test(plugin): compare a composer/installers run against upstream Composer

The fixture project pins composer/installers 2.3.0 and requires two packages
of framework-specific types, so the plugin's LibraryInstaller subclass decides
where they land. Upstream Composer and Shirabe install the same project and
the whole resulting tree is compared.

The plugin tarball is fetched by `fixtures/e2e-installers/fetch` into a
git-ignored directory and pinned by a digest over the extracted files, so the
third-party source never enters this repository and the test skips itself
while the directory is absent. The tree is staged and only moved into place
once verified, so an unverified tree is never observable under the name the
test looks for.

1 files changed, 1 insertions, 0 deletions

diff --git a/crates/shirabe/tests/plugin/main.rs b/crates/shirabe/tests/plugin/main.rs
index 02db6b03..0b404ee9 100644
--- a/crates/shirabe/tests/plugin/main.rs
+++ b/crates/shirabe/tests/plugin/main.rs
@@ -6,6 +6,7 @@ mod config_stub;
 mod e2e_command_provider_test;
 mod e2e_extension_installer_test;
 mod e2e_installer_test;
+mod e2e_installers_test;
 mod e2e_normalize_test;
 mod plugin_installer_test;
 mod subscriber_test;