host: preserve bundle symlinks and finish integration test isolation

host/tests/README.md

@@ -11,9 +11,17 @@ cargo test -p sausage --test it -- --test-threads=1
 Use `nix develop -c` and the required build slot wrapper for these commands.
 Set `CARGO_TARGET_DIR` to your executor's target directory.
 
+The journal timing benchmark keeps its 10% threshold but does not run in the default suite.
+Run it by hand on an idle machine:
+
+```sh
+cargo test --release -p sausage --test it -- --ignored undo_cost
+```
+
 Add new modules under `host/tests/it/` and declare them in `it/main.rs`.
 Cargo does not discover separate test executables in `host/tests/`.
 Fixture sources remain in `builder-fixture/`.
+The bundle-copy regression preserves relative symlink targets, including broken links.
 
 `common.rs` shares the target lookup and the cached userland Git build.
 A shared mutex protects the cwd-init output and the brush checkout during fixture builds.
@@ -24,5 +32,5 @@ Child processes receive environment variables through `Command`, not through cha
 SIGKILL parents use fully qualified test filters with `--exact`.
 
 The `hook::hook_git` and `hook_git` registrations both existed before this move.
-Both remain to preserve the test count.
+Both remain as wrappers around one shared helper to preserve the test count.
 The shared `hook_guest` module now builds its fixture once per process.