refactor(subagent): split extension into modules

src/session.ts

@@ -0,0 +1,21 @@
+import { createHash } from "node:crypto";
+import * as os from "node:os";
+import * as path from "node:path";
+
+// Session Path - Persist child sessions as <agent>_<uuid>.jsonl under a cwd hash.
+export function getSubagentSessionPath(
+  cwd: string,
+  agentName: string,
+  sessionId: string,
+): string {
+  const cwdHash = createHash("sha256").update(cwd).digest("hex").slice(0, 16);
+  const safeAgent = agentName.replace(/[^\w.-]+/g, "_");
+  const safeSessionId = sessionId.replace(/[^\w.-]+/g, "_");
+  return path.join(
+    os.homedir(),
+    ".pi",
+    "subagent-sessions",
+    cwdHash,
+    `${safeAgent}_${safeSessionId}.jsonl`,
+  );
+}