diff --git a/src/lib/block-types.ts b/src/lib/block-types.ts
index c0ace94..0dbc5e9 100644
--- a/src/lib/block-types.ts
+++ b/src/lib/block-types.ts
@@ -469,7 +469,7 @@ export type CalendarBlockData = Omit<
 };
 
 /** Internal component block (_type: "internal_component"). */
-export type InternalComponentId = "form-contact";
+export type InternalComponentId = "form-contact" | "form-mitmachen";
 
 export interface InternalComponentBlockData {
   _type?: "internal_component";
diff --git a/src/lib/components/blocks/InternalComponentBlock.svelte b/src/lib/components/blocks/InternalComponentBlock.svelte
index c9fe302..8bf76c5 100644
--- a/src/lib/components/blocks/InternalComponentBlock.svelte
+++ b/src/lib/components/blocks/InternalComponentBlock.svelte
@@ -2,6 +2,7 @@
   import { getBlockLayoutClasses } from "$lib/block-layout";
   import type { InternalComponentBlockData } from "$lib/block-types";
   import ContactFormComponent from "$lib/components/internal/ContactFormComponent.svelte";
+  import MitmachenFormComponent from "$lib/components/internal/MitmachenFormComponent.svelte";
 
   let { block }: { block: InternalComponentBlockData } = $props();
 
@@ -12,6 +13,8 @@
 <div class={layoutClasses} data-block="InternalComponent" data-block-type="internal_component" data-block-slug={block._slug}>
   {#if component === "form-contact"}
     <ContactFormComponent />
+  {:else if component === "form-mitmachen"}
+    <MitmachenFormComponent />
   {:else}
     <p class="text-sm text-stein-500">Unbekannte interne Komponente: <code>{component}</code></p>
   {/if}
diff --git a/src/lib/components/internal/MitmachenFormComponent.svelte b/src/lib/components/internal/MitmachenFormComponent.svelte
new file mode 100644
index 0000000..54110dd
--- /dev/null
+++ b/src/lib/components/internal/MitmachenFormComponent.svelte
@@ -0,0 +1,389 @@
+<script lang="ts">
+  import { onMount, onDestroy } from "svelte";
+  import { env as publicEnv } from "$env/dynamic/public";
+  import Button from "$lib/ui/Button.svelte";
+  import TextInput from "$lib/ui/TextInput.svelte";
+  import Textarea from "$lib/ui/Textarea.svelte";
+  import Checkbox from "$lib/ui/Checkbox.svelte";
+  import { useTranslate, T } from "$lib/translations";
+  import {
+    FILE_ACCEPT,
+    LIMITS,
+    validateFiles,
+    validateMitmachen,
+    type MitmachenErrors,
+    type MitmachenFields,
+  } from "./mitmachen-form-validation";
+
+  type FormState = "idle" | "pending" | "success" | "error";
+
+  const t = useTranslate();
+
+  const TURNSTILE_SITE_KEY = publicEnv.PUBLIC_TURNSTILE_SITE_KEY ?? "";
+  const TURNSTILE_ENABLED = TURNSTILE_SITE_KEY !== "";
+
+  let title = $state("");
+  let description = $state("");
+  let contactName = $state("");
+  let phone = $state("");
+  let email = $state("");
+  let consent = $state(false);
+  let files = $state<File[]>([]);
+  let fileInputEl = $state<HTMLInputElement | null>(null);
+
+  // Honeypots — three with realistic names. Real users never see them.
+  let honeypot = $state("");
+  let website = $state("");
+  let company = $state("");
+
+  const pageLoadedAt = Date.now();
+
+  let formState = $state<FormState>("idle");
+  let serverError = $state("");
+  let submitAttempted = $state(false);
+
+  let turnstileToken = $state("");
+  let turnstileEl = $state<HTMLDivElement | null>(null);
+  let turnstileWidgetId: string | null = null;
+
+  const fields = $derived<MitmachenFields>({
+    title,
+    description,
+    contactName,
+    phone,
+    email,
+    consent,
+  });
+  const errors = $derived<MitmachenErrors>(validateMitmachen(fields));
+  const fileError = $derived(validateFiles(files));
+  const isValid = $derived(Object.keys(errors).length === 0 && !fileError);
+
+  function showError(field: keyof MitmachenFields): string {
+    if (!submitAttempted) return "";
+    const e = errors[field];
+    return e ? t(e.key, e.params) : "";
+  }
+
+  const descriptionRemaining = $derived(LIMITS.DESCRIPTION_MAX - description.length);
+  const descriptionHelp = $derived(
+    descriptionRemaining >= 0
+      ? t(T.contact_message_remaining, { n: descriptionRemaining })
+      : t(T.contact_message_overflow, { n: -descriptionRemaining }),
+  );
+
+  function onFilesChosen(e: Event) {
+    const input = e.currentTarget as HTMLInputElement;
+    const chosen = [...(input.files ?? [])];
+    // Anhängen statt ersetzen — Nutzer kann in mehreren Schritten auswählen.
+    files = [...files, ...chosen].slice(0, LIMITS.MAX_FILES + 1);
+    input.value = "";
+  }
+
+  function removeFile(idx: number) {
+    files = files.filter((_, i) => i !== idx);
+  }
+
+  function fmtSize(bytes: number): string {
+    if (bytes >= 1024 * 1024) return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
+    return `${Math.max(1, Math.round(bytes / 1024))} KB`;
+  }
+
+  type TurnstileAPI = {
+    render: (
+      el: HTMLElement,
+      opts: {
+        sitekey: string;
+        theme?: "light" | "dark" | "auto";
+        size?: "normal" | "compact" | "flexible";
+        callback?: (token: string) => void;
+        "expired-callback"?: () => void;
+        "error-callback"?: () => void;
+      },
+    ) => string;
+    reset: (id?: string) => void;
+    remove: (id: string) => void;
+  };
+
+  function getTurnstile(): TurnstileAPI | undefined {
+    return (window as unknown as { turnstile?: TurnstileAPI }).turnstile;
+  }
+
+  function renderTurnstile() {
+    if (!TURNSTILE_ENABLED || !turnstileEl) return;
+    const ts = getTurnstile();
+    if (!ts) return;
+    if (turnstileWidgetId !== null) return;
+    turnstileWidgetId = ts.render(turnstileEl, {
+      sitekey: TURNSTILE_SITE_KEY,
+      theme: "light",
+      size: "flexible",
+      callback: (token) => {
+        turnstileToken = token;
+      },
+      "expired-callback": () => {
+        turnstileToken = "";
+      },
+      "error-callback": () => {
+        turnstileToken = "";
+      },
+    });
+  }
+
+  function loadTurnstileScript() {
+    if (!TURNSTILE_ENABLED) return;
+    if (document.querySelector("script[data-turnstile]")) {
+      renderTurnstile();
+      return;
+    }
+    const s = document.createElement("script");
+    s.src = "https://challenges.cloudflare.com/turnstile/v0/api.js?render=explicit";
+    s.async = true;
+    s.defer = true;
+    s.dataset.turnstile = "1";
+    s.onload = renderTurnstile;
+    document.head.appendChild(s);
+  }
+
+  onMount(loadTurnstileScript);
+  onDestroy(() => {
+    if (turnstileWidgetId !== null) {
+      getTurnstile()?.remove(turnstileWidgetId);
+      turnstileWidgetId = null;
+    }
+  });
+
+  function resetTurnstile() {
+    if (!TURNSTILE_ENABLED) return;
+    turnstileToken = "";
+    if (turnstileWidgetId !== null) getTurnstile()?.reset(turnstileWidgetId);
+  }
+
+  async function handleSubmit(e: SubmitEvent) {
+    e.preventDefault();
+    submitAttempted = true;
+    if (formState === "pending") return;
+    if (!isValid) {
+      const first = Object.keys(errors)[0];
+      const el = document.querySelector<HTMLElement>(`[data-field="${first}"]`);
+      el?.focus();
+      return;
+    }
+    if (TURNSTILE_ENABLED && !turnstileToken) {
+      serverError = t(T.contact_captcha_pending);
+      formState = "error";
+      return;
+    }
+
+    formState = "pending";
+    serverError = "";
+
+    try {
+      const fd = new FormData();
+      fd.set("title", title);
+      fd.set("description", description);
+      fd.set("contactName", contactName);
+      fd.set("phone", phone);
+      fd.set("email", email);
+      fd.set("consent", consent ? "true" : "false");
+      fd.set("_honeypot", honeypot);
+      fd.set("website", website);
+      fd.set("company", company);
+      fd.set("_client_age_ms", String(Date.now() - pageLoadedAt));
+      fd.set("cf_turnstile_token", turnstileToken);
+      for (const f of files) fd.append("file", f, f.name);
+
+      const res = await fetch("/api/mitmachen", { method: "POST", body: fd });
+
+      if (res.ok) {
+        formState = "success";
+        return;
+      }
+
+      const body = await res.json().catch(() => ({}));
+      if (res.status === 422) {
+        serverError = t(T.contact_server_error_validation);
+      } else if (res.status === 413) {
+        serverError = t(T.mitmachen_error_files_size, { mb: LIMITS.MAX_FILE_MB });
+      } else if (res.status === 429) {
+        serverError = t(T.contact_server_error_throttle);
+      } else if (res.status === 403) {
+        serverError =
+          body?.error === "captcha"
+            ? t(T.contact_server_error_captcha)
+            : t(T.contact_server_error_blocked);
+      } else {
+        serverError = body?.error || t(T.contact_server_error_generic);
+      }
+      formState = "error";
+      resetTurnstile();
+    } catch {
+      serverError = t(T.contact_server_error_network);
+      formState = "error";
+      resetTurnstile();
+    }
+  }
+</script>
+
+{#if formState === "success"}
+  <div class="rounded-sm border border-wald-300 bg-wald-50 px-4 py-5 text-center shadow-sm">
+    <p class="text-base font-semibold text-wald-700">{t(T.mitmachen_success_title)}</p>
+    <p class="mt-1 text-sm text-stein-600">{t(T.mitmachen_success_body)}</p>
+  </div>
+{:else}
+  <form
+    onsubmit={handleSubmit}
+    novalidate
+    class="space-y-3"
+    aria-busy={formState === "pending"}
+  >
+    <!-- Honeypots: visually hidden, off the keyboard, off the a11y tree -->
+    <div aria-hidden="true" class="pointer-events-none absolute left-[-9999px] top-auto h-px w-px overflow-hidden opacity-0">
+      <label for="mitmachen-hp-1">leer lassen</label>
+      <input id="mitmachen-hp-1" name="_honeypot" type="text" tabindex="-1" autocomplete="off" bind:value={honeypot} />
+      <label for="mitmachen-hp-2">Website</label>
+      <input id="mitmachen-hp-2" name="website" type="url" tabindex="-1" autocomplete="off" bind:value={website} />
+      <label for="mitmachen-hp-3">Firma</label>
+      <input id="mitmachen-hp-3" name="company" type="text" tabindex="-1" autocomplete="off" bind:value={company} />
+    </div>
+
+    <div data-field="title">
+      <TextInput
+        size="sm"
+        name="title"
+        label={t(T.mitmachen_label_title)}
+        placeholder={t(T.mitmachen_placeholder_title)}
+        required
+        bind:value={title}
+        error={showError("title")}
+      />
+    </div>
+
+    <div data-field="description">
+      <Textarea
+        size="sm"
+        name="description"
+        label={t(T.mitmachen_label_description)}
+        placeholder={t(T.mitmachen_placeholder_description)}
+        required
+        rows={5}
+        bind:value={description}
+        error={showError("description")}
+        helpText={descriptionHelp}
+      />
+    </div>
+
+    <div data-field="contactName">
+      <TextInput
+        size="sm"
+        name="contactName"
+        label={t(T.mitmachen_label_contact_name)}
+        placeholder={t(T.mitmachen_placeholder_contact_name)}
+        bind:value={contactName}
+        error={showError("contactName")}
+      />
+    </div>
+
+    <div class="grid gap-3 sm:grid-cols-2">
+      <div data-field="phone">
+        <TextInput
+          size="sm"
+          name="phone"
+          type="tel"
+          label={t(T.mitmachen_label_phone)}
+          placeholder={t(T.mitmachen_placeholder_phone)}
+          bind:value={phone}
+          error={showError("phone")}
+        />
+      </div>
+      <div data-field="email">
+        <TextInput
+          size="sm"
+          name="email"
+          type="email"
+          label={t(T.mitmachen_label_email)}
+          placeholder={t(T.mitmachen_placeholder_email)}
+          bind:value={email}
+          error={showError("email")}
+        />
+      </div>
+    </div>
+
+    <div data-field="files">
+      <span class="mb-1 block text-sm font-medium text-stein-700">{t(T.mitmachen_label_files)}</span>
+      <input
+        bind:this={fileInputEl}
+        type="file"
+        multiple
+        accept={FILE_ACCEPT}
+        class="sr-only"
+        onchange={onFilesChosen}
+        tabindex="-1"
+      />
+      <!-- Nativer Button: ui/Button forwarded kein onclick. Klassen = Button
+           secondary/sm. -->
+      <button
+        type="button"
+        class="inline-flex h-9 items-center justify-center gap-2 rounded-xs border-[1.5px] border-wald-500 bg-transparent px-4 py-2 text-sm font-semibold text-wald-500 transition-colors duration-150 hover:bg-wald-50 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-wald-300 focus-visible:ring-offset-2 active:bg-wald-100"
+        onclick={() => fileInputEl?.click()}
+      >{t(T.mitmachen_files_add)}</button>
+      <p class="mt-1 text-[0.7rem] text-stein-500">
+        {t(T.mitmachen_files_help, { n: LIMITS.MAX_FILES, mb: LIMITS.MAX_FILE_MB })}
+      </p>
+      {#if files.length > 0}
+        <ul class="mt-2 space-y-1">
+          {#each files as f, idx}
+            <li class="flex items-center gap-2 rounded-sm border border-stein-200 bg-stein-50 px-2 py-1 text-xs">
+              <span class="min-w-0 flex-1 truncate">{f.name}</span>
+              <span class="shrink-0 text-stein-500">{fmtSize(f.size)}</span>
+              <button
+                type="button"
+                class="shrink-0 text-stein-500 underline hover:text-stein-700"
+                onclick={() => removeFile(idx)}
+              >{t(T.mitmachen_files_remove)}</button>
+            </li>
+          {/each}
+        </ul>
+      {/if}
+      {#if submitAttempted && fileError}
+        <p class="mt-1 text-[0.7rem] text-error" role="alert">{t(fileError.key, fileError.params)}</p>
+      {/if}
+    </div>
+
+    <div data-field="consent" class="pt-1">
+      <Checkbox
+        size="sm"
+        name="consent"
+        bind:checked={consent}
+        label={t(T.mitmachen_label_consent)}
+      />
+      {#if showError("consent")}
+        <p class="mt-1 text-[0.7rem] text-error" role="alert">{showError("consent")}</p>
+      {/if}
+      <p class="mt-1 text-[0.7rem] leading-snug text-stein-500">{t(T.mitmachen_privacy_note)}</p>
+    </div>
+
+    {#if TURNSTILE_ENABLED}
+      <div bind:this={turnstileEl} class="pt-1"></div>
+    {/if}
+
+    {#if serverError}
+      <div class="rounded-sm border border-error bg-error-subtle px-3 py-2 text-sm text-error shadow-sm" role="alert">
+        {serverError}
+      </div>
+    {/if}
+
+    <div class="flex items-center gap-3 pt-2">
+      <Button
+        type="submit"
+        variant="primary"
+        size="sm"
+        loading={formState === "pending"}
+        disabled={!isValid && submitAttempted}
+        label={formState === "pending" ? t(T.contact_submitting) : t(T.mitmachen_submit)}
+      />
+      {#if !isValid && submitAttempted && !serverError}
+        <span class="text-xs text-error">{t(T.contact_fix_errors)}</span>
+      {/if}
+    </div>
+  </form>
+{/if}
diff --git a/src/lib/components/internal/mitmachen-form-validation.ts b/src/lib/components/internal/mitmachen-form-validation.ts
new file mode 100644
index 0000000..5152ea5
--- /dev/null
+++ b/src/lib/components/internal/mitmachen-form-validation.ts
@@ -0,0 +1,141 @@
+/**
+ * Shared validation for MitmachenFormComponent + /api/mitmachen server route.
+ * Single source of truth for limits and rules.
+ */
+
+export const LIMITS = {
+  TITLE_MIN: 2,
+  TITLE_MAX: 120,
+  DESCRIPTION_MIN: 10,
+  DESCRIPTION_MAX: 4000,
+  CONTACT_NAME_MAX: 80,
+  PHONE_MAX: 40,
+  EMAIL_MAX: 200,
+  MAX_URLS_IN_DESCRIPTION: 2,
+  MIN_CLIENT_AGE_MS: 3000,
+  MAX_FILES: 5,
+  MAX_FILE_MB: 5,
+} as const;
+
+export const HONEYPOT_FIELDS = ["_honeypot", "website", "company"] as const;
+
+/** Muss mit ALLOWED_UPLOAD_MIMES im CMS-Forms-Plugin übereinstimmen. */
+export const ALLOWED_FILE_TYPES = [
+  "image/jpeg",
+  "image/png",
+  "image/webp",
+  "image/gif",
+  "application/pdf",
+] as const;
+
+export const FILE_ACCEPT = ALLOWED_FILE_TYPES.join(",");
+
+export type MitmachenFields = {
+  title: string;
+  description: string;
+  contactName: string;
+  phone: string;
+  email: string;
+  consent: boolean;
+};
+
+/** Error as translation-key + optional params (resolved in the UI). */
+export type MitmachenError = {
+  key: string;
+  params?: Record<string, string | number>;
+};
+
+export type MitmachenErrors = Partial<Record<keyof MitmachenFields, MitmachenError>>;
+
+const EMAIL_RE = /^[^\s@]+@[^\s@]+\.[^\s@]{2,}$/;
+const URL_RE = /\b(?:https?:\/\/|www\.)\S+/gi;
+const CONTROL_CHAR_RE = /[\x00-\x08\x0B\x0C\x0E-\x1F]/;
+const PHONE_RE = /^[0-9+()/\-.\s]*$/;
+
+function trim(s: unknown): string {
+  return typeof s === "string" ? s.trim() : "";
+}
+
+export function validateMitmachen(input: Partial<MitmachenFields>): MitmachenErrors {
+  const errors: MitmachenErrors = {};
+  const title = trim(input.title);
+  const description = trim(input.description);
+  const contactName = trim(input.contactName);
+  const phone = trim(input.phone);
+  const email = trim(input.email);
+
+  if (title.length < LIMITS.TITLE_MIN) {
+    errors.title = { key: "mitmachen_error_title_min", params: { n: LIMITS.TITLE_MIN } };
+  } else if (title.length > LIMITS.TITLE_MAX) {
+    errors.title = { key: "mitmachen_error_title_max", params: { n: LIMITS.TITLE_MAX } };
+  } else if (URL_RE.test(title) || CONTROL_CHAR_RE.test(title)) {
+    errors.title = { key: "mitmachen_error_title_invalid" };
+  }
+
+  if (description.length < LIMITS.DESCRIPTION_MIN) {
+    errors.description = {
+      key: "mitmachen_error_description_min",
+      params: { n: LIMITS.DESCRIPTION_MIN },
+    };
+  } else if (description.length > LIMITS.DESCRIPTION_MAX) {
+    errors.description = {
+      key: "mitmachen_error_description_max",
+      params: { n: LIMITS.DESCRIPTION_MAX },
+    };
+  } else {
+    const urlMatches = description.match(URL_RE) ?? [];
+    if (urlMatches.length > LIMITS.MAX_URLS_IN_DESCRIPTION) {
+      errors.description = {
+        key: "mitmachen_error_description_too_many_links",
+        params: { n: LIMITS.MAX_URLS_IN_DESCRIPTION },
+      };
+    } else if (CONTROL_CHAR_RE.test(description)) {
+      errors.description = { key: "mitmachen_error_description_invalid" };
+    }
+  }
+
+  if (contactName.length > LIMITS.CONTACT_NAME_MAX) {
+    errors.contactName = {
+      key: "mitmachen_error_contact_name_max",
+      params: { n: LIMITS.CONTACT_NAME_MAX },
+    };
+  } else if (CONTROL_CHAR_RE.test(contactName) || URL_RE.test(contactName)) {
+    errors.contactName = { key: "mitmachen_error_contact_name_invalid" };
+  }
+
+  if (phone.length > LIMITS.PHONE_MAX || !PHONE_RE.test(phone)) {
+    if (phone) errors.phone = { key: "mitmachen_error_phone_invalid" };
+  }
+
+  // E-Mail ist optional — nur prüfen wenn ausgefüllt.
+  if (email && (email.length > LIMITS.EMAIL_MAX || !EMAIL_RE.test(email))) {
+    errors.email = { key: "mitmachen_error_email_invalid" };
+  }
+
+  if (input.consent !== true) {
+    errors.consent = { key: "mitmachen_error_consent_required" };
+  }
+
+  return errors;
+}
+
+/** Datei-Checks (client- + serverseitig identisch). */
+export function validateFiles(
+  files: Pick<File, "size" | "type">[],
+): MitmachenError | null {
+  if (files.length > LIMITS.MAX_FILES) {
+    return { key: "mitmachen_error_files_count", params: { n: LIMITS.MAX_FILES } };
+  }
+  for (const f of files) {
+    if (!(ALLOWED_FILE_TYPES as readonly string[]).includes(f.type)) {
+      return { key: "mitmachen_error_files_type" };
+    }
+    if (f.size > LIMITS.MAX_FILE_MB * 1024 * 1024) {
+      return { key: "mitmachen_error_files_size", params: { mb: LIMITS.MAX_FILE_MB } };
+    }
+    if (f.size === 0) {
+      return { key: "mitmachen_error_files_type" };
+    }
+  }
+  return null;
+}
diff --git a/src/lib/translations.ts b/src/lib/translations.ts
index bda2ead..e0a98f7 100644
--- a/src/lib/translations.ts
+++ b/src/lib/translations.ts
@@ -317,6 +317,42 @@ const TRANSLATION_KEYS = [
   "contact_error_consent_required",
   "contact_captcha_pending",
   "contact_server_error_captcha",
+  // Mitmachen form (MitmachenFormComponent.svelte). Generische Submit-/
+  // Server-Error-Texte werden aus contact_* wiederverwendet.
+  "mitmachen_label_title",
+  "mitmachen_placeholder_title",
+  "mitmachen_label_description",
+  "mitmachen_placeholder_description",
+  "mitmachen_label_contact_name",
+  "mitmachen_placeholder_contact_name",
+  "mitmachen_label_phone",
+  "mitmachen_placeholder_phone",
+  "mitmachen_label_email",
+  "mitmachen_placeholder_email",
+  "mitmachen_label_files",
+  "mitmachen_files_help",                 // {{n}}, {{mb}}
+  "mitmachen_files_add",
+  "mitmachen_files_remove",
+  "mitmachen_label_consent",
+  "mitmachen_privacy_note",
+  "mitmachen_submit",
+  "mitmachen_success_title",
+  "mitmachen_success_body",
+  "mitmachen_error_title_min",            // {{n}}
+  "mitmachen_error_title_max",            // {{n}}
+  "mitmachen_error_title_invalid",
+  "mitmachen_error_description_min",      // {{n}}
+  "mitmachen_error_description_max",      // {{n}}
+  "mitmachen_error_description_too_many_links", // {{n}}
+  "mitmachen_error_description_invalid",
+  "mitmachen_error_contact_name_max",     // {{n}}
+  "mitmachen_error_contact_name_invalid",
+  "mitmachen_error_phone_invalid",
+  "mitmachen_error_email_invalid",
+  "mitmachen_error_consent_required",
+  "mitmachen_error_files_count",          // {{n}}
+  "mitmachen_error_files_size",           // {{mb}}
+  "mitmachen_error_files_type",
 ] as const;
 
 export type TranslationKey = (typeof TRANSLATION_KEYS)[number];
diff --git a/src/routes/api/mitmachen/+server.ts b/src/routes/api/mitmachen/+server.ts
new file mode 100644
index 0000000..ab20afd
--- /dev/null
+++ b/src/routes/api/mitmachen/+server.ts
@@ -0,0 +1,157 @@
+import { json } from "@sveltejs/kit";
+import { env as publicEnv } from "$env/dynamic/public";
+import { env as privateEnv } from "$env/dynamic/private";
+import type { RequestHandler } from "./$types";
+import {
+  HONEYPOT_FIELDS,
+  LIMITS,
+  validateFiles,
+  validateMitmachen,
+} from "$lib/components/internal/mitmachen-form-validation";
+
+const TURNSTILE_SECRET = privateEnv.TURNSTILE_SECRET ?? "";
+const TURNSTILE_ENABLED = TURNSTILE_SECRET !== "";
+
+async function verifyTurnstile(token: string, ip: string): Promise<boolean> {
+  if (!TURNSTILE_ENABLED) return true;
+  if (!token) return false;
+  try {
+    const res = await fetch("https://challenges.cloudflare.com/turnstile/v0/siteverify", {
+      method: "POST",
+      headers: { "Content-Type": "application/x-www-form-urlencoded" },
+      body: new URLSearchParams({ secret: TURNSTILE_SECRET, response: token, remoteip: ip }),
+    });
+    if (!res.ok) return false;
+    const data = (await res.json()) as { success?: boolean };
+    return data.success === true;
+  } catch (e) {
+    console.error("[mitmachen] turnstile verify failed:", e);
+    return false;
+  }
+}
+
+const ALLOWED_ORIGINS = new Set([
+  "https://windwiderstand.de",
+  "https://www.windwiderstand.de",
+  "http://localhost:5173",
+  "http://localhost:4173",
+]);
+
+export const POST: RequestHandler = async ({ request, getClientAddress }) => {
+  // Origin/Referer must match — blocks naive cross-site POSTs
+  const origin = request.headers.get("origin") ?? "";
+  const referer = request.headers.get("referer") ?? "";
+  const refererOrigin = referer ? safeOrigin(referer) : "";
+  if (!ALLOWED_ORIGINS.has(origin) && !ALLOWED_ORIGINS.has(refererOrigin)) {
+    return json({ error: "Ungültige Anfrage." }, { status: 403 });
+  }
+
+  let form: FormData;
+  try {
+    form = await request.formData();
+  } catch {
+    return json({ error: "Ungültige Anfrage." }, { status: 400 });
+  }
+  const text = (key: string): string => {
+    const v = form.get(key);
+    return typeof v === "string" ? v : "";
+  };
+
+  // Honeypots — must all be empty
+  for (const hp of HONEYPOT_FIELDS) {
+    if (text(hp).trim() !== "") {
+      // Pretend success so bots don't learn the trap exists
+      return json({ ok: true }, { status: 201 });
+    }
+  }
+
+  // Client age — bots usually post immediately
+  const clientAge = Number(text("_client_age_ms"));
+  if (!Number.isFinite(clientAge) || clientAge < LIMITS.MIN_CLIENT_AGE_MS) {
+    return json({ error: "Bitte etwas mehr Zeit lassen." }, { status: 429 });
+  }
+
+  // Cloudflare Turnstile (skipped when no secret configured)
+  if (TURNSTILE_ENABLED) {
+    const ok = await verifyTurnstile(text("cf_turnstile_token"), getClientAddress());
+    if (!ok) {
+      return json({ error: "captcha" }, { status: 403 });
+    }
+  }
+
+  // Full validation
+  const fields = {
+    title: text("title"),
+    description: text("description"),
+    contactName: text("contactName"),
+    phone: text("phone"),
+    email: text("email"),
+    consent: text("consent") === "true",
+  };
+  const errors = validateMitmachen(fields);
+  if (Object.keys(errors).length > 0) {
+    return json({ errors }, { status: 422 });
+  }
+
+  const files = form
+    .getAll("file")
+    .filter((v): v is File => v instanceof File && v.size > 0);
+  const fileError = validateFiles(files);
+  if (fileError) {
+    return json({ errors: { files: fileError } }, { status: 422 });
+  }
+
+  // Forward to CMS forms plugin (multipart: data-JSON-Part + file-Parts)
+  const cmsBase = (publicEnv.PUBLIC_CMS_URL || "http://localhost:3099").replace(/\/$/, "");
+  const cmsEnv = publicEnv.PUBLIC_CMS_ENV || "";
+  const cmsUrl = cmsEnv
+    ? `${cmsBase}/api/forms/mitmachen/submit-multipart?_environment=${encodeURIComponent(cmsEnv)}`
+    : `${cmsBase}/api/forms/mitmachen/submit-multipart`;
+
+  const payload = {
+    title: fields.title.trim(),
+    description: fields.description.trim(),
+    contact_name: fields.contactName.trim(),
+    phone: fields.phone.trim(),
+    email: fields.email.trim(),
+    consent_at: new Date().toISOString(),
+    submitted_via: "windwiderstand.de/api/mitmachen",
+    user_agent: (request.headers.get("user-agent") ?? "").slice(0, 200),
+  };
+
+  const outgoing = new FormData();
+  outgoing.set("data", JSON.stringify(payload));
+  for (const f of files) outgoing.append("file", f, f.name);
+
+  let res: Response;
+  try {
+    // No Origin header — we already validated it at this server.
+    // CMS forms plugin (REQUIRE_ORIGIN=false) accepts requests without one.
+    res = await fetch(cmsUrl, {
+      method: "POST",
+      headers: { "X-Forwarded-For": getClientAddress() },
+      body: outgoing,
+    });
+  } catch (e) {
+    console.error("[mitmachen] CMS fetch failed:", e);
+    return json({ error: "Server nicht erreichbar." }, { status: 502 });
+  }
+
+  if (res.ok) {
+    return json({ ok: true }, { status: 201 });
+  }
+  if (res.status === 429) {
+    return json({ error: "Zu viele Anfragen. Bitte später erneut versuchen." }, { status: 429 });
+  }
+  const text2 = await res.text().catch(() => "");
+  console.error("[mitmachen] CMS error", res.status, text2);
+  return json({ error: "Fehler beim Senden." }, { status: 502 });
+};
+
+function safeOrigin(u: string): string {
+  try {
+    return new URL(u).origin;
+  } catch {
+    return "";
+  }
+}