Fix LSM snapshot restoration by resolving double path nesting

The LSM session was being initialised with the full lsmPath as both the
HasBlockIO root and the session's FsPath inside it, producing a doubled
on-disk layout like:
<state-dir>/lsm/<state-dir>/lsm/{active,snapshots,...}
instead of:
<state-dir>/lsm/{active,snapshots,...}.

Effect on snapshots: scripts/postgresql-setup.sh --create-snapshot looks
for the LSM tree at <state-dir>/lsm/snapshots/<slot>, didn't find it
because of the doubled path, silently fell back to the InMemory branch,
and produced a tarball missing the LSM tree files. On --restore-snapshot
+ db-sync startup the snapshot couldn't be loaded (ErrSnapshotDoesNotExist)
and sync replayed from genesis.

Fix:
Pass mkFsPath [] as the session's FsPath so it's rooted at the
HasBlockIO root directly. Also harden the snapshot script to abort with
a clear error when an lsm/ subtree exists but no LSM snapshot is found
at the expected path, instead of producing an incomplete tarball.

Files staged for commit:
- cardano-db-sync/src/Cardano/DbSync/Ledger/State.hs
- scripts/postgresql-setup.sh

Author: ArturWieczorek

cardano-db-sync/src/Cardano/DbSync/Ledger/State.hs

@@ -118,7 +118,7 @@ import Ouroboros.Network.Block (HeaderHash, pointSlot)
 import System.FS.API (SomeHasFS (..), mkFsPath)
 import System.FS.API.Types (MountPoint (..))
 import System.FS.IO (ioHasFS)
-import System.FilePath (splitDirectories, (</>))
+import System.FilePath ((</>))
 import System.Mem (performMajorGC)
 import System.Random (genWord64, newStdGen)
 
@@ -227,7 +227,13 @@ mkHasLedgerEnv trce protoInfo dir nw maxLovelaceSupply systemStart syncOptions b
     LedgerBackendLSM mPath -> do
       let lsmPath = fromMaybe (unLedgerStateDir dir </> "lsm") mPath
       salt <- fst . genWord64 <$> newStdGen
-      let args = LSM.LSMArgs (mkFsPath $ splitDirectories lsmPath) salt (LSM.stdMkBlockIOFS lsmPath)
+      -- The HasBlockIO is rooted at lsmPath, so the session's FsPath inside it
+      -- must be the empty path. Passing the full lsmPath here causes the LSM
+      -- session to be created at <lsmPath>/<lsmPath>, which breaks snapshot
+      -- bundling in scripts/postgresql-setup.sh (it falls back to the InMemory
+      -- branch and ships an incomplete tarball; on restore db-sync then can't
+      -- find the snapshot and replays from genesis).
+      let args = LSM.LSMArgs (mkFsPath []) salt (LSM.stdMkBlockIOFS lsmPath)
       res <-
         runWithTempRegistry $
           (,())

scripts/postgresql-setup.sh

@@ -176,6 +176,15 @@ function create_snapshot {
 	      # The active/ directory is not needed — it gets cleared on session restore.
 	      tar czf "${tmp_dir}/${ledger_dir_name}.tar.gz" \
 	        -C "${state_dir}" "${ledger_dir_name}" "lsm/snapshots/${ledger_dir_name}" "lsm/metadata"
+	    elif [ -d "${state_dir}/lsm" ]; then
+	      # State directory contains an lsm/ subtree but the expected snapshot path is missing.
+	      # Refuse to silently fall back to the InMemory branch — the resulting tarball would
+	      # exclude the LSM tree files and restoration would replay from genesis.
+	      echo "ERROR: ${state_dir}/lsm exists but no LSM snapshot found at ${lsm_snap_dir}." >&2
+	      echo "       The LSM session may be using a non-standard layout. Aborting to avoid" >&2
+	      echo "       producing an incomplete snapshot." >&2
+	      rm "${recursive}" "${force}" "${tmp_dir}"
+	      exit 1
 	    else
 	      echo "Detected InMemory backend snapshot at slot ${ledger_dir_name}"
 	      # InMemory backend: just the ledger snapshot directory