feat(db): conversations.findOrCreateForSpace for the ambient companion

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/db/repos/conversations.js

@@ -42,3 +42,20 @@ export async function setSummary(id, summary) {
   );
   return r;
 }
+
+export async function findOrCreateForSpace(space_id, agent_id, actor) {
+  const { rows: [existing] } = await pool.query(
+    `SELECT * FROM conversations
+     WHERE space_id=$1 AND agent_id=$2 AND status='open'
+     ORDER BY started_at DESC LIMIT 1`,
+    [space_id, agent_id]
+  );
+  if (existing) return existing;
+  const { rows: [r] } = await pool.query(
+    `INSERT INTO conversations(title, space_id, agent_id, metadata)
+     VALUES($1,$2,$3,$4) RETURNING *`,
+    ['Companion', space_id, agent_id, {}]
+  );
+  await recordAudit(actor, 'create', 'conversation', r.id, null, r);
+  return r;
+}