
+          })
+        ) {
           // Key the claim on (envId, token), task-independent, to match the DB's
           // task-independent oneTimeUseToken constraint (see the constant's
           // comment). The TTL is a fixed pipeline-dwell bound, NOT the customer
@@ -426,7 +430,9 @@ export class IdempotencyKeyConcern {
     // a pathological client. shouldUseV2RunTable is checked first so a v2 org
     // skips the mollifier-flag resolve entirely.
     const claimEligible =
-      shouldUseV2RunTable(orgFeatureFlags) ||
+      shouldUseV2RunTable(orgFeatureFlags, {
+        nativeRealtimeEnabled: env.REALTIME_BACKEND_NATIVE_ENABLED === "1",
+      }) ||
       (!request.body.options?.resumeParentOnCompletion &&
         !request.body.options?.debounce &&
         !request.options?.oneTimeUseToken &&

apps/webapp/app/runEngine/services/triggerTask.server.ts

@@ -159,7 +159,9 @@ export class RunEngineTriggerTaskService {
           // trigger hot path. Downstream routing is by id format only.
           const runFriendlyId =
             options?.runFriendlyId ??
-            (shouldUseV2RunTable(environment.organization.featureFlags)
+            (shouldUseV2RunTable(environment.organization.featureFlags, {
+              nativeRealtimeEnabled: env.REALTIME_BACKEND_NATIVE_ENABLED === "1",
+            })
               ? RunId.generateKsuid()
               : RunId.generate()
             ).friendlyId;