diff --git a/package.json b/package.json
index 2fd237e..4da142f 100644
--- a/package.json
+++ b/package.json
@@ -16,7 +16,7 @@
     "i18n": "node scripts/i18n-validate.cjs",
     "i18n:validate": "node scripts/i18n-validate.cjs",
     "deploy": "wrangler deploy",
-    "deploy:kv": "wrangler deploy -c wrangler.kv.toml",
+    "deploy:kv": "node scripts/ensure-kv.cjs && wrangler deploy -c wrangler.kv.toml",
     "deploy:demo": "npm run build:demo && wrangler pages deploy dist --project-name nw-demo"
   },
   "keywords": [
diff --git a/scripts/ensure-kv.cjs b/scripts/ensure-kv.cjs
new file mode 100644
index 0000000..af0bdb9
--- /dev/null
+++ b/scripts/ensure-kv.cjs
@@ -0,0 +1,64 @@
+#!/usr/bin/env node
+/**
+ * Make `deploy:kv` idempotent across repeated builds.
+ *
+ * KV namespaces are referenced in wrangler config by account-scoped `id`, not
+ * by name. The template ships without an id so fresh accounts can provision one
+ * on first deploy. In non-interactive builds, wrangler may try to create the
+ * same namespace again on later builds and fail with code 10014.
+ */
+const { execSync } = require('node:child_process');
+const fs = require('node:fs');
+const path = require('node:path');
+
+const CONFIG = path.resolve(__dirname, '..', 'wrangler.kv.toml');
+const BINDING = 'ATTACHMENTS_KV';
+
+const wrangler = (args) =>
+  execSync(`npx wrangler ${args}`, { encoding: 'utf8', stdio: ['ignore', 'pipe', 'inherit'] });
+
+function bindingBlockHasId(toml) {
+  const blocks = toml.match(/\[\[kv_namespaces\]\][^[]*/g) || [];
+  const block = blocks.find((entry) => new RegExp(`binding\\s*=\\s*"${BINDING}"`).test(entry));
+  return block ? /^\s*id\s*=/m.test(block) : false;
+}
+
+function expectedTitle(toml) {
+  const name = (toml.match(/^\s*name\s*=\s*"([^"]+)"/m) || [])[1] || 'worker';
+  return `${name}-${BINDING.toLowerCase().replace(/_/g, '-')}`;
+}
+
+function resolveId(title) {
+  const list = JSON.parse(wrangler('kv namespace list'));
+  const hit =
+    list.find((namespace) => namespace.title === title) ||
+    list.find((namespace) => typeof namespace.title === 'string' && namespace.title.endsWith('attachments-kv'));
+  if (hit) {
+    console.log(`[ensure-kv] reusing existing namespace "${hit.title}" (${hit.id})`);
+    return hit.id;
+  }
+
+  const out = wrangler(`kv namespace create "${title}"`);
+  const id = (out.match(/id\s*=\s*"([0-9a-fA-F]{32})"/) || [])[1];
+  if (!id) throw new Error(`[ensure-kv] could not parse new namespace id from:\n${out}`);
+  console.log(`[ensure-kv] created namespace "${title}" (${id})`);
+  return id;
+}
+
+function main() {
+  let toml = fs.readFileSync(CONFIG, 'utf8');
+  if (bindingBlockHasId(toml)) {
+    console.log(`[ensure-kv] ${BINDING} already pinned in wrangler.kv.toml; nothing to do`);
+    return;
+  }
+
+  const id = resolveId(expectedTitle(toml));
+  toml = toml.replace(
+    new RegExp(`(\\[\\[kv_namespaces\\]\\]\\s*\\n\\s*binding\\s*=\\s*"${BINDING}")`),
+    `$1\nid = "${id}"`
+  );
+  fs.writeFileSync(CONFIG, toml);
+  console.log('[ensure-kv] pinned id into wrangler.kv.toml for this build');
+}
+
+main();