feat(broker): one-off owner_pubkey backfill script

Populates mesh.mesh.owner_pubkey for pre-18c rows by generating a
fresh ed25519 keypair per mesh + emitting the secret key to stdout
for out-of-band hand-off.

Idempotent: only patches rows WHERE owner_pubkey IS NULL. Machine-
readable output (tab-separated: mesh_id, slug, pubkey, secret_key)
so operators can pipe into a secure store.

Usage:
  DATABASE_URL=... bun apps/broker/scripts/backfill-owner-pubkey.ts > owners.tsv
  # then securely distribute secrets to mesh owners

Verified locally: nulled smoke-test mesh's owner_pubkey → ran backfill
→ fresh keypair written, secret emitted.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/broker/scripts/backfill-owner-pubkey.ts

@@ -0,0 +1,65 @@
+#!/usr/bin/env bun
+/**
+ * One-off backfill: populate `mesh.mesh.owner_pubkey` for meshes
+ * created before Step 18c landed.
+ *
+ * Runs idempotently: only touches rows where owner_pubkey IS NULL.
+ * Generates a fresh ed25519 keypair per mesh and writes the owner
+ * SECRET KEY to stdout (paired with mesh_id) so an operator can
+ * hand it back to the mesh owner out-of-band.
+ *
+ * Usage:
+ *   DATABASE_URL=... bun apps/broker/scripts/backfill-owner-pubkey.ts
+ *
+ * Output format (per row): `<mesh_id> <mesh_slug> <owner_pubkey> <owner_secret_key>`
+ * Redirect stdout to a secure file — the secret keys grant admin
+ * invite-signing power and must be stored carefully.
+ */
+
+import sodium from "libsodium-wrappers";
+import { eq, isNull } from "drizzle-orm";
+import { db } from "../src/db";
+import { mesh } from "@turbostarter/db/schema/mesh";
+
+async function main(): Promise<void> {
+  await sodium.ready;
+
+  const missing = await db
+    .select({ id: mesh.id, slug: mesh.slug, name: mesh.name })
+    .from(mesh)
+    .where(isNull(mesh.ownerPubkey));
+
+  if (missing.length === 0) {
+    console.error("[backfill] no rows to patch");
+    return;
+  }
+  console.error(`[backfill] patching ${missing.length} mesh(es)`);
+
+  for (const row of missing) {
+    const kp = sodium.crypto_sign_keypair();
+    const pubHex = sodium.to_hex(kp.publicKey);
+    const secHex = sodium.to_hex(kp.privateKey);
+    await db
+      .update(mesh)
+      .set({ ownerPubkey: pubHex })
+      .where(eq(mesh.id, row.id));
+    // stdout: machine-readable, one mesh per line
+    console.log(`${row.id}\t${row.slug}\t${pubHex}\t${secHex}`);
+    console.error(
+      `[backfill] patched mesh "${row.slug}" (${row.id}) — save its secret key`,
+    );
+  }
+  console.error(
+    "[backfill] done. SECURELY HAND OFF secret keys to mesh owners.",
+  );
+}
+
+main()
+  .then(() => process.exit(0))
+  .catch((e) => {
+    console.error(
+      "[backfill] error:",
+      e instanceof Error ? e.message : String(e),
+    );
+    process.exit(1);
+  });