add prod data migration schema preflight

scripts/migrate-compatible-data.ps1

@@ -26,6 +26,23 @@ function Invoke-Postgres($Namespace, $Sql) {
   kubectl -n $Namespace exec statefulset/postgres -- sh -lc "PGPASSWORD=\`$POSTGRES_PASSWORD psql -U postgres -d $Database -Atc '$escapedSql'"
 }
 
+function Get-TableColumns($Namespace, $TableName) {
+  $sql = "select column_name || '|' || udt_name || '|' || is_nullable || '|' || coalesce(column_default, '') from information_schema.columns where table_schema='public' and table_name='$TableName' order by ordinal_position"
+  $lines = @(Invoke-Postgres $Namespace $sql)
+  $columns = @()
+  foreach ($line in $lines) {
+    if (-not $line) { continue }
+    $parts = $line -split '\|', 4
+    $columns += [pscustomobject]@{
+      Name = $parts[0]
+      UdtName = $parts[1]
+      Nullable = $parts[2]
+      Default = if ($parts.Count -ge 4) { $parts[3] } else { '' }
+    }
+  }
+  return $columns
+}
+
 Write-Host "Compatible business tables planned for migration: $($tables.Count)"
 Write-Host "Excluded tables: databasechangelog, databasechangeloglock, V3 runtime audit/outbox/maintenance derived tables."
 
@@ -36,6 +53,40 @@ $missingNew = $tables | Where-Object { $_ -notin $newTables }
 if ($missingOld) { throw "Old namespace is missing expected tables: $($missingOld -join ', ')" }
 if ($missingNew) { throw "New namespace is missing expected tables. Run ircs-prod core migrator first: $($missingNew -join ', ')" }
 
+$schemaIssues = @()
+foreach ($table in $tables) {
+  $oldColumns = @(Get-TableColumns $OldNamespace $table)
+  $newColumns = @(Get-TableColumns $NewNamespace $table)
+  $newByName = @{}
+  foreach ($column in $newColumns) {
+    $newByName[$column.Name] = $column
+  }
+  $oldByName = @{}
+  foreach ($column in $oldColumns) {
+    $oldByName[$column.Name] = $column
+    if (-not $newByName.ContainsKey($column.Name)) {
+      $schemaIssues += "${table}: old column '$($column.Name)' is missing in target"
+      continue
+    }
+    $target = $newByName[$column.Name]
+    if ($column.UdtName -ne $target.UdtName) {
+      $schemaIssues += "$table.$($column.Name): type mismatch old=$($column.UdtName) new=$($target.UdtName)"
+    }
+  }
+  foreach ($column in $newColumns) {
+    if (-not $oldByName.ContainsKey($column.Name) -and $column.Nullable -eq 'NO' -and -not $column.Default) {
+      $schemaIssues += "${table}: target required column '$($column.Name)' has no old value and no default"
+    }
+  }
+}
+
+if ($schemaIssues.Count -gt 0) {
+  $schemaIssues | ForEach-Object { Write-Host "SCHEMA ISSUE: $_" }
+  throw "Schema preflight failed with $($schemaIssues.Count) issue(s)."
+}
+
+Write-Host "Schema preflight passed for $($tables.Count) compatible business tables."
+
 if (-not $Execute) {
   Write-Host "Dry run only. Add -Execute to stream data from $OldNamespace to $NewNamespace."
   exit 0