feat(prune): R2 dry-run prune shell + persist wiring, report-only

Add ReaSamplerSession::pruneDryRun enumerating the resolved current bank
folder, feeding the R1 core, and returning a PruneReport (count/bytes/list).
New pure bankRelativeForName + buildPruneReport keep spelling and tally
testable. Register forever-stable BANK_PRUNE_FOLDER action, report-only. No deletion.

src/persist.cpp

@@ -77,10 +77,13 @@
 
 #include <filesystem>
 #include <string>
+#include <system_error>
+#include <unordered_map>
 #include <vector>
 
 #include "app_version.h"
 #include "capture_paths.h"
+#include "prune_reconcile.h"
 
 #define REAPERAPI_MINIMAL
 #define REAPERAPI_WANT_EnumProjects
@@ -243,6 +246,67 @@ bool ReaSamplerSession::saveToActiveProject() {
 
 namespace {
 
+// The dry-run file-list display cap: the orphan COUNT and reclaimed SIZE are always
+// exact (tallied over the full orphan set), but the enumerated file list handed to the
+// console is clipped to this many entries so a project with thousands of orphans does
+// not flood the report. PruneReport::truncated flags the clip. R3's confirm surface can
+// choose its own presentation; this is purely the Wave-2 dry-run readout ceiling.
+constexpr std::size_t kPruneListDisplayCap = 64;
+
+}  // namespace
+
+PruneReport ReaSamplerSession::pruneDryRun() const {
+    PruneReport report;
+
+    std::string rppPath;
+    void* proj = readActiveProject(rppPath);
+    if (!proj || rppPath.empty()) return report;  // no active/saved project -> nothing
+
+    // Resolve the CURRENT bank folder the same way the index does (M4): project dir of
+    // the live .rpp + the fixed bank subfolder. Never a stored absolute path, so a
+    // Save-As relocation is followed automatically. resolveBankFile is the shared M4
+    // arithmetic; feeding it the bank subfolder as the "relative path" yields the folder.
+    const std::string projectDir = projectDirOf(rppPath);
+    const std::string bankDir = resolveBankFile(projectDir, kBankSubfolder);
+    if (bankDir.empty()) return report;  // unresolvable (no project dir) -> nothing
+
+    std::error_code ec;
+    if (!fs::exists(bankDir, ec) || !fs::is_directory(bankDir, ec)) {
+        return report;  // no bank folder captured yet -> nothing to reclaim
+    }
+
+    // Enumerate the folder into project-relative index-spelled paths, spelled the SAME
+    // way the capture path spelled them (bankRelativeForName == deriveBankPaths's
+    // convention) so the pure core's exact-string match lines up with referencedPaths()
+    // and the manifest. Non-recursive: the bank folder is flat (capture writes files
+    // directly here); skip any subdirectory. Size is stat'd here and cached by relative
+    // path so the report's byte tally reuses the same on-disk read.
+    std::vector<std::string> present;
+    std::unordered_map<std::string, std::uint64_t> sizeByRel;
+    for (const auto& entry : fs::directory_iterator(bankDir, ec)) {
+        if (ec) break;
+        std::error_code fec;
+        if (!entry.is_regular_file(fec)) continue;  // skip subdirs / specials
+        const std::string name = entry.path().filename().string();
+        const std::string rel = bankRelativeForName(name);
+        if (rel.empty()) continue;
+        present.push_back(rel);
+        const std::uintmax_t sz = entry.file_size(fec);
+        sizeByRel[rel] = fec ? 0 : static_cast<std::uint64_t>(sz);
+    }
+
+    // The decision lives in the pure core — read-only inputs from the session's book and
+    // manifest (NO save, NO MarkProjectDirty, NO mutation). referencedPaths() unions
+    // across the whole book (pool included); owned().paths() is the manifest set. The
+    // count / byte-sum / display-truncation tally is the pure buildPruneReport, so this
+    // shell only enumerates, resolves, and stats — no report logic re-implemented here.
+    const std::vector<std::string> orphans =
+        pruneOrphans(present, book_.referencedPaths(), owned_.paths());
+    return buildPruneReport(orphans, sizeByRel, kPruneListDisplayCap);
+}
+
+namespace {
+
 // Load the Design-View model from a project's view_state key, or return a fresh
 // default. An absent/empty key (older project with no view state) yields a
 // default-constructed model (Arrange + Design seeded, active = Arrange) — graceful,