package: one bank leaves the project as one .rsbank, or the export refuses and says why

Pure planner classifies missing/unreadable/unrepresentable and repairs transport
names; the verb digests, streams and commits atomically over a const session.

src/shell/actions/package_export_action.h

@@ -0,0 +1,18 @@
+#pragma once
+// package_export_action — the "export bank as package" action body: survey and
+// report first, confirm what is absent, pick a destination, write. Every prompt in
+// the flow lives here; shell/package/export_bank stays promptless. Registration and
+// dispatch for its FOREVER-STABLE id ride main.cpp's action table.
+
+#include <string>
+
+namespace reasampler {
+
+class ReaSamplerSession;
+
+// Exports one bank (the pool included — it is structurally a bank) to a .rsbank the
+// user picks. Read-only against the project: the session is const, so no ext-state
+// write, generation bump or undo point is reachable from here.
+void doBankPackageExport(const ReaSamplerSession& session, const std::string& bankId);
+
+}  // namespace reasampler