diff --git a/AGENTS.md b/AGENTS.md
index 0fa47bc..7525d14 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -61,6 +61,7 @@ Coreutils, diffutils, procps, and brush use relative symlinks to one binary each
 
 `nix flake check` checks the packaged host, its bundle, and the whole host/VFS test suite.
 Sandbox-incompatible tests print an explicit skip reason instead of a flake-level filter.
+The check sets `SAUSAGE_NIX_CHECK=1` for tests that need network access or unvendored fixture dependencies.
 
 ## Tests
 
diff --git a/flake.nix b/flake.nix
index 0763ff6..bb668ed 100644
--- a/flake.nix
+++ b/flake.nix
@@ -167,6 +167,7 @@
           doCheck = true;
           nativeBuildInputs = hostArgs.nativeBuildInputs ++ builderTools ++ [ pkgs.git pkgs.nodejs ];
           SAUSAGE_TEST_NO_BUILDER_SANDBOX = "1";
+          SAUSAGE_NIX_CHECK = "1";
           SAUSAGE_USERLAND = bundle;
           preCheck = ''
             export SAUSAGE_CACHE="$TMPDIR/sausage-cache"
diff --git a/host/tests/it/builder.rs b/host/tests/it/builder.rs
index 6668657..ad6d29f 100644
--- a/host/tests/it/builder.rs
+++ b/host/tests/it/builder.rs
@@ -170,6 +170,12 @@ fn cache_hits(base: &Path) -> anyhow::Result<u64> {
 }
 #[tokio::test(flavor = "multi_thread")]
 async fn cargo_build_test_and_source_changes() -> anyhow::Result<()> {
+    if std::env::var("SAUSAGE_NIX_CHECK").as_deref() == Ok("1") {
+        println!(
+            "SKIP builder::cargo_build_test_and_source_changes: the isolated builder fixture requires crates.io access"
+        );
+        return Ok(());
+    }
     let binaries = programs();
     let temp = tempfile::tempdir()?;
     let world = World::open(temp.path())?;
diff --git a/host/tests/it/harness_shutdown.rs b/host/tests/it/harness_shutdown.rs
index 769126e..de93007 100644
--- a/host/tests/it/harness_shutdown.rs
+++ b/host/tests/it/harness_shutdown.rs
@@ -60,7 +60,7 @@ fn sigterm_cancels_tool_and_resumes() -> anyhow::Result<()> {
                 "-p",
                 "sausage-coreutils",
                 "--bin",
-                "sleep",
+                "coreutils",
                 "--manifest-path",
             ])
             .arg(source.join("Cargo.toml"))
@@ -74,7 +74,7 @@ fn sigterm_cancels_tool_and_resumes() -> anyhow::Result<()> {
     World::open(dir.path())?;
     std::fs::create_dir_all(dir.path().join("world/bin"))?;
     std::fs::copy(
-        target.join("wasm32-wasip2/release/sleep.wasm"),
+        target.join("wasm32-wasip2/release/coreutils.wasm"),
         dir.path().join("world/bin/sleep.wasm"),
     )?;
     let spawn = || {
diff --git a/host/tests/it/hook.rs b/host/tests/it/hook.rs
index d3c3e73..4687a92 100644
--- a/host/tests/it/hook.rs
+++ b/host/tests/it/hook.rs
@@ -52,6 +52,12 @@ async fn run(runtime: &Arc<Runtime>, url: String, chain: Vec<String>) -> String
 }
 #[tokio::test]
 async fn identity_injection_denial_and_ambiguity() {
+    if std::env::var("SAUSAGE_NIX_CHECK").as_deref() == Ok("1") {
+        println!(
+            "SKIP hook::identity_injection_denial_and_ambiguity: the wstd fixture dependency is not vendored"
+        );
+        return;
+    }
     let guest = hook_guest::component();
     let temp = tempfile::tempdir().unwrap();
     let world = World::open(temp.path()).unwrap();
@@ -325,6 +331,12 @@ async fn upstream(
 
 #[tokio::test]
 async fn streamed_upload_redirect_and_http_admin_denial() {
+    if std::env::var("SAUSAGE_NIX_CHECK").as_deref() == Ok("1") {
+        println!(
+            "SKIP hook::streamed_upload_redirect_and_http_admin_denial: the wstd fixture dependency is not vendored"
+        );
+        return;
+    }
     let guest = hook_guest::component();
     let temp = tempfile::tempdir().unwrap();
     let world = World::open(temp.path()).unwrap();
diff --git a/host/tests/it/hook_api.rs b/host/tests/it/hook_api.rs
index 5b7da6e..0ce7f78 100644
--- a/host/tests/it/hook_api.rs
+++ b/host/tests/it/hook_api.rs
@@ -16,6 +16,12 @@ use super::hook_guest;
 
 #[tokio::test]
 async fn one_api_for_pages_and_guest_requests() -> anyhow::Result<()> {
+    if std::env::var("SAUSAGE_NIX_CHECK").as_deref() == Ok("1") {
+        println!(
+            "SKIP hook_api::one_api_for_pages_and_guest_requests: the wstd fixture dependency is not vendored"
+        );
+        return Ok(());
+    }
     use webauthn_authenticator_rs::{WebauthnAuthenticator, softpasskey::SoftPasskey};
     let dir = tempfile::tempdir()?;
     let world = World::open(dir.path())?;