refactor(channels): unify dm pairing policy flows

src/pairing/pairing-challenge.ts

@@ -0,0 +1,48 @@
+import { buildPairingReply } from "./pairing-messages.js";
+
+type PairingMeta = Record<string, string | undefined>;
+
+export type PairingChallengeParams = {
+  channel: string;
+  senderId: string;
+  senderIdLine: string;
+  meta?: PairingMeta;
+  upsertPairingRequest: (params: {
+    id: string;
+    meta?: PairingMeta;
+  }) => Promise<{ code: string; created: boolean }>;
+  sendPairingReply: (text: string) => Promise<void>;
+  buildReplyText?: (params: { code: string; senderIdLine: string }) => string;
+  onCreated?: (params: { code: string }) => void;
+  onReplyError?: (err: unknown) => void;
+};
+
+/**
+ * Shared pairing challenge issuance for DM pairing policy pathways.
+ * Ensures every channel follows the same create-if-missing + reply flow.
+ */
+export async function issuePairingChallenge(
+  params: PairingChallengeParams,
+): Promise<{ created: boolean; code?: string }> {
+  const { code, created } = await params.upsertPairingRequest({
+    id: params.senderId,
+    meta: params.meta,
+  });
+  if (!created) {
+    return { created: false };
+  }
+  params.onCreated?.({ code });
+  const replyText =
+    params.buildReplyText?.({ code, senderIdLine: params.senderIdLine }) ??
+    buildPairingReply({
+      channel: params.channel,
+      idLine: params.senderIdLine,
+      code,
+    });
+  try {
+    await params.sendPairingReply(replyText);
+  } catch (err) {
+    params.onReplyError?.(err);
+  }
+  return { created: true, code };
+}