feat(acp): add experimental ACP support

Co-authored-by: Jonathan Taylor <visionik@pobox.com>

src/sessions/session-key-utils.ts

@@ -0,0 +1,35 @@
+export type ParsedAgentSessionKey = {
+  agentId: string;
+  rest: string;
+};
+
+export function parseAgentSessionKey(
+  sessionKey: string | undefined | null,
+): ParsedAgentSessionKey | null {
+  const raw = (sessionKey ?? "").trim();
+  if (!raw) return null;
+  const parts = raw.split(":").filter(Boolean);
+  if (parts.length < 3) return null;
+  if (parts[0] !== "agent") return null;
+  const agentId = parts[1]?.trim();
+  const rest = parts.slice(2).join(":");
+  if (!agentId || !rest) return null;
+  return { agentId, rest };
+}
+
+export function isSubagentSessionKey(sessionKey: string | undefined | null): boolean {
+  const raw = (sessionKey ?? "").trim();
+  if (!raw) return false;
+  if (raw.toLowerCase().startsWith("subagent:")) return true;
+  const parsed = parseAgentSessionKey(raw);
+  return Boolean((parsed?.rest ?? "").toLowerCase().startsWith("subagent:"));
+}
+
+export function isAcpSessionKey(sessionKey: string | undefined | null): boolean {
+  const raw = (sessionKey ?? "").trim();
+  if (!raw) return false;
+  const normalized = raw.toLowerCase();
+  if (normalized.startsWith("acp:")) return true;
+  const parsed = parseAgentSessionKey(raw);
+  return Boolean((parsed?.rest ?? "").toLowerCase().startsWith("acp:"));
+}