feat: harden auto-next continuity receipt linkage

scripts/approved_plan_dispatch_binding.mjs

@@ -81,6 +81,7 @@ function buildReceipt(payload) {
   const receipt = {
     planId: payload?.planId ?? null,
     currentTask: payload?.currentTask ?? null,
+    nextTaskId: payload?.nextTaskId ?? null,
     nextDerivedAction: nextAction,
     dispatchedAt: payload?.dispatchedAt ?? null,
     dispatchRunId: payload?.dispatchRunId ?? null,
@@ -97,6 +98,7 @@ function validateReceipt(receipt) {
   for (const field of [
     'planId',
     'currentTask',
+    'nextTaskId',
     'nextDerivedAction',
     'dispatchedAt',
     'dispatchRunId',