docs: scope deletion-authority wording to bank folder + guard growing-read NUL terminator

src/shell/persist/session.h

@@ -11,8 +11,11 @@
 //     writeAssignmentRequest: the ext-state ↔ JSON serialization bridge, plus GUID
 //     minting and bank-folder relocation (see ext_state_io.h for the key contract).
 //   * prune_fs.cpp     — pruneDryRun / pruneOrphanSet / pruneReclaim: the prune scan
-//     and THE SINGLE FILE-DELETION AUTHORITY in ReaSampler (deleteOrphanFile via
-//     SHFileOperationW). Nothing else in the system deletes bytes.
+//     and THE SINGLE FILE-DELETION AUTHORITY over USER files in the bank folder in
+//     ReaSampler (deleteOrphanFile via SHFileOperationW). Nothing else in the system
+//     deletes bank-folder bytes; a shell's self-cleanup of a transient scratch file
+//     it just created (the drop path's .vstpreset temp, the realtime finalize temp)
+//     is excluded from this authority.
 //
 // Save: serialize the BankModel JSON -> SetProjExtState under namespace
 //   "reasampler" (ext state lives inside the .rpp, so the index travels with the