WP-30/31/32: contract and failing tests for backup management; OS scan skips container dirs

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/Cargo.lock

@@ -101,10 +101,12 @@ dependencies = [
  "chrono",
  "cron",
  "domain",
+ "hex",
  "rand",
  "serde",
  "serde_json",
  "sha2",
+ "tempfile",
  "tokio",
  "uuid",
 ]
@@ -1305,6 +1307,12 @@ dependencies = [
  "vcpkg",
 ]
 
+[[package]]
+name = "linux-raw-sys"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a66949e030da00e8c7d4434b251670a91556f4144941d37452769c25d58a53"
+
 [[package]]
 name = "litemap"
 version = "0.8.3"
@@ -1813,6 +1821,19 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "rustix"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6fe4565b9518b83ef4f91bb47ce29620ca828bd32cb7e408f0062e9930ba190"
+dependencies = [
+ "bitflags",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "rustls"
 version = "0.23.43"
@@ -2379,6 +2400,19 @@ dependencies = [
  "syn 2.0.119",
 ]
 
+[[package]]
+name = "tempfile"
+version = "3.27.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
+dependencies = [
+ "fastrand",
+ "getrandom 0.4.3",
+ "once_cell",
+ "rustix",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "thiserror"
 version = "2.0.20"