diff --git a/gerbil-manager-web/.gitignore b/gerbil-manager-web/.gitignore
index cf0e91e..0677d0d 100644
--- a/gerbil-manager-web/.gitignore
+++ b/gerbil-manager-web/.gitignore
@@ -25,4 +25,6 @@ dist-ssr
 
 # QA-1: Playwright-Artefakte
 test-results/
-playwright-report/
+playwright-report/
+blob-report/
+playwright/.cache/
diff --git a/gerbil-manager-web/e2e/mock-api.ts b/gerbil-manager-web/e2e/mock-api.ts
index 2aea058..ea19acb 100644
--- a/gerbil-manager-web/e2e/mock-api.ts
+++ b/gerbil-manager-web/e2e/mock-api.ts
@@ -20,7 +20,9 @@ const newId = (prefix: string) => `${prefix}-e2e-${++seq}`
 /** Gridify-Escapes entfernen (\, vor Sonderzeichen). */
 const unescapeGridify = (s: string) => s.replace(/\\(.)/g, '$1')
 
-/** Mini-Gridify: genau die Ausdrücke, die die App baut (==, contains, ',', '|'). */
+/** Mini-Gridify: genau die Ausdrücke, die die App baut (=, contains, ',', '|').
+ * Gleichheit akzeptiert '=' (kanonisch) UND '==' (alt) — POLISH-1 stellte den
+ * Client auf Gridifys echtes '=' um; der Mock bleibt für beide robust. */
 function matchesFilter(row: Row, filter: string | null): boolean {
   if (!filter) return true
   return filter.split(',').every((andPart) =>
@@ -31,7 +33,7 @@ function matchesFilter(row: Row, filter: string | null): boolean {
           .toLowerCase()
           .includes(unescapeGridify(m[2]).toLowerCase())
       }
-      m = cond.match(/^(\w+)==(.*)$/)
+      m = cond.match(/^(\w+)==?(.*)$/)
       if (m) return String(row[m[1]] ?? '') === unescapeGridify(m[2])
       return true
     }),
diff --git a/gerbil-manager-web/src/api/client.ts b/gerbil-manager-web/src/api/client.ts
index 90498e0..dbddb10 100644
--- a/gerbil-manager-web/src/api/client.ts
+++ b/gerbil-manager-web/src/api/client.ts
@@ -13,15 +13,27 @@ export class ApiError extends Error {
   readonly status: number | null
   /** The request path that failed (for diagnostics/logging). */
   readonly path?: string
+  /** Parsed error response body, if any (e.g. { code, ... } for 400s). */
+  readonly body?: unknown
 
-  constructor(message: string, status: number | null, path?: string) {
+  constructor(message: string, status: number | null, path?: string, body?: unknown) {
     super(message)
     this.name = 'ApiError'
     this.status = status
     this.path = path
+    this.body = body
   }
 }
 
+/** Read a `code` field off a parsed ApiError body, if present. */
+export function errorCode(err: unknown): string | null {
+  if (err instanceof ApiError && err.body && typeof err.body === 'object' && 'code' in err.body) {
+    const code = (err.body as { code: unknown }).code
+    return typeof code === 'string' ? code : null
+  }
+  return null
+}
+
 function errorMessageFor(status: number): string {
   if (status === 404) return de.api.errors.notFound
   if (status >= 500) return de.api.errors.server
@@ -40,7 +52,14 @@ async function request<T>(path: string, init?: RequestInit): Promise<T> {
   }
 
   if (!response.ok) {
-    throw new ApiError(errorMessageFor(response.status), response.status, path)
+    // Best-effort parse of a JSON error body (e.g. { code: "InvalidParentGender" }).
+    let body: unknown
+    try {
+      body = await response.clone().json()
+    } catch {
+      body = undefined
+    }
+    throw new ApiError(errorMessageFor(response.status), response.status, path, body)
   }
 
   if (response.status === 204) {
diff --git a/gerbil-manager-web/src/api/gridify.ts b/gerbil-manager-web/src/api/gridify.ts
index 19bf8dd..cce4f66 100644
--- a/gerbil-manager-web/src/api/gridify.ts
+++ b/gerbil-manager-web/src/api/gridify.ts
@@ -47,8 +47,10 @@ export function condition(c: FilterCondition): string {
     const suffix = c.caseInsensitive === false ? '' : '/i'
     return `${c.field}=*${escaped}*${suffix}`
   }
+  // Gridify's equals operator is a single '='; callers use '==' semantically.
+  const op = c.op === '==' ? '=' : c.op
   const suffix = c.caseInsensitive ? '/i' : ''
-  return `${c.field}${c.op}${escaped}${suffix}`
+  return `${c.field}${op}${escaped}${suffix}`
 }
 
 /** Join conditions with AND (comma). Falsy/empty conditions are dropped. */
diff --git a/gerbil-manager-web/src/components/GroupComposer.tsx b/gerbil-manager-web/src/components/GroupComposer.tsx
index 46eb221..1e143c3 100644
--- a/gerbil-manager-web/src/components/GroupComposer.tsx
+++ b/gerbil-manager-web/src/components/GroupComposer.tsx
@@ -1,4 +1,5 @@
 import { useMemo, useState } from 'react'
+import { useNavigate } from 'react-router-dom'
 import JSZip from 'jszip'
 import { de } from '../strings/de'
 import type { Gerbil } from '../api/types'
@@ -29,6 +30,7 @@ function groupGender(animals: Gerbil[]): string {
 
 export default function GroupComposer({ groupNumber, animals, farbschlagOf }: GroupComposerProps) {
   const t = de.pages.abgabe
+  const navigate = useNavigate()
   const [status, setStatus] = useState<SaleStatus>('free')
   const [reservedName, setReservedName] = useState('')
   const [tagline, setTagline] = useState('')
@@ -244,7 +246,13 @@ export default function GroupComposer({ groupNumber, animals, farbschlagOf }: Gr
         <button type="button" className="btn" disabled={ai.pending} onClick={improveWithAi}>
           {ai.pending ? t.ai.generating : t.ai.improve}
         </button>
-        <button type="button" className="btn" title={t.export.finishHint} disabled>
+        <button
+          type="button"
+          className="btn"
+          onClick={() =>
+            navigate(`/vertraege/neu?tiere=${animals.map((a) => a.id).join(',')}`)
+          }
+        >
           {t.export.finish}
         </button>
       </div>
diff --git a/gerbil-manager-web/src/pages/GerbilDetailPage.tsx b/gerbil-manager-web/src/pages/GerbilDetailPage.tsx
index 4a52b27..3cec5fd 100644
--- a/gerbil-manager-web/src/pages/GerbilDetailPage.tsx
+++ b/gerbil-manager-web/src/pages/GerbilDetailPage.tsx
@@ -181,7 +181,7 @@ export default function GerbilDetailPage() {
         <p className="muted">{t.detail.genotypeNotSet}</p>
       )}
 
-      <h3 className="visually-hidden">Weitere Daten</h3>
+      <h3 className="visually-hidden">{t.detail.moreData}</h3>
       <div className="tabs" role="tablist">
         {(['photos', 'health', 'weight'] as const).map((key) => (
           <button
diff --git a/gerbil-manager-web/src/pages/GerbilsPage.tsx b/gerbil-manager-web/src/pages/GerbilsPage.tsx
index 79d3ceb..776af1b 100644
--- a/gerbil-manager-web/src/pages/GerbilsPage.tsx
+++ b/gerbil-manager-web/src/pages/GerbilsPage.tsx
@@ -225,7 +225,7 @@ export default function GerbilsPage() {
       )}
 
       {totalPages > 1 && (
-        <nav className="pager" aria-label="Seitennavigation">
+        <nav className="pager" aria-label={de.common.pageNav}>
           <button
             type="button"
             className="btn"
diff --git a/gerbil-manager-web/src/pages/WuerfeListPage.tsx b/gerbil-manager-web/src/pages/WuerfeListPage.tsx
index 58fce9c..d0bdda7 100644
--- a/gerbil-manager-web/src/pages/WuerfeListPage.tsx
+++ b/gerbil-manager-web/src/pages/WuerfeListPage.tsx
@@ -171,7 +171,7 @@ export default function WuerfeListPage() {
           )}
 
           {totalPages > 1 && (
-            <nav className="pager" aria-label="Seitennavigation">
+            <nav className="pager" aria-label={de.common.pageNav}>
               <button
                 type="button"
                 className="btn"
diff --git a/gerbil-manager-web/src/pages/WurfFormPage.tsx b/gerbil-manager-web/src/pages/WurfFormPage.tsx
index 6ba21ba..17d402d 100644
--- a/gerbil-manager-web/src/pages/WurfFormPage.tsx
+++ b/gerbil-manager-web/src/pages/WurfFormPage.tsx
@@ -1,6 +1,7 @@
 import { useMemo, useState, type FormEvent } from 'react'
 import { Link, useNavigate, useParams } from 'react-router-dom'
 import { de } from '../strings/de'
+import { errorCode } from '../api/client'
 import { createLitter, getLitter, updateLitter } from '../api/litters'
 import { listGerbils } from '../api/gerbils'
 import type { CreateLitter } from '../api/types'
@@ -49,6 +50,7 @@ export default function WurfFormPage() {
 
   const [form, setForm] = useState<FormState>(EMPTY)
   const [errors, setErrors] = useState<Partial<Record<keyof FormState, string>>>({})
+  const [submitError, setSubmitError] = useState<string | null>(null)
   const [goHomeTouched, setGoHomeTouched] = useState(false)
   const [initializedFor, setInitializedFor] = useState<string | null>(null)
 
@@ -116,9 +118,18 @@ export default function WurfFormPage() {
       expectedGoHomeDate: nn(form.expectedGoHomeDate),
       notes: nn(form.notes),
     }
+    setSubmitError(null)
     const result = await mutation.run(body)
-    if (result.ok) navigate(`/wuerfe/${result.value.id}`)
-    // On failure mutation.error drives the inline alert; run() never throws.
+    if (result.ok) {
+      navigate(`/wuerfe/${result.value.id}`)
+      return
+    }
+    // Localize the backend's parent-gender 400 by its code; else generic message.
+    setSubmitError(
+      errorCode(result.cause) === 'InvalidParentGender'
+        ? t.validation.invalidParentGender
+        : result.error,
+    )
   }
 
   if (isEdit && existing.loading) return <p className="muted">{de.common.loading}</p>
@@ -223,7 +234,7 @@ export default function WurfFormPage() {
           <textarea value={form.notes} onChange={(e) => set('notes', e.target.value)} />
         </label>
 
-        {mutation.error && <div className="alert alert--error">{mutation.error}</div>}
+        {submitError && <div className="alert alert--error">{submitError}</div>}
 
         <div className="form-actions">
           <button type="submit" className="btn btn--primary" disabled={mutation.pending}>
diff --git a/gerbil-manager-web/src/strings/de.ts b/gerbil-manager-web/src/strings/de.ts
index 24747d0..7083af4 100644
--- a/gerbil-manager-web/src/strings/de.ts
+++ b/gerbil-manager-web/src/strings/de.ts
@@ -97,6 +97,7 @@ export const de = {
         },
         tabPlaceholder: 'Dieser Bereich entsteht in einem späteren Schritt.',
         notFound: 'Diese Rennmaus wurde nicht gefunden.',
+        moreData: 'Weitere Daten',
       },
       // Formular (anlegen/bearbeiten)
       form: {
@@ -184,6 +185,7 @@ export const de = {
       validation: {
         nameRequired: 'Bitte eine Bezeichnung eingeben.',
         dateRequired: 'Bitte ein Wurfdatum angeben.',
+        invalidParentGender: 'Der Vater muss männlich und die Mutter weiblich sein.',
       },
       // Zuchtpaar-Übersicht
       pairs: {
@@ -610,6 +612,7 @@ export const de = {
     no: 'Nein',
     delete: 'Löschen',
     confirmDelete: 'Wirklich löschen?',
+    pageNav: 'Seitennavigation',
   },
   // Genetik-Warnungen: der Engine (src/genetics) liefert nur CODES,
   // die deutschen Texte stehen hier. Schlüssel = GeneticsWarningCode-Werte.