diff --git a/scripts/start-local.ps1 b/scripts/start-local.ps1
index d3b7348..28af2cc 100644
--- a/scripts/start-local.ps1
+++ b/scripts/start-local.ps1
@@ -65,6 +65,11 @@ $ErrorActionPreference = 'Stop'
 $RepoRoot = Split-Path -Parent $PSScriptRoot
 $StateDir = Join-Path $RepoRoot '.local'
 $PidFile = Join-Path $StateDir 'pids.json'
+
+# Whether this run is starting from an empty database. Set below, and read by
+# Start-Backend, which must refuse to reuse a backend that is still serving the
+# previous one. See #257.
+$script:DatabaseIsNew = $false
 # Which database this run uses. Everything downstream reads these four, so the
 # choice is made once here rather than branched at each use.
 if ($E2eDb) {
@@ -184,14 +189,22 @@ function Start-Database {
         Write-Step 'Removing the existing database (-Fresh)'
         docker rm -f $Container *>$null
         Write-Good 'removed'
+        $script:DatabaseIsNew = $true
     }
 
+    # The e2e container stores its data on tmpfs, so it comes up empty whether it
+    # is created or merely restarted. There is no case where it carries anything
+    # over, which is the point of it (#186) — and it means a backend from a
+    # previous run is always stale against it.
+    if ($E2eDb) { $script:DatabaseIsNew = $true }
+
     $existing = (docker ps -a --filter "name=^/$Container$" --format '{{.Names}}')
     if ($existing -eq $Container) {
         Write-Step "Reusing the database container"
         docker start $Container *>$null
     }
     else {
+        $script:DatabaseIsNew = $true
         Write-Step "Creating the database container on port $DbPort"
         # tmpfs for the e2e database only: its contents are worthless the
         # moment the run ends, and storing nothing is what makes it start empty
@@ -269,6 +282,41 @@ function Start-Backend {
     finally { Pop-Location }
 
     if (Test-Listening -Port $ApiPort) {
+        # Leaving a stranger's backend alone is only safe when the database has
+        # not just changed underneath it. When it has, that process is serving a
+        # database it no longer owns, and its in-memory state describes rows that
+        # no longer exist.
+        #
+        # That is not theoretical. The rate limiter keys on customer id and keeps
+        # its buckets in memory for an hour; a recreated database restarts ids at
+        # 1, so a new customer inherits a previous run's spent allowance. It
+        # reproduced exactly the intermittent resend-verification failure in #257
+        # — three refusal toasts where one was expected — and the control (same
+        # id restart, restarted backend) passed. Whatever else is stale, a
+        # process serving the wrong database gives wrong answers confidently,
+        # which is the worst kind.
+        #
+        # So this refuses rather than continuing, and says what to do. A run that
+        # stops loudly is recoverable; one that quietly tests the wrong thing is
+        # what cost two wrong measurements in this project already.
+        $tracked = Get-TrackedProcesses
+        $ours = $tracked.ContainsKey('backend') -and
+                (Get-Process -Id $tracked['backend'] -ErrorAction SilentlyContinue)
+
+        if ($script:DatabaseIsNew -and -not $ours) {
+            throw @"
+Something is already listening on $ApiPort, and this run just created a new database.
+
+That process is serving the previous database. Its in-memory state — rate-limit
+buckets keyed on customer id, most obviously — describes rows that no longer
+exist, and recycled ids will inherit them (#257).
+
+Stop it and run this again:
+
+    .\scripts\start-local.ps1 -Stop
+"@
+        }
+
         Write-Note "something is already listening on $ApiPort; leaving it alone"
         return
     }